Introduction

The Lepidoptera, or butterflies and moths,¹ combine aesthetic appeal with a diversity of problems of scientific interest that have kept their study at the forefront of evolutionary and behavioral biology. The varied tableaus of color and pattern on their wings provide rich material for the study of variation, polymorphism, and mimicry. In the nineteenth century they were widely used to develop, illustrate, and support the theories of evolution (Wallace, 1890,1891) and sexual selection. They have been utilized in some of the earliest ethological studies (Tinbergen et al., 1942), and their pheromonal communication systems were among the first to be analyzed in detail. Interest in lepidopteran communication is greater today than ever before, stimulated in large part by the potentialuse of such knowledge in control programs for economically important species (Birch et al., 1974, and references therein).

As holometabolous insects, lepidopterans develop in a series of distinct morphological stages. The adults are oviparous, and usually deposit their eggs on vegetation. The generally phytophagous larva, commonly referred to as a caterpillar, is a soft-bodied insect with a hydrostatic skeleton, a well-hardened head capsule bearing chewing mouthparts, and usually several pairs of abdominal ambulatory appendages called prolegs in addition to the usual three pair of thoracic legs. Upon completion of feeding, most larvae construct pupal enclosures, often using silk produced by labial salivary glands. Adults are characterized by a covering of scales over most of the body and wings, and in most cases an elongate proboscis used for nectarfeeding. The order shares a common ancestry with the caddisflies, and most probably arose and diversified concurrently with the evolution and diversification of angiosperms in the late Mesozoic and early Cenozoic eras (Common, 1975; MacKay, 1969, 1970; Skalski, 1973).

Even though lepidopterans constitute approximately one-tenth of all animal species, the preceding brief description indicates that at a gross level they exhibit surprisingly little morphological and ecological diversity. Behavior involving communication is similarly limited.Communication between members of the different developmental stages of a species, dominance hierarchies and their associated behavior, and social behavior, even in its most rudimentary forms, are all rare or unknown. Most communication is limited to contexts of individual survival and reproduction, for which very few general patterns of communication have been adopted. For each of these communicative patterns, such as courtship behavior and mimicry, there exists an enormous wealth of detail at the specific level. It is neither possible nor desirable to attempt here a comprehensive survey of this information. Instead, this review will treat, somewhat superficially, the breadth of communicative interactions in which the Lepidoptera take part, with a limited number of examples chosen to illustrate them. The reader is referred to more detailed reviews of each individual topic, and bibliographic references have been kept to the minimum commensurate with access to the literature.

"Communication" is an elusive concept. The author has no desire to become mired in a discussion of the usage of this term, as he sees advantages to both narrow (Otte, 1974) and broad (Wilson, 1971, 1975) interpretations, depending on the emphasis intended by the writer. Readers who wish to pursue this matter will find ample material in the earlier sections of this book, and in the following references: Birch, 1974b; Brown et al., 1970; Burghardt, 1970; Marler, 1961; Morris, 1946; Otte, 1974; Sebeok, 1965; Whittaker and Feeny, 1971; and Wilson, 1971, 1975. In this article, Wilson's (1975) broad concept is employed: ". . . communication is an adaptive relation between the organism that signals and the one that receives, regardless of the complexity and length of the communication channel." However, due to space limitations, the author has arbitrarily excluded certain aspects of communication, such as most host (= prey) detection, most predator detection, and the use of simple physical defense or escape mechanisms. These are discussed only in those specific instances where it is necessary for the understanding of more elaborate communication systems.

The nature of the "complexity and length of the communication channel" may be illustrated by several examples. Communication between the male and female cecropia silkmoth (Hyalophora cecropia, Saturniidae) does not terminate with copulation. The sperm or some other substance produced by the male interacts with the bursa copulatrix of the female, which responds by releasing into the hemolymph a hormone that changes her oviposition rate (Riddiford and Ashenhurst, 1973). Male butterflies in several genera (Parnassius, Acraea, Actinote, Amauris, and others; see Scott, 1973) deposit a large structure (the sphragis) in the female copulatory opening. It is believed that the function of this "plug" is to prevent mating by other males, either by its physical presence or because it inhibits pheromone release by females (Eltringham, 1912; Labine, 1964). Gilbert (pers. comm. and cited in Scott, 1973) has discovered that in at least one species of heliconiine butterfly the male deposits on the female a pheromone that makes her unattractive to other males. Using radioactive tracers, Gilbert has also demonstrated that in Heliconius the male's spermatophore is partially metabolized and contributes nutritionally to the female and the eggs (pers. comm.). In all of these diverse instances a "signal" persists and functions long after the signaling individual has departed.

Any survey of communication must consider the sensory world of the animals concerned. As a result of the partial"overhaul" of the nervous system during "complete" metamorphosis, the successive developmental stages differ so markedly from one another in morphology, sensory physiology, and behavior that they must be considered as distinctly different organisms, each with its own Umwelt, defined to a first approximation by the physiology of its sense organs. For this reason the developmental stages are treated separately. The one feature that all the developmental stages of a species have in common, however, is the need for adequate defense. Therefore a consideration of defense is presented first.

Like most other arthropods, butterflies and moths have numerous and diverse defense adaptations. These include deciduous scales, urticating larval setae, regurgitation (by larvae), defecation (including the use of the meconium by the newly eclosed adult²), and compounds with noxious or toxic properties sequestered in the blood or released from specialized defensive glands (e.g., osmeteria of papilionid larvae) (Aplin and Rothschild, 1972; Bisset et al., 1960; Brower et al., 1968; Duffey, 1970; Edmunds, 1974; Ehrlich and Raven, 1965; Eisner, 1970; Eisner et al., 1971; Eisner and Meinwald, 1965; Eisner et al., 1970; von Euw et al., 1968; Frazier, 1965; Frazier and Rothschild, 1961; Jones et al., 1962; Pesce and Delgrado, 1972; Picarelli and Valle, 1972; Reichstein et al., 1968; Rotberg, 1972; Rothschild, 1971, 1972, 1973; Rothschild et al., 1970, 1972, 1973; and references therein). These features may be communicated to predators in an unambiguous manner by aposematic coloration or behavior. Space considerations prohibit more than the most superficial statement about this subject; the references cited immediately above and below are strongly recommended to readers interested in these aspects of lepidopteran communication.

The spectacular and diverse color patterns of moths and butterflies have long been used as evidence for the existence and mechanism of the evolutionary process (e.g., Brower, 1963; Creed, 1971; Ford, 1945, 1967, 1971; Kettlewell, 1973; Poulton, 1890; Rettenmeyer, 1970; Robinson, 1971; Rothschild, 1971, 1972, 1973; Wallace, 1890, 1891; Wickler, 1968; and references therein). Aposematic, startling, deflective, and mimetic patterns are clearly communicative, but what about crypsis? Camouflage and special protective resemblance (Robinson, 1969) clearly entail energy expenditures on the part of the insect. There is a biosynthetic and developmental cost to make cryptic features, as well as a behavioral one: the insect must be able to choose an appropriate background having little contrast with its own coloration, and it must posture there in an inconspicuous manner (Kettlewell, 1973; Sargent, 1973; and references therein). But is the cryptic individual signaling? Do predators perceive the prey but mistake it for something else, in the same way they discriminate against Batesian mimics by mistaking them for models known to be inedible? Or is no "signal" received at all, the predator being entirely unaware of the existence of the prey? Both probably occur in nature (depending to a large extent on the kind of predator); in either case the prey animal would survive. One may view crypsis as a form of communication in which the prey animal has been selected to decrease, rather than increase (as in aposematism), its signal-to-noise ratio. One would expect corresponding selection on the predator for better sensory and discriminatory abilities. The results of such escalating evolutionary exchanges are seen as the patterns on the wings and bodies of lepidopterans, and the forms they take depend on the strategies employed.

The various protective color patterns are traditionally grouped according to the manner in which they are usually presumed to function in communicative interactions with predators: crypsis (Robinson, 1969), disruptive coloration, disappearing or "flash colors" (Cott, 1940; Ford, 1967), deflective patterns (Blest, 1957; Poulton, 1890), startling or "novelty" coloration (Blest, 1957; Coppinger, 1970; Hinton, 1974), aposematism, Batesian and Müllerian mimicry, etc. Speculation as to the communicative significance of color patterns of particular species is a common practice among lepidopterists, but only in a limited number of cases have these hypotheses been tested by experiment. The notable, pioneering studies of Kettlewell and others on color polymorphisms and camouflage, Blest on the function of "eyespot" patterns, the Browers and their colleagues on mimicry, and others are cited in Brower (1963), Brower et al. (1971), Edmunds, 1974; Ford (1971), Kettlewell (1973), Rettenmeyer (1970), Robinson, 1969, Rothschild (1971, 1972, 1973), Turner (1971a), and Wickler (1968). Since coloration plays other roles besides protection from predators, and since different predators may respond in different ways to the same pattern, generalization from one case to another should be done with caution and with the knowledge that it is only an heuristic exercise until the appropriate experiments have been performed.

The Egg

Lepidopteran eggs do not behave (in the conventional sense), yet in certain cases they may be communicative. Adult butterflies of many species lay eggs singly, often with considerable spacing and away from other, older eggs. This is adaptive because older eggs hatch first, and if food is limited, the second to hatch may be left hungry on a leafless twig. Larvae are often cannibalistic (Alexander, 1961a; Dethier, 1937; Turner, 1971a)—another disadvantage for the younger, hence smaller, larva. Some adult female Heliconius butterflies apparently scan host plants visually (Passiflora spp.) and do not oviposit near other eggs (Alexander, 1961a; Gilbert, 1975). To what extent are the often conspicuous colors of butterfly eggs, and color changes prior to hatching, of signal value to adult butterflies? While we do not know, it is clear that such signals would be adaptive to the sender as well, because they might prevent establishment of competing larvae on the same plant. Experimental testing of this possibility appears to have been done by certain Passiflora species that have stipular "egg-mimics," which may inhibit oviposition by female Heliconius—the only case known to date in which lepidopterans (and mimetic ones at that) may themselves be hoisted with the petard of mimicry (Gilbert, 1975)!

In contrast, some lepidopterans, particularly those with aposematic, aggregated larvae, lay their eggs in clutches. Ovipositing females of Mechanitis isthmia (Ithomiinae, Nymphalidae) can search for and relocate their egg clutches after being disturbed (Gilbert, 1969). Several females of Heliconius sara sometimes even lay their eggs together in mixed clusters (Turner, 1971a). Although the adaptive strategies of such species differ from the solitary egg layers, in both cases the female must be capable of recognizing eggs, and in both cases the subsequent behavior of the female is affected.

The Larva

Most larval behavior is related to growth, individual survival, and preparation for pupation. For the majority of species communication occurs only in the contexts of protective behavior and active defense. Sound production, known in lepidopterous larvae of several groups (references in Frings and Frings, 1970;Haskell, 1961), is generally believed to be defensive in function, but since many larvae respond to airborne sound (Hogue, 1972; Minnich, 1936), it may possibly be used for intraspecific communication as well. Larvae have poorly developed visual abilities but they can distinguish vertical from horizontal figures (Dethier, 1943; Hundertmark, 1937a; de Lépiney, 1928), possess the physiological basis for color vision (Ishikawa, 1969), and show color preferences (Götz, 1936; Hundertmark, 1937b). Their gluttonous appetites are subserved by well-developed senses of olfaction and taste (Schoonhoven, 1973, and references therein).

Most caterpillars live solitary lives, devoid of all but occasional interactions with other larvae and predators. It is among those larvae that have symbiotic relationships with other insects and among those that live together at high densities or in aggregations that we find sophisticated communication systems.

INTERSPECIFIC COMMUNICATION IN SOCIAL SYMBIOSES

Some lepidopterous larvae live among or in association with social insects: usually ants, and rarely with bees, wasps, or termites (Ford, 1945; Hinton, 1951; Wilson, 1971). Their habits include feeding on nest materials and detritus (some members of the families Tineidae, Pyralidae and Noctuidae) or on host brood (some Lycaenidae, Tineidae, Cosmopterygidae, Cyclotornidae, and Pyralidae), but in most cases (most Lycaenidae and some Pieridae) the larvae are simply phytophagous and are tended, guarded, and otherwise protected by the hosts. Some of the nest inhabitants are treated as invaders and suffer attacks; they survive because of their protective integument, silken webwork, or other defensive adaptations. But a few are closely attended, cleaned, and otherwise cared for; the host workers may even construct shelters for the phytophagous species, and some larvae are carried into the nest, where they may feed on ant brood or even solicit food from workers. Such habits are best developed among the "blues," "hairstreaks," "coppers," and "metal-marks" of the butterfly family Lycaenidae (in the broad sense of Ehrlich, 1958), of which most species are myrmecophilous (live in association with ants) in some sense, and a few are obligately so. The overwhelming diversity of these relationships at the species level has been reviewed by Balduf (1939), Hinton (1951), and Malicky (1969). (See also Clark and Dickson, 1971; Farquharson, 1921; Lamborn, 1913; Owen, 1971; Ross, 1966; and Wilson, 1971.)

Certain characteristics of these attended and "guest" larvae serve to distinguish them from others that would be attacked, killed, and eaten or discarded. These features appear to be chemical, tactile, and perhaps visual. Most such species have glandular setae, tubercles, or elaborate, often eversible glands that produce secretions the hosts find attractive and upon which they may feed. Consider, for example, the "Large Blue," Maculinea (=Lycaena ) arion, the larvae of which undergo a change from ordinary phytophagy to carnivory at the fourth instar. After the third molt, the larvae leave the host plant and wander about. Ants find and stroke them with their antennae. A gland on the seventh abdominal tergite of the larva produces a secretion upon which the ant feeds. After a while the larva suddenly swells up its thoracic segments, markedly changing its form and perhaps providing other signals. The ant responds by picking up the larva with its mandibles and carrying it to the nest, where for the remainder of its larval life the caterpillar consumes ant larvae (references in Hinton, 1951).

Our knowledge of the complexity of these kinds of relationship is limited mostly to descriptions of observations made on a wide range of species, principally in the Lycaenidae. It is not clear to what extent, if any, the hosts benefit from the larval secretions, and for the majority of the larvae that are simply tended by ants on vegetation but which do not enter the nests, it is not clear if the larvae benefit by reduced aggression on the part of the ants (Lenz, 1917), protection from predators and parasitoids (Thomann, 1901), or both (Edmunds, 1974). The details of the communication between the larvae and their hosts are largely unknown. While the histology, ontogeny, and distribution of the glands that produce these "appeasement substances" have been described in considerable detail (Hinton, 1951; Malicky, 1969), none of the larval secretions have been chemically identified. That each species of lycaenid has but one or a few host species and that the larvae are attacked by "wrong" ants indicate a considerable level of complexity in the signals and responses. Malicky (1970a) has shown that even within one host genus (Formica), some species respond aggressively to the caterpillars in the vicinity of the nest entrance but not at a distance, others do not respond aggressively at all, and in one the "mood" of the ants was important but the distance from the entrance was not. In addition to the glands, certain other morphological and behavioral features of such larvae are evidently adaptations for living among or with ants (Malicky, 1970b). The behavior of some lycaenid larvae in soliciting food from ant workers may involve mimicry of the intraspecific food-solicitation signals of other workers or of larvae (Malicky, 1970b), as has been demonstrated for certain myrmecophilous beetles (Hölldobler, 1967, 1970, 1971). Mimicry of pheromones has also been suggested (Malicky, 1970b), but chemical evidence is wanting. The adults of nest-inhabiting lepidopterans lack those attributes that inhibit aggression by the hosts. However, the newly eclosed butterfly or moth bears a heavy coat of scales that readily come off in the jaws of attacking ants, facilitating escape from the nest.

Larvae of a few lycaenids have the remarkable habit of soliciting honeydew from various homopterans (references in Hinton, 1951). Lachnocnema bibulus does so by vibrating its elongated prothoracic legs over the dorsal surface of the membracid or jassid in a manner similar to that of an ant soliciting with its antennae.³ It also solicits food from the ants that tend these homopterans. And larvae of another lycaenid, Megalopalpus zymna, use a similar tactic as a ruse to approach more closely membracids and jassids, which they suddenly attack and devour—a case of tactile aggressive mimicry.

COMMUNICATION AMONG GREGARIOUS LARVAE

Larvae of a large number of lepidopterous species live in aggregations or at high densities. This habit is widely distributed among the various families. Usually all of the larvae in an aggregation have hatched from a single cluster of eggs.

Such larvae do many things together. They all begin and cease feeding at about the same time. When a predator threatens, they may all respond similarly and simultaneously, giving the impression of concerted defense. Many species produce highly ordered silk structures that, superficially at least, appear to involve coordinated activity employing communication. Unfortunately only a few species have been studied in detail.

One need not invoke complex communication systems to explain much of the seemingly coordinated behavior of such larvae. Their feeding times are usually regulated by extrinsic and intrinsic factors such as temperature, light level and photoperiod, and hunger. It is only to be expected that individuals of the same species, age, and usually parentage, would behave somewhat similarly in the same environment. Concerted defenses may in many cases simply be a simultaneous response of many or all larvae to some disturbing stimulus, and not to some alarm signal sent by the first larva that detects the predator. Larvae do of course respond to tactile stimuli of one another's movements, and this seems to be the means by which a disturbance may spread through some larval aggregations. Communicative synchronization of feeding and movement is known to occur in some species (Alexander, 1961a; McManus and Smith, 1972; Symczak, 1950; Wellington, 1957, 1974). Coordinated responses, especially in defense, are certainly adaptive (Edmunds, 1974; Ford, 1945; Hogue, 1972; Poulton, 1898), but experimental study of this aspect of larval behavior has unfortunately been neglected.

Gregarious larvae in several unrelated groups have been reported to follow one another's paths on feeding excursions. This trail-following behavior has been attributed to odor (Symczak, 1950) and to the silk laid down by the larvae (Long, 1955; McManus and Smith, 1972; Wellington, 1974), but it is not known if the stimuli involved are chemical, tactile, or both. Individual larvae lay down silk lines for many purposes, including safety lines, secure footholds (e.g., Alexander, 1961a), tying together of food materials (Bell, 1920; Ford, 1945; Alexander, 1961a), and orientation to lead them back to resting places. It is hardly remarkable that groups of larvae show similar behavior, but it is of course more easily noticed, especially when their trails build up to form structures visible from a distance. Variation in the behavior of larvae that use silk trails for orientation has produced an interesting communication system in certain tent caterpillars (Lasiocampidae). Some larvae in each brood are more reluctant than others to explore new areas, and they follow the more adventurous individuals, which lay the first silk trails (Wellington, 1957, 1974). Selection probably operates strongly at the colony level against those broods that contain an imbalanced ratio of leaders to followers (Wellington, 1974). (Adult moths derived from these caterpillars also differ in behavior.)

Silk enclosures, trails, platforms, and other structures made by groups of larvae are often of elaborate construction. But so also are similar structures (molting and resting platforms, hibernacula, cocoons, etc.) built by single individuals. The behavior involved in making a complex cocoon is both complicated and relatively inflexible, but cocoons are rarely identical since their forms are affected to some extent bythe physical limitations of the environment (Van der Kloot and Williams, 1953a, 1953b, 1954; Yokoyama, 1951). For larvae that live together, the environment includes silken structures already made by other larvae, and a succession of building activities by many larvae on the ever-enlarging construction may result in the spectacular enclosures of such species as tent caterpillars (Malacosoma spp., Lasiocampidae) and webworms (Hyphantria spp., Arctiidae). This process, in which the summation of relatively simple behavior patterns by individuals results in a complex construction, is similar in principle to the process of "stigmergy" hypothesized by Grassé (1959) to account for the complexity of nest construction by termites and other social insects (see also Wilson, 1971), a concept recently generalized by Wilson (1975) under the name "sematectonic communication." Such communication is characterized by individuals responding to the inanimate products of their labors, rather than directly with one another. (In this context it should be mentioned that an individual that interacts with its own constructions, such as a caterpillar building a cocoon, is in a similar sense communicating with itself.) Unlike social insects, caterpillars are not known to recruit other individuals to assist in building. But recruitment may be unnecessary for the production of community enclosures or multiple cocoons if, as is usually the case among gregarious lepidopterous larvae, their development and behavior is synchronized. Larvae that live communally are believed to gain a measure of protection from predators (Ford, 1945; Hogue,1972; Tinbergen, 1958), and communal living is adaptive in other ways as well (Rathke and Poole, 1975). The tendency to build silken structures together with other larvae has been demonstrated as heritable (in the case of double-cocooned and polypupal-cocooned silk-moths: Yokoyama, 1959). Thus the prerequisites for the evolution of such behavior (selective pressure and heritability) are present, but no elaborate communication system need evolve. And in spite of the fact that tent caterpillars share a number of behavioral attributes with certain social insects—siblings living together, behavioral synchronization, polyethism (some larvae "adventurous"), (silk-) trail-following, the construction of elaborate dwellings by means of sematectonic communication, and probably strong selection at the colonylevel—they are in comparison with social insects merely "communal" (in the sense of Michener, 1969, as modified by Wilson, 1971).

Intraspecific competition is the context for interlarval communication of a rather different kind. Larval density can affect adult development, morphology, and physiology (Long, 1959; Long and Zaher, 1958). In some tortricid larvae spacing of individuals is achieved through defense of a feeding territory (Russ, 1969). Recent studies of Ephestia {͇Anagasta) kiihniella (Pyralidae) and some related species have revealed that antagonistic interactions between the competitive and agressive larvae, especially the release of a mandibular gland pheromone, affect larval spacing and survivorship (Corbet, 1971; Cotter, 1974; Mudd and Corbet, 1973). The pheromone therefore has been reported to have an "epideictic" effect, which is enhanced by the chemical's role as a host-detection kairomone (Brown et al., 1970) for parasitoid hymenopterans (Corbet, 1971). In contrast, among silkmoth larvae (Bombyx, Bombycidae), aggregation rather than spacing is mediated by pheromones (Okui, 1964).

The Pupa and Pharate Adult

Pupae, like eggs, seem to be relatively inert and devoid of communicative behavior. This is not universally true, however.

Pupae of some species have a number of active defensive adaptations (Cole, 1959; Hinton, 1955), certain of which can be regarded as communicative. (These adaptations are distinguished from passive defenses such as crypsis and warning colors of one sort or another, which may also have communicative functions.) Audible sounds are produced by stridulation or by knocking or scraping the body against the wall of the pupal cell (Hinton, 1948, 1955; Downey, 1966; Downey and Allyn, 1973; Hoegh-Guldberg, 1972). Similar sounds may also be produced by the pharate adult, using the appropriate structures on the overlying pupal cuticle (Hinton, 1948, 1955; Alexander, 1961b). The communicative value of these sounds has not been experimentally investigated; they are usually presumed to be defensive (Downey and Allyn, 1973). But as Gilbert (1975) has pointed out, the potential for intraspecific auditory communication between pupae and adults exists in at least one species (Heliconius erato), the pupa of which stridulates (Alexander, 1961b) and the adult of which can hear (Swihart, 1967a). It should be pointed out, however, that the lowest threshold for hearing in Heliconius adults as measured electrophysiological^ by Swihart was about 60 db (at about 1.2 khz). The intensity of the pupal sounds has not been measured, but is probably below that level.

Heliconius pupae also emit species-specific odors, which have been interpreted as defensive (Alexander, 1961b) and pheromonal (Gilbert, 1975). Males ofthe Heliconius erato species group are attracted by pheromones to female pupae and await eclosion before attempting copulation (L. E. Gilbert, pers. comm.). But male H. charitonia "invade" the pupal integument with their genitalia and "rape the female pupa⁴ as a routine mating procedure" (Gilbert, 1975, and pers. comm.). These observations support the idea that such pupae (or pharate adults) have pheromonal(and perhaps sonic) means of indicating their presence and precise location to adult males. Sex-attractant pheromones are generally not released until after eclosion in most species (Jacobson, 1972).

Numerous instances of lycaenid pupae that are tended, protected, and sometimes even sheltered by ants have been documented and are reviewed by Hinton (1951, 1955) and Downey and Allyn (1973). Like the larvae (q.v.) of these and many other lycaenid species, such pupae are reported to secrete attractive substances; in addition, many lycaenid pupae produce audible sounds (Downey, 1966). Unfortunately, none of these relationships are understood in enough detail to be able to say more about the nature or significance of auditory or chemical communication by these fascinating insects.

The Adult

The behavioral repertoire of adult lepidopterans is far more complex than that of the immature stages. Reproduction and dispersal are added to defense and (in many cases) feeding as requisite activities of successful adults. Sex, flight, (usually) nectar location, and (for ovipositing females) larval host-plant identification all require a high degree of sensory capability and motor coordination. Before surveying adult communication we must first briefly examine the physiology of the senses involved.

SENSORY PHYSIOLOGY OF ADULTS

Vision

The visual Umwelt of lepidopterans differs significantly from our own. The visual spectrum of some butterflies appears to be the broadest in the animal kingdom, extending from the edge of terrestrial ultraviolet (around 300 nm) through the red (700 nm); it therefore includes our own spectral range plus 300 to 400 nm in the ultraviolet (Crane, 1955; Gilbert, 1975; Mazokhin-Porshniakov, 1969, and references therein; Obara, 1970; Petersen et al., 1952; Post and Goldsmith, 1969; Swihart, 1967b). Color vision has been demonstrated in both butterflies (Crane, 1955; Ilse, 1928, 1932a, 1932b, 1937, 1941; Ilse and Vaidya, 1956; Mazokhin-Porshniakov, 1969; Post and Goldsmith, 1969; Swihart, 1963, 1964, 1965, 1967b; C. Swihart, 1971; Swihart and Swihart, 1970) and moths (Knoll, 1922, 1925, 1927; Mazokhin-Porshniakov, 1964, 1969; Schremmer, 1941).

On the basis of anatomical, physiological, and behavioral studies, and by analogy with other terrestrial arthropods with well-developed compound eyes, lepidopterans are believed to be most behaviorally responsive to light of short wavelengths, able to adapt over a wide range of light intensities, and able to detect (if present) the plane of polarization. Significant morphological and physiological differences occur between species and are especially pronounced between nocturnal and diurnal forms (Autrum, 1965; Bernhard, 1966; Burkhardt, 1962, 1964; Dethier, 1963; Eltringham, 1919; Goldsmith, 1961; Goldsmith and Bernard, 1974; Mazokhin-Porshniakov, 1969; Miller et al., 1968; von Frisch, 1967; Wehner, 1972; Yagi and Koyama, 1963; and references therein).

Tapetal interference filters of unknown function (but believed to increase sensitivity to certain colors) have been reported in the eyes of some butterflies (Bernard and Miller, 1970; Bernhard et al., 1970; Miller and Bernard, 1968). (It has been suggested that some lepidopterans are sensitive to infrared light but not via the visual organs; see olfaction.) The role of vision in adult behavior is discussed under flower visitation and courtship.

Sound

Many lepidopterans are capable of hearing. Tympanic organs located on the metathorax or abdomen in diverse groups of moths are believed to have evolved independently at least ten times⁵ (Kiriakoff, 1956, 1963; Treat, 1964, and pers. comm.). Saclike inflated structures located at the wing bases in some nymphalid butterflies (Swihart, 1967a) and organs associated with the mouthparts in some Sphingidae⁶ (Roeder, 1971, 1972, 1974a; Roeder and Treat, 1970; Roeder et al., 1968, 1970) have also been identified as auditory in function. In addition to these organs, lepidopterans, like other insects, possess displacement-sensitive setae and subgenual and other scolopophorous organs that might act as receptors of air- or substrate-borne vibration. (See also Busnel, 1963; Frings and Frings, 1960.)

The "ears" of moths are most sensitive to ultrasound (Roeder, 1965, 1967a, 1971, 1972, 1974a, 1974b, 1975; Roeder and Treat, 1957; Sales and Pye, 1974; Schaller and Timm, 1950; Treat, 1964). It is now well known that the adaptive significance of the hearing of moths is that it enables them to detect echolocating insectivorous bats before they themselves are detected. Moths that hear bats perform a wide variety of defensive behavior, the nature of which depends on the distance at which the predator is detected and the species of moth concerned. Turning, looping, power diving or dropping to the ground, and other evasive tactics are used (Roeder, 1965, 1966, 1967a, 1967b, 1970, 1971; Roeder and Fenton, 1973; Treat, 1964).

Some arctiid and amatid moths, many of which are unpalatable or otherwise "protected" (Beebe and Kenedy, 1957; Blest, 1964; Eisner, 1970; Rothschild, 1965, 1973; Rothschild and Alpin, 1971) employ an additional strategy: they answer the ultrasonic cries of bats with aposematic clicking calls produced by a thoracic "microtymbal" (Blest et al., 1963; Fenton and Roeder, 1974; Dunning and Roeder, 1965). Bats confronted with such calls veer away from the prey (Dunning and Roeder, 1965). Some noisy palatable species are also avoided and are therefore Batesian mimics (Dunning, 1968). Probably some of the sounds produced by other moths (references in Frings and Frings, 1960; Haskell, 1961; see also Lloyd, 1974; Rothschild and Haskell, 1966) are defensive as well.

Auditory communication between lepidopterans has rarely been documented. Roeder and Treat (1957) suggested that ultrasonic components of wing sounds might be audible to other moths. Dahm et al. (1971) demonstrated that auditory signals produced by wing vibration are an important component of the mating system of the lesser waxmoth (Achroia grisella, Pyralidae). The males of this species (like the females of most moths) release a complex mixture of sex-attractant pheromones. Females are excited by the chemicals but do not orient to the source unless vibrations, such as the fluttering of a male's wings, are also present.

There are few other reports of even potential auditory communication between lepidopterans (Bourgogne, 1951).(Reference has already been made to the possibility of pupa-adult communication among certainheliconiine butterflies.) Perhaps the most widely cited case is that of the "cracker" butterflies of the genusHamadryas (=Ageronia Nymphalidae), which produce (in an as yet undetermined manner) a loud, rapid series of clicking sounds during flight. Adult Hamadryas can hear (Swihart, 1967a). The behavioral significance of these sounds, often produced during close pursuit of other butterflies, is unknown; it has often been suggested that they are involved with territoriality (q.v.) and/or courtship. A few other butterflies make audible sounds of unknown function during flight (e.g., some Charaxes) or while stationary (F. Scott, 1968). One of the most peculiar cases of sound production is that of the "Death's Head" sphinx moth (Acherontia atropos, Sphingidae), which has been reported to enter the hives of honeybees to obtain honey; when attacked by bees it emits a sound similar to that of "piping" by the queen (Bourgogne, 1951; see also Busnel, 1963).

Direct mechanoreception (not involving sound) is probably important for communication during contact between the sexes, but it remains uninvestigated (however, see Doane and Cardé, 1973).

Olfaction

Sensitivity to airborne chemical stimuli plays an important role in feeding and in the sexual lives of moths and butterflies. Floral odors are important orientation cues for flower visiting (q.v.), and pheromones are involved in the courtship of all intensively studied species.

The antennae are the primary olfactory organs. The frequent sexual dimorphism in these structures among moths (usually with greater surface area and receptor number in males) is generally believed to be related to their use as "odor filters" for the detection of (usually female) sex pheromones. Butterflies rely to a much greater extent on visual cues and exhibit little sexual dimorphism of antennal structure (Payne, 1974; Schneider, 1964).

The sensory physiology of insect olfaction has recently been reviewed by Kaissling (1971) and, with respect to pheromones, by Payne (1974). Sensilla basiconica and sensilla trichodea, located on the antennae, are the olfactory receptors (see Albert et al., 1974). Those involved in phermone reception are often highly specialized and respond only to a narrow range of chemical stimuli.⁷ The response threshold for individual receptors is as low as a single molecule, and whole-organism behavioral responses are elicited with as few as 200 molecules (Kaissling and Priesner, 1970; Schneider, 1974). Comparative studies of response to pheromones and to various chemically related compounds (pheromone analogs, or "parapheromones," that differ in carbon chain length, location and orientation of unsaturated bonds, and attached functional groups) have revealed that even those that are stereochemical^ very similar to the natural pheromones are required in greater concentrations in order to elicit the same electrophysiological or behavioral responses, and that effectiveness decreases with increasing stereochemical discrepancy (e.g., Gaston et al., 1972; Payne et al., 1973; Roelofs and Comeau, 1971a; Schneider et al., 1967; and other references in Payne, 1974). The mechanism of transduction is not presently understood (Davies, 1971; Payne, 1974; and references therein). Theories currently in vogue differ in details but most suggest a chemical and/or physical interaction between pheromone molecules and matching acceptor (receptor) sites on the receptor cell membrane, which in some manner affects permeability to inorganic ions and thus initiates electrical events.

Early studies of sex pheromones concentrated on the pheromone of each species, since it was believed that species-specificity was conferred primarily or exclusively by chemical diversity. It is now clear that chemical specificity (hence reproductive isolation) is also conferred in many species by mixtures of two or more compounds. A compound that elicits behavioral and/ or electrophysiological responses may, when combined with others as a mixture, be more or less effective (depending on the species and compounds concerned). Synergistic or inhibitory effects are believed to provide species-specificity in the communication system with a limited diversity of compounds (e.g., Comeau, 1971; Klun and Robinson, 1971; Minks et al., 1973; O'Connell, 1972; Roelofs and Cardé, 1974, and references therein; Roelofs et al., 1973; Roelofs and Comeau, 1968, 1971a, 1971b). Additional specificity is provided by concentration and by relative concentrations of components in mixtures (Bartell and Shorey, 1969a; Keae et al., 1973a; Klun and Robinson, 1972; Roelofs and Cardé, 1974, and references therein; Roelofs et al., 1971).

Behavioral responses to pheromones are also affected by previous exposure (Bartell and Lawrence, 1973; Bartell and Roelofs, 1973; Shorey, 1974, and references therein; Traynier, 1970), light intensity and photoperiod (Bartell and Shorey, 1969b; Shorey and Gaston, 1965), temperature (Batiste et al., 1973; Cardé and Roelofs, 1973; Collins and Potts, 1932; Klun, 1968; Shorey, 1966), and other factors (Jacobson, 1972; Shorey, 1974). These features of olfaction, together with others that surely remain to be discovered, are interrelated with one another and with similar factors affecting pheromone release by the opposite sex. The lack of diversity in a single variable (chemical structure) is compensated by tremendous complexity in the rest of the communication system.

The behavioral responses of insects to sex pheromones have been reviewed by Shorey (1973, 1974). With increasing concentrations of "attractant" pheromones a "hierarchy of responses" is elicited in males, which consists of antennal movements, increased activity, flight and orientation towards the source, followed by cessation of flight, localization of the source, release (in some species) of male-produced pheromones, and copulatory attempts (Bartell and Shorey, 1969a, 1969b; Daterman, 1972; Tränier, 1968). In some species additional chemical stimuli are needed at various points along the "hierarchy"; if they are not present the behavioral sequence is not completed (Cardé et al., 1975a). A "hierarchy" of responses has also been demonstrated among females in the "reversed-role" chemical communication system of the greater and lesser waxmoths, the males of which produce long-range chemical attractants (Dahm et al., 1971; Roller et al., 1968). Another "reversed-role" system has been reported to occur among certain ithomiine butterflies (Nymphalidae), the males of which produce pheromones that presumably function as intra- and interspecific attractants mediating aggregation (L. E. Gilbert, 1969 and pers. comm.; W. A. Haber, pers. comm.; but see also Pliske, 1975b). Orientation to a pheromone source during flight is probably mediated by anemotaxis combined with crosswind flights that are believed to enable the insect to remain within the active space; several other mechanisms of orientation have also been postulated (Farkas and Shorey, 1974, and references therein; Kennedy and Marsh, 1974).

In contrast, sex pheromones produced by males generally inhibit locomotion in females. The most extensively studied male pheromone system is that of the queen butterfly, Danaus gilippus (Danainae, Nymphalidae). The male queen butterfly overtakes the female in flight and disseminates (with everted and splayed brushlike "hair-pencils" extruded from his abdomen), a cuticular dust bearing a pheromone that induces her to land and become quiescent (Brower et al., 1965). Other danaine butterflies have similar structures, andin some cases the pheromones have been chemically identified (Brower and Jones, 1965; Edgar and Culvenor, 1974; Edgar et al., 1971, 1973; Meinwald and Meinwald, 1966; Meinwald et al., 1966, 1969a, 1969b, 1969c, 1971, 1974; Myers, 1972; Myers and Brower, 1969; Pliske and Eisner, 1969; Pliske and Salpeter, 1971; Schneider and Seibt, 1969; Seibt et al., 1972). Such "aphrodisiac" pheromones are believed to be of wide occurrence in the order (Birch, 1974c, and references therein). (See below.)

The idea that moths might orient to infrared radiation and specifically to the characteristic absorption and transmission energies of pheromones and other biologically relevant molecules (Callahan, 1965a, 1965b, 1965c, 1966, 1967, 1968, 1969a, 1969b, 1970, 1971; Callahan et al., 1968; Laithwaite, 1960; Wright, 1963) has not been supported by evidence gathered from controlled experiments (Griffith and Süsskind, 1970; Hsiao, 1972; Hsiao and Hackwell, 1970; Hsiao and Süsskind, 1970; Levengood and Limperis, 1967).

COMMUNICATIONS EQUIPMENT: SCALES AND PHEROMONES

Moths and butterflies are invested with a covering of flattened integumental outgrowth called scales. Each scale is produced during the pupal stage by a single epidermal cell, which usually dies before eclosion. Scales cover the entire body surface, except for the compound eyes (which may have a few scales or scalelike setae scattered between the ommatidia). (The structural diversity of wing scales is reviewed by Downey and Allyn, 1975.)

Scales serve many functions, including (1) aerodynamic: increasing lift during flight (Nachtigall, 1965, 1974); (2) sensory: acting as mechanoreceptors (trichogen cell derivatives of sensilla squamiformia: Dethier, 1963; Eltringham, 1933; Wiggles worth, 1972); (3) thermoregulatory: acting as insulation (Adams and Heath, 1964) or as solar-radiation-absorbing outgrowths (Kettlewell, 1973; Watt, 1968) that may also aid circulation by producing convection currents in the wing veins through uneven heat absorption (Bourgogne, 1951); (4) defensive: as the seat of most cryptic, startling, deflective, aposematic, mimetic, or other adaptive colors, patterns, and structures; as detachable and dispensable integumentary structures (Eisner, 1965; Eisner and Shepherd, 1965, 1966; Eisner et al., 1964; Hinton, 1951, and references therein); and (5) reproductive: as the seat of colors and patterns that play significant roles in courtship, and as a source of or disseminating organ for sex pheromones (references below). Thus, in considering the colors of lepidopterans and the structures of their scales, one must bear in mind that many, often conflicting, selective pressures have over the course of evolutionary time affected these features. The colors and structures of scales found on the bodies, wings, and legs of butterflies and moths thus represent compromises.

The communicative role of color in courtship is widely recognized as a major factor in the evolution of the diurnal Lepidoptera. But while conspicuous coloration is advantageous as a high-intensity sexual signal, it may be detrimental with respect to protection from predators. It is probably for this reason that the brilliant courtship colors of male butterflies are located on the upper surfaces of the wings, where they are exposed during flight but disappear when the insect comes to rest. (An adventitious benefit gained from such color distribution is that aerial predators may be left with a search image that "disappears" when the insect lands— so-called flash coloration). Shifting epigamic signals out of the sensory range of predators accomplishes the same function. The use of patterns that lie beyond the vertebrate-visible spectrum is one means of limiting sexual signals to "intended" receivers. Such ultraviolet signals are widely distributed among the diurnal Lepidoptera (Mazokhin-Porshniakov, 1957, 1969; Nekrutenko, 1964, 1968; Obara, 1970; Scott, 1973b; Silberglied, 1969, 1973; Silberglied and Taylor, 1973).

Color, produced by both pigmental and structural means in wing scales, plays an important role in the courtship of diurnal species. Because of their finely divided morphology at the ultrastructural level, unpigmented scales are generally white due to surface scattering.⁸ Their ridged, reticulated structure serves as a substrate for a wide range of pigments, including melanins in the case of very dark scales (Ford, 1945; Kolyer and Reimschuessel, 1970; Mason, 1926; Wigglesworth, 1972; Yagi, 1955). In addition, the integument constituting the scale ridges (Morpho, Eurema, Colias) or base (Urania) may have a regular laminated structure that acts as an optical interference filter that reflects either "visible" (to man) or ultraviolet light (Anderson and Richards, 1942; Eisner et al., 1969; Gentil, 1942; Ghiradella et al., 1972; Kinder and Süffert, 1943; Lippert and Gentil, 1959; Mason, 1927; Silberglied, 1969; Süffert, 1924).

The latter surfaces are called "iridescent" and occur widely as patterns of scales on the wings of butterflies and a few moths. The light reflected from such surfaces is generally of high intensity and spectral purity. The wavelengths, intensity, and polarization of the light reflected depend on the relative geometric positions of the light source, lamellar array, and observer. Crane (1954) pointed out that a chromatic modulation of the light reflected from the wing occurs with every wingbeat. In addition to the unusual physical properties of the reflected light, iridescence may have an advantage over pigment in that the color depends on the physical properties of the cuticle, over which the insect already has considerable control during development. The animal need not produce unusual pigments at high metabolic cost to achieve a brilliant color. Iridescent reflection may also be added to pigment-based color to produce combinations not readily achievable by pigment alone, as among those butterflies that combine iridescent ultraviolet reflection with "visible" color patterns of all kinds. But the behavioral significance of iridescent colors in general, and of the modulation of intensity, color, and polarization in particular, is poorly understood at present.

In addition to "ordinary" scales, trichogen cells form a diverse array of glandular cells specialized for sexual functions. These "androconia," "scent-scales," or "scent-hairs" [sic] occur on males (and on some female Thyridia spp., Ithomiinae: B. Drummond, pers. comm.) They may be scattered among the wing scales, or concentrated as special patches, tufts, "brands," "hair-pencils," etc., on eversible or inflatable sacs or tubes ("coremata") on various parts of the legs, wings, or body. Reference has already been made to the "hair-pencils" of male danaine butterflies; similar male organs and "sex scaling" occur in a wide array of butterflies and moths (Barth, 1960; Birch, 1972, 1974c; Jacobson, 1972; McColl, 1969; Percy and Weatherston, 1974; Varley, 1962). Observations on the use of these structures are lacking in the overwhelming majority of species (Varley, 1962), but in the few species studied the organs are exposed or everted during courtship and are considered to be the disseminating organs for "aphrodisiac" pheromones, which function (where known) by inhibiting locomotion of the female (Birch, 1974c; Brower et al., 1965; Pliske and Eisner, 1969; Tinbergen, 1968; Tinbergen et al., 1942).

Sex pheromones produced by females are also products of specialized epidermal cells. These cells are associated with intersegmental membranes that are everted (presumably by blood pressure), and the pheromones are released at the time of "calling." The morphology and histology of these glands have been reviewed by Percy and Weatherston (1974).

The chemistry of lepidopteran sex pheromones has received considerable attention in recent reviews (Beroza, 1970; Evans and Green, 1973; Jacobson, 1972, 1974; Roelofs and Cardé, 1974; Roelofs and Comeau, 1971a) and will not be treated here in detail. The most interesting feature of these pheromones is the contrast between the low chemical diversity of female-produced sex pheromones and the high chemical diversity of the pheromones produced by males. Most of the former are C12, C₁₄ or slightly longer straight-chain, unsaturated (monoene or diene) alcohols, acetates and aldehydes (identified from members of the families Arctiidae, Bombycidae, Lymantriidae, Noctuidae, Pyralidae and Tortricidae). Differing only slightly from these are a hydrocarbon, an epoxide of a hydrocarbon, and a branched ester, of similar chain length (references in Evans and Green, 1973; Roelofs and Cardé, 1974). In contrast, some of the compounds isolated from male "androconia," scentorgans, etc., include small carboxylic acids, benzaldehyde, benzyl alcohol, and 2-phenethyl alcohol, various small terpenoids (all isolated from Noctuidae: Aplin and Birch, 1970; Birch, 1972, 1974c; Clearwater, 1972; Grant et al., 1972), citral (geranial and neral: Bergström and Lundgren, 1973), a bicyclic sesquiterpene alcohol (tentatively identified from a lycaenid butterfly: Lundgren and Bergström, 1975), and large heterocyclic ketones (from danaine butterflies:⁹ Edgar and Culvenor, 1974; Edgar et al., 1974; Meinwald et al., 1966, 1969a, 1969b, 1969c, 1971). The larger molecular weight of the sex "attractant" pheromones (usually produced by females), which operate over long distances and persist in time, and the high volatility of many "aphrodisiac" pheromones (produced by males), which are used for a moment at close range, are well in accord with the theoretical constraints on molecular size in chemical communication systems (Bossert and Wilson, 1963; Wilson and Bossert, 1963).

ADULT BEHAVIOR

Courtship

With few exceptions courtship follows a single basic pattern throughout the order. Males are generally attracted to females by long-distance communication, either visual (as in most butterflies) or chemical (as in most moths). Close approach and persistent courting by males is mediated in many species by female pheromones. The male may then perform stereotyped behavior patterns, disseminating aphrodisiacs and/or presenting visual, auditory, or tactile signals, the response to which is inhibition of locomotion in receptive females. Females play an active role in acquiescing to males, and can usually reject inappropriate males (e.g., the wrong species)¹⁰ or those that attempt to mate with them when they are not receptive. Rejection involves moving or flying away, or the assumption of a stereotyped "rejection posture." If the female acquiesces (by ceasing activity; sometimes lowering the abdomen and exposing the genitalia but often having no outward behavioral manifestation) copulation may occur. Various aspects of courtship and related activities have been reviewed by Birch (1974), Farkas and Shorey (1974), Jacobson (1972, 1974), Miller and Clench (1968), Myers (1972), Roelofs and Cardé (1974), Scott (1973a, 1974), Shields and Emmel (1973), and Shorey (1973, 1974).

The courtship of butterflies (and some other diurnal forms) differs from that of most moths, primarily in its early stages. Male butterflies usually initiate courtship, but "solicitation" by receptive females has also been reported to occur (Crane, 1955; Scott, 1973a). Magnus (1963) distinguished between two strategies, "seeking" and "waiting,"¹¹ by means of which male butterflies locate potential mates. Approaches and subsequent courtship behavior by males are released by visual stimuli. Color (including ultraviolet components), motion, and size of the female have been shown to be important cues, while the details of pattern that enchant lepidopterists seem to play little or no role in courtship. Males usually distinguish conspecific females from other males on the basis of either color, odor, or both, but may be highly indiscriminate in their initial approaches (Brower et al., 1967; Crane, 1955; Johnson, 1974; Lederer, 1960; Magnus, 1950, 1958, 1963; Myers and Brower, 1969; Shapiro, 1972, 1973; Stride, 1956, 1957, 1958a, 1958b; Tinbergen 1968; Tinbergen et al., 1942). If the individual being courted turns out to be male, the sequence is usually terminated; "homocourtship" rarely goes so far as to end in "copulation."

Among sexually dimorphic species color plays an important role (Magnus, 1963; Stride, 1956, 1957, 1958a, 1958b), which must be somewhat diminished in species both sexes of which are similar or mimetic. As Poulton (1907) first pointed out, in species of the latter type, visual cues alone will not suffice to enable males to distinguish females, or even males, from members of other species in the mimicry complex. In sex-limited mimicry (where only females resemble other species), males cannot distinguish conspecific females on the basis of visual cues (except ultraviolet; see Remington, 1973), but females could still use them to discriminate among courting males. The reliability of visual cues may also be a problem among butterflies with seasonal forms and polymorphism (Burns, 1966; but see also Pliske, 1972). Brower (1963b) suggested that scent-dissemination organs and odors detectable to man, hence pheromonal means of communication, are more (?) common among Müllerian mimics (but see Vane-Wright, 1972). It is now apparent that the courtship of just about all lepidopterans studied involves pheromones at some stage. It is not surprising that Müllerian mimics are fragrant; that is indeed one of the means by which unpalatability is communicated to potential predators.

An alternative means by which males of mimetic species might differentiate conspecific females, and females recognize conspecific males, is by way of ultraviolet reflection patterns invisible to vertebrate predators. Survey of several mimicry complexes in the ultraviolet by Silberglied (1969, 1973, and unpublished) and C. L. Remington (1973, and pers. comm.), revealed differences between some species and between the sexes of some nondimorphic species, but in the absence of behavioral experiments these results are difficult to interpret. However, among the Pieridae, most species of which show strong dimorphism of ultraviolet reflection patterns not evident in visible light (Mazokhin-Porshniakov, 1957, 1969; Nekrutenko, 1964, 1968; Obara, 1970; Scott, 1973b; Silberglied, 1969, 1973; Silberglied and Taylor, 1973), these patterns are used both as sexual-recognition signals (Obara, 1970; Silberglied, 1973) and as partial isolating mechanisms (Silberglied, 1973).

The activities of moths during the early stages of courtship contrast strongly with those of butterflies in two ways: female moths initiate courtship and the first cues are generally olfactory rather than visual. Females "call" by releasing at the appropriate time sex pheromones¹² that elicit in males a "hierarchy of responses" (see above) that lead them to the source (Shorey, 1973, 1974). Orientation may be accomplished by means of anemotaxis and/or chemical cues (Farkas and Shorey, 1974), but sound (Dahm et al., 1971) and vision (Shorey and Gaston, 1970) are sometimes involved, especially for closerange orientation. Visual cues are certainly not necessary for some species as they are with butterflies; mating in complete darkness has been reported in Catocala (Noctuidae: Sargent, 1972). While a few moths are known to have color vision (q.v.), it is not known whether color plays any role in their courtship behavior. The role of color in the courtship of day-flying moths, many of which are bejeweled with iridescence (e.g., Uraniidae, Amatidae) and striking color patterns (e.g., Arctiidae), is an unexplored field.

Once in the immediate vicinity of a female, subsequent attentive behavior by the male depends in many cases on continued or additional olfactory cues. Magnus (1958) found that male Argynnis paphia (Nymphalidae) responding to moving female models by chasing would soon lose interest if the scent of a female were lacking. In the almond moth (Cadra cautella: Pyralidae), female-produced compounds different from the long-range sex-"attractant" are required for excitation of the male and a complete courtship sequence ending in copulation (Brady et al., 1971b; see also Cardé et al., 1975a). In many other moth species (e.g., Ephestia kiihniella, Pyralidae: Traynier, 1968; Porthetria dispar, Lymantriidae: Brady et al., 1971a) a single pheromone serves both to attract and to excite males. However, close-range stimulant pheromones are not required in all species; in Colias eurytheme (Pieridae) males will court and attempt to mate with paper models in the absence of females (O. R. Taylor and R. E. Silberglied, unpublished).

In many butterflies the initial meeting of the two sexes is aerial, and the female must be induced to land before attempts at copulation can be made. Female moths generally "call" from a stationary position in an exposed place, but may take flight if disturbed. At this point "seduction" is in order. Males may release highly volatile, "aphrodisiac" pheromones (either airborne or on cuticular dust particles), inhibiting female locomotion. Reference has already been made to the "hair-pencilling" behavior of male danaine butterflies. Male Eumenis (Satyrinae, Nymphalidae) enfold the female's antennae between the forewings in an elaborate "bowing" display; there her antennae are exposed to a patch of "androconial" scales (Tinbergen, 1968; Tinbergen et al., 1942). Vane-Wright (1972) suggests that scales transferred from wings to abdominal scent-brushes of Antirrhea (Satyrinae, Nymphalidae) function in a manner similar to the cuticular "hair-pencil dust" of danaine butterflies. In Eurema daira (Pieridae) the male lowers one forewing and "buffs" the female's antennae with a patch of specialized scales (Silberglied, 1973, and unpublished). Male noctuid moths expose and splay their "brush-organs" immediately before attempting copulation, but no contact is ordinarily made with the female's antennae (Birch, 1970, 1974c; Grant, 1970, 1971); male pheromones are also required to elicit receptivity in female phycitid moths (Grant and Brady, 1975; Grant et al., 1975). Such behavior patterns areprobably general throughout the order in most cases where special male scent organs or "sex scaling" is found, but are not known to occur in well-studied species (e.g., in the Bombycidae and Saturniidae), which lack such organs.

Female moths have excellent control over their sex lives since they may "call" whenever receptive. Receptivity is governed by both internal (age, physiological condition, time since last mating) and external (time of day, light level) factors. If not receptive, they do not "call." Female butterflies, on the other hand, constantly exposed to the view of actively searching males, are often subject to close-range copulation attempts. In response to persistent males, unreceptive female butterflies either fly away, flap their wings, or assume stereotyped rejection postures. Scott (1973) has collated much of this information and should be consulted for details.

Aggregations

Some butterfly species (and more rarely certain moths) are occasionally or regularly found in dense aggregations. Individuals of aposematic species are believed to benefit from close proximity to one another, the general argument being that they provide a bigger (and perhaps more memorable) visual stimulus to predators. Aggregations of individuals also occur around food sources and mud puddles. Heliconius butterflies roost in groups at night, as do monarch butterflies (Danaus plexippus, Danainae, Nymphalidae) during migration (see Benson and Emmel, 1973; Turner, 1975). Bogong moths (Argrotis infusa, Noctuidae) aggregate by the thousands at their aestivation sites (Common, 1954), and dense clusters of inactive butterflies have also been reported (Muyshondt and Muyshondt, 1974).

Little is known about communication between individuals in such aggregations. In their choice of resting site they (i.e., the first to land) are certainly responding to various stimuli in their environment, but individuals also recognize others of their kind and orient to them. "Mudpuddling" by butterflies (and occasionally moths) is one of the more intriguing cases (Downes, 1973; Norris, 1936). The fact that such aggregations (mud-puddle "clubs") consist almost entirely of males has led to some interesting hypotheses; Wynne-Edwards (1962), for example, included them under "group nuptial displays." Recently, Arms et al. (1974) demonstrated that, in addition to visual cues, one proximate stimulus for mudpuddling by tiger swallowtail butterflies (Papilio glaucus) is sodium. Visual recognition is also involved in the attraction of numerous additional individuals to the site (Collenette and Talbot, 1928). However, it remains a mystery why males are so disproportionately overrepresented at mud puddles, carrion, urine, rotting carcasses, fruits, and other such sources. Another curious aggregation phenomenon not presently understood occurs only in those populations of the African butterfly Acraea encedon (Nymphalidae, Acraeinae) in which there is a highly imbalanced sex ratio with females predominating. Females aggregate and lay infertile eggs on non-host plants and on one another as well (Owen, 1971).

The communal roosting and "social chasing" of heliconiine butterflies is well known to lepi-dopterists who have worked in the Neotropics, and numerous other butterfly species have been reported to roostgregariously (e.g., Clench, 1970; Crane, 1955; Jones, 1930, 1931; Muyshondt and Muyshondt, 1974; Myers, 1930; Poulton, 1931a, 1931b; Poulton et al., 1933; Young, 1971). Benson (1971) and Turner (1971a, 1975) speculate that communal roosting, in addition to being protective ("it being usually believed that it helps a distasteful species to be gregarious"; Turner, 1971a), in Heliconius is part of a combination of behavioral features holding closely related individuals together in highly restricted home ranges and having some connection with "altruism" in the Hamiltonian sense (Hamilton, 1964). Gilbert (1974) combines these ideas with the consideration that the communal roosting habit in Heliconius may have evolved as an integral part of their coevolution with floral resources (see also below): young individuals perhaps learn roosting sites as well as "trap-lines" by following older, more experienced individuals. Crane (1955) performed extensive ethological experiments on Heliconius erato and discovered that while color plays an important role as a releaser of sexual behavior and "social chasing" in these butterflies, it is unimportant in roosting.

Flower-Visitation and Pollination

Butterflies and moths obtain their largely carbohydrate diet mostly from the nectaries of flowers, and in so doing often act as pollinators (Proctor and Yeo, 1973). The long evolutionary history of this relationship is reflected in the extreme morphological and behavioral adaptations of the organisms concerned. In the Lepidoptera, these include well-developed olfactory and visual senses used for locating flowers, the elongate, tubular proboscis (= haustellum or "tongue" [sic]) for feeding from nectaries deeply recessed within the flower, and in one instance an independent method of extra-oral pollenfeeding (Gilbert, 1972). Corresponding botanical developments include floral odors (Yeo, 1973), brilliantly colored perianths, nectaries (often concealed within tubular flowers or "spurred" organs, e.g., Emmel, 1971) that produce secretions rich in carbohydrates (and in some cases amino acids: Baker and Baker, 1973a, 1973b), and flowering phenologies corresponding to the activity periods of the insects concerned. Pollination relationships of great complexity (e.g., Gilbert, 1975) have evolved, occasionally to the point of obligate interdependence of both the plant and the lepidopteran, as in the oft-cited case of the yucca moths of the genus Tegeticula (= Pronuba) (McKelvey, 1947; Powell and Mackie, 1966; Riley, 1892).

Visual cues are the main signals used for flower-localization and identification, but in some species floral odor plays an important role as well (Ilse, 1928, 1941; Knoll, 1922, 1925, 1927; Lederer, 1951; Myers and Walter, 1970; Schremmer, 1941). For example, Schremmer (1941) found that the noctuid moth Plusia gamma uses odor cues to locate flowers for its first meal after eclosion, but thereafter it is imprinted with the visual pattern and will use it in addition to odor as an orientation cue. On the other hand, many species, including sphingid moths (Knoll, 1922, 1925, 1927) and some butterflies, rely entirely or almost exclusively on floral color and pattern. Crepuscular and nocturnal as well as diurnal species have been shown to use color vision in locating, identifying, and feeding from flowers. Most species have innate color preferences, but in some cases these may be modified by experience or training (Ilse, 1928; C. Swihart, 1971).

Detailed features of the flowers, such as the amount of "dissection" (the ratio of perimeterto area) of the corolla may be important identifying characteristics (Ilse, 1932a). Contrasting "guidemarks"(also known as "honey-guides," "nectarguides," "Saftmale," and "Pollenmale"; see Proctor and Yeo, 1973) are used for location of the flower entrance (Knoll, 1922, 1925, 1927). Thus lepidopterans use both innate and imprinted "search images" (C. Swihart, 1971), which, together with olfaction and other behavioral adaptations, enable them to engage in a spectrum of floral-feeding relationships ranging from fortuitous, entirely facultative, situations to obligate mutualisms. Gilbert's (1972, 1975) fine study of coevolution of Heliconius (Heliconiinae, Nymphalidae) butterflies with their larval (Passifloraceae) and adult (certain Cucurbitaceae) food plants is illustrative of the complexity of such interrelationships. The great longevity of these butterflies (Gilbert, 1972; Turner, 1971b), made possible by their unpalatability to predators (Brower et al., 1963; Brower and Brower, 1964) and mutualism with cucurbit vines as nectar and pollen sources, appears to have evolved with behavioral sophistication unparalleled elsewhere in the Lepidoptera (Gilbert, 1975).

Territoriality and Antagonistic Behavior

Males of a large number of butterflies behave in a manner that has frequently been interpreted as territorial. Characteristically, a male chases other butterflies (or falling leaves, insects, birds, or lepidopterists) persistently until they leave the immediate area (e.g., Fleming, 1965; Hendricks, 1974; Pyle, 1972; Slansky, 1971). (Such species are often called "pugnacious." This aggressive behavior has been studied experimentally by Ross (1963), who found that marked Hamadryas butterflies (Nymphalidae) rarely remained in the same place for long periods. (See also Lederer, 1951, 1960; Swihart, 1967a). But recent studies of several species in this genus by D. Windsor (pers. comm.) indicate that while males are aggressive but not territorial at feeding sites, they will vigorously defend for weeks or even months perches from which females can be pursued. Baker (1972) has observed similar behavior in several other nymphalids (but see Scott, 1974), and L. E. Gilbert (unpublished, cited in Maynard Smith, 1976) and R. C. Lederhouse (pers. comm.) also have strong evidence for territoriality in certain swallowtail butterflies (Papilio spp., Papilionidae), the males of which defend hilltops to which females fly when receptive.

More experimental studies of territoriality are needed to determine the signals males use to recognize other males (see Stride, 1957). In many species it is not clear if and how aggressive behavior differs from "inspection" flights which characterize the earliest stage of courtship in many butterfly species (Swihart, 1967a). There are a number of situations that are often confused with territorial defense. Owen (1971) noted that some territories change "from day to day and even within a few minutes. The term 'individual distance' ... is perhaps more appropriate than territory." (See also Scott, 1974.) Territoriality should also be distinguished from long-term residency within a small area, which is well known in a number of butterfly species. If this area is not defended it should be considered a home range (e.g., Ross, 1963; Turner, 1971a, 1971b). Males of some species actively search for females, flying ("seeking") often within a restricted area. More than one such male may be competing, not for the physical space but for females within it.

Lepidopterans seem at times to be more defensive of their food than of potential mates. Large butterflies such as Anteos sp. (Pieridae) and Charaxes spp.(Nymphalidae) often displace one another at food by shoving with the forewings, the front edges of which may be thickened and serrated (Owen, 1971). Heliconius butterflies sometimes defend the flowers at which they feed, but several male H. charitonia may wait on a female pupa with which one of them will eventually mate. As on flowers, males do attempt to prevent one another from landing, but once alighted little antagonistic behavior occurs (L. E. Gilbert, pers. comm.). Doane and Cardé (1973) have demonstrated that aggressive competition also occurs between male gypsy moths (Porthetria dispar, Lymantriidae) attempting to alight at a pheromone source. Two cases of a female butterfly coupled simultaneously with two males have recently been reported (Masters, 1974; Perkins, 1974). Intermale communication also occurs in instances where (1) one male rejects (David and Gardiner, 1961) orinhibits (Stride, 1956) "homocourtship" attempts by other males, (2) the male of a pair signals in a similar manner to other males that are attracted to his mate, possibly preventing "takeover" (Parker, 1970) by the intruders (O. T. Taylor and R. E. Silberglied, unpublished), and (3) the male transfers to a female a pheromone that renders her unattractive to other males (L. E. Gilbert, pers. comm. and cited in Scott, 1973).

Reproductive Isolation

Sexual reproduction is nearly universal in the Lepidoptera,¹³ and most intraspecific communication between adults is sexual in nature. The highly stereotyped, species-specific courtship behavior patterns of adult lepidopterans serve not only to bring the sexes together; they function as one of the major reproductive isolating mechanisms between closely related species.

The breakdown of prezygotic isolating mechanisms results in hybridization when postzygotic isolating mechanisms are weak or absent (e.g., Ae, 1965; Cockayne, 1940; Taylor, 1972; Tutt, 1906). Since hybrids can often be readily obtained by hand pairing (Clarke and Sheppard, 1956; Lorkovic, 1954) but are rather exceptional occurrences in nature, prezygotic isolating mechanisms are believed to be of greater importance than genetic incompatibility or sterility as barriers to hybridization between closely related species.

Despite the extraordinary diversity of genitalic differences between males in most groups of Lepidoptera, physical or mechanical ("lock and key") isolating mechanisms do not appear to be of importance in the group (Jordan, 1905; Sengün, 1944).¹⁴ Even intergeneric matings sometimes occur (e.g., Perkins, 1973). The major prezygotic isolating mechanisms are temporal (seasonal and circadian), ecological (e.g., habitat preferences), and ethological (courtship behavior). Often the effects of several different mechanisms, no one of which provides complete isolation, combine to isolate sympatric populations of different species (e.g., Petersen and Tenow, 1954).

TEMPORAL AND ECOLOGICAL ISOLATIONE

Separation in time or space serves in many cases to isolate populations that might otherwise interbreed. Habitat preferences of adults may isolate closely related species (Petersen and Tenow, 1954; Shapiro and Cardé, 1970). Mating may be restricted to particular sites within the habitat, such as hilltops (Scott, 1970, 1974; Shields, 1968) or near food plants (Smith, 1953, 1954). Differences in altitudinal range as in Pieris (Petersen and Tenow, 1954) and among members of the Papilio glaucus group (Brower, 1959), not fundamentally distinguishable from grosser aspects of geographic isolation (often with physiological limits on range), may also be effective. While not obviously communicative in nature, the behavior that brings conspecific lepidopterans together for mating (or alternatively, restricts them from locations where the probability of locating conspecifics is low) is a necessary prerequisite before individuals can communicate directly with one another by means of shorterrange visual and chemical cues.

Similarly, temporal synchrony of reproductive behavior within a species is an important partof the mating system, and is sometimes of critical importance as an isolating mechanism. Seasonal isolation has been relatively little studied but is obviously important, especially in univoltine species. In the genus Papilio, closely related members of the glaucus group are to some extent seasonally isolated (Brower, 1959). Seasonal isolation may also result from reproductive diapause, which is especially common during the dry season in the tropics (O. R. Taylor, pers. comm.). Circadian rhythms of activity, pheromone release and receptivity to mating by females, and similar rhythms of activity and response to pheromones by males, are speciesspecific and have been shown to be controlled by photoperiod (George, 1965; Shorey and Gaston, 1965; Sower et al., 1970, 1971; Traynier, 1970) and temperature (Cardé and Roelofs, 1973; Cardé et al., 1975b). (Release of these behavior patterns is probably mediated by hormones; see Truman and Riddiford, 1974.) Such periodicity in reproductive behavior has been known since Fabre (1916); the subject has been surveyed by Jacobson (1972) and discussed recently by Roelofs and Cardé (1974) and Shorey (1974). Species-specific temporal patterning of butterfly courtship behavior is also known (e.g., Shields, 1968; Shields and Emmel, 1973; Miller and Clench, 1968), but in most cases does not differ significantly between closely related species within the same habitat.

Diel rhythms of reproductive behavior appear to be the main isolating mechanisms among sympatric Callosamia (Saturniidae: Ferguson, 1971-1972). Interspecific and in some cases intergeneric cross sensitivity of male antennae to female sex pheromones is common among saturniids (Priesner, 1968; Schneider, 1963); diel activity rhythms may therefore be expected to play a more important role in such groups than in those characterized by high pheromonal diversity. Unfortunately, little is known about the chemistry of saturniid sex pheromones, so the chemical basis of their cross sensitivity (e.g., a single component of species-specific mixtures?) remains unknown. It is indeed possible that chemical complexity yet to be discovered may provide additional specificity and effect, in part, reproductive isolation in this family.

One disadvantage to temporal partitioning among species using the same chemical communication system is that they are subject to competition for optimal times. Environmental conditions change during the day and night, and some times are better than others for communication. Reproductive activity periods (Watt, 1968), rhythms of pheromone release (Cardé, 1971; Comeau, 1971; Sanders and Lucuik, 1972; Sower et al., 1971), and male responsiveness (Batiste, 1970; Batiste et al., 1973; Cardé and Roelofs, 1973; Collins and Potts, 1932; Klun, 1968; Shorey, 1966) are all affected by temperature. Cardé et al. (1974) suggest that the mating period of the gypsy moth (Porthetria dispar, Lymantriidae) has become lengthened in North America (where it was introduced from Europe over a century ago) because of ecological release from competition for calling time. In Europe, where the gypsy moth coexists with the nun moth (Lymantria monacha, Lymantriidae), both use the same pheromone but are temporally isolated to some extent.

SPECIFICITY IN THE COMMUNICATION SYSTEM

The color patterns of diurnal lepidopterans undoubtedly play an important role in reproductive isolation. Only limited isolation results from the indiscriminate male responses to the patterns of females, especially among similarly colored sympatric congeners. But it is widely believed that mate choice (acquiescence or rejection) by females is determined in part by male color pattern. Unfortunately, as Brower (1963) points out, few experimental attempts have been made to test this hypothesis. In recent work with Colias butterflies (Pieridae), R. Silberglied and O. R. Taylor (data in Silberglied, 1973) "painted" male sulfur butterflies many different colors; they found no breakdown of reproductive isolation or discrimination by females against grossly miscolored males, except when the ultraviolet patterns were changed. Thus females may exert a selective force on male coloration, but this "coloration" may be outside the range of vertebrate vision. Coloration (especially iridescent colors) may vary in both time and space with respect to intensity, spectral quality, saturation, and polarization; future experimental work on visual signals should attempt to determine which of these parameters are most relevant to the communication system.

Chemical diversity of sex pheromones is only one of several possible means of conferring specificity within the pheromonal communication system. Some closely related moths use different geometric isomers (eis or trans) of the same longdistance sex attractants (e.g., two Bryotropha species, Gelechiidae: Roelofs and Comeau, 1969; two Amathes species, Noctuidae: Roelofs and Comeau, 1970). Concentration differences are a second possibility; for example the alfalfa looper (Autographa californica, Noctuidae) is attracted to lower concentrations of dr-7-dodecenyl acetate than the cabbage looper ( Trichoplusia ni, Noctuidae) and is inhibited by high concentrations (Kaae et al., 1973). In areas of sympatry, males of the alfalfa looper might be expected to search for nonexistent ("phantom") conspecific females where the concentration of sex attractant (emitted at a high rate by female cabbage loopers) first becomes inhibitory. Since interspecific matings are presumed to be disadvantageous to both participants, one would expect strong selection for more specificity in the two communication systems. In the case of these noctuid moths, such specificity appears to be conferred by incomplete temporal partitioning (Kaae et al., 1973) and by the rejection behavior by females in response to the "wrong" male scent-organ pheromones disseminated later in courtship (Shorey et al., 1965).

Another means of adding specificity to the communication system involves the use of more complex pheromonal mixtures. The relative proportions of two or more compounds (an attractant plus "synergists" or "inhibitors") can be varied. Such systems effect isolation of several pairs of tortricid species (Minks et al., 1973; Roelofs and Comeau, 1971a). Other types of specificity were reviewed recently by Roelofs and Cardé (1974), to which readers are referred for details.

Reproductive isolation can also be based on a combination of visual signals in addition to pheromones. Our two commonest native North American sulfur butterflies, Co lias eruy theme and Coliasphilodice (Pieridae), are so isolated (Taylor, 1970, 1972, 1973; Silberglied, 1973; Silberglied and Taylor, 1973).

THE ORIGIN OF PHEROMONESE

Research on lepidopteran pheromones has largely been limited to chemical identification of active compounds and behavioral and physiological studies on their activity. Considerations of the sources of pheromones (whether biosynthesized or acquired from extraneous sources) and the evolutionary origin of pheromonal communication systems require different kinds of information and a broader data base, and consequently have until recently been neglected.

One likely possibility for the origin of certain pheromones and pheromone glands is that of defense. Several of the compounds identified as lepidopteran sex pheromones (e.g., citral) are chemically identical with defensive secretions, and there is little reason why, once evolved, such defensive compounds might not be used in intraspecific communication (Birch, 1970b, 1974c; T. Eisner, pers. comm.; M. Rothschild, pers. comm.). Birch (1974c) also argues that release of defensive compounds during mating, when the male and female are indisposed, would be protective of the pair.

It has long been known that certain male butterflies, especially many danaines and ithomiines (as well as certain moths), are attracted to certain kinds of vegetation. For example, Owen (1971) reported danaine butterflies gathering and feeding in large numbers on plant juices of Heliotropium (Boraginaceae) that had been damaged by the feeding activities of grasshoppers (see also Pliske, 1975b). Collectors in the tropics have for years used the technique of hanging heliotrope to dry in order to attract large numbers of butterflies and moths (e.g., Beebe, 1955; Gilbert and Ehrlich, 1970; Masters, 1968; Morrell, 1960; Pliske, 1975c). The similarity between this behavior and that of male orchid bees has often been pointed out; since it has been suggested that the bees use terpenes obtained from orchid flowers in some sexual context (Dodson et al., 1969; Vogel, 1963), a similar hypothesis has frequently been made about male ithomiines and danaines with whatever-it-is they get from borages. In a recent confirmation of ideas such as these (originally postulated by Miriam Rothschild, cited in Birch, 1970b), Edgar and Culvenor (1974) have shown that the hair-pencil-disseminated pheromones of both Danaus and Euploea (Danainae) are dihydropyrrolizines of plant origin. Their findings explain the deficiency of sex pheromone in male queen butterflies reared indoors by Pliske (Pliske and Eisner, 1969); it was due to a lack of contact with plants from which they might obtain the necessary compounds (see also Edgar et al., 1973, 1974; Pliske, 1975b; Schneider, etal., 1975). The monarch butterfly (D. plexippus) appears to have evolved independence from plant-derived pyrrolizine pheromones via a different courtship sequence involving only occasional "hair-pencilling" (Pliske, 1975a).

Hendry et al. (1975c and pers. comm.) have offered some speculations on the origin of sex pheromones produced by female moths. They reported that male oak leaf roller moths (Archips semi/eranus, Tortricidae) became sexually active in the vicinity of oak leaves and "frequently attempted to copulate with host leaves that had been damaged by larval feeding." Chemical analysis of oak leaves revealed the presence of many compounds that had been identified as active components (?) of the complex sex pheromone mixture of female moths (Hendry et al., 1974a, 1974b, 1975a, 1975b). (These compounds were not detected in female moths reared on semisynthetic diets lacking oak leaves.) The compounds were also reported to be present in the immature stages.

Hendry et al. (1975c), interpreting these findings, suggest the possibilities that (1) these species might be deriving their pheromones directly from plants during their development, and that (2) the males become "imprinted" in some sense on the compounds they will later employ in courtship. Since different host plants have various combinations of such compounds, they suggest further that (3) populations that as larvae feed on different species might be reproductively isolated. These suppositions culminate with the suggestion that "diversification of insect species may be primarily due to the pheromone complexes available during evolution of host plants." (In a manner perhaps analogous, speciation via host-plant shifts has been reported in certain fruit flies [Bush, 1969a, 1969b] in which mating takes place at the oviposition sites.) It should be noted, however, that there is little evidence for most of Hendry's speculations at present. Pliske (1975c) feels that exogenous precursors should be unnecessary for the long-chain aliphatic compounds produced by female moths, and recent experiments by W. L. Roelofs, R. T. Carde, et al. (pers. comm.) shed doubt on some of his basic assumptions. For example, the fact that many apple-feeding tortricid moths have unique pheromonal systems is difficult to interpret with his model.¹⁵

Further studies of pheromone metabolism will be needed before such hypotheses can be evaluated, and a long time may elapse before a broad picture emerges of the origin of pheromones in lepidopterous species. Nevertheless, this remains one of the more exciting areas for research and should a plant origin for some lepidopterous pheromones turn out to be of general occurrence it would have important implications for the evolution of plant-insect interactionsat the community level. It would certainly be ironic if Müller's (1883) suggestion, that floral odors attract lepidopterans because of a similarity to sexual attractants, were to be reversed with the implication that theodor of the opposite sex would excite a moth or butterfly through the remembrance of food fragrances past.

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