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Journal of the Lepidopterists' Society
A SUGGESTION REGARDING HINDWING DIVERSITY AMONG MOTHS OF THE GENUS CATOCALA (NOCTUIDAE)
Theodore D. Sargent Department of Zoology, University of Massachusetts, Amherst, Mass.
Throughout much of North America, moths of the genus Catocala occur in a bewildering array of species and varieties (e.g., Barnes & McDunnough, 1918). In New England alone, there are at least 52 Catocala species, and 43 additional distinctive varieties (Forbes, 1954). For the past five years (1964-68), I have been studying Catocala in central Massachusetts (Hampshire and Franklin counties), and during that time have collected or observed well over 1000 individuals of 27 species.
The numbers and variety of sympatric Catocala species, together with their relatively narrow ecological niche (phytophagous larvae, cryptic adults which rest on tree trunks), raise a number of interesting evolutionary questions. One question that has intrigued me for some time concerns the various patterns and colors of the hindwings of these moths. It is generally assumed that these hindwings serve to startle predators, being flashed when crypsis fails to deter attack. A startled predator is then momentarily confused, during which time the moth may escape. But why are these hindwings typically banded in many species, and uniformly black (on the upper surface) in others? And why, among the species having banded hindwings, do the ground colors vary through yellows, oranges, pinks, and reds? In short, what factors have been operating to promote specific hindwing diversity in this genus?
One suggestion for this diversity might be based on phylogenetic affinities within the genus, closely related species having similar hind-wing patterns and colors. However, a glance at taxonomic arrangements of the Catocala (e.g., Barnes & McDunnough, 1918; Forbes, 1954) is sufficient to show that closely related species may exhibit a variety of hindwing types.
A second suggestion might ascribe a role to the hindwings in courtship and mating behaviors, the different patterns and colors serving as releasers, and so functioning to isolate various species. Virtually nothing is known of courtship and mating in the Catocala, so this suggestion must remain quite tentative. If, however, these behaviors occur at night, then a releaser role for the hindwings (especially with respect to color) seems somewhat questionable.
Another suggestion for hindwing diversity recently occurred to me
262 Sargent: Schizomimicry in Catocala Vol. 23 no. 4
while examining my records of Catocala gracilis Edwards, C. sordida Grote, and C. andromedae Guenee. These three species are widely sympatric, are of approximately the same size (wingspread 45 mm), and have very similar gray forewings (Forbes, 1954). However, the hind-wings are banded with yellow-orange and black in gracilis and sordida, and are an unhanded black in andromedae. [Specific distinctions between gracilis and sordida were not attempted in the field, and the two species are considered together throughout this note. It is possible that there is only one species here (see Adams & Bertoni, 1968).] My records indicated that these species often occur together in central Massachusetts, coming to bait on the same nights, and resting by day on trees in the same woodlots. The inclusive dates of occurrence for 67 gracilis and sordida taken over the past five summers are 16 July and 31 August; these dates for 25 andromedae are 26 July and 28 August. Furthermore, the resting habits of these moths are apparently identical. I have found 21 gracilis and sordida, and 10 andromedae, resting on tree trunks. All of these moths were resting in a head-down attitude, and ranged between 5 and 12 feet above the ground (average height of 6 feet for gracilis and sordida, and 7 feet for andromedae).
The similarities in dates of occurrence, forewing patterns, and resting habits between Catocala gracilis and C. sordida on the one hand, and C. andromedae on the other, suggested the possibility that selection-pressures have been operating in these two cases to promote convergence with respect to cryptic adaptations, and divergence with respect to startle adaptations. This kind of situation, in which two or more species resemble one another in cryptic characteristics, but differ markedly in startle characteristics, might be termed schizomimicry.
Although schizomimicry is purely conjectural at the present time, it would seem to provide a selective advantage to at least one of the species involved. Coppinger (1969a, 1969b) has experimentally demonstrated that birds may not attack (and may actively avoid) novel insects in their diets, novelty here being defined in terms of stimulus change with respect to the previous experience of the birds. Thus, in the proposed schizomimicry situation, novelty might enhance the effectiveness of the startle patterns. Using the example discussed here, a predator might habituate to the startle pattern of C. gracilis after a number of encounters, but be effectively startled again upon encountering C. andromedae. In this way, at least the rarer species in a schizomimicry complex might derive some protection from predators. Actually, all of the species could benefit from their association, if the predator's startle response was in part a function of its most recent experience.
Journal of the Lepidopterists' Society
The process proposed here for producing hindwing diversity among the Catocala is similar to that described as "apostatic selection" by Clarke (1962), in that both processes would promote diversity among sympatric species having common predators. However, Clarke related his concept to the "specific searching image" hypothesis of Tinbergen (1960), i.e., that predators develop tendencies to take one type of prey at a time, overlooking others which appear different; while the present proposal views novelty, or a novel stimulus effect, as the factor which deters predation on prey which differ in appearance. In addition, of course, the process proposed here would result in mimicry, as well as apostasy, between species.
This explanation of some of the hindwing diversity among the Catocala does pose one seemingly perplexing question: if this diversity among otherwise similar moths is advantageous, why has not disruptive (Mather, 1955), or apostatic (Clarke, 1962), selection resulted in considerable infraspecific hindwing diversity? A partial answer might be that many Catocala species simply lack the genetic potential for effective hindwing diversity (i.e., for startling patterns which are sufficiently novel to deter predation). It might also be suggested that some of the observed hindwing diversity is indeed the product of disruptive selection. In this view, some of the variants would be morphs, rather than species; or, if species, would have arisen sympatrically from morphs. Sympatric speciation might be envisioned in these circumstances, if crosses involving unlike hindwings (heterogamy) produced intermediate moths which were at a selective disadvantage, in terms of startle characteristics, to moths produced in crosses involving like hindwings (homogamy).
The situation of C. gracilis and C. sordida versus C. andromedae would seem the most likely possible example of schizomimicry among the Catocala of my experience. However, certain other pairs and groups of Catocala species might also exhibit such a relationship. For example, in central Massachusetts, C. habilis Grote and C. concumbens Walker have overlapping dates of occurrence, roughly similar pale gray fore-wings, identical head-down resting attitudes, and similar tendencies to rest low on light trees; but habilis has orange and black banded hindwings, and concumbens has pink and black banded hindwings. (C. robinsonii Grote, a black hindwinged species, might also be included in this latter association.) Another possible example involves C. palaeogama Guenee (yellow and black banded hindwings) and C. lacrymosa Guenee (black hindwings): these species exhibit similar forewings, with parallel variations; extensive sympatry; and the same seasonal occurrence (Forbes,
264 Wood: Eurema at MV light Vol. 23, no. 4
1954). Other examples might be cited, but perhaps these will suffice to suggest the possible extent of schizomimicry in the Catocala.
The ideas advanced here are admittedly quite speculative. However, the proposed advantage of hindwing diversity is certainly experimentally testable, and one of my graduate students, Charles G. Kellogg, is currently devising such experiments. We would be interested in receiving comments and suggestions from others on any matters relating to this note.
I would like to express my appreciation to Dr. Raymond P. Coppinger of Amherst College for allowing me to read pre-publication copies of his important papers; and to Dr. Ronald R. Keiper of Pennsylvania State University for providing me with records of his observations of Catocala in the field.
Adams, M. S., and M. S. Bertoni, 1968. Continuous variation in related species
of the genus Catocala (Noctuidae). J. Lepid. Soc., 22: 231-236. Barnes, W., and J. McDunnough, 1918. Illustrations of the North American
species of the genus Catocala. Mem. Amer. Mus. Nat. Hist., 3(1), 47 pp., 22 pi. Clarke, B., 1962. Balanced polymorphism and the diversity of sympatric species.
Systematics Assoc. Publ., 4: 47-70. Coppinger, R. P., 1969a. The effect of experience and novelty on avian feeding
behavior with reference to the evolution of warning coloration in butterflies.
Part I: Reactions of wild-caught adult blue jays to novel insects. Behaviour
(in press). 1969b. The effect of experience and novelty on avian feeding behavior with
reference to the evolution of warning coloration in butterflies. Part II: Reactions
of naive birds to novel insects. (in prep.) Forbes, W. T. M., 1954. Lepidoptera of New York and Neighboring States.
Part III. Noctuidae. Cornell Univ. Agric. Exp. St., Memoir 329, 431 pp. Mather, K., 1955. Polymorphism as an outcome of disruptive selection. Evolution, 9: 52^61. Tinbergen, L., 1960. The natural control of insects in pine woods. I. Factors
influencing the intensity of predation by song birds. Arch. Neerl. Zool., 13:
SWARM OF EUREMA LISA UNDER MERCURY VAPOR LAMP
Migration swarms of Eurema lisa Boisduval & LeConte, have been often reported in the past, and specimens of Rhopalocera are occasionally taken at lights, but the two combined are an unusual occurrence, at least for this collector. On the night of September 27, 1968, at 11:50 P.M., I found a swarm of several hundred E. lisa resting on pavement beneath a mercury-vapor lamp rated at 20,500 lumens (400 watts). The temperature at the time, obtained later from the nearest ESS A station, was 61° F. The lamp is located in the parking area of a business establishment near my home in Henderson, western Kentucky. The specimens appeared dazed, and were not resting vertically, but with folded wings tilted to about 75 degrees. Only eleven samples were collected, and the sexes were about evenly represented, six males and five females.—J. B. Wood, 140 Pines Drive, Henderson, Kentucky.