Download A suggestion regarding hindwing diversity among

1969
Journal of the Lepidopterists' Society
261
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 b een studying Catocala in
central Massachusetts (Hampshire and Franklin counties), and during
that time have collccted 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 hindwing 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 diHerent 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 fois 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 m e
262
SARGENT:
Schizomimicry in Catocala
Vol. 23 no. 4
while exammmg 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 hindwings are banded with yellow-orange and black in gracilis and sordida,
and are an un banded 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).J 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 fe et for gracilis
and sordida, and 7 feet for andromedae).
The similarities in dates of occurrence, forewing patterns, and resting
habits b etween CatocaZa gracilis and C. sordida on the one hand, and
C. andromedae on the oth er, suggested the possibility that selectionpressures 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 schizomimiC1·Y.
Although schizomimicry is purely conjectural at the present time, it
would seem to provide a sel ective 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 dis cussed 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.
1969
JOtlrnal of the Lepidopterists' Society
263
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 oth ers whi ch 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 h ere would result in mimicry, as well as apostasy, b etween species.
This explanation of some of the hindwing diversity among the Catocala
does pose one seemingly p erplexing question: if this diversity among
otherwise similar moths is advantageous, why has not disruptive (Mather,
1955), or apostatie (Clarke, 1962) , selection resulted in considerable
infraspecific hindwing diversity? A partial answer might b e 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 b e suggested that some of the obs erved 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 sympatricaUy 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
h ave overlapping dates of occurrence, roughly similar pale gray forewings, 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. laclymosa Guenee
(black hindwings): these species exhibit similar forewings , with parallel
variations; extensive sympatry; and the same seasonal occurrence (Forbes,
264
WOOD:
EUl'ema at MV light
Vol. 23, no. 4
1954). Other examples might bc 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 C. Kellogg, is currently devising such experiments. W e would be interested in receiving
comments and suggestions from others on any matters relating to this
note.
r 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.
LITERATURE CITED
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. M em. Amer. Mus. Nat. Hist., 3( 1), 47 pp., 22 pI.
CLARKE, B., 1962. Balanced polymorphism and the diversity of sympatric species.
Systematics Assoc. Pub!., 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: R eactions 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 dismptive selection. Evolution, 9: 52-61.
TINBERGEN, L., 1960. The natural control of insects in pine woods. 1. Factors
influencing the intensity of predation by song birds. Arch. Neerl. Zool., 13:
265-343.
SWARM OF EUREMA LISA UNDER MERCUFlY 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 ESSA station, was 61 0 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
w ere collected, and the sexes were about evenly represented, six males and five
females.-J. 13. WOOD, 140 Pines Drive, Henderson, Kentucky.