RELATIVE EFFECTS OF CLIMATE AND CROWDING ON WING POLYMORPHISM IN THE SOUTHERN GROUND CRICKET, ALLONEMOBIUS SOCIUS (ORTHOPTERA: GRYLLIDAE)

Abstract

Many factors determine the formation of flight wings in wing-polymorphic insects. Earlier studies on a cricket (Gryllus firmus) population producing spring and summer generations showed a declining frequency of macropterous, or long-winged, adults towards the end of a growing season. Numerous confounding factors can explain this seasonal decline, one of which is increasing mortality rates of juveniles that may otherwise emerge as macropterous adults. To test this hypothesis, we measured rates of juvenile mortality and adult macroptery in Allonemobius socius Scudder (Orthoptera: Gryllidae), an organism with a seasonal phenology similar to that of G. firmus. After rearing A. socius juveniles exclusively under “spring” versus “summer” conditions and at different population densities, we found that crickets reared in groups under “summer” conditions tended to emerge as macropters, with females being more likely than males to emerge long-winged. Juvenile mortality did not adequately explain the emergence pattern of macropters. Surprisingly, variation among families accounted for <1% of total variation in frequency of long-winged adults. Thus, seasonal climate, followed by population density, and then their interaction with each other appear to be the three major determinants of wing morph frequencies in A. socius. We discuss the possible adaptive significance of wing polymorphism in insects with respect to habitat persistence and mating success.

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