Sinistrality in the Southern and Tawny Mole Crickets (Gryllotalpidae: Scapteriscus)

Abstract

Wing folding in the Insecta evolved early in the history of the group and often the wings are folded one on top of the other over the abdomen. Whether or not the right wing is folded over the left or vice versa is of little importance except when the two wings have evolved different tasks. Such is the case in a number of families of Orthoptera: Gryllidae, Gryllotalpidae, Haglidae, and Tettigoniidae. In these families the forewings of the males are specialized for sound production. The plectrum, or scraper, of one wing is drawn across the pars stridens, or file, on the underside of the other wing. This action causes certain membranes of the wing to vibrate and produce sound. Usually the right wing rests over the left in crickets and the left rests over the right in katydids. Interestingly, the females, whose wings are not usually adapted to produce sound, follow the same rules (Masaki et al. 1987). In many species, because of the specialization of the two wings, they differ considerably with respect to pigmentation, reduction in the number of teeth on the file, and in retrogression of the file (Masaki et al. 1987). In the haglids the males may sing using the left over the right or the right over the left (Morris & Gwynne 1978) and apparently can switch while singing (Spooner 1973). I have examined the wingedness of both sexes in two species of mole cricket, Scapteriscus acletus and S. vicinus, to determine how they relate to the other three groups. Individuals were collected as part of another study (Forrest 1986 ) from the routine sound-trapping station on the Agronomy Farm of the University of Florida (Walker et al. 1983). Quarter-monthly samples of up to 50 individuals were collected during the crickets' spring and fall flights of 1981 and 1982. A total of 1431 S. acletus females, 1222 S. acletus males, 714 S. vicinus females, and 284 S. vicinus males were captured and classified as to wing overlap. These are the largest samples of singing Orthoptera where the wingedness of individuals has been studied. In neither sex of either species did rightand left-wingedness differ from 50:50. Female acletus were 51% right-winged (734:697), males were 49% right-winged (602:620). For vicinus, females were 51% right-winged (367:347) and males were 48% right-winged (135:149). I also examined 19 (2 males and 17 females) Neocurtilla hexadactyla, the northern mole cricket, from the Florida State Collection of Arthropods. Both males had right wings over left but only 5 of the 17 females were this way. Checking two other species of mole cricket, Scapteriscus abbreviatus [n= 13; males (4:4), females (1:4)] and Gryllotalpa africana (n=4), revealed at least some specimens with each configuration. Masaki et al. (1987) found equal numbers of left-winged and right-winged males of a scaly cricket, Ornebius kanetataki. I examined 30 male Cycloptilum antillarTium, another mogoplistine, from the collection and found 16 (53%) with their right wing over their left. It is interesting that the mole crickets and scaly crickets would differ so greatly from the other gryllids and tettigoniids with respect to the constancy of wing overlap. One possible reason for the differences might be because of the ancestry of the group. Evidence from the fossil record leaves no doubt that mole crickets developed from