Abstract
Adults of a stink bug, Pyrrhocoris sibiricus, were collected from natural populations and investigated for wing length variation. The environmental factors (nymphal density, temperature and photoperiod conditions) affecting wing length variation were also investigated in the laboratory. Adults were collected in Okayama, western Japan, from July to September of 1991. To clarify the effect of nymphal density, first-instar nymphs were reared at densities of 1, 2, 4, 8 and 16 individuals per Petri dish (9 cm in diameter, 2cm in depth) under 16L-8D at 30°C. The effect of temperature was investigated by rearing first-instar nymphs at 20, 25 and 30°C under 16L-8D at a nymphal density of 8 individuals. To clarify the effect of photoperiod, first-instar nymphs were reared under 8L-16D, 12L-12D and 16L-8D at 30°C at a nymphal density of 8 individuals. The relative forewing length (RFL) and relative hindwing length (RHL) of adults collected from the field were continuously distributed in both sexes. Environmental factors such as high temperature, short day-length and moderate crowding tended to promote the production of longer hindwinged adults, although no decisive factors were determined.
