ENVIRONMENTAL-FACTORS AFFECTING WING LENGTH VARIATION OF A STINK-BUG,PYRRHOCORIS-SIBIRICUS (HETEROPTERA, PYRRHOCORIDAE)

Adults of a stink bug, Pyrrhocoris sibiricus, were collected from natu ral populations and investigated for wing length variation. The enviro nmental factors (nymphal density, temperature and photoperiod conditio ns) affecting wing length variation were also investigated in the labo ratory. Adults were collected in Okayama, western Japan, from July to September of 1991. To clarify the effect of nymphal density, first-ins tar nymphs were reared at densities of 1, 2, 4, 8 and 16 individuals p er Petri dish (9 cm in diameter, 2 cm in depth) under 16L-8D at 30 deg rees C. The effect of temperature was investigated by rearing first-in star nymphs at 20, 25 and 30 degrees C under 16L-8D at a nymphal densi ty of 8 individuals. To clarify the effect of photoperiod, first-insta r nymphs were reared under 8L-16D, 12L-12D and 16L-8D at 30 degrees C at a nymphal density of 8 individuals. The relative forewing length (R FL) and relative hindwing length (RHL) of adults collected from the fi eld were continuously distributed in both sexes. Environmental factors such as high temperature, short day-length and moderate crowding tend ed to promote the production of longer hindwinged adults, although no decisive factors were determined.