Abstract
Seasonal adaptations were studied in a partially bivoltine population of Poecilocoris lewisi that overwinters as nymphs. Under short-day conditions, the final (5th) instar nymphs entered diapause, whereas under long-day conditions they emerged as adults within 2 weeks. The critical daylength for induction of the nymphal diapause was between 14 and 15 h at 25°C in the Osaka population. P. lewisi entered diapause in the adult stage also, under long-day conditions. Adults emerging in late spring started oviposition only after July. Insects transferred from long-day to short-day conditions at adult emergence began to lay eggs earlier and more synchronously than those kept continuously under long-day conditions due to prevention of the adult diapause. The critical daylength for induction of the adult diapause was also between 14 and 15 h at 25°C, as in the induction of nymphal diapause. The dogwood Cornus controversa, a principal host plant of P. lewisi, did not develop seeds until early July. Therefore, this suggests the absence of host plant seeds in late spring is the ultimate factor for the evolution of adult diapause in P. lewisi.
