Photoperiodic induction and termination of summer diapause in adult Epilachna admirabilis (Coleoptera: Coccinellidae) from a warm temperate region

In warm temperate and subtropical regions an adult summer diapause regulates the timing of oviposition.Epilachna admirabilis is a univoltine phytophagous lady beetle ranging from south to north Japan, Taiwan, China and Myanmar.In Japan the species hibernates in the full-grown larval stage.In cool temperate Sapporo (43°04´N) the adults never enter summer diapause but pass a second winter in diapause.This study revealed that in Kyoto (35°01´N), the adults had a summer diapause induced by an intermediate photoperiodic response; they had a critical photoperiod of approximately 14.5 h light per day.All females entered reproductive diapause under a long photoperiod of 16L (light) : 8D (dark) and 6.7% of them did so under shorter photoperiods of 13L : 11D and 12L : 12D.However, diapause incidence was 40% at 8L : 16D, suggesting the existence of a second critical photoperiod at a photophase slightly less than 8 h.At photophases of 12-15 h, non-diapausing females laid eggs on average between 27.1 to 39.0 days after emergence.Photoperiod reversibly regulated the induction, maintenance and termination of the adult diapause.Temperatures of 20-30°C did not affect the incidence and termination of diapause at 16L : 8D.Adult winter diapause at the higher latitude Sapporo might have originated from adult summer diapause at middle latitude regions such as Kyoto.Selection at increasing latitudes would have forced northerly populations of the species to lose the adult summer diapause in the range of natural daylengths.Subsequent selection pressure should have favored adults that avoided futile oviposition in late summer or autumn, survived cold winters in diapause and commenced an additional oviposition in the second summer.Thus, a latitudinal difference in photoperiodic responses might have developed.