Mating and reproduction of predaceous diving beetles, Dytiscus sharpi, observed under artificial breeding conditions

Mating season and embryonic development of the predaceous diving beetles, Dytiscus sharpi, (Coleoptera; Dytiscidae) were observed under artificial breeding conditions. Female and male adult insects started mating from November to March and gave first instar larvae mainly in April. When the mating was artificially delayed until February, first instar larvae appeared from the end of March to the middle of May. I also investigated the effects of temperature on larval development. Apparent hatchability of eggs was not affected by high temperature, however, their normal development after hatching was significantly interfered. Most of the first instar larvae kept at 20-25 degrees C from before hatching died within one day after hatching. By contrast, juveniles kept outdoors (7.0-20.9 degrees C) could develop at least until second instar larvae. Temperature >23 degrees C after hatching had no effects on larval development. From these observations, it was concluded that the reproduction strategy of Dytiscus sharpi, i.e. mating in late autumn and hatching in early spring would be the reasonable results of adaptation to the warm habitats where they are collected.