Two Types of Overwintering Larvae in a Wild Multivoltine Bruchid, Kytorhinus sharpianus BRIDWELL(Coleoptera:Bruchidae)

Abstract

We studied the seasonal prevalence and the overwintering stage(s) of a wild multivoltine bruchid, Kytorhinus sharpianus, on the host, Sophola flavescens, in Tokyo and Tsukuba. Adult K. sharpianus appeared first on S. flavescens in late April and oviposited on the fresh pods of S. flavescens in mid-June. First-generation adults emerged from early to late August and oviposited until late August. A few second-generation adults emerged form mid-September to mid-October, with most females laying eggs by late October without adult feeding. However, most second-generation larvae did not grow to adulthood in fall, remained at the late final instar during winter, pupated in early April and emerged in late April. The third-generation larvae which hatched in October remained at the first instar during winter and grew to the second instar in late March and to the third instar in early April. A laboratory experiment showed that the late final-instar larvae diapaused at 24°C and 12L-12D, although they grew to adults at 24°C and 16L-8D. These results suggested that K. sharpianus over-winters either at the late final instar in the second generation or at the young instar in the third generation. This species seems to be basically bivoltine in the Kanto district and a few individuals show a trivoltine cycle.