Effects of Photoperiod and Temperature on Reproductive Diapause in the Camphor Tree Weevil, Dyscerus hylobioides (Desbrochers)(Coleoptera : Curculionidae)

Under field conditions, newly-emerged adults of Dyscerus hylobioides showed a high feeding rate in mid-summer, but this declined rapidly. After hibernation, feeding was resumed in early spring and continued until late autumn. Most newly-emerged females did not lay eggs during the year of emergence, and overwintered females laid eggs from late spring to early autumn. Most adults survived over a second spring and, as a matter of course, they could lay eggs. The longest life span was 46 months. At 20℃ and 25℃, post-diapause females continued oviposition over 250-500 days under long photoperiods, but diapause was induced again under short photoperiods after about 65-110 days from the start of incubation. Diapause reinduced under short photoperiods was again terminated by transfer to a long photoperiod in the laboratory. Newly-emerged females kept at 25℃ needed a long period of time (more than 60 days) before ovipositing under long photoperiods (LD 15 : 9 and 14 : 10), but they did not lay eggs under short photoperiods (LD 13 : 11 and 12 : 12). Thus, new females could avert diapause and oviposit in the field during the year of their emergence only if they emerge in the earliest part of the season (by July). Oviposition activities of adults transferred periodically from outdoor conditions to an incubator regulated at 20℃ throughout the winter suggest that the diapause of overwintering adults was terminated by mid-January in the field, since after that time the incubation period until the start of oviposition under diapause-maintaining short photoperiod (LD 12 : 12) was equal to that under diapause-terminating long photoperiod (LD 15 : 9).