Influence of oviposition timing on offspring diapause and growth in Monochamus alternatus endai (Coleoptera: Cerambycidae)

Abstract

ABSTRACTMonochamus alternatus endai Makihara is the primary vector of pine wilt disease in Japan and South Korea. Larvae of this cerambycid beetle exhibit induced diapause in the final instar. To determine the effects of seasonal environments that female adults had experienced on the diapause, growth, and development of offspring, parents of two Japanese strains were allowed to oviposit on Pinus densiflora logs over 12 or 4 periods of 6 or 7 days each between June and September under natural outdoor conditions. The offspring were reared at 25°C under a photoperiod of LD 12:12 h or LD 16:8 h for 17 weeks, then larvae in diapause were chilled at 10°C under LD 12:12 h for 8 or 16 weeks and transferred to 25°C under LD 12:12 h. Though maternal environments did not affect the diapause of offspring, early seasonal environments that parents had experienced made the offspring larval and adult body masses larger than late seasonal environments. The proportion of larvae that terminated diapause was smaller after an 8-week chilling period than after a 16-week chilling period, indicating that sufficient time of chilling was needed to terminate diapause in the laboratory. The proportion of larvae that terminated diapause was smaller when having experienced LD 16:8 h before chilling treatment than when experienced LD 12:12 h, indicating that LD 16:8 h made the diapause more intense than LD 12:12 h. That suggests that pre-diapause larvae early in the summer induce intense diapause while those early in the autumn induce weak diapause.