Effects of photoperiod and chilling on diapause induction, intensity and termination in Monochamus alternatus endai (Coleoptera: Cerambycidae)

Abstract

ABSTRACTMonochamus alternatus Hope adults vector the pinewood nematode, which is the causal agent of pine wilt disease. Larvae of this cerambycid beetle enter diapause in the final instar. To determine the effects of photoperiod and temperature on diapause in the subspecies M. a. endai, which is native to Japan, and to predict the effects of invasion by M. a. alternatus, the exotic subspecies with facultative diapause, immature stages of two M. a. endai strains (collected at 36°48ʹN, 136°48ʹE; 34°24ʹN, 132°43ʹE) were reared in Pinus densiflora bolts at 25°C under one of three LD photoperiods: 8:16 h, 12:12 h, and 16:8 h for 17 weeks, then chilled at 10°C under LD 10:14 h for 8 or 16 weeks, and finally transferred to 25°C under LD 12:12 h. All larvae entered diapause regardless of photoperiod during the initial incubation, verifying obligate diapause. The 16-week chilling period caused a greater incidence of diapause termination (0.908) than the 8-week chilling period (0.083). Diapause termination was also affected by the photoperiod treatment before chilling, M. a. endai strain, and their interaction. There was a difference in the diapause intensity between strains. The intensity of diapause was affected by photoperiods before chilling. If a small number of M. a. alternatus invade Japan, the obligate diapause requirement in M. a. endai, which is a dominant trait that a previous study verified, would not cause the inter-subspecies hybridization to change the life cycle of M. alternatus and consequently the epidemic pattern of pine wilt disease in Japan.