Bark thickness of host pine trees and female body size affecting ovipositional success ofSirex nitobei matsumura (hymenoptera: Siricidae)

We examined the effect of bark thickness of host trees on the ovipositional success ofSirex nitobei in relation to female body size by analyzing the relationships between female body-weight and ovipositor length and between bark thickness ofP. densiflora andP. thunbergii trees and oviposition proportion (the proportion of eggs laid to the potential female lifetime fecundity) of the woodwasp. The ovipositor length ranged from 6 to 14 mm and was correlated positively with the fresh body-weight of females. The bark thickness of host trees had no significant correlation with the oviposition proportion of large females of more than 100 mg f.wt, whereas it was correlated negatively with that of small females of less than 100 mg f.wt. Thus,P. densiflora, which has thinner bark as a whole thanP. thunbergii, may be more suitable for oviposition, especially for smaller females. Research Fellow of the Japan Society for the Promotion of Science. This study was supported in part by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Science, Sports, and Culture (No. 80003292).