The effect of host tree on the natural enemy complex of Ips typographus japonicus Niijima (Col, Scolytidae) in Hokkaido, Japan

The effect of host tree on the ecology of the insect natural enemy complex of Ips typographus was investigated. Tree species was found to influence parasitoid composition and abundance, with pteromalids being more abundant in Picea jezoensis than in P. abies. Within trees, bark texture had a significant influence on pteromalid density with higher densities occurring in smooth bark. Bark hardness was also shown to affect density of both pteromalid and braconid parasitoids. Pteromalid parasitoids were found to respond density dependently to host density. Predators showed no consistent response to host tree. Only the clerid predator Thanasimus substratus showed a density-dependent response to prey density. A predatory dolichopodid fly, Medetera sp., was shown to be a significant mortality factor for Ips typographus larvae. These results are compared to those of previous studies and their relevance to biological control commented upon.