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The impact of natural enemies on the reproduction and survival of Ips typographus japonicus Niijima in Hokkaido was tested by sequentially caging off cohorts of a single beetle generation so as to investigate the effects of natural enemies at different developmental stages. A consistent increase in mortality of between 17-18% in the first 2-3 weeks of exposure to natural enemies was observed, after which mortality remained relatively constant. Natural enemies which were found to occur in logs exposed during this time were the predators Medetera sp., Thanasimus substriatus, and the adult parasitoid Tomicobia watanabei. Of these, only the first two were found to be significantly associated with beetle brood mortality. However, a confounding factor was the fact that beetle density also significantly increased in logs during the period when mortality was increasing. It was found that larval mine density, and hence intraspecific mortality, was the single most important factor correlated with beetle mortality during this period. It was thus concluded that increased intraspecific competition was responsible for most of the increase in mortality during the first 2-3 weeks exposure, with predators playing a more minor role. Parasitoids were observed to occur in logs late in the exposure period when mortality was relatively constant and so appeared to have little effect on beetle reproduction and survival. The results of this study were compared to results from similar previous exclusion experiments with bark beetles and the fact that beetle density-dependent effects as a mortality factor was not considered in many of these studies noted. It is therefore suggested that some of these previous studies may have overestimated the importance of natural enemies and associates as mortality factors and subsequently underestimated the importance of intraspecific competition. Suggestions are made to improve bark beetle exclusion methodology so as to remove the confounding factor of beetle density from the analysis. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Reproduction and survival of I. typographus japonicus at non-outbreak densities in relation to two tree species, its natural host, Picea jezoensis, and an introduced host, Picea abies, was investigated in 1990 and 1991 in the natural mixed forest zone of Hokkaido, Japan. Beetles did not discriminate between logs of the two species during the attack phase, however, female beetles produced significantly longer egg galleries in P. jezoensis logs than in P. abies logs, particularly in 1990. Regression analysis showed that egg galleries were on average 2 cm longer in P. jezoensis in both years. A consistent trend toward higher larval survival in P. jezoensis logs was also observed. It is postulated that these differences were caused by a combination of differences in tree ages used in the studies and therefore their physiological status and inherent differences in the suitability of each tree species as breeding resource. Intraspecific density dependent effects on reproduction and survival were similar to those previously reported for outbreak or post-outbreak populations, with the strongest effects being on reductions in egg gallery length and larval survival as beetle density increased. These factors were important even at the relatively low densities found in this study. The relevance of these results to the management of I. typographus in the spruce forests of Japan and the importance of native insects exploiting non-native host plants as new resources is briefly discussed. [ABSTRACT FROM AUTHOR]