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This paper presents a method with accuracy to estimate instars for insects which have large number of instars, especially at long growth period. We clarified the colony composition of the wood-feeding cockroach Panesthia angustipennis spadica Shiraki (Blaberidae) in a field, estimating the instars of field-collected individuals through a cluster analysis using field and laboratory data. Overall, 84.8% sampled units contained multiple individuals, and the largest colony consisted of 65 individuals. The colonies were composed of adults and nymphs (43.5%), or nymphs without adults (52.2%). The number of instars in this species was estimated as ca. ten. Furthermore, some colonies contained an adult pair and nymphs at multiple developmental stages, whereas other colonies contained only small nymphs (estimated instars 1–3). These results demonstrate that the social structure of P. angustipennis spadica varies widely, and that colonies containing both adults and nymphs may indicate the origin of subsociality in cockroaches.

We dissected the trunk of a Quercus serrata Murray tree that had suffered from Japanese oak wilt, measured the gallery diameters of ambrosia beetles, and recorded the related insect fauna in the galleries of ambrosia beetles. In total, 545 individuals of nine species were captured from 494 galleries; these belonged to nine species [Cossoninae sp. (Curculionidae), Litargus japonicus Reitter (Mycetophagidae), Platypus calamus Blandford (Platypodidae), Platypus quercivorus (Murayama) (Platypodidae), Ambrosiodmus lewisi (Blandford) (Scolytidae), Ambrosiophilus atratus Eichhoff (Scolytidae), Xyleborus sp. (Scolytidae), Bitoma siccana Pascoe (Zopheridae), and Gempylodes ornamentalis (Reitter) (Zopheridae)]. The diameter of the gallery entrance on the surface of a debarked log may serve as a cue for species estimation of major ambrosia beetles in Q. serrata trees suffering from Japanese oak wilt in this study area. From the relationships between the body width and the gallery diameter, the distribution pattern within the tree, and the taxonomical analogy, a zopherid species, G. ornamentalis, was inferred as a possible predator and/or parasitoid of a causal agent in Japanese oak wilt, P. quercivorus.

We mainly examined the community structure and seasonal population trends of scolytid and platypodid species captured via ethanol-baited traps in a natural cool-temperate forest in Japan. The scolytid species in the tribe Xyleborini represented more than 70 % of individuals captured in ethanol-baited traps, although the platypodid species could be abundant in this study area. These results indicate that the scolytid species in tribe Xyleborini might have higher sensitivity to ethanol-baited traps than others and the ethanol-baited trapping method could target the limited number of scolytid and platypodid species. Therefore, analysis based only on the ethanol-baited trapping method may lead to misunderstanding the community structure of scolytid and platypodid species. The analysis of the seasonal changes in number of scolytid and platypodid species, using a generalized linear model (GLM) showed that the ethanol-baited traps appeared to function more effectively in spring than in other seasons. Hence, the trapping season should be considered when analyzing the data obtained from ethanol-baited trapping census, especially with scolytid and platypodid species.