A field study of the colony composition of the wood-feeding cockroach Panesthia angustipennis spadica (Blattodea: Blaberidae)

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.