Aggregation behaviors of young nymphs in Panesthia angustipennis spadica (Blaberidae)

The wood-feeding cockroach Panesthia angustipennis spadica Shiraki (Blaberidae) lives in a tunnel of decayed logs and is considered as gregarious species. However, decayed logs are distributed in a forest in clumps, and woody tunnels in decaying logs provide a semi-enclosed environment for nymphs. We performed laboratory experiments to determine whether first- and second-instar nymphs of P. angustipennis spadica show gregariousness in small spaces like woody tunnels. We also compared the aggregation intensity of sibling groups and mixed groups in the second instar. The laboratory experiments demonstrated that both the first- and second-instar nymphs show gregariousness, with no difference in aggregation behavior regardless of kin relatedness. These results suggest that non-kin-based gregariousness may help to maintain colonies of P. angustipennis spadica that contain individuals derived from multiple families in a field.