Nymphal occurrence pattern and predation risk in the subsocial shield bug, Parastrachia japonensis (Heteroptera: Cydnidae)

Abstract

Parastrachia japonensis (Heteroptera: Cydnidae) is a subsocial shield bug: females guard eggs and nymphs against predators, and provision their nymph-containing nests with drupes of the single host tree, Schoepfia jasminodora. We observed the occurrence pattern of nymphs in a foraging area under natural field conditions as an indication of nymphal stadium at independence, and experimentally compared the degree of predation risk of independent nymphs among four of the five nymphal stadia. A field monitoring census indicated that most nymphs became independent during the 4th stadium in 1998. Field experiments using carabid beetles as predators, however, indicated that predation risk during the 2nd to 4th stadia was equally high, and that of the 5th stadium was significantly lower.