ADAPTIVENESS OF PARENTAL CARE IN PARCTSTRACHIA-JAPONENSIS (HEMIPTERA, CYDNIDAE)

To understand the adaptiveness of the advanced parental care seen in Parastrachia japonensis Scott, some characters of egg guarding and progressive provisioning were examined through field experiments and observations of natural nests. A carabid beetle is the first known predator of this species. Females of P. japonensis could not distinguish their own eggs from those of other females and guarding of eggs against the predator was strictly defensive; they primarily used their bodies as shields or escaped with the egg mass. The sole food resource, drupes of the deciduous tree Schoepfia jasminodora (Sieb. et Zucc.), is scarce and ephemeral, and, because conditions around the host tree are generally unsuitable for nesting, most nests are located well out of range of the fallen drupes. Females repeatedly left the nests on foraging trips and provisioned nests with drupes. Survival rate of nymphs with a female and drupes paralleled that of nymphs with only drupes when the danger from predation was eliminated. The number of drupes provisioned was positively correlated with the duration of the nymphal nesting period. Further, nymphs in nests with drupes remained aggregated longer than those in nests without drupes. Because aggregations are apparently essential for successful feeding in the early stages and a prolonged nesting period probably affords protection against predation and desiccation, progressive provisioning may have evolved in response to these environmental pressures as well as in response to the resource constraints.