Comparison of the Effects of Larval Aggregation between Gregarious and Solitary Species of Sawflies : Arge nigrinodosa MOTSCHULSKY and Arge nipponensis ROHWER : Hymenoptera : Argidae

Abstract

A laboratory experiment was carried out to compare the effects of larval density between two congeneric sawflies, Arge nipponensis ROHWER and A. nigrinodosa MOTSCHULSKY. The former lives in scattering, and the latter in aggregation in the larval stage.In A. nipponensis crowded rearing resulted in a high mortality rate, though there was no clear relationship between this and the larval density. In A. nigrinodosa, the artificial isolation of larvae did not result in high mortality and prolonged development. This species was considered to be rather peculiar among gregarious insects.Although the modes of their larval life are quite different, there were no appreciable differences between the two species in density-related changes of many characters such as the number of instars and the growth ratio in weight.