An Analysis of Mortality Process of Young Larvae in Gregarious Insects

Abstract

Many experimental studies have examined the effect of larval aggregation on the survival and development of gregarious insects, but the cause of high mortality of young larvae in small rearing groups and the relation between the young larval mortality rate and the size of the rearing group are not well understood. If the mortality of newly emerged larvae is due solely to their inability to bite their food foliage, the mortality rate in a group of n larvae can be stated as Mn = (1-p)11, where p is the probability that an arbitrarily chosen larva is able to bite its food foliage within a limited time. Larvae of three gregarious species, Spilarctia imparilis Butler, Neodiprion sertifer Geoffroy and Eurydema rugosum Motschul,SKY, were reared in different group sizes. The mortality rate of first instar larvae in each group of S. imparilis coincided well with the theoretical value caluculated from the model. It is suggested as an alternative interpretation of the model that there are two types of newly emerged larvae, one which can bite and one which cannot bite food when isolated. Larval mortality when the number of hatchlings from an egg mass becomes small due to egg parasitism is also discussed in connection with the model. © 1977, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.