On the biology of some Collembola of the family Isotomidae

Abstract

The stadia of the life cycle, age at oviposition, frequency of oviposition and fecundity of parthenogenetic individuals of Folsomia distincta are recorded. Notes on the behaviour of this species are given particularly in relation to the formation of groups. Semi-permanent social aggregations are formed and maintained by an olfactory stimulation from the animal or a secretion from them, especially by the fourth and fifth instars. The relationship between the mean individual fecundity of cultures of F. distincta and the mean area available per individual is given. Both the individual fecundity and the number of individuals ovipositing is reduced by disturbances whilst ovipositing or feeding. The population levels of F. distincta, Isotomina thermophila F. nana and Isotoma notabilis in a meadow are recorded for two years. The greater ability of F. nana and I. notabilis to withstand drought is noted. The differences in population at the different stations were most easily explained by the exposure of the station to the climate. The concept of aggregation under natural conditions is discussed. The aggregation of the four species is compared and it is shown that young and old individuals of the same species are equally aggregated. The relationship between the environment and microdistribution of each species is investigated. It is noted that the position of young individuals may be due to physical conditions and that the older individuals tend to form social aggregations.