A study of some factors governing the choice of hosts and distribution of progeny by the ChalcidOoendrytus KuvanaeHoward

Abstract

Although the problem of host selection in insects is one which has received considerable attention from various workers within the last twenty-five years, no agreement has yet been reached on the general factors involved in this selection. Apart from its purely academic interest to the insect physiologist, the fact that certain species of insects are restricted to one given host, while others attack numerous species, is one of considerable practical importance. Recently attempts have been made to determine the precise nature of the attraction exercised by hosts on their known insect parasites with a view to the utilization of the knowledge in problems of biological control. Thus, it is thought that if the factors which determine the oviposition response of a given parasite can be found it should be possible to predict the hosts of this parasite in any given environment. Both monophagous and polyphagous parasites are known to select appropriate hosts for oviposition, but it was assumed that in a population of any single host species, a parasite laid its eggs without reference to the nature of the hosts available. This assumption followed from the observed prevalence of superparasitism (the occurrence of more than one immature parasite in one host) in field samples of any given host. This view was shown by Salt (1934) to be incorrect, and he concluded that parasites were capable of distinguishing between parasitized and unparasitized hosts. This worker further showed that previous mathematical treatment of the interactions of host and parasite populations, which assumed a random distribution of the progeny of the parasite in the host populations, was invalidated by this selective faculty. It is proposed in the present work to attempt to determine, in so far as these can be examined in the laboratory, some of the factors governing the incidence of superparasitism in a given host: the study of these factors will naturally involve a consideration of the nature of host selection by the parasite. The effect of climatic and geographical factors upon the distribution of the parasite and its progeny will not be discussed.