Analysis of Life Tables for a Host and Parasite (Plodia-nemeritis) Ecosystem

Abstract

This is the second part of a study aimed to investigate processes operating in the regulation of populations of the Indian meal-moth (Plodia interpunctella (Hubner)). The importance of such a study was discussed in a preceding paper (Podoler 1974). In the present part of the study, interactions between the Indian meal-moth and its ichneumonid parasite Nemeritis canescens (Gravenhorst) were studied together with other processes affecting both species. Unlike the first part, the study reported here was carried out in a continuous system in which both the host and the parasite were left to develop undisturbed, except for sampling and food replacement, for about 1 year. Similar systems have already been analysed under laboratory conditions by several authors with other stored products insects (e.g. Hassell & Huffaker 1969a, b; White & Huffaker 1969b). These laboratory studies and others that were carried out under natural conditions (Varley & Gradwell 1968) indicate that processes which occur during the early stages of development are very important in the determination of population level in each generation. Because of the difficulties arising in sampling eggs and young larvae, workers have often avoided this and included all that happens during these early stages in one category with only one value for mortality. This was expressed as k1 in the studies of Varley & Gradwell (1968), Hassell & Huffaker (1969a) and Benson (1972). The present study tried to distinguish the numerous factors which are involved in the early mortality that occurs in a continuous system under laboratory conditions. Another goal for this study was to examine if the 'quest theory' equation developed by Hassell & Varley (1969) could be applied to this system, and to compare the quest constant (Q) and mutual interference constant (m) obtained for Nemeritis attacking larvae of the almond moth, Ephestia cautella (Wlk.) (Hassell 1971) with those values obtained when the same parasite attacks a different host. The validity of the analysis of all the processes involved will be checked by constructing a model for the populations of both species and comparing it graphically with the observed fluctuations in the population levels.