Effects of Intraspecific Competition in the Indian Meal-Moth (Plodia interpunctella Hubner) (Lepidoptera: Phycitidae) on Populations of the Moth and its Parasite Nemeritis canescens (Gravenhorst) (Hymenoptera: Ichneumonidae)

Abstract

The Indian meal-moth (Plodia interpunctella Hiibner) is a world-wide pest which infests a very wide range of stored products. It constitutes a serious threat to grains, seeds and various other human food stores (Williams 1964; Reyes 1969). A lot of work has been done on its biology, but very little on the dynamics of its populations. Snyman (1949) did some work on the effects of densities on the development of this moth and Takahashi (1957) mentioned some results which he obtained with a continuous system which also included the ichneumonid parasite Nemeritis canescens (Gravenhorst). Very little is known about the dynamic processes operating on the populations of this insect and much more needs to be done before a detailed study of the natural populations can be carried out. This is clearly shown in a recent review (Benson 1973) which summarizes the present knowledge of the biology of Lepidoptera infesting stored products, with special reference to population dynamics. The present study adds more information to the knowledge and understanding of the processes involved. This knowledge may be helpful later to control the populations below the economic threshold. The study was in two parts. The first included controlled experiments in which some effects of intraspecific competition among the larvae of the host were analysed together with the effects of this competition on the ichneumonid parasite N. canescens, which is one of the most important parasites of the moth. Nemeritis is a thelytokous, solitary, internal parasite of larvae of several species of flour moths. Much work has already been done on its biology and behaviour, usually in relation to Ephestia species as hosts (e.g. Ahmed 1936; Takahashi 1961; Corbet & Rotheram 1965; Corbet 1971; Hassell 1971). The second part of the study will be reported later (Podoler 1974) and includes analysis of a continuous host-parasite system.