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Density‐dependent prophylaxis: evidence from Lepidoptera–baculovirus interactions?
Author(s) -
WILSON KENNETH,
REESON ANDREW F.
Publication year - 1998
Publication title -
ecological entomology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.865
H-Index - 81
eISSN - 1365-2311
pISSN - 0307-6946
DOI - 10.1046/j.1365-2311.1998.00107.x
Subject(s) - citation , library science , lepidoptera genitalia , biology , ecology , computer science
Insects from a range of taxa use early larval density as a cue to the future deterioration of their current habitat (Dingle, 1996). Their response to this cue is often to redirect resources away from activities favouring immediate reproduction at the natal site (e.g. egg maturation) towards those that favour reproduction in a different location or at a different time (e.g. the development of wings and flight muscles or the deposition of lipid reserves). As well as predicting a decline in the quality or quantity of the larval food resource, early larval density may also predict the risk of exposure to pathogens, which often increases in a predictable manner with population density. Under such circumstances, natural selection will favour those individuals that use early larval density to predict the optimal level of resources to allocate to pathogen resistance later in life. Such an adaptive prophylactic response to larval density may explain the results of several recent studies of moth caterpillars and their baculoviruses. Kunimi & Yamada (1990) reared caterpillars of the Oriental armyworm moth ( Mythimna separata ) at densities ranging between one and twenty larvae per container. They then orally inoculated newly emerged fourth-instar caterpillars with various concentrations of nuclear polyhedrosis virus (NPV) and recorded the number of deaths. They found that NPV-induced mortality declined gradually from 95% for insects reared solitarily to 37% for those reared at a density of twenty larvae per container. The LC 50 value for caterpillars reared at the highest density was about tenfold that for individuals reared solitarily. In a second experiment, Kunimi & Yamada (1990) allowed second-instar caterpillars to feed for 2 days on artificial diet contaminated with a granulosis virus (GV) before rearing them for a further 36 days under either solitary or crowded conditions. They found that larvae reared at high densities (twenty per container) were about fourfold more resistant to GV than those reared singly. Thus, in this species at least,