Density-dependent resistance of the gypsy moth <Emphasis Type="Italic">Lymantria dispar</Emphasis> to its nucleopolyhedrovirus,and the consequences for population dynamics |
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Authors: | James R Reilly Ann E Hajek |
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Institution: | (1) Department of Entomology, Comstock Hall, Cornell University, Ithaca, NY 14853-2601, USA |
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Abstract: | The processes controlling disease resistance can strongly influence the population dynamics of insect outbreaks. Evidence
that disease resistance is density-dependent is accumulating, but the exact form of this relationship is highly variable from
species to species. It has been hypothesized that insects experiencing high population densities might allocate more energy
to disease resistance than those at lower densities, because they are more likely to encounter density-dependent pathogens.
In contrast, the increased stress of high-density conditions might leave insects more vulnerable to disease. Both scenarios
have been reported for various outbreak Lepidoptera in the literature. We tested the relationship between larval density and
disease resistance with the gypsy moth (Lymantria dispar) and one of its most important density-dependent mortality factors, the nucleopolyhedrovirus (NPV) LdMNPV, in a series of
bioassays. Larvae were reared in groups at different densities, fed the virus individually, and then reared individually to
evaluate response to infection. In this system, resistance to the virus decreased with increasing larval density. Similarly,
time to death was faster at high densities than at lower densities. Implications of density–resistance relationships for insect–pathogen
population dynamics were explored in a mathematical model. In general, an inverse relationship between rearing density and
disease resistance has a stabilizing effect on population dynamics. |
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Keywords: | Disease resistance Density-dependent prophylaxis Stress Crowding Population dynamics Mathematical model NPV |
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