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Responses of Mamestra brassicae (Lepidoptera: Noctuidae) to crowding: interactions with disease resistance, colour phase and growth

journal contribution
posted on 2023-06-08, 19:03 authored by Dave GoulsonDave Goulson, Jenny S Cory
This study examines phenotypic plasticity in relation to rearing density in larvae of the moth, Mamestra brassicae. Larval phase, growth rate, weight at moulting and susceptibility to disease were quantified when reared at five densities. Larvae develop more quickly, but attain a smaller size and are more susceptible to disease, when reared at high than at intermediate densities. They also exhibit a higher degree of melanisation than larvae reared at intermediate densities, or singly. A review of the literature suggests that a switch to a rapidly developing dark phase at high densities is a widespread phenomenon within the Lepidoptera. Rapid development at the expense of attaining a large size, and increased melanisation, are interpreted as adaptive responses to reach pupation before food supplies are depleted, as is likely when larval density is high. High susceptibility to viral infection at high density may be a result of physiological stress associated with rapid development, or due to a shift in allocation of resources from resistance to development: larvae that developed quickly were more susceptible to infection. Larvae reared singly appeared to be less fit than larvae reared at intermediate densities: they exhibited many of the characteristics of larvae reared at high density, particularly low weight, a right-hand skew in their weight frequency distribution, and high susceptibility to disease. I hypothesise that expression of resistance may be phenotypically plastic with regard to environment. Contact with other larvae may, up to a point, stimulate both growth and resistance to infection, for the risk of infection will increase with the density of conspecifics.

History

Publication status

  • Published

Journal

Oecologia

ISSN

0029-8549

Publisher

Springer Verlag

Issue

4

Volume

104

Page range

416-423

Department affiliated with

  • Evolution, Behaviour and Environment Publications

Full text available

  • No

Peer reviewed?

  • Yes

Legacy Posted Date

2014-11-26

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