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Physical defences wear you down: progressive and irreversible impacts of silica on insect herbivores
Article first published online: 3 SEP 2008
DOI: 10.1111/j.1365-2656.2008.01472.x
© 2008 The Authors. Journal compilation © 2008 British Ecological Society
Additional Information
How to Cite
Massey, F. P. and Hartley, S. E. (2009), Physical defences wear you down: progressive and irreversible impacts of silica on insect herbivores. Journal of Animal Ecology, 78: 281–291. doi: 10.1111/j.1365-2656.2008.01472.x
Publication History
- Issue published online: 11 DEC 2008
- Article first published online: 3 SEP 2008
- Received 12 March 2008; accepted 4 August 2008; Handling Editor: Graeme Hays
- Abstract
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- Cited By
Keywords:
- dietary mixing;
- food utilization;
- herbivory;
- mandible wear;
- nutrients
Summary
- 1Silica in the leaves of grasses can act as a defence against both vertebrate and invertebrate herbivores. The mechanisms by which silica affects herbivore performance are not well characterized. Here we expose an insect herbivore Spodoptera exempta to high-silica diets and test two mechanisms by which silica has been proposed to act as a defence. First, that silica reduces the digestibility of leaves and second, that silica causes wear to insect mandibles, both of which could potentially impact on herbivore performance.
- 2Silica reduced the efficiency with which S. exempta converted ingested food to body mass and the amount of nitrogen absorbed from their food, leading to reduced insect growth rates. The measure of how efficiently herbivores utilize digested food (ECD) was unaffected by silica.
- 3These effects occurred even with short-term exposure to silica-rich diets, but they also increased markedly with the duration of exposure and affected late instars more than early instar larvae. This appears to be due to the progressive impacts of silica with longer exposure times and suggests that herbivores cannot adapt to silica defences, nor do they develop a tolerance for silica with age.
- 4Exposure to silica-rich diets caused increased mandible wear in S. exempta. This effect was extremely rapid, occurring within a single instar, further reducing feeding efficiency and growth rates. These effects on insect growth and feeding efficiency are nonreversible, persisting after the herbivore has switched diets. Up to a third of this residual impact can be explained by the degree of mandible wear caused by previous silica-rich diets.
- 5The impacts of silica on S. exempta larvae were progressive with exposure time and could not be compensated for, even by switching to a different diet. Thus, herbivores cannot easily adapt to physical defences such as silica, suggesting this defence will have major implications for herbivore fitness.