A field test of inducible resistance to specialist and generalist herbivores using the water lily Nuphar luteum |
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Authors: | Robin C Bolser Mark E Hay |
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Institution: | (1) Institute of Marine Sciences, University of North Carolina at Chapel Hill, 3431 Arendell Street, Morehead City, NC 28557, USA, US |
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Abstract: | We tested whether grazing by the specialist beetle Galerucella nymphaeae (Coleoptera: Chrysomelidae) induced resistance to herbivory in the water lily Nuphar luteum macrophyllum (Nymphaeaceae) using both the specialist beetle and the generalist crayfish Procambarus clarkii (Decapoda: Cambaridae). For 2 months, we allowed natural densities of beetles to develop on control plants of Nuphar, while removing beetles every 2–3 days from adjacent plants that were paired by location within our field site. By the end
of the 2-month manipulation, beetle grazing had damaged twice as much leaf surface on control plants as on removal plants
(30.6% vs. 14.2%, respectively). We then offered tissues from control and removal plants to adult and larval beetles and to
crayfish in laboratory assays. Increased levels of previous attack by the specialist beetle either did not affect or increased
water lily attractiveness to beetles, but significantly decreased attractiveness to the generalist crayfish. Beetle larvae
did not feed preferentially on control vs. removal Nuphar in assays using either immature, undamaged leaves that had not yet reached the pond surface or intermediate aged leaves that
had reached the surface and experienced some beetle grazing. Adult beetles consumed significantly more immature leaf tissue
from the heavily grazed controls than from the less grazed removal plants but did not discriminate between control and removal
leaves of intermediate age in either feeding or oviposition preference. In contrast, generalist crayfish consumed significantly
more plant tissue from the less grazed treatment than from the more heavily grazed controls. Crude chemical extracts from
Nuphar strongly deterred crayfish feeding, but neither phenolic content, protein content, nor differential effects of crude extracts
from control vs. removal plants explained crayfish feeding on control versus removal leaves. Our assays suggest that induced
resistance to crayfish may be chemically mediated, but the particular mechanisms producing this response remain unclear. Responses
may be due to defensive metabolites that degrade rapidly following extraction.
Received: 23 July 1997 / Accepted: 8 February 1998 |
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Keywords: | Chemical ecology Induced defenses Plant-herbivore interactions Specialist vs generalist herbivores Water lily |
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