Journal
JOURNAL OF EXPERIMENTAL BIOLOGY
Volume 220, Issue 21, Pages 3955-3966Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jeb.160887
Keywords
Eupelmus vuilleti; Flow-through respirometry; Contest resolution; Resource value; Resource holding potential; Oviposition costs
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Funding
- University of Montana (Missoula, MT, USA)
- Institut de Recherche sur la Biologie de l'Insecte (IRBI, Universite Francois Rabelais, Tours, France)
- Ecole Normale Superieure (Paris, France)
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Oviposition sites may be challenging and energetically costly to access for females in the presence of competitors contesting that resource. Additionally, oviposition sites may be difficult to reach, and penetrating a hard substrate can raise energy costs. In the seed-drilling parasitic wasp Eupelmus vuilleti, females actively fight with conspecific competitors over access to hosts. They are often observed laying eggs on already parasitized hosts (superparasitism) living inside cowpea seeds despite the resulting larval competition. Using flow-through respirometry, we quantified the metabolic costs of fighting and of drilling through the seed to access the host, to understand the wasp's fighting strategies and the occurrence of superparasitism. Agonistic interactions such as kicks or pushes generated very small instantaneous costs, but the females that won their contests had higher pre-contest metabolic rates, suggesting a potential long-term cost associated with dominance. We also found that drilling holes through the seed accounted for approximately 15% of a wasp's estimated daily energy budget, and that females can reduce these drilling costs by reusing existing holes. Because exploiting new seeds incurs both drilling costs and the risk of fights, it appears cost effective in some situations for females to avoid confrontations and lay eggs in existing holes, on already parasitized hosts. Our study helps explain the evolution of superparasitism in this system.
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