Benefits of gregarious feeding by aposematic caterpillars depend on group age structure.
Gregarious feeding is a common feature of herbivorous insects and can range from beneficial (e.g. dilution of predation risk) to costly (e.g. competition). Group age structure should influence these costs and benefits, particularly when old and young larvae differ in their feeding mode or apparency to predators. We investigated the relative value of gregarious feeding by aposematic larvae of Uresiphita reversalis that we observed feeding in groups of mixed ages and variable densities on wild Lupinus diffusus. In a manipulative field experiment, the survivorship and growth of young larvae were enhanced in the presence of older conspecifics, but not in large groups of similarly aged larvae. Estimates of insect damage and induced plant responses suggest that mixed-age groups enhance plant quality for young larvae while avoiding competition. We conclude that benefits of gregariousness in this species are contingent on group age structure, a finding of significance for the ecology and evolution of gregariousness and other social behaviours.
Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, 14853, USA. sa.campbell@utoronto.ca.|Department of Entomology, Cornell University, Ithaca, NY, 14853, USA. sa.campbell@utoronto.ca.|Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada. sa.campbell@utoronto.ca.
Stuart A
SA
Campbell
Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, 14853, USA.|Department of Biology, University of Ottawa, 30 Marie-Curie, Ottawa, ON, K1N 6N5, Canada.
Michael
M
Stastny
D000818:Animals; D001522:Behavior, Animal; D005075:Biological Evolution; D004463:Ecology; D005247:Feeding Behavior; D020387:Food Chain; D060434:Herbivory; D006801:Humans; D007814:Larva / Q000254:growth & development; D007915:Lepidoptera / Q000254:growth & development; D031297:Lupinus; D018515:Plant Leaves; D011235:Predatory Behavior; D012919:Social Behavior