Costly leaf shelters protect moth pupae from parasitoids
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Many caterpillars construct shelters by folding leaves and feeding from within. Many shelter-constructing species suffer high rates of parasitism as larvae or pupae. In spite of the likely significance, the effects of these shelters on the survival of pupae and the trade-off between feeding and constructing shelters have attracted little experimental attention. In both field and laboratory experiments, fern-feeding caterpillars [Herpetogramma theseusalis (Walker) (Lepidoptera: Crambidae)] invested heavily in shelters, losing weight and significantly delaying pupation rather than feeding or pupating in exposed locations. Experimentally thinning the walls of shelters in the field doubled the parasitism rate. Parasitism of pupae exceeded predation by an order of magnitude or more in both seasons of this study. Caterpillars constructed similarly sized shelters regardless of availability of fern fronds, resulting in incomplete shelters on especially small fronds, putting pupae at increased risk of parasitism. We suggest that similar interactions are common and merit more attention.
KeywordsLeaf shelters Host–parasitoid interactions Indirect interactions Caterpillars Pupae
We thank E.K. Morse, G.Chapman and N.H. Rose for assistance in the field; and K.J. Eckelbarger, T.E. Miller, L. Healy and other staff members of the Darling Marine Center of the University of Maine for facilitating work on the premises. B. Hawkins, R. Karban, N.H. Rose, J.K. Waage, J.D. Witman, I. Pearse and several anonymous reviewers read earlier drafts of the manuscript and contributed much helpful commentary. We thank D.L. Wagner, University of Connecticut, for identifying Herpetogramma theseusalis; M.J. Sharkey, University of Kentucky, for identifying Alabagrus texanus; and D. Wahl, American Entomological Institute, Gainesville, Florida, for determination of the ichneumonid wasps. R. Carlson, D. Bragg and E. Diller provided many useful references and much information on the parasitoids. E.F. LoPresti was supported by a Brown University undergraduate research award 2009–2010.
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