Between predators and parasitoids: Complex interactions among shelter traits, predation and parasitism in a shelter-building caterpillar community

Shelter-building is widespread in the animal world and such shelters often influence the success of their builders. Shelters built by caterpillars influence the likelihood of attacks by natural enemies, but how particular shelter traits influence caterpillar survival is not known. Furthermore, the differential effects of certain shelter traits on some natural enemies, such as predators, may lead to 'enemy-free space' for other natural enemies (parasitoids). The parasitoid enemy-free space hypothesis has not been directly tested for shelter-building caterpillars. To understand how shelter traits influence caterpillar survival, shelter traits, predation and parasitism were measured simultaneously for 24 caterpillar morphospecies (1,465 caterpillars) in a tropical dry forest and analysed in a phylogenetic context. Shelter type, shelter openness and whether shelters accumulated frass had different amounts of phylogenetic signal, with frass accumulation displaying the most and shelter openness the least. All three traits affected the frequency with which caterpillar species experienced predation. Predation was elevated in two shelter types (leaf folds and leaf rolls) compared to cut-and-fold shelters. Combinations of shelter openness and frass accumulation also affected predation, with closed frass-free shelters having the lowest predation and closed frass-filled shelters having the highest. Parasitism was not affected by shelter traits but was strongly correlated with evolutionary history and negatively correlated with predation. These results confirm a trade-off between predation and parasitism and demonstrate that predation can be more frequent than parasitism. Different shelter types result in different amounts of predation. These defensive shelter traits and their effectiveness also vary phylogenetically. Together, our results suggest that predation and parasitism determine the success of shelter-building caterpillars, and that success is a function of the specific shelter they construct. More generally, our results demonstrate the importance of considering the effects of defensive traits on both predators and parasitoids when investigating interactions between herbivores and natural enemies. A freePlain Language Summarycan be found within the Supporting Information of this article.