Herbivorous larvae have many ways of protecting themselves from their natural enemies including behavioral, chemical and physical defense mechanisms. Physical defenses may be either defensive structures that the larva has constructed itself, such as a fecal shield, or part of the larva’s morphology, such as spines. Larvae in the moth family Limacodidae employ a wide variety of defense mechanisms to protect themselves from their natural enemies. Some larvae are cryptic and are presumably able to hide from natural enemies while other larvae are both chemically and physically defended with stinging spines. While stinging spines may protect herbivorous larvae from generalist predators, we predicted that koinobiont parasitoids might actually target these physically defended larvae. Unlike idiobiont parasitoids that kill their host immediately, koinobiont parasitoids do not kill the host immediately and indeed require that the host remain alive for at least a few days, often weeks or months, in order to complete their development. Hence, the larvae of koinobiont parasitoids may actually benefit from the physical defenses of their herbivorous host because these defenses, while no longer offering a fitness advantage to the parasitized herbivore, may still protect the parasitoid larva from generalist predators. The concept of enemy-free space is commonly described from the perspective of members of the second trophic level; for instance, an herbivore searching for host plants or habitats that offer protection from third trophic-level enemies such as predators and parasitoids. We suggest that parasitoids of Limacodids, as members of the third trophic level, may select herbivorous hosts that offer protection from other third trophic-level predators.
Results/Conclusions
Here we present the results from 4 years of data on the parasitism rates of Limacodid larvae in the field. We have collected over 1,100 larvae of 13 Limacodid species from 7 host plant species at 4 sites near Washington, D.C. We have found that spiny larvae that are defended with stinging spines are significantly more likely to be parasitized than non-spiny larvae. Furthermore, we have found that koinobiont parasitoids are significantly more likely to attack spiny larvae than non-spiny larvae. These results support the hypothesis that parasitoids may select larval hosts that offer enemy-free space from their own natural enemies.
