Meeting Abstract

P2.4  Sunday, Jan. 5 15:30  Real, live chest-bursters and vomiting caterpillars: Alien flies meet Exorcist caterpillars in the American Southwest WOODS, H. A.*; WILSON, J. K.; Univ. of Montana; Univ. of Montana art.woods@mso.umt.edu

A key source of mortality for caterpillars worldwide is parasitoid flies in the family Tachinidae, which deposit eggs or fully-developed larvae onto the cuticles of caterpillars. Once hatched, fly larvae burrow through the cuticle and live in the caterpillar’s hemocoel, where they feed on hemolymph and host tissues even as the caterpillar continues to grow. Eventually the fly larvae kill the caterpillar, consume most of its internal tissues, and pupate inside the husk that remains, or just outside it. For the host caterpillar, parasitization by tachinid larvae is almost always a death sentence, and we hypothesized that caterpillars would show strong defensive behaviors against flies and their eggs. In a study of wild Manduca sexta and M. quinquemaculata in southeastern Arizona, we showed that caterpillars (field-collected fourth and fifth instars) were parasitized at rates exceeding 30%, and that caterpillars used at least eight distinct defensive behaviors, including camouflage, biting, several kinds of grooming, regurgitation, secretion of anal fluids, and increases in hemolymph pressure. We examined in more detail the defensive roles played by regurgitation, showing that it defended caterpillars from unembryonated eggs (fertilized but requiring additional development on the host) laid by one fly species, but not ovalarvaposited eggs (containing a fully developed first-instar fly larva) laid by another, which hatched within 10 minutes of deposition on the caterpillar. We hypothesize that these defenses evolved in response to the high risk that any one defense would fail, and in response to the physiological and behavioral diversity shown by tachinid flies.