Document: GRA-3-56-17

A multi-taxa assessment of the effectiveness of caterpillar defenses against parastioids

GENTRY, G.* and L.DYER

Mesa State College, Grand Junction, Colorado 81502 USA ¹

Abstract:
A caterpillar often has several types of defense at its disposal and may use them all to escape predators or parasitoids. Many previous studies determined if a defense works against a particular enemy, but which defenses are most effective against which type of enemy has not been examined closely. We assessed the efficacy of different caterpillar defenses against parasitoids using a statistical approach that considers defenses across multiple taxa. Determining the relative importance of different defenses against enemies will further our understanding of the evolution of these defenses, and the role of enemies in determining insect herbivore diet breadths. Third to fifth instar caterpillars from 55 species in 17 families were collected in the field during the wet and dry seasons in 1994 -1999, scored for various behavioral and morphological defenses, then reared in the laboratory. Defenses were used as predictor variables in log linear models with parasitism as the response variable. This analysis allowed us to separate the relative effectiveness of each type of defense. Overall parasitism for all caterpillars was 24.75%. Levels of parasitism in the dry season were always higher than in the wet season. The most important predictors of parasitism, in order of importance, were behavior, then season, then morphology. Caterpillars that dropped off the plant were the least likely to be parasitized, whereas caterpillars that did nothing were the most likely. Thrashing was a good protective behavior, but biting and vomiting were not. Spiny and hairy caterpillars were parasitized more often than glabrous ones. Caterpillar coloration was not important. The results suggest that parasitoids had difficulty physically placing eggs or larvae on or into caterpillars with defenses involving movement (dropping/thrashing), or re-encountering larvae that had moved. Fixed morphological defenses (hairs), venom delivery (some spines), or warning/cryptic coloration may be more oriented to defense against insect or vertebrate predators than to parasitoids.

Keywords: parasitoid, lepidoptera, natural enemies, caterpillar, defenses

This abstract is being presented at: 1:30 PM in session:
Oral Session #15: Parasitoids and Diseases.