Dietary specialization in herbivorous insects is typically viewed as an evolutionary consequence of either the top-down effect of natural enemies,the bottom-up effect of host plant chemistry, or a combination of the two. While multiple studies have supported these hypotheses by demonstrating
that chemically protected specialist herbivores are better protected than generalists against predators, few of these studies have examined relationships between herbivore diet breadth, plant-derived chemical defenses, and parasitism. We assessed the efficacy of narrow diet breadth and chemical defenses of different caterpillars against parasitoid wasps,
flies, and nematodes. Third to fifth instar caterpillars from 266 species and 30 families were collected in the field during wet and dry seasons from 1996 through 1999, scored for diet breadth, chemical defense, and other defenses and then reared in the laboratory. Diet breadth and chemical defense were used as predictor variables in loglinear models with parasitism as a response variable. Despite expectations from specialization models, larval attributes other than diet breadth and chemistry were the best predictors of parasitism. In fact, chemically defended specialist herbivores that are undesirable meals for predators,are safe hosts for parasitoids. Mortality caused by all taxa of parasitoids was high for caterpillars that are normally protected from predators by a variety of other defenses as well. Thus, the selective advantages of narrow diet breadth and chemical defenses enjoyed by many herbivores are not applicable to the significant source of mortality inflicted by parasitoids.
Keywords: dietary specialization, tritrophic interactions
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA