Predators, pathogens, and parasitoids as mortality agents in phytophagous insect populations

• Howard V. Cornell
• Bradford A. Hawkins

Abstract
Insect herbivores are killed by a diverse array of natural enemies, however not all herbivores suffer enemy attacks to the same degree. Various ecological and biological factors influence the rate of enemy-induced mortality suffered by herbivore populations. The major goal of this project is to quantify the effects of these factors on enemy-induced mortality, as revealed by a life table database of holometabolous herbivores. Although enemy mortality will be emphasized, we will also examine mortality caused by weather, competition, and plant factors. A secondary goal will be to compile and analyze a life table database of hemimetabolous herbivores. All databases will be made available to other workers when the analysis is complete. Enemy-induced mortality will be characterized by type (predator, parasitoid, or pathogen), and the relative importance of each type as well as other causes of death will be tested for differences associated with five ecological characteristics of the herbivores (feeding biology, invasion status, and the successional stage, cultivation status, and latitudinal zone of the habitat). The information will also reveal if herbivore ecology affects all enemies equally, or if tradeoffs exist such that reductions in the rate of attack by one type of enemy may be offset by increased attacks by other types. If so, than the already complex dynamics identified for plant vs. enemy interactions may be further enriched by interactions among the enemies themselves.