PREDATORS, PARASITOIDS, AND PATHOGENS AS MORTALITY AGENTS IN PHYTOPHAGOUS INSECT POPULATIONS

We compiled life tables for 78 holometabolous herbivorous insect speci es to quantify levels of apparent enemy-induced mortality of immature insects. Enemies were classified by type (predator, parasitoid, or pat hogen), and mortalities caused by each type in each herbivore immature stage were tested with Analysis of Deviance for differences associate d with four ecological characteristics of preadult herbivores: feeding biology, invasion status, and the cultivation status and latitudinal zone of the habitat. Total enemy-induced mortality is higher in the la te developmental stages, and overall, parasitoids kill more herbivores than do either predators or pathogens. Among the ecological variables , both feeding biology and latitude showed significant enemy effects i n at least one late developmental stage, whereas neither cultivation s tatus nor invasion status was associated with enemy-induced mortality in any stage. Bonferroni adjustment of probabilities for multiple comp arisons resulted in few significant interactions between enemy type an d the ecological variables. However, raw probabilities and comparisons across herbivore immature stages suggest several patterns that deserv e attention in future studies: (1)endophytic herbivores suffer lower m ortality by predators and pathogens than exophytics, and endophytic le af miners suffer the greatest parasitoid-induced mortality, while endo phytic gallers/borers/root feeders suffer the least; (2) overall enemy -induced mortality is similar in natural and cultivated habitats; (3) exotic insects do not suffer lower enemy-induced mortality rates than natives; and (4) predation and disease may be greater in tropical/subt ropical habitats, whereas parasitism is greater in the temperate zone. These results identify several general patterns in insect demographic s that should be useful for hypothesis testing.