Population biology of entomopathogenic nematodes: Concepts, issues, and models

Entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) are lethal obligatory parasites of insects and are found in soils throughout the world. The recognition that these nematodes are major natural enemies of soil insect pests has stimulated research into various aspects of their biology and enabled their use in augmentation and conservation biological control programs. Unfortunately, relatively little is known about the structure and dynamics of their populations or the factors that influence them. This knowledge is required if these nematodes are to fulfill their considerable potential as manageable components of cultivated ecosystems. The unusual life history of entomopathogenic nematodes imposes important constraints on their population biology. The host cadaver serves as the focus for many of the fundamental interactions associated with their population dynamics because feeding, development, mating, and reproduction are confined to the cadaver environment. Only non-feeding infective juveniles (dauer larvae) leave the host, but their production, dispersal, persistence, and infection potential provide critical links for the survival and proliferation of populations. Infective juveniles also carry symbiotic bacteria (Enterobacteriaceae) that are released within the host, are largely responsible for host death, and form an integral part of their life history. In this paper, we discuss the structure of entomopathogenic nematode populations, the various biotic and abiotic factors that influence them, and procedures for sampling and modeling their spatial and temporal dynamics. Environmental degradation and the economic and social realities of modern agriculture assure that entomopathogenic nematodes will remain prime subjects for continuing basic and applied ecological research.