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We compared the efficacy of 2 endemic strains of entomopathogenic nematodes isolated from Hermiston, OR, with that of 3 exotic nematode species for control of Colorado potato beetle, Leptinotarsa decemlineata (Say). In laboratory experiments, the exotic Heterorhabditis species were more pathogenic to Colorado potato beetle than were the endemic Heterorhabditis strains. Exotic Steinernema species were less pathogenic to Colorado potato beetle than the exotic Heterorhabditis species. No Colorado potato beetle adults emerged from soil treated with H. marelatus Liu & Berry, a new species collected from Seaside, OR. Nematode pathogenicity was detected up to 14 wk after application in Galleria mellonella (L.) in soil taken from field plots treated with endemic and exotic nematode species.

Entomopathogenic nematodes are excellent biological control agents. Utilization of these nematodes is developing rapidly with almost a doubling of newly described species in the past five years. Advances in molecular biology and phylogenetic reconstruction have revolutionized understanding of population structure, identification, genetic improvement, systematics, and the symbiosis between entomopathogenic nematodes and their bacteria. Population structure provides the most fundamental information for reliable identification of species and unique genetic variants. Such information could be further assessed for nematode potential as biological control agents. Phylogenetic reconstruction is an important approach for understanding multitrophic interactions among entomopathogenic nematodes, symbiotic bacteria, and their insect hosts. Phylogenetic reconstruction is also important for the development of a natural and stable type of systematics, which can provide guidelines for selecting appropriate entomopathogenic nematode species for particular biological control programs.