Submitted to: Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/29/2001
Publication Date: N/A
Citation: Interpretive Summary: Entomopathogenic nematodes hold great promise as biological alternatives to chemicals for the control of soil-inhabiting insect pests. They can be mass produced, have high virulence, possess a broad host range and are exempt from registration by the Environmental Protection Agency. However, sensitivity to environmental stress is one of the key factors causing an inconsistency in their field performance and is a road block to their greater use. We evaluated the variation in 15 strains of the most commonly used entomopathogenic nematode and found significant differences in the stress tolerance between them. Up to three-fold differences were found in the ability of the nematodes to survive dryness and a lack of oxygen. In addition, differences were found in the ability of the nematodes to kill host insects and to reproduce in those insects. These results will help scientists and those engaged in the commercial production of entomopathogenic nematodes, to develop stress tolerant characteristics in the nematodes which will make them more effective at being maintained in the environment and in killing pest insects.
Technical Abstract: Genetic variability in stress tolerance (heat, desiccation, and hypoxia) and fitness (virulence and reproductive potential among natural populations of Steinernema carpocapsae was assessed by estimating phenotypic differences. Significant differences were observed in stress tolerance among populations. Populations isolated from North Carolina showed significantly more stress tolerance than those isolated from Ohio. Significant differences were also observed in populations isolated from the same locality. Survival of infective juveniles after exposure to 40 deg C for 2 hours ranged from 37-82%. A three-fold difference was observed in infective juvenile survival following exposure to osmotic desiccation or hypoxic conditions. Several populations tested were superior to the most widely used strain ('All' strain) in stress tolerance traits, with one population KMD33 being superior to the 'All' strain in all traits. Fitness, as expressed by virulence and reproductive potential, differed significantly among populations, but showed less variability than with the stress tolerance traits. All populations tested had a reproductive potential greater than, or similar to, that of the 'All' strain and most of them caused >60% insect mortality of the greater wax moth larvae, Galleria mellonella. The high variability in stress tolerance among natural populations suggests the feasibility of using selection for genetic improvement of these traits.