Colorado potato beetle larvae drop from the plant when they are mature to burrow into the soil to pupate. This provides an opportunity for the beetles to come into contact with entomopathogenic nematodes sprayed on the soil surface. However, results with several species of nematodes for control of larvae and prepupae have been variable, indicating that this beetle may not be as susceptible to some nematode species as are many other insect pests.
The efficacy of two endemic strains of Heterorhabditis collected during surveys for entomopathogenic nematodes in northeastern Oregon, were compared with 3 "exotic" strains (not from the immediate area) and 2 species of Steinernema. All of the nematodes tested reduced the number of beetles emerging. Mortality appeared to occur in the prepupa or pupal stages, and none of the nematodes reproduced in Colorado potato beetle. In these lab experiments the exotic Heterorhabditis species were more pathogenic to the beetles than the endemic species or the Steinernema species.
No beetles emerged from soil treated with H. marelatus, a new species collected from Seaside, Oregon. The symbiotic bacterium of H. marelatus is significantly different from that of other Heterorhabditis species, and may produce different toxins that act on the Colorado potato beetle's immune system, resulting in better control.
All the nematodes persisted in field plots for up to 14 weeks, suggesting their potential to provide initial and residual control.
Berry, R. E., J. Liu, and G. Reed. 1998. Comparison of endemic and exotic entomopathogenic nematode species for control of Colorado potato beetle (Coleoptera: Chyrsomelidae). J. Econ. Entomol. 90(6): 1528-1533.
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