The Colorado potato beetle (Leptinotarsa decemlineata Say) (CPB) is the key pest of potatoes and other solanaceous crops in the United States and much of Europe. The beetle rapidly develops resistance to most pesticides used against it, and transgenic crops are not currently favored by the general public for pest control. Hence, we are examining biological control of the beetle, by using the entomopathogenic nematode Heterorhabditis marelatus Liu & Berry. The nematode kills nearly 100% of beetles in field trials, but does not reproduce in the beetle. Here we examine the hemolymph chemistry effects on the nematode and its symbiotic bacteria. Previous research indicated the symbiotic bacteria switched rapidly to a secondary form when placed in CPB hemolymph. Unlike the primary form of the bacteria, the secondary form does not provide nutrients or protection against competing pathogens for the nematode. The research discussed here examines the effects of the host’s immune system and hemolymph toxicity on the nematodes and associated bacteria. We found that the immune system rarely inhibits bacterial or nematode growth. However, a previously identified toxic protein, leptinotarsin, causes the bacterial switch to the secondary form. When the leptinotarsin is denatured, the nematodes still cannot reproduce. Evidence suggests that lipids are not available to the nematodes in CPB hemolymph, limiting reproduction. We hypothesize that the glycoalkaloids from the plants on which the CPB feeds bind to the lipid-transport proteins in the hemolymph, halting the movement of cholesterol in the hemolymph, and thus negatively affecting the nematodes.
Species 1: Coleoptera Chrysomelidae Leptinotarsa decemlineata (Colorado potato beetle)
Species 2: Nematoda Heterorhabditidae Heterorhabditis marelatus
Keywords: hemolymph, entomopathogenic nematodes
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