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Control of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), with the entomopathogenic nematode Heterorhabditis marelata Liu and Berry (Nematoda: Heterorhabditidae) was examined in the laboratory and in potato fields in north central Oregon. This research tested the hypothesis that varying nitrogen fertilizer levels would affect foliar alkaloid levels, which would stress the host, and allow increased nematode reproduction and long-term control of the CPB. Laboratory results indicated that nematodes tended to reproduce more readily in CPB fed on potato plants with high levels of fertilizer. Field trials tested CPB population responses to four treatments: application of nematodes vs. no nematodes, with application of low vs. high rates of nitrogen fertilizer. The higher nitrogen application rate increased field foliar levels of the alkaloids solanine by 35%, and chaconine by 41% over the season. Nematodes were applied twice during the season, causing a 50% reduction in adult CPB populations, and producing six times as many dead prepupae in nematode-treated soil samples as in the untreated samples. However, no reproducing nematodes were found in the 303 dead prepupae and pupae collected from nematode-treated plots. Nitrogen fertilizer levels, and their related alkaloid levels, did not affect nematode infection rates or reproduction in the field. Foliar alkaloid levels of plants from the growth chamber were 3–6-fold as high as those in the field, which may explain the variation in nematode response to nitrogen applications to host plants of the CPB. Heterorhabditis marelata is effective for controlling CPB in the field, and does not have negative non-target effects on one of the most common endemic CPB control agents, Myiopharus doryphorae (Riley) (Diptera: Tachinidae), but the low rate of nematode reproduction cannot be manipulated through alkaloid stress to the beetle. Until H. marelata can be mass-produced in an inexpensive manner, it will not be a commercially viable control for CPB. [ABSTRACT FROM AUTHOR]

Field studies were conducted in 1992 and 1993 in Hermiston, Oregon, to evaluate nontarget impacts of transgenic Bt potato (Newleaf) expressing Cry3Aa protein derived from Bacillus thuringiensis (Bt) Berliner subsp, tenebrionis and conventional insecticides for control of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say). Pitfall traps were used to estimate the abundance of nontarget ground-dwelling arthropods in different treatment plots. There were no significant differences in the trap captures of major ground-dwelling coleopteran predators such as carabids (Coleoptera: Carabidae) and staphylinids (Coleoptera: Staphylinidae) among Bt and non-Bt potato fields treated with weekly sprays of a microbial Bt-based formulation containing Cry3Aa, biweekly applications of permethrin, early and mid season in-furrow applications of systemic insecticides (phorate and disulfoton), or no insecticides. While weekly sprays of permethrin significantly reduced the trap capture of ground-dwelling spiders (Araneae), there were no significant differences in the capture of spiders between Bt and non-Bt-potato fields treated with Bt sprays, systemic insecticides, or no insecticides. Significantly more springtails (Collembola: Entomobryidae and Hypogastruridae) were captured in potato fields treated with permethrin than with any other CPB control regime (transgenic Bt potato alone, microbial Bt formulation containing Cry3Aa, applications of systemic insecticides, or no action controls), among which there were no significant differences. The relevance of these findings to field evaluation of nontarget impacts of transgenic Bt crops is discussed. [ABSTRACT FROM AUTHOR]