The efficacy of both B. thuringiensis and B. bassiana in the irrigated potato agroecosystem, the presence of the fungus in CPB in subsoil habitats and compatibility of the two microbials with insect natural enemies is encouraging. However, the potential for replacing broad-spectrum insecticides with microbial insecticides to control CPB in certain growing regions may actually depend primarily upon pests other than CPB. In the Pacific Northwest, the most damaging insect pest of potatoes is the green peach aphid, be- cause it is the primary vector of potato leaf roll virus in the area. Only extremely low densities of the aphid can be tolerated, and insect pest management in the Northwest revolves around controlling this species, not CPB (which is incidentally controlled by prod- ucts directed at the aphid). Thus, a biological control program directed at CPB would be accepted by grow-
ers only if aphid-control was not negatively affected. In the present study, wingless aphids never became abundant in any of the plots, even though densities of migrants (winged aphids) were fairly high. This observation suggests that natural enemies were active in the microbial-treated plots. It is unknown, however, whether the densities observed in the microbial-treated plots were sufficiently low to prevent economic dam- age due to leaf roll virus. Considerably more research is necessary to determine the manner in which micro- bial control of CPB affects the aphid-potato interac- tion, particularly in the growing regions of western North America.
The efficacy of both B. thuringiensis and B. bassiana in the irrigated potato agroecosystem, the presence of the fungus in CPB in subsoil habitats and compatibility of the two microbials with insect natural enemies is encouraging. However, the potential for replacing broad-spectrum insecticides with microbial insecticides to control CPB in certain growing regions may actually depend primarily upon pests other than CPB. In the Pacific Northwest, the most damaging insect pest of potatoes is the green peach aphid, be- cause it is the primary vector of potato leaf roll virus in the area. Only extremely low densities of the aphid can be tolerated, and insect pest management in the Northwest revolves around controlling this species, not CPB (which is incidentally controlled by prod- ucts directed at the aphid). Thus, a biological control program directed at CPB would be accepted by grow-ers only if aphid-control was not negatively affected. In the present study, wingless aphids never became abundant in any of the plots, even though densities of migrants (winged aphids) were fairly high. This observation suggests that natural enemies were active in the microbial-treated plots. It is unknown, however, whether the densities observed in the microbial-treated plots were sufficiently low to prevent economic dam- age due to leaf roll virus. Considerably more research is necessary to determine the manner in which micro- bial control of CPB affects the aphid-potato interac- tion, particularly in the growing regions of western North America.
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