THE EFFECT OF ECONOMIC THRESHOLDS AND LIFE-HISTORY PARAMETERS ON THE EVOLUTION OF PESTICIDE RESISTANCE IN A REGIONAL SETTING

We explore the dynamics of alleles conferring insecticide resistance i n agroecosystems in which economic thresholds are used to manage insec t pest populations. The dynamics of economic thresholds on resistance evolution are first explored in a single-field model. A two-dimensiona l cellular automata model is then used to examine the effects of migra tion, refuges, and crop rotation in a large region of fields under dif ferent management strategies. The single-field model indicates that ec onomic thresholds may have important implications for pesticide manage ment strategies, because resistance evolution is no longer independent of the growth process. In the regional model, the growth rate of the population, the selection pressure on the resistant allele, and migrat ion all affect the time to resistance. Rotation is most beneficial whe n migration rates are either very high or very low and has little effe ct at intermediate migration rates. Resistance develops in large patch es, so the level of resistance in a given field may be only weakly rel ated to the history of pesticide treatment in that field. This finding may explain the high regional variability found in field studies of r esistance in pests such as Colorado potato beetle.