Modeling evolution of resistance of sugarcane borer (Lepidoptera: Crambidae) to transgenic Bt corn.

Diatraea saccharalis (F.) (Lepidoptera: Crambidae) is a target pest of transgenic corn expressing Bacillus thuringiensis (Bt) protein, and the first evidence of resistance by D. saccharalis to Cry1Ab corn was detected in a field population in northeast Louisiana in 2004. We used a model of population dynamics and genetics of D. saccharalis to 1) study the effect of interfield dispersal, the first date that larvae enter diapause for overwintering, toxin mortality, the proportion of non-Bt corn in the corn patch, and the area of a crop patch on Bt resistance evolution; and 2) to identify gaps in empirical knowledge for managing D. saccharalis resistance to Bt corn. Increasing, the proportion of corn refuge did not always improve the durability of Bt corn if the landscape also contained sugarcane, sorghum, or rice. In the landscape, which consisted of 90% corn area, 5% sorghum area, and 5% rice area, the durability of single-protein Bt corn was 40 yr when the proportion of corn refuge was 0.2 but 16 yr when the proportion of corn refuge was 0.5. The Bt resistance evolution was sensitive to a change (from Julian date 260 to 272) in the first date larvae enter diapause for overwintering and moth movement. In the landscapes with Bt corn, non-Bt corn, sugarcane, sorghum, and rice, the evolution of Bt resistance accelerated when larvae entered diapause for overwintering early. Intermediate rates of moth movement delayed evolution of resistance more than either extremely low or high rates. This study suggested that heterogeneity in the agrolandscapes may complicate the strategy for managing Bt resistance in D. saccharalis, and designing a Bt resistance management strategy for D. saccharalis is challenging because of a lack of empirical data about overwintering and moth movement.