Abstract
Extensive cultivation of crops genetically engineered to produce insecticidal
proteins from the bacterium Bacillus thuringiensis (Bt) has suppressed some
major pests, reduced insecticide sprays, enhanced pest control by natural
enemies, and increased grower profits. However, these benefits are being eroded
by evolution of resistance in
pests. We report a strategy for combating
resistance by crossing transgenic Bt plants with conventional non-Bt plants and
then crossing the resulting first-generation (F1) hybrid progeny and sowing the
second-generation (F2) seeds. This strategy yields a random mixture within
fields of three-quarters of plants that produce Bt toxin and
one-quarter that
does not. We hypothesized that the non-Bt plants in this mixture promote
survival of susceptible insects, thereby delaying evolution of resistance. To
test this hypothesis, we compared predictions from computer modeling with data
monitoring pink bollworm (Pectinophora gossypiella) resistance to Bt toxin
Cry1Ac produced
by transgenic cotton in an 11-y study at 17 field sites in
six provinces of China. The frequency of resistant individuals in the field
increased before this strategy was widely deployed and then declined after its
widespread adoption boosted the percentage of non-Bt cotton plants in the
region. The correspondence between the predicted and observed outcomes implies
that this strategy countered evolution of resistance. Despite the increased
percentage of non-Bt cotton, suppression of pink bollworm was sustained. Unlike
other resistance management tactics that require regulatory intervention,
growers adopted this strategy voluntarily, apparently because of advantages that
may include better performance as well as lower costs for seeds and
insecticides.