Seed mixtures as a resistance management strategy for European corn borers(Lepidoptera : Crambidae) infesting transgenic corn expressing Cry1Ab protein

Dispersal of neonate European corn borers, Ostrinia nubilalis (Hubner), in seed mixtures of transgenic corn expressing Cry1Ab protein (Bt+) and nontra nsgenic corn (Bt-) was evaluated in a 2-yr field study. The main objective was to determine if larval dispersal limits the effectiveness of seed mixtu res as a resistance management strategy. Mixtures evaluated included (1) al l Bt+ plants, (2) every fifth plant Bt- with remaining plants Bt+, (3) ever y fifth plant Bt+ with remaining plants Bt-, and (4) all Bt- plants. The tr ansformation events MON 802 (B73 BC1F2 X Mo17) and MON 810 (B73 BC1F1 X Mo1 7), which express the Cry1Ab endotoxin isolated from Bacillus thuringiensis subsp. kurstaki, were used as the sources of Bt+ seed in 1994 and 1995 res pectively (YieldGard, Monsanto, St. Louis, MO). At corn growth stage V6-V8, subplots within each mixture (15-20 plants each) were infested so that eve ry fifth plant in mixtures 1 and 4, every Bt- plant in mixture 2, and every Bt+ plant in mixture 3 received two egg masses. Larval sampling over a 21- d period indicated increased neonate dispersal off of Bt+ plants, reduced s urvival of larvae that dispersed from Bt+ plants to Bt- plants, and a low i ncidence of late-instar movement from Bt- plants to Bt+ plants. Computer si mulations based on mortality and dispersal estimates from this study indica te that seed mixtures will delay the evolution of resistant European corn b orer populations compared with uniform planting of transgenic corn. However , resistant European corn borer populations likely will develop faster in s eed mixes compared with separate plantings of Bt and non-Bt corn.