Abstract
Corn earworm, Helicoverpa zea (Boddie), is a major target of pyramided Bacillus thuringiensis (Bt) corn. In the U.S. Corn Belt, a refuge-in-the-bag (RIB) strategy has been adopted to provide susceptible populations for insect resistance management (IRM) in planting pyramided Bt corn. In this study, eight field trials were conducted to evaluate occurrence and injury of H. zea in three planting patterns of non-Bt and Bt corn containing the Agrisure® Viptera™ 3111 trait. Viptera 3111 corn possesses two Bt genes, Vip3A and Cry1Ab, targeting above-ground lepidopteran pests. Occurrence of H. zea eggs was similar between non-Bt and Bt corn ears. Eggs of H. zea were distributed either randomly or uniformly in all three planting patterns. Field trials consistently showed that Viptera 3111 corn was extremely effective in H. zea control in both structured and RIB plantings. Across all the trials, there were very little or no larval survival and damage on Bt corn ears. Ear damage and larval occurrence at the peak of 3rd to 4th instars on refuge ears in the RIB plantings were not less than those observed in the structured non-Bt corn plantings. However, larval development on RIB refuge ears was significantly delayed relative to that on ears of structured non-Bt corn plantings. Information generated from this study should provide useful information to improve IRM modeling for Bt corn.
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