Large-scale assessment of lepidopteran soybean pests and efficacy of Cry1Ac soybean in Brazil.

The soybean technology MON 87701 × MON 89788, expressing Cry1Ac and conferring tolerance to glyphosate, has been widely adopted in Brazil since 2013. However, pest shifts or resistance evolution could reduce the benefits of this technology. To assess Cry1Ac soybean performance and understand the composition of lepidopteran pest species attacking soybeans, we implemented large-scale sampling of larvae on commercial soybean fields during the 2019 and 2020 crop seasons to compare with data collected prior to the introduction of Cry1Ac soybeans. Chrysodeixis includens was the main lepidopteran pest in non-Bt fields. More than 98% of larvae found in Cry1Ac soybean were Spodoptera spp., although the numbers of Spodoptera were similar between Cry1Ac soybean and non-Bt fields. Cry1Ac soybean provided a high level of protection against Anticarsia gemmatalis, C. includens, Chloridea virescens and Helicoverpa spp. Significant reductions in insecticide sprays for lepidopteran control in soybean were observed from 2012 to 2019. Our study showed that C. includens and A. gemmatalis continue to be primary lepidopteran pests of soybean in Brazil and that Cry1Ac soybean continues to effectively manage the target lepidopteran pests. However, there was an increase in the relative abundance of non-target Spodoptera spp. larvae in both non-Bt and Cry1Ac soybeans.