Ten years of Cry1Ac Bt soybean use in Argentina: Historical shifts in the community of target and non-target pest insects

Long-term changes in the insect communities in genetically modified (GM) crops expressing target-specific pesticidal proteins can occur and matter for optimized integrated pest management. Using monitoring data of commercial soybean fields from 2012 to 2022, we documented shifts in the abundance of target and non-target insects of the GM Cry1Ac Bacillus thuringiensis (Bt) soybean in two provinces of northwestern Argentina. Before adoption of Bt soybean, lepidopterans prevailed in the crop-associated insect-pest community. They were 65% more abundant than stink bugs and weevils, and the highest population levels (a mean of 169 individuals/plot) were recorded during the vegetative and early reproductive stages. After introducing Bt soybean, the abundance of target lepidopterans (i.e., erebids, heliothines, and plusiines) was the lowest in the 2017-2018 crop season. In the 2020-2021 and 2021-2022 seasons, Rachiplusia nu larvae (Lepidoptera: Noctuidae: Plusiinae) were recorded in Bt soybean fields. The numbers of non-target lepidopterans (Spodoptera spp.) increased year by year, and they were the prevailing lepidopteran species on Bt soybean in 2020-2021 and the R1-R5 (reproductive) soybean growth stages. Weevil abundance was higher on Bt soybean than non-Bt soybean. Stink bugs were more frequent in Tucum ' an than Catamarca, and their abundances were higher during R1-R5 than during vegetative and late-reproductive stages. The temperature, precipitation, and solar radiation conditioned the abundance of some of the pest complexes. Efforts to monitor and manage secondary or Bt-resistant populations of insect pests are necessary and should be continued and complemented with studies of pest-susceptibility shifts to inform sound locally adapted integrated pest management programs.