Association between landscape composition and the abundance of predator and herbivore arthropods in Bt and non-Bt soybean crops

Abstract

Cropland expansion has been occurring over the last century, especially in South America, displacing non-crop areas mainly with soybean. Changes at a landscape level were followed by changes at a local scale, such as the adoption of insect-resistant transgenic crops. The homogenization of agroecosystem composition and agronomic practices have a great impact on arthropod predators and herbivore insects, which has not been quantified to a great extent in South America. We evaluate the effects of cover composition (1 km radii) as a landscape variable, and Bt adoption as a local variable on the quantity of the main predators and pests in soybean fields in Uruguay. Over a two-year period, we sampled 60 soybean fields with sweep net and beating sheet. We found that Bt and non-Bt soybean fields did not differ in the number of predators and stink bugs, while Bt fields were associated with less caterpillars’ abundance. The proportion area of soybean negatively affected the quantity of some predators in this crop. In contrast, the landscape cover with natural grassland, commercial forest and maize positively affected some of these beneficial organisms. The number of stink bugs in soybean was highly affected by the surrounding cover composition. Arthropod responses depend on soybean’s phenological period. We demonstrate the effects of the agriculturalization process on soybean predators and pests, suggesting that Bt adoption does not affect predators and each vegetation cover impacts them differentially. Different non-crop landscape cover and the abundance of predators in the field margin are positively associated with the abundance of predators in soybean fields.