Local and landscape factors determining the abundance and richness of insect pests and arthropod predators in Bt and non-Bt soybean

Abstract

Agricultural landscapes of the Pampas and Campos biome have changed considerably due to the expansion of annual crops over non-crop areas, soybean seeding and the adoption of lepidopteran-resistant varieties (Bt technology). These changes have a great impact on predatory and phytophagous arthropods, which have been scarcely studied in Uruguay. The following aspects were evaluated: (a) the effect of vegetation cover composition (landscape factor), Bt technology (varieties expressing Cry1Ac protein) and field margins (local factors), on the abundance of the main pests and predators of soybean; b) the role of refuge areas (non-Bt soybean) in determining the abundance and richness of arthropod predators in Bt soybean crops, and c) the effect of Cry1Ac protein on the biology, reproduction and feeding behavior of Piezodorus guildinii (Hemiptera: Pentatomidae). In the northern Uruguayan littoral, during two years, predators and pests were sampled in 90 commercial non-Bt and Bt soybean fields and refuge areas. Biological and reproductive parameters of P. guildinii fed with Bt soybean pods and their possible effect on feeding behavior were evaluated using the electrical penetration graph technique. The main results obtained were: a) i. Bt soybean presented lower abundance of defoliating lepidoptera, without affecting predator abundance; ii. Soybean predators’ abundance was negatively related to the proportion of this crop in the landscape, but positively related to natural grassland and other crops; iii. Predators’ abundance between margins and within soybean fields was positively associated; b) Bt predators’ abundance and richness was positively associated with their values in refuge areas, evidencing for the first time their role in the conservation of beneficial fauna; c) biological and reproductive parameters and feeding behavior of P. guildinii were not affected by the ingestion of Cry1Ac protein expressed in Bt soybean pods. These results contribute to the possibilities of ecological intensification designs of national and regional production systems through pest management approached from a landscape perspective.