FLUTUAÇÃO POPULACIONAL DE INSETOS-PRAGAS E PREDADORES EM ÁREAS COMERCIAIS DE SOJA BT E SOJA NÃO BT

Abstract

This study aimed to evaluate the population dynamics of insect pests and predators in commercial Bt and non-Bt soybean fields across the 2018/2019 and 2024/2025 seasons to understand shifts in species composition, abundance, and distribution. Monitoring was conducted weekly using the beat-sheet method and visual inspections in irrigated and rainfed fields. The 2018/2019 season assessed conventional systems with RR technology (non-Bt for lepidopterans), whereas the 2024/2025 season involved Bt varieties expressing IPRO and I2X technologies. The results demonstrated a sharp reduction in the looper complex (Chrysodeixis includens and Rachiplusia nu) population following the introduction of Bt soybean, with the mean density decreasing from 1.44 individuals per sample (aggregated pattern) to 0.01 (random pattern). Conversely, defoliating coleopterans of the genus Megascelis exhibited a population increase in the Bt crop season, rising from 1.34 to 1.61 individuals per sample, coupled with a high aggregate overdispersion index (6.39). The predatory insect community showed a higher mean density in the 2024/2025 season (0.21) compared to 2018/2019 (0.16), indicating that the reduction in chemical insecticide applications targeting caterpillars favored the conservation of these natural enemies within the agroecosystem. Principal Component Analysis (PCA) confirmed ecological segregation between the seasons, associating the non-Bt period with high lepidopteran pressure and the Bt period with the dominance of secondary pests. In conclusion, while Bt technology is highly effective in controlling target pests, it triggers indirect cascading effects on the entomofauna structure through the emergence of non-target pests, emphasizing the need for the continuous adaptation and execution of Integrated Pest Management (IPM) practices.