Dynamics of lepidopteran pests and a phylogeographic approach of three Spodoptera species (Lepidoptera: Noctuidae) on soybean fields in Brazil

• Autor(a) principal: Horikoshi, Renato Jun
• Data de Publicação: 2022
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/11/11146/tde-08062022-155839/
• topic: Bt plant; Cry1Ac soybean; Genética de população; IPM; MIP; Planta Bt; Population genetics; Soja Cry1Ac

Soybean is one of the most important sources of oil and protein worldwide. The area planted with soybean significantly increased in the last 50 years, and currently, Brazil is the largest producer. Several agricultural innovations were needed to increase production such as no-tillage system cultivation, soil acid correction and fertilization, new crop varieties adapted to a range of latitudes, inoculation of nitrogen-fixing bacteria, multi-crop system with at least two cropping seasons per year and the use of genetically modified plants. 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. Despite the importance to Integrated Pest Management, knowledge on the population dynamics, shifts and genetic structure of agriculture pest populations in Brazil are still incipient. Here, is presented evidence of the regional reduction in insecticide use across areas in Brazil where Cry1Ac soybean is grown, with up to 50% reduction in the number of insecticide applications for managing lepidopteran pests on non-Bt soybean observed at specific locations. Furthermore, a reduced number of Chrysodeixis includens moths were captured across years in a pest-monitoring study in four mesoregions. The number of Helicoverpa spp. moths captured also were reduced at three mesoregions. In a large-scale sampling of larvae on commercial soybean fields during the 2019 and 2020 crop seasons, C. 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 spp. 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. To investigate the population genetic diversity, population structure, and demographic pattern of Spodoptera eridania, Spodoptera cosmioides and Spodoptera frugiperda, a mitochondrial COI sequence-based analyzes were performed. High genetic diversity was observed for S. eridania sampled on soybean in Brazil. The genetic diversity index of S. eridania was higher than that observed for S. cosmioides and S. frugiperda. Low genetic structure was observed for the three Spodoptera species. The highest 𝝫ST observed was for S. cosmioides (0.058) followed by for S. eridania (0.058) and S. frugiperda (0.017). There is evidence that the three Spodoptera species evaluated in this study are in demographic and spatial expansion. The results of the study also suggest that corn strain is the major lineage of S. frugiperda occurring in soybean in Brazil. This research clarified and updated the knowledge of insect pest populations attacking soybean in Brazil. A regional suppression of lepidopteran pests and reduced insecticide use with the widespread adoption of Cry1Ac soybean has been observed, bringing economic and environmental benefits. Chrysodeixis includens and A. gemmatalis continue to be primary lepidopteran pests of soybean in Brazil and Cry1Ac soybean continues to effectively manage the target lepidopteran pests. Increase in the relative abundance of non-target Spodoptera spp. larvae in both non-Bt and Cry1Ac soybeans confirmed the emerging importance of this genera in soybean. Finally, these Spodoptera species show low genetic structure and are at demographic and spatial expansion, probably driven by agriculture expansion, especially soybean fields.