Chrysodeixis includens (Walker, 1858) and Rachiplusia nu (Guenée, 1852) are important defoliating pests belonging to the Plusiinae subfamily in the Western hemisphere. C. includens is a major lepidopteran pest of soybean in the Americas, whereas, until 2021, R. nu was more restricted to the temperate regions of South America. Recently, reports of R. nu feeding on Cry1Ac soybean and occurring in tropical regions of Brazil have raised questions regarding the distribution of this species. The morphological similarity of the larvae from the two species makes it difficult to correctly identify the species in the field, which may lead to an underestimation of R. nu in Brazilian territory. This study aimed to address these questions by using a molecular approach to identify Plusiinae caterpillars throughout three seasons in non-Bt, Cry1Ac, and Cry1Ac × Cry1F soybean fields. Here, we carried out a comprehensive spatial sampling of the primary soybean-producing regions in Brazil. The results showed that R. nu has been the main Plusiinae occurring in soybean over the last three years, and it was present in all sampled regions. For Cry1Ac and Cry1Ac × Cry1F soybeans, up to 99% of the samples collected in 2023/24 were identified as R. nu. Non-Bt soybeans had higher variations in the proportion of the two species among the regions and across seasons, indicating that populations of C. includens and R. nu are co-occurring throughout the country. This is, to our knowledge, the most robust report assessing the distribution of C. includens and R. nu in Brazil using a molecular tool. This study provides clarification of R. nu occurrence and highlights the importance of pest monitoring from an integrated pest management perspective.

The fall armyworm (FAW), Spodoptera frugiperda, is a significant pest of many crops in the world and it is native to the Americas, where the species has shown the ability to rapidly evolve resistance to insecticides and transgenic plants. Despite the importance of this species, there is a gap in the knowledge regarding the genetic structure of FAW in South America. Here, we examined the genetic diversity of FAW populations across a wide agricultural area of Brazil and Argentina using a Genotyping-by-Sequencing (GBS) approach. We also characterized samples by their host strain based on mitochondrial and Z-linked genetic markers. The GBS methodology enabled us to discover 3309 SNPs, including neutral and outlier markers. Data showed significant genetic structure between Brazil and Argentina populations, and also among the Argentinian ecoregions. Populations inside Brazil showed little genetic differentiation indicating high gene flow among locations and confirming that structure is related to the presence of corn and rice strains. Outlier analysis indicated 456 loci putatively under selection, including genes possibly related to resistance evolution. This study provides clarification of the population genetic structure of FAW in South America and highlights the importance of genomic research to understand the risks of spread of resistance genes.

The corn leafhopper Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) is a specialist insect vector of the corn stunting disease complex. This leafhopper has been reported from different overwintering plants, and more information is required regarding other potential Brazilian plants that may serve as reproductive hosts for this specie. The present study aimed to evaluate possible plants for leafhopper reproduction usually found near the maize fields and the D. maidis reproductive differences among maize genotypes. Three trials were conducted to assess D. maidis survival and oviposition on different maize genotypes and other potential host plants. Survival, nymph presence, oviposition, and nymph eclosion rates were observed. No nymphs were observed in plants other than maize. The number of D. maidis adults was influenced by the different maize inbreds, and the mean number of laid eggs varied across the tested maize materials. Oviposition and nymph emergence was observed in pearl millet [Pennisetum glaucum (L.) R. Br., Poaceae] when D. maidis adults were offered only this plant as substrate, although significantly lower than those recorded on maize. Our results suggest that eliminating maize plants in the off-season could be used as a tool to reduce D. maidis reproduction, thereby minimizing the vector population size in the following season.

Chrysodeixis includens and Rachiplusia nu are two species belonging to the Plusiinae subfamily within the Noctuidae family. Due to their morphological similarity, the identification of their larvae is difficult and time-consuming. A rapid and accurate identification of these two species is essential for their management as these species exhibit differential susceptibilities to insecticides and crops engineered to express Bacillus thuringiensis (Bt) proteins, and a molecular tool can easily provide this differentiation. Currently, molecular analysis can identify these species through genetic sequencing, an expensive and time-consuming process. In our study, after sequencing part of the mtDNA cytochrome c oxidase I (COI) gene and based on the differences found in the gene of each species, a set of species-specific primers was developed: one reverse primer common to both species and two forward primers, specific to each species, amplifying fragments of 199 base pairs (bp) for C. includens and 299 bp for R. nu. Our results indicate that the primers were specific for these species, enabling the identification of individuals directly through agarose gel. The new methodology proved to be accurate, rapid, and reliable for the correct identification of these two species of loopers.