Biotransformação de flavonoides em lagartas do gênero Spodoptera

Abstract

Caterpillars of the genus Spodoptera are polyphagous herbivorous insects, meaning they feed on a wide variety of crops, which are of great economic interest in Brazil, including corn, cotton, sorghum, and soybeans. Although these crops are well protected by their main defensive compounds, such as flavonoids, larvae of species in this genus are still able to develop in plantations, suggesting a high detoxification capacity against these compounds, despite little being known about the products of this metabolism. Available data on the adaptation of phytophagous insects to plant chemical defenses suggest that, although the chemical structure of some synthetic insecticides is similar to these xenobiotics, defense characteristics differ between these two selection classes. Thus, this work aimed to identify and compare the products of flavonoid metabolism by these insects and the genes and enzymes involved in these biotransformations, which may provide information about their high capacity to adapt to new host plants, potentially revealing new strategies for their control in the field. This study aimed to investigate the detoxification capacity of flavonoids and isoflavones in species of the genus Spodoptera. Qualitative analysis of fecal extracts from these insects was performed by LC-MS/MS after oral administration of the compounds of interest, and the data obtained from each species were compared. The resulting molecular network from mass spectrometry (MS/MS) analyses in positive mode consisted of 3457 precursor ions for S. frugiperda extract, 1644 for S. cosmioides extract, and 728 for S. eridania extract, which were presented as nodes (interconnected or unique). Additionally, the GNPS platform was able to annotate a total of 36, 42, and 29 substances for S. frugiperda, S. cosmioides, and S. eridania, respectively, providing a comprehensive visualization of the compounds present in the extracts of the respective treatments. It is worth noting that among these compounds annotated by GNPS, only 7 substances were considered of interest for the discussion of S. frugiperda results, 9 substances for S. cosmioides, and 8 for S. eridania. Furthermore, an additional 9 substances, which were not annotated, were considered derivatives of compounds with a flavanic nucleus. In addition to mono-glycosylated derivatives in fecal extracts from the 3 tested caterpillar species with the 4 aglycones, other compounds were identified in fecal extracts of Spodoptera frugiperda, S. cosmioides, and S. eridania larvae fed only with diet enriched with aglycone standards, including different regioisomers. It was observed that S. eridania was able to glycosylate only the daidzein standard, while S. frugiperda and S. cosmioides presented glycosylated derivatives of all administered standards, generating possibly less toxic compounds. Our results provide qualitative information about possible biochemical reactions employed by 3 species of the genus Spodoptera in the metabolism of compounds with a flavanic skeleton and significantly contribute to future research on their chemically defended "insect-plant" interactions.