Microbiome analysis of Spodoptera frugiperda (Lepidoptera, Noctuidae) larvae exposed to Bacillus thuringiensis (Bt) endotoxins

Abstract

Background Spodoptera frugiperda (or fall armyworm, FAW) is a polyphagous pest native to Western Hemisphere and recently discovered in the Eastern Hemisphere. In Colombia, S. frugiperda is recognized as a pest of economic importance in corn. The species has genetically differentiated into two host populations named “corn” and “rice” strains. In 2012, a study made in central Colombia demonstrated that the corn strain is less susceptible to Bacillus thuringiensis (Bt) endotoxins (Cry1Ac and Cry 1Ab) than the rice strain. In this country, Bt transgenic corn has been extensively produced over the last 15 years. Since gut microbiota plays a role in the physiology and immunity of insects, and has been implicated in promoting the insecticidal activity of Bt, in this study an analysis of the interaction between Bt endotoxins and FAW gut microbiota was made. Also, the detection of endosymbionts was performed here, as they might have important implications in the biological control of a pest. Methods The composition and diversity of microbiomes associated with larval specimens of S. frugiperda(corn strain) was investigated in a bioassay based on six treatments in the presence/absence of Bt toxins and antibiotics (Ab) through bacterial isolate analyses and by high throughput sequencing of the bacterial 16S rRNA gene. Additionally, species specific primers were used, to detect endosymbionts from gonads in S. frugiperda corn strain. Results Firmicutes, Proteobacteria and Bacteroidota were the most dominant bacterial phyla found in S. frugiperda corn strain. No significant differences in bacteria species diversity and richness among the six treatments were found. Two species of Enterococcus spp., E. mundtii and E. casseliflavus were detected in treatments with Bt and antibiotics, suggesting that they are less susceptible to both of them. Additionally, the endosymbiont Arsenophonus was also identified on treatments in presence of Bt and antibiotics. The results obtained here are important since little knowledge exists about the gut microbiota on this pest and its interaction with Bt endotoxins. Previous studies made in Lepidoptera suggest that alteration of gut microbiota can be used to improve the management of pest populations, demonstrating the relevance of the results obtained in this work.

Comparative analysis of Spodoptera frugiperda (J. E. Smith) (Lepidoptera, Noctuidae) corn and rice strains microbiota revealed minor changes across life cycle and strain endosymbiont association

“…In this study, we identified the endosymbionts Arsenophonus and Spiroplasma in CS and RS, respectively. Castañeda-Molina et al (2023) also detected the genus Arsenophonus in CS in a work carried out concurrently with ours. However, our work further demonstrated the presence of this bacterium in Colombian FAW populations using an NGS approach.…”

“…However, our work further demonstrated the presence of this bacterium in Colombian FAW populations using an NGS approach. Castañeda-Molina et al (2023) used specific primers to detect several endosymbionts, including Arsenophonus sp., Spiroplasma sp., Cardinium sp., and Wolbachia sp. Our work added more information about FAW microbiota since we detected Arsenophonus sp.…”

“…FAW is known to have genetic resistance to insecticides and Bt endotoxin ( Yainna et al, 2022 ; Fiteni et al, 2022 ; Gimenez et al, 2020 ); however, the swift development of FAW’s resistance to insecticides and Bt ( Gimenez et al, 2020 ; Castañeda-Molina et al, 2023 ) highlights the need for finding more efficient ways to control it. The effects of microbiota on host insects have now provided new perspectives for the development of alternative strategies for pest control ( Fu et al, 2023 ).…”

“…Additionally, the endosymbiont Arsenophonus sp. was detected in the gonads of both male and female FAWs using specific primers ( Castañeda-Molina et al, 2023 ). In Brazil, Almeida et al (2017) identified Enterococcus mundtii, Enterococcus casselflavus, Delftia lacustris, Leclercia adecarboxylata, Microbacterium paraoxydans, Pseudomonas stutzeri, Arthrobacter nicotinovorans, Pseudomonas psychrotolerans, Microbacterium arborescens, and Staphylococcus sciuri subsp.…”

“…These bacteria can tolerate and break down several insecticides, such as deltamethrin, lambda-cyhalothrin, chlorpyrifos ethyl, spinosad, and lufenuron, as observed in laboratory experiments. The microbiota isolated from insects through culture-dependent approaches is also essential for understanding the physiological potential of isolated organisms and can be used in other experiments ( Higuita-Palacio et al, 2021 ), particularly from insect’s life cycles ( Chen et al, 2016 ; Li et al, 2022 ; Fu et al, 2023 ) as they can be tested against Bt endotoxins ( Castañeda-Molina et al, 2023 ) or insecticides ( Almeida et al, 2017 ; Gomes, Omoto & Cônsoli, 2020 ), even though their diversity is higher from field samples ( Gomes, Omoto & Cônsoli, 2020 ) as they have to be kept under laboratory conditions. The discovery of endosymbionts can also be crucial in finding new strategies for insect control.…”