Detection of Arsenophonus and Spiroplasma throughout the life cycle of Colombian populations of Spodoptera frugiperda : evidence of potential vertical transmission

Background Spodoptera frugiperda , commonly known as the fall armyworm (FAW), is a pest of great economic importance in corn. The species has recently expanded from the Western Hemisphere to Africa, Asia, and Oceania, increasing its global impact. FAW has diverged into two strains, corn and rice, which differ in genetics, reproductive isolation, resistance to insecticides and to Bacillus thuringiensis , and, more recently found, in their microbiota. Endosymbionts such as Arsenophonus and Spiroplasma have been detected using next-generation sequencing (NGS) of the 16S rRNA gene. However, information on additional endosymbionts and their transmission dynamics remains limited. Therefore, the objectives of this study were to (i) evaluate the presence of endosymbionts such as Arsenophonus, Cardinium , Spiroplasma , and Wolbachia as well as the intracellular parasite Microsporidia, throughout the life cycle of both strains of S. frugiperda , (ii) assess their potential vertical transmission, and (iii) examine possible associations between these symbionts and life-history traits in this insect. Methods Larvae were sampled from corn and rice fields in central and eastern Colombia. Laboratory colonies of the corn and rice strains of S. frugiperda were maintained under controlled conditions. Strain identity was confirmed using diagnostic molecular markers ( MspI , SacI , FR). Within each strain, one-to-one crosses were performed to construct life cycle tables and estimate life-history traits components. DNA was subsequently extracted from parental individuals and from eggs, larvae, pupae, and adults. Following extraction, conventional and real-time polymerase chain reaction (PCR) using an intercalating dye were conducted to identify the genera Arsenophonus, Cardinium , Spiroplasma , and Wolbachia , the intracellular parasite Microsporidia and positive amplifications were confirmed by Sanger sequencing. Results Arsenophonus was detected exclusively in the corn strain using conventional PCR and confirmed by Sanger sequencing. Additionally, Spiroplasma was detected in both strains using real-time PCR using an intercalating dye. The detection of these endosymbionts across developmental stages is consistent with, vertical transmission. Differences in life-history traits components were observed between the two strains, but no clear association was detected between these differences and the presence of either endosymbiont under the conditions evaluated. These results highlight the need for further studies to evaluate the potential role of endosymbionts in the biology of this pest and to further on to better understand their transmission dynamics and possible ecological interactions.