Host-microbe interactions in field populations of the migratory pest African armyworm, Spodoptera exempta

Wolbachia are common vertically transmitted endosymbiotic bacteria found in <70% of insect species. They have generated considerable interest due to the capacity of some strains to protect their insect hosts against virus infections, and the potential for this to reduce vector competence of a range of human diseases. In our study, we looked at the interactions of Wolbachia and a nucleopolyhedrovirus (SpexNPV) in the lepidopteran crop pest, African armyworm (Spodoptera exempta). We show that the prevalence and intensity of SpexNPV infection is positively associated with infection of Wolbachia. We also demonstrate that Wolbachia infection increases viral mortality by up to 14 times. These findings suggest that rather than protecting their lepidopteran host from viral infection, Wolbachia instead make them more susceptible to this particular natural disease. This finding potentially has implications for the biological control of this migratory species and other insect crop pests.