Print PageAfrican armyworm larvae are a major pest of cereal crops in eastern Africa. During the rainy season, there may be 6 or 7 generations of high-density larval outbreaks, starting in Tanzania and Kenya and progressively moving from these ‘source’ populations to higher latitudes over time as adult moths migrate on the prevailing winds. During the dry season, when there is little rain-fed vegetation for the armyworm to feed on, high-density outbreaks do not occur and the population persists at low density in coastal regions. Armyworms are naturally infected with a baculovirus – Spodoptera exempta nucleopolyhedrovirus (SpexNPV) and virus prevalence can exceed 90% in some populations late in the rainy season. The virus is transmitted horizontally between feeding larvae, but may also be passed trans-generationally via vertical transmission (parent to offspring), which is believed to be the main mode of viral persistence during the dry season. This study aims to understand the dynamics of overt and covert SpexNPV infections in both outbreak populations of armyworm larvae and in migrating adult moths, using both traditional methods and quantitative PCR.
Results/Conclusions
PCR results indicate that 100% of armyworm moths are covertly infected with SpexNPV, even during the long dry season. However, qPCR indicates that viral loads exhibit considerable variation both within and between years and appears to be correlated with moth population density and/or the incidence of larval outbreaks. We discuss the implications of these findings for understanding the dynamics of this important migratory crop pest and its baculovirus. We also discuss the potential for SpexNPV to be used as a strategic biological control agent against armyworms across eastern Africa.
