Could fall armyworm, Spodoptera frugiperda (J. E. Smith) invasion in Africa contribute to the displacement of cereal stemborers in maize and sorghum cropping systems

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), which has recently invaded the African continent, has become a new threat to cereal production. Being an invasive pest with certain competitive advantages, the impact of FAW on other lepidopteran pests is unclear. This study assessed the infestation of FAW and cereal stemborers on maize and sorghum under mono-cropped systems that are adjacently placed in five districts in Uganda. Data on maize and sorghum infestation cereal stemborers and FAW was collected at 6, 9 and 16 weeks after planting (WAP), to determine intensity and severity. Cereal stemborer infestations on maize at 6, 9 and 16 WAP were only 36.7%, 48.2% and 24.0%, respectively, which was significantly lower than the infestations on sorghum, at 55.5%, 53.2%, 64.0%, respectively. On the contrary, the infestations of FAW on maize at 6, 9 and 16 WAP were 89.5%, 84.7% and 86.0%, respectively, while on sorghum they were 51.0%, 56.5% and 47.0, respectively. The severity of stemborers on sorghum was statistically higher than on maize, whereas the damage severity of FAW was generally higher on maize than on sorghum. Intensity of damage and cavity length due to stemborer on sorghum was higher than on maize. Historical records showed that in maize stemborer infestation could reach 60%. This infestation started significantly declining in 2016, suggesting an early arrival of FAW in Uganda. The present study indicates a possible displacement of stemborer from maize onto sorghum. Any Integrated Pest Management (IPM) package should consider managing FAW and stemborer together in both maize and other cereal hosts.