Potential patterns of fall armyworm seasonal migration in West Africa modeled with atmospheric trajectory analyses

BACKGROUND: The migratory invasive species fall armyworm (Spodoptera frugiperda, FAW) has established year-round populations in several West African countries following its initial invasion of Africa in early 2016. However, its seasonal migratory dynamics within West Africa remain poorly understood. If FAW populations in West Africa were able to successfully cross the Sahara Desert and serve as a major source population in North Africa, this could increase the risk of further invasion into southern Europe. In this study, we used atmospheric data to perform trajectory simulations, predicting the seasonal migratory pathways of short-distance migratory FAW individuals within West African breeding habitats and assessing the monthly probabilities of long-distance migrants departing from West Africa successfully crossing the Sahara Desert. RESULTS: The results indicate that from May to September, the vast majority of short-distance migrants (>70%) remained within West African breeding habitats, whereas in other months, a larger proportion of individuals were blown into the Atlantic Ocean. Moreover, short-distance migrants exhibited clear seasonal movement patterns within West Africa: shifting southwestward from January to May, turning northeastward in June and July, and returning southwestward from August to December. Long-distance migrants had an extremely low success rate (≤0.3%) of crossing the Sahara Desert, which occurred only between February and April each year. CONCLUSION: This study revealed the seasonal migration patterns of FAW within West Africa, providing important insights for predicting regional outbreak risks and optimizing management strategies in the region.