Annual dynamics of fall armyworm populations in West Africa and biology in different host plants

Since its recent introduction in West Africa, the fall armyworm Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) has severely damaged maize and other crops. Control efforts face many challenges as the knowledge on this invasive pest is still limited. In this study, we assessed the annual population dynamics by monitoring this species using pheromone traps and visual observations, so as to contribute to the development of an integrated management strategy. In addition, we also evaluated some life history traits of S. frugiperda on different local host plants to identify the most suitable hosts in Burkina Faso. Adult captures were recorded throughout the year, as a result of a favorable mean annual temperature (29°C). Two population peaks occured: one peak (15.5±3.1 adults per trap and per month) was recorded in December and January (dry season) while the second peak (17.5±2.5) occured in July and August (rainy season). These peaks were synchronized with the major maize production periods of the region, usually 1 to 2 months after planting, when the plants had 6 to 12 leaves. In addition, the proportion of infested maize fields and infested plants per field was higher in the dry season (94.0% and 44.9%) than in the rainy season (80.0% and 26.2%). Based on the larva to adult survival rate (65-80%), mean fecundity (700-1000 eggs per female) and short life span of 36-38 days, pearl millet, maize and groundnut were found the most suitable hosts for the insect development. To better manage this insect pest, we suggest monitoring efforts in all crops associated with maize, the use of short-cycle varieties and early planting. In addition, curative treatments are more effective when applied on young maize plants, as the early instars are the most susceptible.