Abstract
Maize farmers in sub-Saharan Africa recently experienced unusual damage in their farms, attributed to the fall armyworm (FAW) Spodoptera frugiperda (J. E. Smith). This pest was first recorded in Africa in 2016, but detailed information on its distribution and damage and farmer’s response in invaded areas are largely lacking. In this study, we determined FAW distribution, genetic diversity, host plants, crop damage, and farmers’ responses. S. frugiperda was recorded in the 10 regions of Cameroon. Average percentage of infested plants and damage severity (on a scale of 1 to 5) were lowest—20.7 ± 7.4% and 2.1 ± 0.1 respectively—in the Sahelian regions and greatest—69.0 ± 4.3% and 3.1 ± 0.1 respectively—in the Western Highlands. Altitude did not influence FAW incidence and severity and its larvae infrequently co-occurred with maize stemborers on the same plants, suggesting possible direct and/or indirect competition between the two groups of maize pests. In response to this new threat to maize production, farmers have opted for the application of synthetic pesticides. Although our experiments were not designed to determine pesticide efficacy, as parameters such as time since application were not considered, our observations suggest lack of a drastic effect on S. frugiperda infestations on maize. There were two haplotypes of FAW co-occurring in Cameroon corresponding to the rice and corn strains and separated by 1.7% sequence divergence, which does not support the existence of cryptic species. S. frugiperda larvae were also recorded on Sorghum bicolor (L.) Moench (10.6%), Solanum tuberosum L. (2.8%), Ipomoea batatas (L.) Lam. (1.9%), Saccharum officinarum L (0.8%), Phaseolus vulgaris L. (0.4%) and Gossypium hirsutum L. (1.9%). This study show that two strains are present in all agroecological zones in Cameroon, and probably in neighboring countries of central Africa sharing the same agroecologies. Management options should therefore consider the use of specific natural enemies and an informed decision of intervention based on strain capture and damage threshold, to avoid pesticide resistance that may arise from inadequate use of chemicals. Further studies should also be undertaken to assess the response of the two S. frugiperda strains to biopesticides and botanical insecticides.
Highlights
Maize (Zea mays L.) remains one of the most important crops in tropical areas and constitutes with wheat and rice, the main proportion of daily food intake of the inhabitants [1,2,3]
Management of fall armyworm that consider the use of natural enemies and an informed decision of intervention based of moth capture and damage threshold is necessary to avoid resistance that may arise from inappropriate insecticide use [41,42,43]
Management option should consider the use of more specific natural enemies and an informed decision of intervention based on strain capture and damage threshold, to avoid pesticide resistance that may arise from inadequate use of chemicals
Summary
Maize (Zea mays L.) remains one of the most important crops in tropical areas and constitutes with wheat and rice, the main proportion of daily food intake of the inhabitants [1,2,3]. In Cameroon, maize provides almost half of the calories consumed in both rural and urban areas. It is largely grown in the west and northwest region of the country and has increasingly become a staple food in many parts of the country. Maize production in Cameroon like in many other crops in sub-Saharan Africa are hampered by many biotic and abiotic factors, including poor soils, droughts, crop pests, diseases and weeds, and unsuitable temperatures [6,7,8,9,10]. Other important groups of insects—thrips and sap-sucking bugs (leafhoppers and aphids) [11]— serve as vectors for disease agents (viruses, mycoplasms, bacteria, and fungi)
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