Date Published: April 29, 2019
Publisher: Public Library of Science
Author(s): Apollin Fotso Kuate, Rachid Hanna, Armand R. P. Doumtsop Fotio, Albert Fomumbod Abang, Samuel Nanga Nanga, Sergine Ngatat, Maurice Tindo, Cargele Masso, Rose Ndemah, Christopher Suh, Komi Kouma Mokpokpo Fiaboe, Juan Luis Jurat-Fuentes.
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.
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 [1–3]. World maize production was estimated at 1,291 million tons in 2016 .
This study has provided insight in the S. frugiperda spread, diversity and farmer’s reaction in Cameroon, and possibly similar agroecologies in central Africa since the report of its invasion in 2016. 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. Many farmers do not apply the recommended doses or as indicated , and in some cases, they use a combination of several insecticides, making it difficult to evaluate their effects. The misuse or overuse of the same pesticide have been cited as major cause of insect resistance to pesticides . In the Americas, resistance to pesticides has been reported for several mode-of-action categories including Carbamates, Organophosphates and Pyrethroids [39,40]. To avoid the occurrence of resistance to pesticides in Africa, farmers should be advised on the proper use of insecticides, includes rates, timing and methods of application. 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 [41–43].
S. frugiperda is present in all regions of Cameroon with two distinct clades that clustered perfectly with the rice and corn strains. Management option should therefore 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. Our observations suggest lack of a drastic effect of pesticide on S. frugiperda infestations on maize. Current efforts are focusing on identifying potential indigenous natural enemies and screening soft insecticides and biopesticide as part of an integrated control of the pest.