The natural control agents of the fall armyworm, Spodoptera frugiperda in Togo: moderating insecticide applications for natural control of the pest?

Authors: KOFFI, DJIMA - Gottingen University; AGBOKA, KOMI - University Of Lome; ADJEVI, M - University Of Lome; ADOM, MEDETISSI - University Of Ghana; TOUNOU, AGBEKO - University Of Lome; Meagher, Robert - Rob

Submitted to: Journal of Pest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2023
Publication Date: 7/6/2023
Citation: Koffi, D., Agboka, K., Adjevi, M.K., Adom, M., Tounou, A.K., Meagher Jr, R.L. 2023. The natural control agents of the fall armyworm, Spodoptera frugiperda in Togo: moderating insecticide applications for natural control of the pest?. Journal of Pest Science. 96:1405-1416. https://doi.org/10.1007/s10340-023-01662-0.
DOI: https://doi.org/10.1007/s10340-023-01662-0

Interpretive Summary: Fall armyworm is a worldwide pest of several agricultural crops especially maize. In sub-Saharan Africa, it has been infesting crops since 2016. Initial control measures predominately consisted of the use of insecticides, however, their effects on population reduction of the pest and performance of natural enemies have not been adequately investigated. A scientist with the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Florida, in collaboration with researchers from the Université de Lomé, Lomé, Togo, compared diversity and abundance of natural biocontrol agents in maize fields sprayed with insecticides compared to those fields without applications. Natural enemies were annually collected from maize farms over 6 years throughout Togo, and included species of bacteria, fungi, viruses, nematodes, predators, and parasitoids. Parasitism rates of both egg masses and larvae increased over that time while insecticide use decreased. Parasitism rates were significantly higher on unsprayed farms than sprayed farms, which demonstrates the importance of conserving natural enemies in agriculture grown under subsistence farming practices.

Technical Abstract: Although there has been intensive use of insecticides for fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) management, their effects on population reduction and performance of natural enemies have not been adequately investigated. Therefore, this study assessed the diversity and performance of natural biocontrol agents under insecticide and insecticide-free applications. Bio-agents were annually collected in 348 maize farms from 2016 to 2022 throughout the west African nation of Togo. The collections included the entomopathogenic nematode Ovomermis sinensis (Nematoda: Mermithidae), unidentified bacteria from Enterobacteriaceae and Enterococcus, unidentified viruses from Ascoviruses and Baculoviruses, and fungi Isaria spp. (Hypocreales: Clavicipitaceae) and Metarhizium rileyi (Hypocreales: Cordycipitaceae). Eggs were parasitized by Telenomus remus (Hymenoptera: Platygastridae), and the egg-larval parasitoid Chelonus bifoveolatus (Hymenoptera: Braconidae). Larval parasitoids included Anatrichus erinaceus (Diptera: Chloropidae), Archytas spp. and Lespesia spp. (Diptera: Tachinidae), Bracon sp., Coccygidium luteum, Cotesia icipe and Meteoridea testacea (Hymenoptera: Braconidae), and Campoletis grioti and Ophion spp. (Hymenoptera: Ichneumonidae). The collected predators included Orius insidiosus (Heteropterans: Anthocoridae), Haematochares obscuripennis, Peprius nodulipes, Rhynocoris sp. and Zelus renardii (Heteroptera: Reduviidae), Calleida sp. (Coleoptera: Carabidae), Cheilomenes sulphurea, Coccinella septempunctata and Cycloneda sanguinea (Coleoptera: Coccinellidae), Euborellia annulipes, Forficula auricularia and F. senegalensis (Dermaptera: Forficulidae), Pheidole megacephala and Polyrhachis lamellidens (Hymenoptera: Formicidae), Chrysoperla carnea (Neuroptera: Chrysopidae), and Mantis religiosa (Mantodea: Mantidae). The parasitism rates were from 14.72% in 2018 to 45.38% in 2022 for egg masses, and from 1.32% in 2016 to 41.85% in 2021 for larvae. The parasitism rates were significantly higher in unsprayed farms than sprayed farms.