Biopesticides Preferred for Control of Fall Armyworm Management

Comparative effects of biopesticides on fall armyworm management and larval parasitism rates in northern Ghana

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Abstract

The outbreak of the fall armyworm, Spodoptera frugiperda, in Africa has led to several recommendations of insecticides, including biopesticides. However, the efects of these products on the environment, especially on parasitoids have not been assessed under feld conditions. Here, we investigated the efect of commonly used biopesticides on S. frugiperda management and larval parasitoids of S. frugiperda in northern Ghana. The experiments were conducted both on-station in Wa and Nyankpala and on-farm in Wa during the 2020 rainy season. Active ingredients tested included neem oil (3% Azadirachtin), maltodextrin (282 g/l), 55% Bacillus thuringiensis (Bt) combined with 45% Monosultap, and a Pieris rapae granulosis virus combined with 5% Bt. A chemical insecticide based on emamectin benzoate and acetamiprid was used as positive control while non-treated maize plots were considered as untreated control. The two most abundant parasitoids in Wa were Coccygidium luteum and Chelonus bifoveolatus, while in Nyankpala they were C. luteum and Meteorus sp. Total larval parasit-ism rates on-station were 18.7% and 17.6% in Wa and Nyankpala, respectively, and 8.8% in Wa on-farm. Parasitoid species diversity and evenness indexes did not vary among treatments, but parasitism rates were signifcantly lower with the chemical on-station in Wa and with the virus and Bt product in Nyankpala. Untreated maize plots showed the highest larval density and plant damage, the highest cob damage, and generated the lowest yields. The other treatments showed hardly any diference in cob damage and yields, suggesting that biopesticides should be preferred over chemical pesticides for S. frugiperda control.

Key message

• This study investigated the efect of commonly used biopesticides on Spodoptera frugiperda management and its larval parasitoids in Ghana, in comparison with a chemical insecticide based on emamectin benzoate and acetamiprid and untreated control.

• The diversity and evenness indexes of the parasitoid species did not vary among treatments, but parasitism rates were signifcantly lower with the chemical on-station.

• The highest larval density and cob damage and the lowest yields were recorded in the untreated maize plots while, the biopesicides and the chemical treatments displayed similar cob damage and yields.

• Biopesticides should be preferred over chemical pesticides for S. frugiperda control.

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