Biology and susceptibility of Spodoptera frugiperda (Fall Armyworm) to selected insecticides

Abstract

Environmental factors and the use of insecticides form a major component in the management of insects of agricultural importance. The development of fall armyworm, Spodoptera frugiperda, an invasive insect pest in Ghana was studied. The efficacy of six selected insecticides against them was also determined. Larvae of fall armyworm were collected from the field at three locations in the Central Region of Ghana and reared at the Entomology laboratory of the University of Cape Coast. The duration of events during the life cycle, including egg hatching, larval moulting, pupation and adult lifespan were studied at two periods at different temperatures and humidity regimes. Five insecticides recommended by the Ministry of Food and Agriculture for the control of fall armyworm in Ghana were assayed for their efficacy against the eggs and second instar larvae of the fall armyworm in a completely randomized design. Aqueous neem extract was also assessed for its potency against the second instar larvae. Study results indicated that, rate of development was faster from February to March when higher range of temperatures were recorded and there were significant differences between the average duration of all the events of the life cycle studied. None of the commercial insecticides assessed prevented treated eggs from hatching. In the larval bioassay, Emamectin benzoate and Bacillus thuringiensis caused 100% mortality 24 hours after larvae fed on treated leaves. Indoxacarb+Acetamiprid caused 100% mortality 48 hours after application while Acetamiprid+Lambda cyhalothrin and Imidacloprid could not cause more than 85% mortality even at twice the recommended doses. Three concentrations of the aqueous neem extract caused 100% mortality by the 8th day after larvae were fed on leaves treated with these concentrations.