ACTIVITY OF SEVERAL BIORATIONAL INSECTICIDES AGAINST THE FALL ARMYWORM

Abstract

The effect of spinosad, methoxyfenozide, and azadirachtin on eggs and larvae of the fall armyworm Spodoptera frugiperda (J. E. Smith) was evaluated. Ovicidal activity was measured on egg masses of < 48 h old laid on brown paper, in different concentrations of each insecticide diluted in 0.01% of sodium dodecyl sulphate. Only spinosad and azadirachtin showed ovicidal activity in concentrations up to 1000 mg L^-1, which caused mortalities between 12 and 31 %. Mortality of larvae that hatched from treated eggs was increased (P ≤ 0.05) only with spinosad and methoxyfenozide. In contrast, the weigh of sixth instar larvae from treated eggs was not affected by the insecticides, except by spinosad at 3.16 mg a.i. L^-1, in this case, the larvae weigh (275.5 mg) became increased (P ≤ 0.05) compared to the control (183.6 mg). In another experiment, third instars S. frugiperda were treated with the three compounds by ingestion and topical application. The LC50 values of spinosad (2.39, 0.93 mg i.a. kg^-1 diet) were lower (P ≤ 0.05) than for methoxyfenozide (8.90, 4.64 mg i.a. kg^-1 diet) and azadirachtin (14.79, 63.49 mg i.a. kg^-1 diet), when diet was mixed with insecticides or when were applied on the diet surface, respectively. In topical application, the LD50 value of methoxyfenozide (1.27 μg i.a. g^-1 larva) was lower than spinosad (2.25 μg i.a. g^-1 larva) and azadirachtin (7.06 μg i.a. g^-1 larva). The three insecticides significantly reduced the larval weight of third instars of S. frugiperda.