Combined and individual effects of a nucleopolyhedrovirus and azadirachtin on the mortality and maize-leaf consumption of Spodoptera frugiperda

Abstract

The combined and alone effects of azadirachtin (AZA) and Spodoptera frugiperda multicapsid nucleopolyhedrovirus (SfMNPV) on the mortality and food consumption of third instar S. frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) were evaluated under laboratory conditions using maize leaf bioassays. The LC50 values for SfMNPV and AZA were determined to be 1.30x106 viral occlusion bodies (OBs)/ml and 6.54 mg l-1 at 192 h and 144 h after treatment, respectively. These LC50 values were estimated for 4 days of continuous exposure. Although the interaction of SfMNPV with AZA increased the percentage of mortality observed in most of the cases, only one mixture (1x106 OBs/ml + 5 mg l-1) resulted in a synergistic effect on mortality of S. frugiperda. Application of SfMNPV (1x106 OBs/ml), AZA (0.5, 0.1 or 0.25 mg l-1) or SfMNPV–AZA mixtures resulted in a significant reduction in the maize-leaf piece consumption of larvae treated in the third instar across the experiment, by onefold, 2–5-fold, and 2–3-fold, respectively, compared with the control. However, the interaction of two SfMNPV–AZA mixtures (1x106 OBs/ml + 5 mg l-1 and 1x106 OBs/ml + 10 mg l-1) did not reduce the food consumption compared with AZA alone. It was concluded that SfMNPV–AZA mixtures require validation to determine whether this mixture may offer a valuable means of improving the efficacy of the SfMNPV.