Bioatividade do extrato aquoso de simarouba versicolor a. St-Hill (Simaroubaceae) sobre Plutella xylostella l. (Lepidoptera: Plutellidae) e toxicidade em organismos não-alvo

Abstract

The diamondback moth (Plutella xylostella) (Linnaeus, 1758) (Lepidoptera: Plutellidae) is one of the main insect pests that attack brassica crops and cause serious damage worldwide. Due to their effectiveness, speed, and practicality, synthetic insecticides are still used as a control method for this microlepidoptera. However, the indiscriminate and incorrect use of pesticides has naturally selected resistant insects, in addition to soil and water contamination and a reduction in biodiversity. Thus, plant based insecticides emerge as an effective, selective, non-accumulative control alternative, with little or no toxicity to the environment and non-target organisms. The objective of this work was to evaluate the action of the aqueous extract of Simarouba versicolor A. St-Hill (Simaroubaceae) at different concentrations on the biology of P. xylostella and to determine the concentration of less toxicity of this plant on the free living nematode Caenorhabditis elegans (Maupas, 1900) (Rhabditidae). Concentrations of 0.01; 0.05; 0.10 1.00; 5.00 and 10.00% and the control composed of distilled water. The following tests were performed: life cycle and toxicity; oviposition preference, embryotoxicity, and food preference. For the life cycle experiment, treated disks were offered to newly hatched caterpillars, with the characteristics of the immature and adult stages being evaluated. In the toxicity experiment, C. elegans nematodes in the L4 phase were incubated with the test plant extract and the control and, subsequently, the percentage of nematode survival was evaluated. In the free choice oviposition preference experiment, a couple of P. xylostella were placed in cages with 4 cabbage discs, 2 immersed in the control and 2 in the test concentration extract. The number of eggs in each treatment was counted daily. For the embryotoxicity experiment, disks with 10 eggs were immersed in the treatments, test concentration extract, and control, and the number of hatched caterpillars was counted. In the experiment of food preference, cabbage discs treated with extract of the test and control concentrations were offered to a third instar caterpillar, with the possibility of choice. The aqueous extract of S. versicolor, at all concentrations, negatively affected the diamondback moth, reducing oviposition, hatching of caterpillars, and feeding, affected the immature and adult phase of P. xylostella and at lower concentrations did not show toxicity to C. elegans.