Bacillus thuringiensis como bioinseticida: uma avaliação do estado da arte e bioensaio

Abstract

The insect Chrysodeixis includens, also known in Brazil as lagarta-falsa-medideira has been highlighted in recent years as a pest that causes great economic losses, especially the crop of soy (Glicyne max). Due to its eating habit of consuming the leaf parenchyma, it impairs the development of the plant directly affecting production. Being considered a pest of difficult control by chemical insecticides and of great economic importance, it is necessary to carry out studies that allow to identify alternative methods of control. Among the alternatives for the control of this pest can be highlighted the use of entomopathogenic microorganisms such as Bacillus thuringiens (Bt) bacteria, with a high quantity of commercial products already available in the market. Bt formulations are mostly produced from isolated lineages in large companies that hold the patents of these products. Alternative control methods are quite efficient and seek to reduce the use of chemicals in order to reduce environmental pollution and deleterious effects on non-target organisms. However, as with chemical insecticides, the pests present defense mechanisms that dribble the action and impair the efficiency of biopesticides. In addition, the selection of resistant individuals may totally compromise the functioning of a control method. Thus, knowing the great diversity of existing Bt strains, it is possible to maintain a great diversity of studies that seek potentially entomopathogenic strains with the objective of always maintaining efficient biopesticides in the market, reducing the amount of chemical insecticides used. The researches that constitute of bioassays to verify the lethality of the isolates in target pests, also count on techniques of molecular biology that allow to identify genes and to relate them to the specific pathogenicity of some lineages. Thus, the present study performed a bioassay of 8 Bt isolates on C. includens. Without insect mortality, it was sought through the molecular characterization to identify which genes were present in these 8 isolates. After characterization, it was possible to observe that the isolates in question did not present genes traditionally described as pathogenic to insects of the Lepidoptera order, confirming the results obtained in the bioassay. Also, 3 other genes were found, which according to the literature have positive effects on the control of coleoptera insects, also frequently reported with representatives causing damage to agriculture and livestock.