ESTIMATIVA DA CONCENTRAÇÃO LETAL MÉDIA MÉDIA (CL50) DE BIOINSETICIDAS MICROENCAPSULADOS E NÃO MICROENCAPSULADOS À BASE DE Bacillus thuringiensis USADOS NO CONTROLE DE Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae)

Abstract

Bacterial based bioinsecticides have been researched and promoted as substitutes for chemical insecticides for the control of Chrysodeixis includens, however, most of the microorganisms used in biological control are sensitive to environmental degradation due to factors such as UV radiation. By using the microencapsulation technique in biocontrol agents, it prolongs the persistence of these microorganisms in the field. Thus, the objective of this work was to estimate the Average Lethal Concentration (LC50) of microencapsulated and non-microencapsulated bioinsecticides, based on toxicity tests, lethal and sublethal effects in C. includens caterpillars. For the CL50 bioassay, the bioinsecticides Dipel WP ® (Bacillus thuringiensis kurstaki) and Dipel WP® + Xentari® (B. thuringiensis kurstaki + B.thuringiensis aizawai) and the same products in microencapsulated form were selected. The concentrations of bioinsecticides used were 100, 150, 200, 300 and 350 times based on the recommendation indicated by the manufacturers, established according to preliminary tests of mortality of neonate caterpillars of C. includens. The bioinsecticide Dipel WP®, microencapsulated and non-microencapsulated, and the mixture of bioinsecticides Dipel WP® + Xentari WG® in its microencapsulated form showed LC50 values ​​in the same intervals indicating similar virulence among the bioinsecticides. The highest value of the LC50 estimate was found in the mixture of Dipel WP® + Xentari WG® without the microencapsulation process. Bioinsecticides, microencapsulated or not, in concentrations of 100 and 150x, caused a greater reduction in larval weight on the tenth day after the application of treatments. It was also observed that most treatments lengthened the larval phase of the surviving caterpillars compared to the control. However, this longer time to form the pupa did not imply a lower pupal weight, which were very similar in all evaluated treatments. The bioinsecticide Dipel WP® in the concentrations of 100 and 150x and its microencapsulated in the concentration of 100x, promoted the greatest sublethal effect of increasing the days of the caterpillars until the transformation into pupae. Adults were also affected, showing, for example, deformation of the wings. All bioinsecticides affected the development of C. includens, mainly in the most concentrated treatments.