Suscetibilidade de lagartas desfolhadoras do algodoeiro ao fungo Beauveria bassiana misturado ao caulim

Abstract

Alabama argillacea and Chrysodeixis includens are two important defoliating pests of cotton. They have different levels of feeding specialization (monophagy and polyphagia, respectively), and are usually controlled with synthetic chemical insecticides. These products increase production costs and can cause undesirable environmental impacts. In this work, the effects of the kaolin inert powder and the entomopathogenic fungus Beauveria bassiana on the mortality of A. argillacea and C. includens were determined under laboratory conditions. Initially, using the caterpillar submersion method, it was found that the CG 138 B. bassiana isolate is the most pathogenic against A. argillacea when compared to CG 70, GC 82, ESALQ 634, and ESALQ 645. There were no significant effects of the five tested isolates on C. includens. Then, by applying the leaf- disc feeding method, the effects of B. bassiana (CG 138) and kaolin on the mortality of caterpillars of A. argillacea and C. includens were determined. Higher A. argillacea mortalities were observed in the B. bassiana treatments (CG 138), regardless of the presence of kaolin. However, in C. includens, the activity of kaolin + B. bassiana (CG 138) was superior to the individual actions of each ingredient, indicating an additive action of these two ingredients against larvae of C. includens. There was no significant difference between A. argillacea and C. includens treated with kaolin + B. bassiana (CG 138). However, A. argillacea mortalities were higher than C. includens when kaolin and B. bassiana (GC 138) were applied separately. It is concluded that the treatment kaolin + B. bassiana (CG 138) is the most promising method for the simultaneous management of these two species of defoliating pests, and should be tested in field conditions, in the cotton crop. In addition, the monophagous A. argillacea is more susceptible to both kaolin and B. bassiana (GC 138) than the polyphagous C. includens, suggesting that nutritional ecology plays an important role in the susceptibility of these defoliating species to alternative insecticides.