Efeito da mistura de teflubenzuron e adjuvantes em linhagem resistente e suscetível de Chrysodeixis includens (lepidoptera: noctuidae) a benzoilureias

Abstract

The soybean looper, Chrysodeixis includens (Walker, [1858]) (Lepidoptera: Noctuidae), is one of the main defoliating pest of soybean crop. The main management strategies of this species involves the use of chemical insecticides. Recently, it was been reported that this species field-evolved resistance to chitin synthesis inhibitor insecticides used in soybean crop in Brazil. Based on this, the objective of this study was to evaluate whether adjuvants improve the performance of insecticides in the control of insect pests and also to evaluate the biological effects of adjuvants on resistant and susceptible strains of C. includens to the chitin biosynthesis inhibitor teflubenzuron. In the first article, it was compiled in a bibliographic the effects os adjuvants on the performance of insecticides aaplied to control insect pests. It was found that adjuvants alter the physicochemical characteristics of the insecticide spray, reducing the surface tension, decreasing the contact angle and stabilizing the pH. The addition of adjuvants to the insecticide spray can also increase the control efficacy, but this depends on the insecticide, crop and target pest. In the second article, bioassays were conducted to assess the effects of adjuvants added to teflubenzuron spray on the mortality of C. includens strains (resistant, heterozygous, and susceptible to chitin biosynthesis inhibitors). Using chromatography analysis, it was also evaluated the amount of teflubenzuron deposited on soybean leaves when applied in combination with adjuvants. In diet bioassays, the lethal concentration of teflubenzuron was lower for the susceptible strain of C. includens when adjuvants was added to the spray (LC50 ranging from 0.36 to 0.53 μg a.i./cm2 of diet with adjuvants vs 0.73 μg a.i./cm2 of diet without adjuvants). However, no relevant effects of adjuvants in association with teflubenzuron was verified on heterozygous (LC50 = 1.35 to 1.18 μg a.i./cm2 of diet) and resistant (mortalityfrom 39.0 to 48.3% at the maximum concentration tested) strains. In bioassays with soybean leaves, even those in the upper third part of the plant canopy, in which there was a greater deposition of teflubenzuron (3.4 mg/kg vs < 1.7 mg/kg), the mortality of susceptible (97.5 to 100%), heterozygous (77.5 to 82.5%) and resistant (12.5 to 20.0%) strains, with and without adjuvants on the insecticide spray, were similar. Therefore, it is concluded that adjuvants tested do not increase the mortality of susceptible and resistant strains of C. includens to the chitin biosynthesis inhibitor teflubenzuron.