Efeito subletal de metomil e de Bacillus thuringiensis var. Kurstaki em Spodoptera frugiperda (lepidoptera: noctuidae)

Abstract

Considered the main pest of corn in Brazil, the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), generates considerable production losses, requiring some control measure. Applications of chemical and biological products are commonly carried out. However, due to several factors such as application errors, technical failures and environmental factors, the pest in addition to coming into contact with lethal doses, which lead to immediate death, can also be exposed to sublethal doses, which do not lead to immediate death, but it generates several sublethal effects and, therefore, the objective of this work was to evaluate the sublethal effect of underdosing of Bacillus thuringiensis var. kurstaki (Bt) and methomyl on S. frugiperda. The concentrations used for each active ingredient were: LC5, LC15 and LC30 (LC: Lethal Concentration). The longevity of each life stage (larva-pupa, pupa-adult), pupae mass, and biological parameters such as: survival rate, sex ratio, fertility, fecundity and oviposition were evaluated. The results demonstrate that both products used had sublethal effects on S. frugiperda. The period of pupa-adult and larva-adult development was prolonged when the caterpillars were exposed to sub-doses of Bt. Sublethal exposures to methomyl decreased the survival rate. The sex ratio was not affected by any of the products used. The Bt treatments reduced the longevity of females, while the treatments with methomyl increased the values of this parameter. Both products caused a decrease in fertility and in the average number of eggs produced. Thus, it is possible to conclude that Bt and methomyl when applied in sub-doses cause sublethal effects in S. frugiperda.