Biologia e mortalidade de Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) em milho tratado com silício e inoculante Azospirillum brasilense, sob condições de laboratório e campo

Abstract

Corn crop is very important in the agricultural scenario and its productive potential is affected due to a number of factors, such as pest attack. The species Spodoptera frugiperda is considered the main crop pest, causing qualitative plant losses and quantitative yield losses, depending on the phenological stage of the plant. Currently, its control is mainly carried out with transgenic crops or through the application of insecticides. However, both have caused the selection of resistant populations, making their control difficult. Given this, the search for alternatives that reduce environmental impacts, keep the pest below the control level, is growing. Therefore, this work aimed to use the silicon and inoculant Azospirillum brasilense as a control alternative of S. frugiperda, as well as to verify if their use induces the resistance of the plant to the attack of the caterpillar. To this end, initially S. frugiperda caterpillars were created to perform bioassays to evaluate their biology and behavior, as well as the induction of resistance from the use of silicon and biological inoculant. The results identified lower feeding preference, higher mortality, lower second instar larval development and total larval period, lower pupal weight and larger number of deformed individuals when the caterpillars were fed with silicon treated plants. Subsequently, silicon quantification was performed by the yellow method and resistance induction was evaluated in the leaves where the activity of the enzymes peroxidase and phenylalanine ammonia lyase (FAL) were quantified. The results did not find differences between treatments in the amount of silicon, but higher amount of silicon in old leaves compared to new leaves in treatments containing silicon. In resistance induction, there was no increase in activity in any treatment. Finally, field work was carried out to evaluate defoliation, parasitism and natural enemies. In this study the results did not identify differences between treatments regarding the number of caterpillars, natural parasitism and number of predators. However, there was a reduction in defoliation over the growing season of corn with silicon-containing treatments. Thus, it is possible to conclude that silicon independent of the application form helps control S. frugiperda and acts on behavior and biology. However, in this work silicon did not confer increase in enzymatic activities, requiring further studies