Influência da “ponte verde” na atividade enzimática e eficiência de controle em populações de Spodoptera frugiperda

Abstract

The Fall armyworm, Spodoptera frugiperda is a polyphagous noctuid, that can feed on more than 80 plant species, including crops of great economic and social relevance, such as maize, cotton and rice. Despite being widely studied, it is a particularly difficult pest to control, mainly due to the genetic complexity of the species. S. frugiperda, which is divided in biotypes, and have high dispersion capacity and fast adaptive power to several hosts plants on varied phenological stages. This favors its movement and survival throughout the year in a phenomenon known as the "bridge green" effect. Therefore, it’s important to rationally select proper hosts plants that can minimize the “green bridge” effect in response to the genetic differences’ of FAW biotypes. Understanding these bioecological characters as a unit, can help predict different physiological and behavioral responses in IPM programs, especially regarding the induction / inhibition of detoxification enzymes, which is one of the main mechanisms of plant xenobiotic metabolization, that can also be evolved in insecticides detoxification. Due to the above, in order to investigate proactive IPM strategies, this study aimed to evaluate i) the activity of detoxification enzymes and ii) the susceptibility to chemical insecticides of S. frugiperda populations from different agroecosystems in summer and winter crops simulating the “green bridge” effect. Total protein, esterases and glutathione enzyme activity were measured following Bradford (1978), Hemingway (1998) and Harold & Ottea (2000) methods, respectively. Insecticide efficiency, was held using a Potter’s Tower, and total mortality was corrected by Abbot (1925) formula. The synergism effect of enzyme inhibitors DEF and DEM was measured by applying synergist 24 hours before insecticide application. The experiments were done in all host plants along generations, simulating the “green bridge” effect, in two different S. frugiperda populations, originally collected in geographically distant regions of Brazil, this being Pelotas and Cascavel. Enzymatic activity was higher in Pelotas populations than Cascavel. Insecticide efficiency in population Pelotas didn’t vary significantly during the green bridge effect tested, although insecticide efficiency in Cascavel populations, was higher after feeding on oat (the winter crop tested) and after returning to maize. Synergism effect was low in Cascavel, but high on Pelotas larvae. We conclude, that those differences may be due a sum of factors, such fitness cost, resistance to allelochemicals from host plants and insecticides, varied selection pressure and the biotype, there for, the green bridge effect turns out to be a response to a sum of biotic and abiotic variables in which a population is inserted.