Bacillus thuringiensis e RNA interferente como ferramentas de controle da formiga cortadeira Atta sexdens (Hymenoptera: Formicidae)

Abstract

The forestry sector faces great economic and productivity losses due to the attack of leaf-cutting ants of the Atta genus. These ants cause damage or indirect, cutting large amounts of plant material to maintain the colony and to feed its symbiotic fungus Leucoagaricus gongylophorus. Currently, chemical control is the most used among those available for leaf-cutting ants, however, the most efficient ant killers belong to the class of POPs (persistent organic pollutants) that can cause risks to the environment and human health. The search for alternative methods to chemical control is under intense research, and these alternatives must be less aggressive to the environment and must also meet the efficiency standards for the control of leaf-cutting ants. The objective of this work was to use the mechanism of interfering RNA and the entomopathogenic bacteria Bacillus thuringiensis (Bt) for the control of leaf-cutting ants Atta sexdens. Bioassays performed with eight strains of B. thuringiensis showed that five induced mortality between 45% to 59% in foraging worker ants and the values were confirmed by Koch's postulate. The different concentrations of B. thuringiensis induced mortality between 61% and 41%. Scanning electron microscopy analyzes showed the presence of crystals of up to 2.0 µm longitudinally and of varying shapes, but it was not possible to verify any correlation between mortality and the shape of the crystals. dsRNA molecules homologous to the v-atpase a gene was synthesized in the bacteria Escherichia coli HT115 (DE3) and fed to ants on diets. Two colonies producing ds-v-atpase an exhibited 69% mortality, with onset of mortality on the 6th day of evaluation. It is believed that the HT115 (DE3) bacteria are being able to synthesize dsRNA homologous to the v-atpase a gene, and that this gene is of vital importance to the survival of these ants. The present work provides relevant information about the ability of both B. thuringiensis and interfering RNA to induce ant mortality in in vitro bioassays, placing these two strategies as potential tools to help control leaf-cutting ants.