Plutella xylostella (L.) (Lepidoptera: Plutellidae) is a major insect pest of cruciferous worldwide and both synthetic and biological insecticides are used against this pest. The most common biopesticides used to control P. xylostella are based on the entomopathogenic bacterium Bacillus thuringiensis (Bt) but a number of studies have observed susceptibility variations to Bt in different populations of P. xylostella and high levels of resistance in the field and at laboratory. Recently, researchers have pointed out that midgut flora composition could affect the insect susceptibility to Bt and some doubts about the Bt mode of action emerged due to novel model proposed to the Bt x insect interaction, possible involving the ABCC2 gene as a toxin transporter at the brush border membrane vesicles. The aim of this research is to build on these recently identified factors that could affect the susceptibility of insects to Bt (midgut bacteria and the ABCC2 transporter) to investigate possible correlations between these, and other physiological parameters study, and the susceptibility of five brazilian populations of P. xylostella larvae to three Bt toxins (Cry1Ac, Cry1Ie and Cry2Aa) that are believed to interact with different receptors within the insect midgut.
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