The investigation of factors potentially affecting the susceptibility of native Plutella xylostella populations to Bacillus thuringiensis cry toxins

Despite the prominent and worldwide use of Bacillus thuringiensis (Bt) insecticidal toxins in agriculture, knowledge of the mechanism by which they kill pests remains incomplete, therefore the aim of this research was to investigate on recently identify factors that affect the susceptibility of insects to Bt (protein levels, midgut bacteria and mutations on the ABCC2 transporter) in five brazilian populations of Plutella xylostella larvae and to overcome the mechanism of resistance. The analyses were made in about 60 guts extracts in 1 ml of 50% glycerol solution using the following process: gut analysis (total protein, total proteas, toxin digestion and esterase activities); gut bacteria analysis; and ABCC2 gene analysis. There were not differences in the amount of esterases between the populations, therefore we cannot associate esterase level with resistance. Differences in composition of the larval gut microbiota were not correlated with resistance. It is unclear whether similar interactions occur in the field where the intestinal micrbiotas of lepidopteran larvae may be more complex than the apparent mono-associations described here. However it is possible that gut bacteria may present a novel target for the management of P. xylostella. The nature of the protective effect of gut bacteria is also unclear. Previous studies suggested that lactic acid bacteria may acidify the gut thereby decreasing host susceptibility to alkali-soluble Cry toxins such as CrylAc. There are no mutation in the ABCC2, accordingly there is no association of ABCC2 with Bt resistance.