Respostas imunológicas e mecânicas em população suscetível e resistente Plutella xylostella (L.) (Lepidoptera : Plutellidae) frente a formulações comerciais à base de Bacillus thuringiensis Berliner

Abstract

The resistance of Plutella xylostella (L.) (Lepidoptera: Plutellidae) has been attributed to many mechanisms as alterations in cell membrane receptors on midgut and the immune response to Bacillus thuringiensis Berliner toxin. The research tested the possibility that after expositions to Bt formulations, insects from a susceptible population (SP) and a resistant population (RP) presented qualitative and quantitative differentiated alterations of hemocytes and nitric oxide levels in hemolymph, histopathological and histochemical differenced alterations in midgut and that RP presented capacity of recovery midgut. SP and RP were exposed to Dipel® 1,35 mg/L (SP), 64,93mg/L (RP); XenTari® 5,17 mg/L (SP), 236,24 mg/L (RP) plus witness had hemolymph collected in intervals of 1, 6 and 12 h for total and differential counting of hemocytes and quantification of nitric oxide. The midgut was collected in the intervals: 0, 1, 6, 12 h. The regenerative cells quantification was made through the ImageLab 2000 program. In spite of RP had showed less number of hemocytes, it exhibited greater quantity of plasmatocytes, prohemocytes and spherulocytes, this can be related to resistance. Dipel® was effective in reduction of total numbers of hemocytes of SP and RP, while XenTari® changed significantly the differential counting. The nitric oxide increased in both populations and it not differed between the insecticides, indicating the no participation of it in the resistance. The insecticides induced alterations in different intensities on midgut in SP and RP, Dipel® showed to be more aggressive independently of population, taking to degeneration of epithelium. The presence of spherites covering the epithelial lamina, the hypertrophy of columnar cells and mucus abundance can be involved in midgut preservation in larvae of resistant population, however these features were not sufficient to avoid the degeneration of epithelium or induce the hyperplasia of regenerative cells.