Plutella xylostella (L.) is a major pest of crops in the Brassicaceae. Pesticides based on Bacillus thuringiensis Berliner (Bt) are oneof the most important tools in this pest control; however P. xylostella populations resistant to Bt toxins have been reported. This study tested the hypotheses that susceptible and resistant populations of P. xylostella exhibit different histopathology and histo-chemistry in the midgut upon exposure to Bt-based formulations. After bioassays to determine appropriate concentrations, groups of larvae from one susceptible population (SP) and one resistant population (RP) of the moth were exposed to Dipel® at 1.3 mg/L (SP) and 64.9 mg/L (RP) or XenTari® at 5.2 mg/L (SP) and 236.2 mg/L (PR). Midguts from fourth-instar larvae were collected at 0, 1, 6 and 12 hours after exposure and processed for analysis under light microscope. Regenerative cells were quantified through the application of dots using the ImageLab 2000 program. The insecticide Dipel® was more aggressive in the midgut regardless of population. Resistant populations exhibited dense granules (spherites) covering the surface of the columnar epithelial cells and mucus that may be involved in the preservation of larvae midgut resistant.