Fifth instar Pieris brassicae larvae feeding on mature leaves of cauliflower grown by farmers in Delhi and Haryana, India, were collected from 2004-2007 and transferred to alternate tissues of various host plants such as cabbage, mustard and radish. We report that midgut digestive enzymes belonging primarily to the serine proteinase family, viz. trypsins and chymotrypsins were detected in spectro-photometric and fluorogenic assays using specific substrates and inhibitors. Zymograms revealed that larvae feeding on alternate tissues of various host plants contain different enzyme profiles that differ in their susceptibility to plant proteinase inhibitors.