Assay for inhibition of xylanase activity. (A) Inhibition of HhXyl activity by different amounts of pure recombinant XIP-I. The HhXyl activity was quantified by the DNS method and xylan from oat spelt was used as a substrate. (B) Inhibition of the xylanase activity present in crude protein extracts from the digestive tracts of the borers with different amounts of pure XIP-I. The activity was quantified by the DNS method.