Biochemical analyses were used to characterize the digestive physiology of larval red oak borer Enaphalodes rufulus (Haldeman).  In second-year hardwood feeders, the pH of gut extracts from the hindgut region was 5.4 to 5.6, and increased to 6.2-6.4 in mid and foregut extracts.  The hydrolysis of casein by gut extracts from larval E. rufulus increased steadily from pH 7.2 -11.7.  Zymogram analysis with casein demonstrated two major proteinase activities, approximately 25 and 45 kDa.  A 25 kDa proteinase hydrolyzed substrates with phenylalanine and leucine in the active site, characteristic of chymotrypsin-like proteinases.  A proteinase with a molecular mass greater than 100 kDa hydrolyzed l-BapNA, a substrate for trypsin-like proteinases. Results show that, similar to reports in other Cerambycids, these larvae use serine proteinases to digest food.  We are currently analyzing the digestive proteinases of first-year phloem feeders for a comparison of digestive capability.