The major proteinase activities in the larval midgut of a common poplar tree borer, Anoplophora glabripennis, were characterised. Overall digestive capacity, as measured by casein hydrolysis, showed a p H optimum between 10 and 11.5, suggestive of serine endopeptidase activity. Trypsin, chymotrypsin, and chymotrypsin-like activities were detected using specific p-nitroaniiide synthetic substrates and by use of specific serine endopeptidase inhibitors. These activities also showed pH optima in the extreme alkaline range. The absence of cysteine, aspartic, and metallo-endopeptidases were confirmed using class specific proteinase inhibitors. The dominant exopeptidase in the midgut is leucine aminopeptidase with a p H optimum of 7-9. Carboxypeptidase a and b activity were barely detectable. A large range of serine endopeptidase inhibitors were screened and were found to vary widely in their ability to inhibit casein hydrolysis. Potato proteinase inhibitor 1 (a chyrnotrypsin inhibitor) and wheatgerm trypsin inhibitor 1 inhibited particularly effectively in tandem and represent possible candidates for gene transformation to produce plants tolerant to this pest. 0 1996 Wiley-Liss, Inc.
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