Proteolytic activities in body and faecal extracts of the storage mite, Acarus farris

Trypsin, chymotrypsin, cathepsins B and D, aminopeptidase and carboxypeptidases A and B were detected in body extracts of the storage mite Acarus farris (Oudemans) (Astigmata: Acaridae). Faeces-enriched medium exhibited higher (10-50-fold) specific protease activity rates than those measured with mite body extracts for trypsin, chymotrypsin and carboxypeptidases A and B, suggesting that they are involved in mite digestion. However, the activity of cathepsin B was only three-fold higher in faecal than in body extracts, indicating that its presence in the lumen of the digestive tract is low compared to that of serine proteases. The activity of aminopeptidases was higher in mite bodies, indicating that they might be membrane bound. Cathepsin D activity was only detected in body extracts, indicating that this enzyme is not a digestive protease in this species. Zymograms resolved three major bands of gelatinolytic activity, but at least one protease form was only present in body extracts. Protease inhibitors of different specificity were tested in vivo to establish their potential as control agents. The development of A. farris was significantly retarded when the immature stages were fed on artificial diet containing inhibitors of serine and cysteine proteases and aminopeptidases, whereas no such effect was found with inhibitors of aspartyl proteases and carboxypeptidases. Interestingly, the most significant effects on A. farris occurred when a combination of inhibitors targeting different enzyme classes was supplied mixed in the diet, suggesting a synergistic toxicity. Several plant lectins were also tested, but only wheat germ agglutinin and concanavalin-A affected development.