Digestive Enzymes in the Gut and Salivary Gland of the Adult Horn Fly Haematobia irritans (Diptera : Muscidae)

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In the gut of the horn fly, significantly high proteinase activity was found in a broader pH range from 6.5 to 11.0 with pH optimum at 8.5. With reference to the substrates used, aminopeptidase (stronger), trypsin-like enzyme, carboxypeptidase A-like enzyme and carboxypeptidase B-like enzyme (weak) activities were detected in the gut, with only weak aminopeptidase activity in the salivary gland. In the stable fly, trypsin-like enzyme (stronger), aminopeptidase (stronger) and carbodypeptidase A-like enzyme activities were detected in the gut, with weak aminopeptidase and carboxypeptidase A-like enzyme activities in the salivary gland. The trypsin-like enzyme activity relative to the aminopeptidase activity was lower in the horn fly (A/T>2) than in the stable fly (A/T≒1). The gut of the horn fly contained amylase, pectinase, α-glucosidase, β-glucosidase, α-galactosidase and β-galactosidase, while the salivary gland had only β-glucosidase. The significance of the difference in the relative amounts of trypsin-like enzyme to aminopeptidase in the gut between the horn fly and the stable fly, and of the presence of carbohydrases in the alimentary system of the horn fly is discussed.