Trypsin and chymotrypsin‐Iike enzymes of the sandfly Phlebotomus papatasi infected with Leishmania and their possible role in vector competence

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Abstract
Phlebotomus papatasi (Scopoli) is susceptible to infection with Leishmania major Yakimov & Schokov and resistant to L.donovani Laveran & Mesnil. The possibility that susceptibility depends on midgut levels of trypsin and chymotrypsin‐like (esterolytic) enzymes was investigated. Infection with L. major reduced the trypsin‐like activity to 93.5% and 86% of the control value at 20 and 30 h post feeding and increased it to 106% at 52 h. Infection with L.donovani reduced trypsin‐like activity to 64% and 73% of the control value at 30 and 52 h post feeding. The overall amount of trypsin and chymotrypsin‐like enzymes in L.major infections was reduced to 50% and 34% of the control value at 20 and 30 h post feeding and increased to 184% at 52 h. Only one of the enzymes separated by gel electrophoresis was lower throughout, i.e. peak D. Overall, the midgut enzyme level with L. donovani infection was 86% of the control value at 30 h post feeding and 105% at 52 h; their relative amounts changed throughout. Soybean trypsin inhibitor enabled L.donovani to survive and multiply in P.papatasi. It is suggested that a specific component of the trypsin‐like activity prevents the survival of L.donovani in P.papatasi and that modulation of this factor enables L.major to survive.