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

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.