The sandfly Lutzomyia longipalpis shows specific humoral responses to bacterial challenge.

The presence of immune molecules induced by microorganisms in the haemolymph of Lutzomyia longipalpis sandflies has been investigated. Injections of Escherichia coli and Micrococcus luteus into female sandflies induced anti-bacterial activity in the haemolymph. Inhibition zone assays showed that haemolymph from E. coli and M.luteus injected sandflies differentially inhibited M.luteus growth. This differential effect was specific to M.luteus infection since anti-E.coli activity was similar in haemolymph from both E.coli or M.luteus injected sandflies. Haemolymph following injection of either bacteria showed the induction of a 4 kDa peptide. Haemolymph from M.luteus injected sandflies also contained a 33 kDa polypeptide which was absent in haemolymph from E.coli and control uninfected insects. Sandflies, in common with other insects, were shown to possess general and specific humoral immune responses to the presence of microorganisms.