Rate of trypanosome killing by lectins in midguts of different species and strains of Glossina

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Abstract
The activity of lectins in different species of tsetse was compared in vivo by the time taken to remove all trypanosomes from the midgut following an infective feed and in vitro by agglutination tests. Teneral male Glossina pallidipes Austen, G.austeni Newstead and G.p.palpalis R-D. removed 50% of all Trypanosoma brucei rhodesiense Stephens & Fantham infections within 60 h. A ‘refractory’ line of G.m.morsitans Westwood took 170 h to kill 50% infections while a ‘susceptible’ line of the same species failed to kill 50%. Agglutination tests with midgut homogenates showed differences between fly stocks which accorded with differences in rate of trypanosome killing in vivo. Flies fed before an infective feed were able to remove trypanosomes from their midguts more quickly than flies infected as tenerals. Increasing the period of starvation before infection increased the susceptibility to trypanosome infection of non-teneral flies. Teneral flies showed little agglutinating activity in vitro, suggesting that lectin is produced in response to the bloodmeal. Feeding flies before infection also abolished the differences in rate of trypanosome killing found between teneral ‘susceptible’ and ‘refractory’G.m.morsitans, suggesting that maternally inherited susceptibility to trypanosome infection is a phenomenon limited to teneral flies. Electron micrographs of midguts of G.m.morsitans suggest that pro-cyclic trypanosomes are killed by cell lysis, presumably the result of membrane damage caused by lectin action.