To test the effects of post-bloodmeal nutrition of sand flies on the transmission of Leishmania major, groups of infected P. papatasi females maintained on diets of sucrose, trehalose, albumin or a mixture of sucrose and albumin, were subjected to forced feeding with capillaries. Transmission was evaluated by counting the parasites egested; numbers ranged from 0 to over 1,000 promastigotes. Infections of the anterior midgut were seen in the majority of flies from all the experimental groups but the percentage of transmitting females was significantly higher in the group maintained on a mixture of sucrose and albumin. There were no attached parasites in the pharynx and cibarium of the flies and the presence of free promastigotes in these parts was not itself indicative of infectivity. However, transmission was positively correlated with apparent inability to engorge. The parasites egested were typical infective form promastigotes and identical to those observed in the esophagus and the anterior thoracic midgut.
A mechanism by which infective stage promastigotes from the esophagus and the stomodeal valve may be transmitted by bite is proposed.