Plasmodium gallinaceum: exflagellation stimulated by a mosquito factor.

Midgut tissue from Aedes aegypti stimulated exflagellation of gametocytes of Plasmodium gallinaceum in the absence of bicarbonate, a factor necessary for in vitro exflagellation. Exflagellation was also stimulated when washed infected red cells in a buffered saline (pH 7.4) not containing bicarbonate were introduced into the midgut by enema. The exflagellation-stimulating activity was neither sex nor species specific. Preparations of a mosquito exflagellation factor (MEF) were obtained without tissue disruption by collecting the fluid excreted by Anopheles stephensi females while they were feeding on warm saline. MEF was dialyzable and stable to boiling and decarbonation. Thus, MEF is not bicarbonate.