Low mature salivary gland (SG) infection rates (6%) in <24-hour-old flies fed on blood containing bloodform trypanosomes can be significantly enhanced by feeding flies an artificial mixture containing procyclic forms in a red cell: culture medium mixture (procyclic mixture, SG rate = 21.0%). However, enhancement is not solely a function of the use of procyclic forms since blood forms fed to flies in the same red cell: culture medium mixture produce SG rates (15.4%) intermediate to those of blood forms in blood and procyclic mixtures. Use of these artificial mixtures produces a similar result in 24- to 48-hour-old flies and also tends to equalize their infection rates with those found in <24-hour-old flies. The possible relationships between the different infection rates observed and digestive proteinases in the tsetse fly are discussed.
Present address: Department of Entomology, U.S. Army Medical Component-AFRIMS, APO San Francisco, CA 96346-5000.