ABSTRACT
Although anopheline mosquitoes will ingest plasma without blood cells, Culex spp. and Aedes spp. require the phagostimulatory effect of blood cells; this effect can be duplicated by the addition of adenine-nucleotides to plasma. Because activation of platelets released ADP and ATP into the plasma, they were suspected as the major source of the phagostimulant. This paper describes quantitatively the role of platelets in ingestion by Aedes aegypti (L.) and Culex univittatus Theobald. We found that about 10(6)/mm3 inactivated platelets are required to induce engorgement by 80-90% of the mosquitoes of both species. Thrombin activation of the platelets reduced the effective dose to < 2 x 10(4)/mm3. Other blood fractions also were tested as possible sources of stimulation. A series of washed red blood cells (RBC) dilutions was tested; 5 x 10(5) RBC/mm3 were required to induce 90% engorgement. Several types of leukocytes derived from blood by standard methods also induced engorgement at their physiological concentrations. Macrophages and cultured lymphocytes that do not contain any platelets induced gorging in Cx. univittatus, but not in Ae. aegypti. Because RBC and leukocytes do not release nucleotides unless broken, we suggest that their phagostimulatory effect is due to platelet contamination, which invariably occurs during standard methods of blood fractionation.
