GORGING RESPONSE OF CULICINE MOSQUITOS (DIPTERA, CULICIDAE) TO BLOOD FRACTIONS

Although anopheline mosquitoes will ingest plasma without blood cells, Culex spp. and Aedes spp. require the phagostimulatory effect of bloo d cells; this effect can be duplicated by the addition of adenine-nucl eotides to plasma. Because activation of platelets released ADP and AT P into the plasma, they were suspected as the major source of die phag ostimulant. 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 induc e engorgement by 80-90% of the mosquitoes of both species. Thrombin ac tivation of the platelets reduced the effective dose to <2 x 10(4)/mm3 . Other blood fractions also were tested as possible sources of stimul ation. A series of washed red blood cells (RBC) dilutions was tested; 5 x 10(5) RBC/mm3 were required to induce 90% engorgement. Several typ es of leukocytes derived from blood by standard methods also induced e ngorgement at their physiological concentrations. Macrophages and cult ured 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 phagosti mulatory effect is due to platelet contamination, which invariably occ urs during standard methods of blood fractionation.