It is extremely interesting and important that Drs. Chao and Ball, although unable to maintain the entire insect cycle of Plasmodium relictum in vitro, have succeeded in doing this in steps, thus permitting an in vitro study covering the entire process from gametocyte to sporozoite. Many aspects of their study deserve much further investigation.
It might be of interest to find out what happens in drawn blood samples containing gametocytes maintained aseptically at reduced temperature. It is possible that lowering the temperature of freshly drawn avian blood would permit partial or complete development of the sexual stages in the normal secondary host material. A suggestion of this is paralleled in studies with dog heartworm, Dirofilaria immitis, in which the microfilariae were found to develop to the sausage stage in aseptic blood samples held at room temperature.
In studies to determine effects of mosquito extracts, hemolymph, or tissues on the development of plasmodia or other parasites, the insect material should be prepared so as to minimize melanization, since melanization can markedly reduce the value of such additions.
Insect Pathology Laboratory, Entomology Research Division, Agricultural Research Center, Beltsville, Maryland.