A shared genetic mechanism for melanotic encapsulation of CM-Sephadex beads and a malaria parasite, Plasmodium cynomolgi B, in the mosquito, Anopheles gambiae.

A Plasmodium-refractory strain of Anopheles gambiae that melanizes ookinetes and intrathoracically inoculated CM-Sephadex beads was mated to a Plasmodium-susceptible strain that does not melanize the parasite or the beads. The F1 progeny were then backcrossed to the susceptible strain. Backcross progeny were given a blood meal containing infective Plasmodium cynomolgi B, and the parasites were allowed to develop for 6-7 days, at which time the infected mosquitoes were injected with CM-Sephadex beads. The next day the mosquitoes were dissected and the beads were scored for degree of melanization while the parasites were scored for degree of encapsulation. A Spearman rank order correlation test of the degree of correlation between the bead melanization phenotype and the parasite encapsulation phenotype gave a correlation coefficient of 0.74 (P < 0.01). This strong correlation between the two melanization responses suggests that the mechanisms for differential bead and parasite melanization of these two mosquito strains share at least one major gene.