MAPPING A QUANTITATIVE TRAIT LOCUS INVOLVED IN MELANOTIC ENCAPSULATION OF FOREIGN-BODIES IN THE MALARIA VECTOR, ANOPHELES-GAMBIAE

A Plasmodium-refractory strain of Anopheles gambiae melanotically enca psulates many species of Plasmodium, whereas wild-type mosquitoes are usually susceptible. This encapsulation trait can also be observed by studying the response of refractory and susceptible strains to intrath oracically injected CM-Sephadex beads. We report the results of broad- scale quantitative trait locus (QTL) mapping of the encapsulation trai t using the bead model system. Interval mapping using the method of ma ximum likelihood identified one major QTL, Pen1. The 13.7-cM interval containing Pen1 was defined by marker AGH157 at 8E and AGH46 at 7A on 2R. Pen1 was associated with a maximum LOD score of 9.0 and accounted for 44% of the phenotypic variance in the distribution of phenotypes i n the backcross. To test if this QTL is important for encapsulation of Plasmodium berghei, F-2 progeny were infected with P. berghei and eva luated for degree of parasite encapsulation. For each of the two marke rs that define the interval containing Pen1, a significant difference of encapsulation was seen in progeny with at least one refractory alle le in contrast with homozygous susceptible progeny. These results sugg est that Pen1 is important for melanotic encapsulation of Plasmodium a s well as beads.