COSTS AND BENEFITS OF MOSQUITO REFRACTORINESS TO MALARIA PARASITES - IMPLICATIONS FOR GENETIC-VARIABILITY OF MOSQUITOS AND GENETIC-CONTROL OF MALARIA

The problem of fitness costs associated with host resistance to parasi tism is related to the evolution of parasite virulence, population gen etic diversity and the dynamics of host-parasite relationships, and pr oposed strategies for disease control through the genetic manipulation of mosquito vectors. Two Aedes aegypti populations, refractory and su sceptible to Plasmodium gallinaceum, were previously selected from the Moyo-In-Dry strain (MOYO) through inbreeding (F = 0.5). Reproductive success and survivorship of the two populations were compared, and the influence of the parasite on mosquito fitness also was evaluated. Fit ness components studied include fecundity, adult survivorship and egg- to-adult developmental time, blood-meal size, and adult body size. The refractory population has a significantly shorter egg-to-adult develo pmental time and a smaller body size, takes a smaller blood meal, and subsequently lays fewer eggs than the susceptible population. The mean longevity of the refractory population is significantly shorter than the susceptible population. Exposure to the parasite exhibited little effect on the survivorship and fecundity of either population. Several factors may contribute to the lower fitness of the refractory populat ion, including founder effect, inbreeding depression, the effect of ot her uncharacterized genes linked to genes conferring refractoriness, a nd pleiotropic effects associated with these genes. The results are di scussed in relation to the genetic diversity of natural mosquito popul ations and their implications for the genetic control of malaria.