Background: Malaria prevalence differs between the two islands that comprise the archipelago of\udSão Tomé and Príncipe. This may be due to differences in the biology of local Anopheles gambiae,\udthe only vector on the islands. Survival rate and feeding frequency are two factors influencing\udvectorial capacity. Anophelines generally feed just once per gonotrophic (oviposition) cycle. Newly\udemerged insects, however, may feed two or more times during their first oviposition cycle thus\udincreasing the likelihood of becoming infected. The reasons for multiple feeding are not clearly\udunderstood and it is still uncertain whether the behaviour is facultative or obligatory. We,\udtherefore, determined survival and sporozoite rates, and examined the behaviour of An. gambiae\udfrom the two islands during their first gonotrophic cycle.\udMethods: The wing size of 1,410, abdominal condition of 687, gonotrophic age and mated status\udof 7,264 female M form An. gambiae collected by light-trap, landing catch, resting outdoors or in\udcopula, was determined from four sites in the archipelago. Sporozoite rates assessed by ELISA in\ud15,533 females from São Tomé and 2,111 from Príncipe were determined.\udResults: Estimated survival rates ranged between 0.834–0.849 per day in São Tomé and 0.801–\ud0.818 per day in Príncipe. Sporozoite rates of 0.63% in São Tomé were significantly higher than the\ud0.24% from Príncipe. Overall 49% of females mated on the second night after emergence before\udfeeding, and 51% on the third night and thus fed before mating. The likelihood of mating before\udfeeding increased with wing size. None of the 3,776 parous insects collected showed evidence of\udrecent mating. All but two of the 198 females collected in copula had undeveloped ovaries. Mean\udwing sizes and the number of insects collected in a sentinel light-trap varied but the proportion of\udnewly emerged insects in the collection did not. The estimated survival rate of the smallest insects\udwas lower than other size groups, but the overall size distribution of each age group was normal.\udParous insects were gonotrophically concordant.\udConclusion: Differences in mosquito survival contributed to the lower sporozoite rates and\udendemicity of malaria on Príncipe compared to São Tomé. On both islands all newly emerged\udinsects blood fed on the second night following emergence but only became gonotrophically active\udon the third night after emergence. Smaller insects had a higher 'mortality/emigration' rate than\udlarger ones. We suggest that insufficiency of Juvenile Hormone until the third day of adult life is\udresponsible for gonotrophic inactivity and that by partitioning mating between the second or third\udday after emergence females maximise their chances of out-crossing.\ud(On-line Journal: www.malariajournal.com)
展开▼
