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Anopheles darlingi is the primary malaria vector in Latin America, and is especially important in Amazonian Brazil. Historically, control efforts have been focused on indoor house spraying using a variety of insecticides, but since the mid-1990s there has been a shift to patient treatment and focal insecticide fogging. Anopheles darlingi was believed to have been significantly reduced in a gold-mining community, Peixoto de Azevedo (in Mato Grosso State), in the early 1990s by insecticide use during a severe malaria epidemic. In contrast, although An. darlingi was eradicated from some districts of the city of Belem (the capital of Para State) in 1968 to reduce malaria, populations around the water protection area in the eastern district were treated only briefly. To investigate the population structure of An. darlingi including evidence for a population bottleneck in Peixoto, we analyzed eight microsatellite loci of 256 individuals from seven locations in Brazil: three in Amapa State, three in Para State, and one in Mato Grosso State. Allelic diversity and mean expected heterozygosity were high for all populations (mean number alleles/locus and HE were 13.5 and 0.834, respectively) and did not differ significantly between locations. Significant heterozygote deficits were associated with linkage disequilibrium, most likely due to either the Wahlund effect or selection. We found no evidence for a population bottleneck in Peixoto, possibly because the reduction was not extreme enough to be detected. Overall estimates of long-term Ne varied from 92.4 individuals under the linkage disequilibrium model to
under the heterozygote excess model. Fixation indices and analysis of molecular variance demonstrated significant differentiation between locations north and south of the Amazon River, suggesting a degree of genetic isolation between them, attributed to isolation by distance.
Received December 19, 2005. Accepted for publication January 11, 2006.
Acknowledgments: We are particularly grateful to the field team of M. M. Póvoa (Instituto Evandro Chagas, Belem, Para, Brazil) for logistical support in collecting mosquito samples. We thank T. N. Robinson and T. Hunter (University of Vermont) and L. Meehan (Griffin Laboratory, Wadsworth Center) for technical help and advice.
Financial support: This study was supported by National Institutes of Health grants AI R2940116 and AI R0154139 to Jan E. Conn.
* Address correspondence to Jan E. Conn, Wadsworth Center, New York State Department of Health, Griffin Laboratory, 5668 State Farm Road, Slingerlands, NY 12159. E-mail: jconn{at}wadsworth.org
Authors addresses: Jan E. Conn and Joseph Vineis, Wadsworth Center, New York State Department of Health, Griffin Laboratory, 5668 State Farm Road, Slingerlands, NY 12159, Telephone: 518-869-4575, Fax: 518-869-6487, E-mail: jconn{at}wadsworth.org. Jonathan P. Bollback, Center for Bioinformatics, University of Copenhagen, Copenhagen Ø, Denmark. David Y. Onyabe, Aeras Global Tuberculosis Vaccine Foundation, Rockville, MD 20850. Richard C. Wilkerson, Walter Reed Army Institute for Research, Museum Support Center, Smithsonian Institution, 4210 Silverhill Road, Suitland MD 20746. Marinete M. Póvoa, Instituto Evandro Chagas, Programa de Pesquisas em Malaria, Ananindeua, Para, Brazil.
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