An unusual distribution of the kdr gene among populations of Anopheles gambiae on the Island of Bioko, Equatorial Guinea

Department of Entomology, University of California, Davis, CA 95616, USA.
Insect Molecular Biology (Impact Factor: 2.59). 01/2006; 14(6):683-8. DOI: 10.1111/j.1365-2583.2005.00599.x
Source: PubMed


In West Africa, Anopheles gambiae exists in discrete subpopulations known as the M and S molecular forms. Although these forms occur in sympatry, pyrethroid knock-down resistance (kdr) is strongly associated with the S molecular form. On the island of Bioko, Equatorial Guinea we found high frequencies of the kdr mutation in M form individuals (55.8%) and a complete absence of kdr in the S form. We also report the absence of the kdr allele in M and S specimens from the harbour town of Tiko in Cameroon, representing the nearest continental population to Bioko. The kdr allele had previously been reported as absent in populations of An. gambiae on Bioko. Contrary to earlier reports, sequencing of intron-1 of this sodium channel gene revealed no fixed differences between M form resistant and susceptible individuals. The mutation may have recently arisen independently in the M form on Bioko due to recent and intensive pyrethroid application.

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    • "cAlthough lacking sufficient baseline data to document a shift, a study [42] in Punta Europa on Bioko Island, Equatorial Guinea found unusual high crepuscular and outdoor biting of An. gambiae sensu stricto after several years of indoor residual spraying with pyrethroids followed by several years of spraying with a carbamate insecticide. Although a high frequency of resistance against pyrethroids was found [43], this was not true for resistance against carbamates. "
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    • "It is suggested that the presence of the mutation in the M form may be a result of introgression from the S form [17]. However, observations from the Island of Bioko-Equatorial Guinea, where the mutation was only observed in the M form [19], suggested that the mutation in the M form may have arisen independently due to intensive insecticide application. "
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    • "Populations of An. gambiae s.s. on Bioko island were found to be genetically differentiated from mainland populations, using microsatellite DNA markers [28]. However, Moreno et al. [27] found a higher degree of genetic isolation of Annobón island when compared with Bioko, which is closest to mainland. "
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