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SignificanceEliminating malaria from islands should, in theory, be easier than eliminating malaria from countries in mainland Africa because of restricted movement of insects and people between treated and untreated areas. The example of Bioko Island, where the entomological inoculation rate in 2004 was among the highest in Africa, demonstrates how difficult this can be. Vector control has eliminated two of the four vector species, and malaria has been dramatically reduced. This study demonstrates rapid evolution of resistance following reintroduction of pyrethroid-based control interventions, with the selection of a P450-based mechanism (CYP9K1). Urban malaria, movement of infected people from the mainland, and selection of this pyrethroid-resistance mechanism in addition to knockdown resistance has impeded progress and forced a change to nonpyrethroid indoor residual spraying.

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