Anopheles gambiae, responsible for the majority of malaria deaths annually, is a complex of seven species and several chromosomal/molecular forms. The complexity of malaria epidemiology and control is due in part to An. gambiae's remarkable genetic plasticity, enabling its adaptation to a range of human-influenced habitats. This leads to rapid ecological speciation when reproductive isolation mechanisms develop [1-6]. Although reproductive isolation is essential for speciation, little is known about how it occurs in sympatric populations of incipient species [2]. We show that in such a population of "M" and "S" molecular forms, a novel mechanism of sexual recognition (male-female flight-tone matching [7-9]) also confers the capability of mate recognition, an essential precursor to assortative mating; frequency matching occurs more consistently in same-form pairs than in mixed-form pairs (p = 0.001). [corrected] Furthermore, the key to frequency matching is "difference tones" produced in the nonlinear vibrations of the antenna by the combined flight tones of a pair of mosquitoes and detected by the Johnston's organ. By altering their wing-beat frequencies to minimize these difference tones, mosquitoes can match flight-tone harmonic frequencies above their auditory range. This is the first description of close-range mating interactions in incipient An. gambiae species.

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SummaryDuring extensive sampling in Burkina Faso and other African countries, the Leu-Phe mutation producing the kdr pyrethroid resistance phenotype was reported in both Anopheles gambiae ss and A. arabiensis. This mutation was widely distributed at high frequency in the molecular S form of A. gambiae while it has been observed at a very low frequency in both the molecular M form and A. arabiensis in Burkina Faso. While the mutation in the M form is inherited through an introgression from the S form, its occurrence is a new and independent mutation event in A. arabiensis. Three nucleotides in the upstream intron of the kdr mutation differentiated A. arabiensis from A. gambiae ss and these specific nucleotides were associated with kdr mutation in A. arabiensis. Ecological divergences which facilitated the spread of the kdr mutation within the complex of A. gambiae ss in West Africa, are discussed.

Summaryobjective To investigate through countrywide sampling at 20 localities across the three different agroclimatic zones of Burkina Faso, the distribution of the acetylcholinesterase insensitive mutation ace-1 R , which confers resistance to organophosphates (OP) and carbamates (CM) insecticides in An. gambiae s.l.methods Adult mosquitoes were collected by indoor aerosol spraying from August to October 2006. Specimens were identified to species by polymerase chain reaction (PCR) assay and characterized for the ace-1 R mutation using a PCR-restriction fragment length polymorphism diagnostic.results Collected mosquitoes were a mixture of An. gambiae s.s. and An. arabiensis across the Sudan (98.3% vs. 1.7%), Sudan-sahelian (78.6% vs. 21.4%) and the Sahel (91.5% vs. 8.5%) ecotypes. The An. gambiae S-form predominated in the Sudan sites from the West (69% vs. 31% for the M form) but was not found in the Sahel (100% M form). The ace-1 R mutation was dispersed throughout the Sudan and Sudan-sahelian localities at moderate frequency (<50%) but was absent in the Sahel. It was far more prevalent in S form than M form mosquitoes (0.32 for the S form vs. 0.036 for the M form). No An. arabiensis was detected carrying the mutation. The geographic distribution of ace-1 R in the Sudan and Sudan-sahelian correlated with the cotton growing areas dispersed throughout the two climatic zones.conclusions These results have special significance as OP and CM insecticides have been proposed as alternatives or additions to pyrethroids which are currently used exclusively in many vector control programmes.