A study of the use of gas chromatography of cuticular hydrocarbons for identifying members of the Anopheles gambiae (Diptera: Culicidae) complex

Abstract

Cuticular hydrocarbons were analysed by gas chromatography (GC) in 564 specimens of the Anopheles gambiae Giles complex from several West African sites, to determine whether individual A. gambiae sensu stricto and A. arabiensis Patton can be reliably identified, and to investigate the extent to which distinct chromosomal forms of A. gambiae sensu stricto, which are ecologically restricted as well as in some cases sexually isolated, can be distinguished by their cuticular hydrocarbons. Sympatric A. arabiensis and A. gambiae sensu stricto at Banambani, Mali could be distinguished with 90% correct identifications using the concentrations of four hydrocarbons in a linear discriminant function, but at a second site in Moribabougou, Mali, A. arabiensis was indistinguishable from a small sample of Bamako form of A. gambiae sensu stricto. Sympatric chromosomal forms of A. gambiae sensu stricto could be separated and clearest differences were found between the Mopti and Bamako forms. Direct gene flow between these forms has been found to be completely lacking despite partial intergradation of each form with the savanna form. Ethological isolating mechanisms between these forms have not however been demonstrated. Estimates of the rates of misclassification between the savanna form and the Mopti and Bamko forms reflect the degree of integradation observed amongst these forms by analysis of karyotype frequency in the wild. Discrimination was poor when an allopatric sample of the Mopti form was compared with other samples. An overall test shows that the proportion of correct classifications in discriminant analysis tends to be higher between sympatric than between allopatric populations; however, more extensive sampling would be needed for a rigorous test. The involvement of cuticular hydrocarbons in specific mate recognition systems is discussed.