MORPHOMETRIC MULTIVARIATE-ANALYSIS OF FIELD SAMPLES OF ADULT ANOPHELES ARABIENSIS AND ANOPHELES-GAMBIAE SS (DIPTERA, CULICIDAE)

The Afrotropical complex of sibling species Anopheles gambiae Giles in cludes the most efficient vectors of human malaria south of the Sahara . Anopheles arabiensis Patton and An. gambiae s.s. Giles are the membe rs of the complex more adapted to the human environment. They are symp atric and synchronic over most of their distribution range; however, t hey show a different involvement in malaria transmission, with An. gam biae being more anthropophilic and endophilic than An. arabiensis. Dis criminating between them is essential for a correct assessment of epid emiological parameters. The identification is currently achieved throu gh recognition of species-specific chromosomal inversions or by molecu lar biology techniques. Both methods require considerable technical re sources, not always available in the field. We carried out a morphomet ric analysis of field and laboratory samples of An. arabiensis and An. gambiae s.s. from sites in Madagascar, Burkina Faso, Mali, and Liberi a to evaluate the degree of morphological differentiation. We examined 17 morphometric characters in samples representing each of the geogra phic sites. All of the measures were significantly larger for An. arab iensis (regardless of the collection site), demonstrating an intrinsic greater body size of this species. To assess the reliability associat ed with the multivariate statistic, we applied the discriminant functi on analysis, which provided a method for predicting to which group a n ew case will most likely be assigned. In a blind experiment, the morph ometric method correctly identified approximate to 85% of field-collec ted An. arabiensis and An. gambiae s.s., which provided a relatively s imple method to approximate the relative frequencies of the 2 species in areas in which their concurrent presence was already known. The inf luence of laboratory conditions on the morphometrics of the 2 species was also analyzed.