Zoophily of Anopheles arabiensis and An. gambiae in Madagascar demonstrated by odour-baited entry traps

In Madagascar we used odour-baited entry traps (OBETs) for host choice test s of wild female anopheline mosquitoes (Diptera: Culicidae) at representati ve localities on the East and West sides of the island (villages Fenoarivo and Tsararano, respectively) and at the southern margin of the central plat eau (Zazafotsy village, 800 m altitude). No insecticide house-spraying oper ations have been undertaken at these villages. Odours from a man and a calf of similar mass, concealed in different tents, were drawn by fans into sep arate OBETs set side by side. Traps were alternated to compensate for posit ion effects, and different pairs of individual baits were employed for succ essive replicates. Totals of 266 An. funestus Giles sensu stricto and 362 A n. gambiae Giles sensu late were collected in 48 trap nights during March-J une 1999. For each mosquito species the 'index of anthropophily' was define d as the proportion of females caught in the human-baited trap. For An. fun estus this index was found to be consistently greater than 0.5 (value for r andom choice between traps/hosts), indicating that this species 'preferred' human to calf odour (index=0.83). Conversely, the index of anthropophily f or An. gambiae s.l. indicated they 'chose' calf in preference to human odou r (index=0.26). No significant differences of relative preference for calf or man were detected between villages; geographical variance accounted for <8% of the total experimental variance. Molecular identifications of 181 sp ecimens of the An. gambiae complex (<approximate to>50% of the samples) rev ealed only An. arabiensis Patton at Tsararano and Zazafotsy, but >97% An. g ambiae Giles sensu stricto at Fenoarivo, in accordance with prior knowledge of the differential distributions of these sibling species on the island. Predominant zoophily (i.e. intrinsic 'preference' for cattle odours) by bot h An. arabiensis and An. gambiae s.s. in Madagascar contrasts with their gr eater anthropophily in continental Africa.