Is Outdoor-Resting Behaviour in Malaria Vectors Consistent? Short Report From Northern Ghana.

BackgroundRecent reports of a change in the resting behaviour of malaria vectors, from predominantly indoor resting to outdoor resting following blood feeding, have been attributed to selection pressure from use of vector control tools such as indoor residual spraying and long-lasting insecticide-treated nets. Recent studies have observed vectors resting predominantly outdoors in settings where anti-vector tools are extensively deployed. This present study examined if the outdoor resting behaviour in the vector population, is random or indicative of a consistent preference of one resting site over the other. MethodsMark-release-recapture (MRR) experiments were conducted with outdoor-resting Anopheles gambiae and An. funestus mosquitoes collected from pit shelters, animal houses and granaries in two villages in Northern Ghana. Mosquitoes were marked with fluorescent dyes and released indoors. The experiments were controlled with indoor-resting mosquitoes, which were marked and released outdoors. Species of all recaptured mosquitoes were identified and assessed for consistency in their resting behaviour. ResultsA total of 4,460 outdoor-resting mosquitoes comprising An. gambiae sensu lato (s.l.) (59%) and An. funestus complex (41%) were marked and released. Overall, 31 (0.7%) mosquitoes (25 An. gambiae s.l. and 6 An. funestus complex) were recaptured mostly from outdoor location. Only 3 of the recaptured mosquitoes were found resting indoors where they were released. The majority of the outdoor-recaptured mosquitoes were An. arabiensis (11, 39%), followed by An. coluzzii (7, 25%); whereas the indoor-recaptured mosquitoes were mainly (3) An. coluzzii. For the control experiment, 324 indoor-resting mosquitoes constituting 313 An. gambiae s.l. and 11 An. funestus complex were marked and released. However, none of these was recaptured neither indoors nor outdoors.ConclusionsThe mosquitoes demonstrated the tendency to retain their outdoor-resting behaviour. Further investigations are required to ascertain if emerging preference for outdoor resting behaviour in malaria vector populations is consistent or a random occurrence.