Population dynamics and spatial structure of human-biting mosquitoes, inside and outside of houses, in the Chockwe irrigation scheme, southern Mozambique

Abstract

Abstract. Focal control of malaria vectors, a potentially cost-effective alternative to conventional control, requires a spatio-temporal understanding of the mosquitoes. Trapping of African malaria vectors has generally been limited to inside houses making distribution estimates dependent on the location of dwellings. The development of tent-traps to sample outdoor biting mosquitoes has enabled more independent estimates. Here we describe both temporal and spatial variation in mosquito movements in an irrigation project village in southern Mozambique. Six hundred and ninety-three tent-trap collections (525 of which were paired with light-trap collections), 552 exit collections and 391 collections of mosquitoes resting inside houses were undertaken from March 2005 to April 2006. Fifteen species of mosquito were collected (five exclusively as larvae). Mansonia africana was the most common finding, numbers being greatest away from the village. Only Anopheles funestus, An. tenebrosus and Culex quinquefasciatus were collected in greater numbers in light-traps compared to tent-traps. Among the common mosquitoes, correlations in numbers of mosquito collected in paired tent and in light-traps were significant for all but An. tenebrosus. Inverse distance weighting was used to produce raster density maps of the most common mosquitoes. All species, with minor variations, in both hot and cool seasons, were collected in greatest numbers close to the edges of the village where water suitable for larval development was available. All exophilic anophelines species tested negative for sporozoites. It is suggested that focal control of larvae, applied by the villagers themselves, could be a suitable alternative to conventional control in this and similar villages.

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“…The first maps of densities of outdoor biting mosquitoes from an endemic area were produced using data from Furvela tent-traps from Massavasse, Mozambique. (Charlwood et al, 2013) (Fig 11). Massavasse occupies a 1x2km rectangular area in the middle of rice fields.…”

“…The ratio of tent-trap to light-trap collections can also change as a result of human perturbations including application of a residual insecticide to walls of houses. The indoor/outdoor ratio of mosquitoes before and after the application of Bendiocarb applied by the National Malaria Control Program (NMCP) in an independent study to the interior walls of houses in Massavasse, in southern Mozambique, (redrawn from Charlwood et al, 2013) is shown for six of the most common species collected (Fig 4). (Supplementary file 6)…”

“…They, however, also declined in the tent-trap collections at this time. The insecticide may have been responsible for this decline but as described in Charlwood et al, (2013) the failure of people to pay their water bills meant that the fields were no longer being irrigated and, at least among the exophagic species, the elimination of breeding sites was the more likely to have been responsible for the decline in the population. Anopheles funestus also breeds in the water used by the exophagic mosquitoes, so they, too, would have been affected by the absence of the water.…”

“…A = Anopheles funestus, B = A. arabiensis,, C = A. tenebrosus,, D = Culex quinquefasciatus, E = Cx. tritaeaniorhynchus, F = Mansonia africana (fromCharlwood et al, 2013)…”

“…Numbers collected by distanceMean numbers (standard deviation) of mosquitoes collected in tent traps at different distances away from the center of Massavasse village, Chockwe District, Mozambique (fromCharlwood et al, 2013) …”