A methodological proposal to estimate the total abundance of immature mosquitoes in discarded tyres: Aedes aegypti and Culex pipiens as study cases

Abstract

Estimating the abundance of immature mosquitoes in discarded water-filled tyres is a laborious task due to their shape and size. Our objective was to develop a procedure that allows, by counting individuals in a water sample, to estimate their total abundance. Polynomial functions linking water column height and water volume were fitted for five tyre categories (from cars to tractors) and horizontal/vertical storage positions. A total of 358 discarded water-filled tyres were then surveyed using this method in 16 piles of tyres in temperate Argentina. Tyre capacity was greater in vertical than horizontal position, reaching a maximum of 95.6 L in tractor tyres. In contrast, the volume of water retained under field conditions showed the opposite pattern, being greater in horizontal tyres. Water volume increased significantly across tyre categories in both horizontal (J-T = 7306, p < 0.001) and vertical (J-T = 10,792, p < 0.001) positions. Most infested tyres (n = 150) showed low abundances and a few extremely high values, both for all mosquito species grouped and for Culex pipiens and Aedes aegypti separately. The median abundance of mosquitoes per infested tyre was 35, decreasing to 30 for Cx. pipiens and 17 for Ae. aegypti. These values increased significantly across tyre categories for mosquitoes (J-T = 5525, p < 0.001) and Cx. pipiens (J-T = 2275, p < 0.05), but not for Ae. aegypti (J-T = 1526, p = 0.472). The comparison between vertical and horizontal positions was not significant for both vector species. Our methodological approach could be particularly useful in research addressing the assessment of disease risk associated with mosquitoproductivity.