Relationships between mosquito densities in artificial container habitats, land use and temperature in the Kapiti-Horowhenua region, New Zealand

Land-use change, including deforestation for agriculture and urbanisation, has coincided with increases in vector-borne diseases worldwide. Landuse change is likely to regulate immature (larvae and pupae) mosquito populations through changes in local temperatures owing to manifold changes to the physical environment. However, we still poorly understand the relationship between land use, water temperature, and immature mosquito density. We conducted a field study in the Kapiti-Horowhenua region, New Zealand, to examine the relationship between land use, water temperature, and immature mosquito population dynamics in aquatic larval habitats. Artificial container habitats were sampled for immature mosquitoes in native forest, pastureland and urbanland, at three replicate locations, from October 2002 to April 2003. The endemic species Culex pervigilans constituted 94.5% of all late-instar larvae collected, the remainder being the exotic Ochlerotatus notoscriptus. On average, significantly higher pupal mosquito densities were recorded from urbanland containers compared with pastureland and native forest containers. A similar trend was observed for total mosquito densities, but did not reach statistical significance. Water temperatures in native forest typically did not show as much variation as those in urbanland and pastureland. Pastureland containers had significantly higher maximum and average daily water temperatures and lower minimum daily water temperatures than native forest containers. Using multiple regression analysis, total mosquito densities were best explained by the quadratic effects of maximum daily temperature and average daily temperature. The results of this study show that pastoral and urban development can increase water temperatures in container habitats, and that land-use change may be responsible for higher immature mosquito densities when habitat water temperatures do not consistently exceed a high threshold.