Multivariate analysis of relationships between habitats, environmental factors and occurrence of anopheline mosquito larvae Anopheles albimanus and A. pseudopunctipennis in southern Chiapas, Mexico.
Field surveys of mosquito larval sites on the Pacific coastal plain and foothill regions of southern Chiapas, Mexico, were carried out in the dry and wet seasons of 1988. The sites were a priori classified into 9 habitat categories. At each site, samples for the 2 principal malaria vectors, A. albimanus and A. pseudopunctipennis, were taken and 17 environmental factors were measured or estimated. Canonical correspondence analysis combined with a Monte Carlo permutation test revealed significant dependence of mosquito larval occurrence on environmental factors and habitat categories in the dry season and on environmental factors only in the wet season. G-test of independence and association index Q indicated a positive association between the habitat category 'flooded or irrigated pastures' and A. albimanus occurrence in both seasons, and positive association between 'estuaries' and A. albimanus occurrence in the dry season. The occurrence of A. albimanus was negatively associated with the habitat category 'foothills' in both seasons, and negatively associated with the category 'estuaries' in the wet season. In the dry season, the abundance of phytoplankton and cover of floating macrophytes were significantly greater for sampling sites where A. albimanus was present. Concentrations of K+, Ca2+ and PO4-P and amount of phytoplankton were significantly higher and the amount of filamentous algae significantly lower for A. albimanus positive sites in the wet season. Altitude and the amount of filamentous algae were significantly higher, and Na+ concentration was significantly lower for sampling sites positive for A. pseudopunctipennis in the dry season. In the wet season, the mean abundance of filamentous algae in sites with A. pseudopunctipennis was significantly higher than in sites where this species was absent. In general, the habitat classification used seems to have higher predictive power in the dry season than in the wet season, and several quantified environmental factors appear promising as predictors of anopheline larval occurrence in both seasons.