Influence ofMyriophyllum aquaticum cover onAnopheles mosquito abundance, oviposition, and larval microhabitat.

The surface cover produced by aquatic macrophytes is the primary habitat for immature stages (eggs, larvae, and pupae) ofAnopheles mosquitoes. We hypothesized that both the abundance of immatureAnopheles and the recruitment ofAnopheles (from oviposition or larval movement) is positively related to the amount of surface cover present. Field sampling documented a positive correlation betweenAnopheles egg and larval abundance and the amount of vegetative cover present (measured as the number of emergent stems m-2) in monospecific beds ofMyriophyllum aquaticum in a California, USA, wetland. Experiments conducted to determine the influence ofMyriophyllum stem density on selection of oviposition sites by adultAnopheles females clearly indicate that oviposition rate (eggs m-2 d-1) increases as stem density increases from 0 to 1000 stems m-2 but decreases as stem density approaches 2000 stems m-2. In selecting microhabitats,Anopheles larvae preferred patches with high stem densities over patches with few or no plant stems; this preference correlates with differences in habitat quality (e.g., increased refuge from predation and enriched food sources). The optimal habitat for anopheline mosquitoes apparently occurs above a threshold plant density of approximately 500Myriophyllum stems m-2. Habitat heterogeneity produced by variability in the distribution and structure of aquatic vegetation strongly influences the local distribution and abundance of anopheline mosquitoes.