Anopheles albimanus (Diptera: Culicidae) and cyanobacteria: an example of larval habitat selection

Northern Belize has extensive herbaceous wetlands. Those dominated by sparse emergent macrophytes, rushes (Eleocharis spp.) and sawgrass (Cladium jamaicense Crantz), often develop floating mats of cyanobacteria (blue-green algae). These mats provide suitable habitat for larvae of the malaria transmitting mosquito Anopheles albimanus Wiedemann. Presence/absence of A. albimanus larvae and cyanobacterial mats was assessed in marshes located throughout northern Belize. Of the 21 marshes examined during the 1993 wet and 1994 dry seasons, cyanobacterial mats were found in 11 and A. albimanus larvae were detected in 9 of these 11 marshes. No A. albimanus larvae were found in marshes without cyanobacterial mats. Mosquito larvae were collected along two 1,000 m long transects in both the wet season (August 1993) and the dry season (March 1994) to delineate larval distribution in marshes with cyanobacterial mats. A. albimanus larval densities in cyanobacterial mats were relatively high in both seasons: 2.8 and 2.3 larvae per dip in the wet and dry seasons, respectively, in Chan Chen marsh; and 0.8 and 1.02 larvae per dip in Buena Vista marsh. Numbers of larvae per dip did not significantly change with increasing distance from houses/pastures or margins of the marsh. A field experiment showed a strong preference of ovipositing A. albimanus for cyanobacterial mats. Higher temperatures and higher CO2 emissions from cyanobacterial mats are possible ovipositional cues.