Density of larval Culicoides belkini (Diptera: Ceratopogonidae) in relation to physicochemical variables in different habitats.

Immature density and population size of the biting midge Culicoides belkini (Wirth & Arnaud) were estimated for habitats on Moorea Island, French Polynesia, by means of random, 2- and 3-stage sampling designs. Samples were taken in March 1993 from 5 strata of a large larval habitat: a sandy-mud surface of ≍5,000 m2 (stratum 1) in which ≍12,000 land crab burrows (stratum 2) were counted, a small pond surrounded by ≍300 m2 of muddy bank (stratum 3), and a high organic muddy area (Kopara) of ≍1,200 m2 (stratum 4) with ≍3,500 crab burrows (stratum 5). Larval density was usually higher in the mud of crab burrows, especially those in the Kopara stratum. Larval density was significantly lower in the sediment of the sandy area as compared with pond banks or Kopara surface. The sampling designs and techniques were logistically adequate, statistically relevant, and were recommended for future studies on C. belkini larval density. Larval habitats were characterized by means of multivariate analysis. Comparison of larval densities with selected environmental variables indicated that larvae density was higher in wet sediments with high levels of organic matter (≍8% of dry weight of sediment) and low salinity (≍0.5–1.5% NaCl equivalents). These variables were considered significant if larval control by means of habitat modification has to be achieved. Nevertheless, C. belkini can tolerate a broad spectrum of variation in the other environmental variables measured and breed in a variety of ecological situations. Therefore, it has a high potential for colonizing new habitats.