The spatial distribution of larvae of Culicoides impunctatus biting midges

The spatial distribution of Culicoides impunctatus Goetghebuer (Diptera: Ce ratopogonidae) larvae was sampled at a site in western Scotland, and geosta tistical analyses were used to quantify spatial dependencies. Nested sampli ng and analysis indicated that most of the spatial variance occurred within distances of 160-640cm, levelling off at distances >640cm. Semivariograms for transformed data from three 100m x 100m grids showed similar, isotropic patterns for larval counts, soil organic content, soil water content and t he distribution of Juncus spp. rushes, with the variance increasing with se paration distance. High levels of significance were associated with power m odels used to describe the semivariograms, which was indicative of the abse nce of a plateau (or 'sill') in the respective data. Correlation analysis o f transformed data revealed significantly positive relationships between la rval counts and soil pH, soil percentage organic content, soil percentage w ater content and also the distribution of Sphagnum spp., Juncus spp, and My rica gale. There were also significantly negative relationships between lar val counts and the distribution of Pteridium aquilinum and all mosses other than Sphagnum spp. The results suggest a far more structured and predictab le pattern of C. impunctatus larval sites than previous studies and are dis cussed in relation to their application in localized Culicoides control and to studies of the mechanisms determining the spatial distribution of C. im punctatus larvae.