Analyses of 11 isoenzyme loci of Ochlerotatus eatoni (Edwards, 1916), endemic to two
Macaronesian Islands (Madeira and Tenerife, Canary Islands), revealed substantial genetic structure
in the study populations. Samples from sites on the south and north of Madeira displayed a signiÞcant
reduction of variability compared with those from central Madeira and Tenerife. The Tenerife
population exhibited a severe deÞcit of heterozygosity with similar magnitude across all the loci
examined. The complex pattern of variation in Oc. eatoni is because of interplay of breeding structure,
genetic drift, and geographical and historical factors. From these Þndings, we concluded that island
colonization by Oc. eatoni was not marked by founder effect.
