Genetic variability in biochemical characters of Brazilian field populations of the Leishmania vector, Lutzomyia longipalpis (Diptera : Psychodidae)

The phlebotomine sand fly Lutzomyia longipalpis is the insect vector of vis ceral leishmaniasis, a protozoan disease of increasing incidence and distri bution in Central and South America. Electrophoretic allele frequencies of 15 enzyme loci were compared among the L. longipalpis populations selected across its distribution range in Brazil. The mean heterozygosity of two col onized geographic strains (one each from Colombia and Brazil) were 6% and 1 3% respectively, with 1.6-1.9 alleles detected per locus. In contrast, amon g the seven widely separated field populations, the mean heterozygosity ran ged from 11% to 16% with 2.1-2.9 alleles per locus. No locus was recovered that was diagnostic for any of the field populations. Allelic frequency dif ferences among five field strains from the Amazon basin and eastern coastal Brazil were very low, with Nei's genetic distances of less than 0.01 separ ating them. The two inland and southerly samples from Minas Gerais (Lapinha ) and Bahia (Jacobina) states were more distinctive with genetic distances of 0.024-0.038 and 0.038-0.059, respectively, when compared with the five o ther samples. These differences were the consequence of several high freque ncy alleles (glycerol-3-phosphate dehydrogenase [Gpd(1.69)] and phosphogluc omutase [Pgm(1.69)]) relatively uncommon in other strains. The Pow genetic distances, absence of diagnostic loci, and the distribution of genes in geo graphic space indicate L. longipalpis of Brazil to be a single, but genetic ally heterogeneous, polymorphic species.