POPULATION-GENETICS AND GENE VARIATION IN PRIMARY AND SECONDARY SCREWWORM (DIPTERA, CALLIPHORIDAE)

Allozyme variation in screwworm, Cochliomyia hominivorax (Coquerel), and secondary screwworm, C. macellaria (F.), populations from northwest Costa Rica was examined. Variability was observed in 11 of 13 enzyme loci and frequency of the most common allele was <0.95 for 5 loci in screwworm. In secondary screwworm, 12 of 13 loci were variable and the frequency of the most common allele was <0.95 for 6 loci. Expected heterozygosities were 0.149 and 0.160 for screwworm and secondary screwworm, respectively. Goodness-of-fit statistics for Hardy-Weinberg equilibrium and Wrights F statistics indicated that both species are panmictic with no evidence of population substructuring. Nei's genetic distances were 0.000-0.001 for intraspecific comparisons and 0.899-0.916 for interspecific comparisons. The data indicate a high level of gene flow between populations within each species.