Genetic diversity and structure of Cochliomyia hominivorax populations from the Americas

After a 54-year area-wide program that integrated the Sterile Insect Technique (SIT), the eradication of the screwworm Cochliomyia hominivorax (Coquerel) have been successfully achieved in the USA, Central America, some Caribbean islands and the outbreak in Libya Jamahiriya. However, the screwworm remains one of the most damaging parasites of livestock in South America. Before the beginning of new SIT campaigns in South American countries, a good understanding of the genetic patterns of the target populations is of utmost importance for their effectiveness. Screwworm larvae were collected from 60 geographical sites from the current geographical range of the species. Three mtDNA fragments, corresponding to the B domain of the control region and partial sequences of the genes Cytochrome c oxidase subunits I and II, were amplified by PCR, sequenced and used for the analyses. In general, high haplotype diversity and low nucleotide diversity were observed for the locations analyzed. Comparisons among the populations showed significant F_ST values, demonstrating that this species has genetic structure over the Americas. The Caribbean represented one of the major areas of divergence among screwworm populations, but significant Fst values were also found for the populations from the Brazilian Amazon basin and the North of the Amazon rainforest in South America. Low population differentiation, with no geographic pattern, was observed for most populations at south of the Amazon basin. The genetic diversity distribution pattern of screwworm found here represents a critical step toward a more effective and preventive pest management strategy for the Caribbean and South America.