Cytogenetic Studies of the Screwworm, Cochliomyia hominivorax (Diptera: Calliphoridae), from Chiapas, Mexico

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Abstract
Native screwworms, Cochliomyia hominivorax, in Chiapas, southwestern Mexico, had polymorphic chromosome variation characteristic of a single interbreeding population rather than of highly reproductively isolated gamodemes. Most of the variation found was in the sex chromosomes (eight X types and seven Y types). A strong deficiency of chromosomal heterozygotes in samples taken before the release of sterile flies indicated that populations of screwworms in the study area probably were mating nonrandomly. This was judged by the differential rates of frequency change observed for several chromosome types when comparing two sterile-fly-treated areas with the untreated area. Preliminary evidence suggests that both a sterile strain derived from a single native female and a broader-based strain derived from multiple native females may have had some positive assortative mating tendencies when mating with native flies.