Variation in Spine Morphology among Pre-eradication Screwworm Larvae, Cochliomyia hominivorax (Coquerel), in Relation to Larval Habitats

Abstract

Despite 10 years of debate concerning genetically based mating incompatibility among target populations of screwworm flies ( Cochliomyia hominivorax [Coquerel]), no morphological characters, varying among populations, have been identified, quantified, and analyzed for any screwworm developmental stages. This study identifies and analyzes variation in an unambiguous set of characters. Single-, double-, and triple-pointed thoracic spines were analyzed from third instar larvae. All specimens were collected from naturally occurring wounds before initiation of the eradication program. Host animal and wound type are statistically significant ecological factors associated with this variation in simple analysis but may interact. Neither factor provides clear grouping of larvae when they are assigned to groups by posterior discriminant analysis. This suggests that host animals or wound types alone are unlikely to result in speciation processes for marginal screwworm populations.