Are the apple maggot, Rhagoletis pomonella, and blueberry maggot, R. mendax, distinct species ? Implications for sympatric speciation

Rhagoletis pomonella (Walsh) and R. mendax (Curran) (Diptera : Tephritidae) are major economic pests of apple and blueberry fruits, respectively, in eastern North America. The taxonomic status of these flies as distinct species has been in dispute because of their close morphological similarity, broadly overlapping geographic distributions and inter-fertility in laboratory crosses. Starch gel electrophoresis of soluble proteins was performed to establish the extent of genetic differentiation and levels of gene flow between blueberry infesting populations of R. mendax and apple and hawthorn infesting populations of R. pomonella. R. mendax and R. pomonella were found to be genetically distinct sibling species as eleven out of total of twenty-nine allozymes surveyed possessed species specific alleles. Data from three sympatric apple and blueberry fly populations in Michigan indicated that these flies do not hybridize in nature and gave no evidence for nuclear gene introgression. Differences in host plant recognition were implicated as important pre-mating barriers to gene flow between R. pomonella and R. mendax; a result supporting a sympatric mode of divergence for these flies.