The apple maggot, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), is an important pest of apples (Malus spp.) and model system for sympatric speciation via host shifting for phytophagous insects. The distribution of R. pomonella is well-characterized in the United States and Canada, but it is poorly characterized in Mexico, where it may represent a different, allopatrically isolated taxon. Here, we report results of a nationwide survey aimed at determining the distribution and host range of hawthorn-infesting Rhagoletis in Mexico. Eight of the 13 endemic species of hawthorn (Crataegus spp.) were collected in temperate high-altitude habitats (1,600–2,800 m) across 21 Mexican states. Five of the eight hawthorns were confirmed to be hosts for Mexican R. pomonella. Fly populations were found throughout most of the natural distribution of hawthorn in Mexico. Mean pupal mass for fly populations clustered into two large weight groups associated with hawthorn species exhibiting different fruiting phenologies. Pupae infesting early fruiting hawthorns along the Sierra Madre Oriental were lighter than pupae infesting late-fruiting hawthorns across the Eje Volcánico Trans Mexicano. The differences in pupal weight may reflect host-related environmental effects or be genetically based, the latter implying the possible existence of two phenologically differentiated and geographically distinguishable fly taxa in Mexico. We discuss the significance of our findings for the phylogeography and adaptive radiation of the R. pomonella sibling species group, to which the hawthorn race belongs.
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Vol. 99 • No. 4