Evolution of host use in fruit flies of the genus Blepharoneura (Diptera: Tephritidae): Cryptic species on sexually dimorphic host plants

Blepharoneura, a neotropical genus of tephritid fruit flies, includes newly discovered morphologically cryptic species that are highly host specific. Several species of fly, each specific to a different host tissue, can infest a single species of sexually dimorphic host. Using allozyme electrophoresis, we analysed morphologically similar populations of flies reared from various tissues of five species of host plant representing three subtribes of the Cucurbitaceae. In Venezuela, we found three sympatric species of Blepharoneura feeding on Gurania spinulosa Cogn. (one species on male flowers, another on female flowers, and a third on seeds). In Costa Rica, we found four non-interbreeding populations of Blepharoneura feeding on G. costaricensis Cogn.: two sympatric 'lowland' populations (one feeding on male flowers and another oil female flowers) and two sympatric 'highland' populations (also specific to flowers of different sexes). Phylogenetic analyses revealed a species-rich clade of specialists associated with flowers of the Guraniinae, and a species-poor clade of generalists associated with seeds of the Guraniinae. Specialization on male vs. female flowers appears to have occurred repeatedly. Patterns of larval dispersal may underlie differences in diversification of seed vs. flower clades: larvae that feed on seeds are dispersed by bats; lan ac Feeding on flowers are not dispersed. (C) 1997 The Linnean Society of London.