First Laboratory Culture of Phortica variegata (Diptera, Steganinae), a Vector of Thelazia callipaeda

[Extract] The family Drosophilidae includes ~4,500 species in the two subfamilies Drosophilinae and Steganinae that are generally known as fruit flies or pomace flies because of their habit of feeding and growing on fermenting fruit. Within the Drosophilinae, Drosophila species are among the best characterized model organisms in genetic and genomic research. Conversely, knowledge of species ranked within the Steganinae is limited to a few morphological, taxonomic, and systematic investigations of selected members and information of the biology and ecology of most species is scarce. Over the past decade, fruit flies of the genus Phortica have been the subject of intense investigations aimed at identifying the arthropod vector and intermediate host of Thelazia spp. eyeworms (Otranto et al. 2003, 2005, 2006a, 2006b, Dorchies et al. 2007, Roggero et al. 2010). In particular, while Phortica okadai (Maca, 1977), Phortica magna (Okada 1968), and Amiota nagatai Okada, 1971 are vectors of Thelazia spp. in Asian countries (Kamakura et al. 1998), Phortica variegata (Fallen 1823) has been demonstrated, under both experimental (Otranto et al. 2005) and natural conditions (Otranto et al. 2006b), to harbor larvae of Thelazia callipaeda Railliet and Henry 1910 "eyeworm" nematodes in Europe. Phortica spp. differ remarkably from other fruit flies in that they are known to feed not only on decaying fruit and slime fluxes, but also on lachrymal secretions of animals and humans (Bachli et al. 2004). When feeding on the conjunctiva of vertebrates infested with T. callipaeda, P. variegata ingests the first-stage larvae released by adult female nematodes; within the body cavities of the arthropod vector, these larvae develop to second-stage larvae and, subsequently, to infective third-stage larvae which reach the proboscis of the fly and are invade the conjunctival sac of a new, receptive host (reviewed by Otranto et al. 2003). While both adult female and male P. variegata have been shown to harbour larvae of T. callipaeda under experimental settings (Otranto et al. 2005), only the latter gender has been demonstrated to act as a vector of this parasitic nematode under natural conditions (Otranto et al. 2006b, reviewed by Otranto et al. 2008a). The biological bases of this host-parasite relationship are still unclear.