DrosophilidsSecretophagous non-biting fliesThe secretaphagous non-biting flies being of relevance for the transmission of two Thelazia species in dogs are belonging into the genus Phortica. These drosophilids, commonly known as ‘fruit flies’, display a slightly ‘unusual’ behavior as they feed on lachrymal secretions of humans and carnivores. They are furthermore used by pathogens to invade vertebrate hosts. General AspectsTaxonomyThe family Drosophilidae comprises two recognized subfamilies, Drosophilinae and Steganinae, which together represent about 3800 species commonly known as ‘fruit flies’. Whereas members of the subfamily Drosophilinae feed and develop mostly on fruits and other vegetable matter (Bächli et al., 2004), flies belonging to the Steganinae subfamily display unusual feeding habits and their ecology is much less known. Phortica variegata as transmitter of larvae of the ‘oriental eyeworm’ is belonging into the subfamily Steganinae, genus Phortica. DistributionAccording to Bächli et al. (2004) P. variegata is widespread in Europe and Eastern Asia, and is recorded from Great Britain and Germany. In Scandinavia there are only a few, mostly doubtful, records from Sweden and Finland, another one from Norway and non from Denmark. Veterinary and Medical ImportanceP. variegata has been identified as the transmitter of larvae of the ‘oriental eyeworm’ T. callipaeda, which has been detected among others in dogs and humans. General MorphologyOverviewP. variegata is a small, two-winged insect belonging to the family Drososphilidae, subfamily Steganinae. The key characteristics for morphological identification can be found in Otranto et al. (2006a). In studies it could be demonstrated that only P. variegata males may act as an intermediate host under natural conditions for T. callipaeda (Otranto et al., 2006b). It was further speculated that the specificity in the development of T. callipaeda in male P. variegata might have biased the zooophilic behaviour of the fly (Otranto et al., 2006b). The secretophagous non-biting flies feed on the secretions of dogs, e.g., and may become infected with the L1 of T. callipaeda. Further development of the nematode will occur within the arthropod. For details see Pathogenesis and Transmission of T. callipaeda. The infective L3 of the nematode will be transmitted to a new vertebrate host during feeding of the fly on lachrymal secretions. Feeding BehaviorActivity DynamicsA seasonal activity in the reproduction of T. callipaeda, coinciding with the presence/absence of the vector could be observed. The activity of P. variegata ranged from early spring to early autumn (Otranto et al., 2004). Host SpectrumSteganinae larvae often exhibit zoophilic feeding habits (Ashburner, 1981), but in the adult stages this behavior is confined to three genera: Amiota, Phortica and the very rare genus Apsiphortica (Otranto et al., 2006a). Adults of these genera are reported as feeding on fermenting tree sap (Okada, 1962), as well as on rotten fungi and fox faeces (Papp, 2002). But they are also attracted by the eye secretions of humans and animals such as dogs and other carnivores (Bächli et al., 2004). Concerning P. variegata, Otranto et al. (2006b) could only collect male flies around the eyes, feeding on a human bait, whereas a 1:4 male:female ratio was registered around a fruit bait. The zoophilic behaviour and thus the vector capacity for T. callipaeda were hypothesized to be restricted to male P. variegata. ControlA special control of fruit flies is not performed. Control of thelaziosis is administered in form of local or systemic chemotherapy against the nematodes themselves (see Treatment of thelaziosis). Further Information
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Definitions of parasitologic terms