Laboratory breeding of two Phortica species (Diptera: Drosophilidae), vectors of the zoonotic eyeworm Thelazia callipaeda

Abstract

Background: Some species of drosophilid flies belonging to the genus Phortica feed on ocular secretions of mammals, acting as biological vectors of the zoonotic eyeworm Thelazia callipaeda. This study describes an effective breeding protocol of Phortica variegata and Phortica oldenbergi in insectary conditions. Methods: Alive gravid flies of P. oldenbergi, P. variegata and Phortica semivirgo were field collected in wooded areas of Lazio region (Italy) and allowed to oviposit singularly to obtain isofamilies. Flies were maintained in ovipots (200 ml) with a plaster-covered bottom to maintain high humidity level inside. Adult feeding was guaranteed by fresh apples and a liquid dietary supplement containing sodium chloride and mucin proteins, while larval development was obtained by Drosophila-like agar feeding medium. The breeding performances of two media were compared: a standard one based on cornmeal flour and an enriched medium based on chestnut flour. All conditions were kept in a climatic chamber with a photoperiod of 14:10 h light:dark, 26 ± 2 °C and 80 ± 10% RH. Results: From a total of 130 field-collected Phortica spp., three generations (i.e. F1 = 783, F2 = 109, F3 = 6) were obtained. Phortica oldenbergi was the species with highest breeding performance, being the only species reaching F3. Chestnut-based feeding medium allowed higher adult production and survival probability in both P. oldenbergi and P. variegata. Adult production/female was promising in both species (P. oldenbergi: 13.5 F1/f; P. variegata: 4.5 F1/f). Conclusions: This standardized breeding protocol, based on controlled climatic parameters and fly densities, together with the introduction of an enriched chestnut-based feeding medium, allowed to investigate aspects of life history traits of Phortica spp. involved in the transmission of T. callipaeda. Obtaining F3 generation of these species for the first time paved the road for the establishment of stable colonies, an essential requirement for future studies on these vectors in controlled conditions. Graphical abstract: [Figure not available: see fulltext.].