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

Abstract

Background - The establishment of arthropod colonies is an important tool to manipulate disease vectors, investigate their life history traits, and their vector competence, prevention of vector borne pathogen transmission, or to assess insecticidal/repellent activities. 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. Materials and methods - 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 (200ml) with a plaster-covered bottom to maintain high humidity level inside. Adult feeding was guaranteed by freshly apple and a liquid dietary supplement containing NaCl 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 14:10h light:dark, 26±2°C and 80±10% RH. Results - From a total of 130 field collected Phortica spp. three generations (i.e., 783 F1, 109 F2, 6 F3) were obtained. Phortica oldenbergi was the species with higher 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), indicating the possibility to obtain stable colonies.Conclusions - This standardized breeding protocol, based on controlled climatic parameters and fly densities, together with the introduction of an enriched 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.