| Summary: | During the last decade, Europe was confronted with the emergence of two <i>Culicoides</i>-borne viruses, bluetongue virus and Schmallenberg virus. Both diseases caused economic losses in cattle, sheep, and goats. Despite their importance, only limited knowledge is available on the developmental stages of <i>Culicoides</i> <i>obsoletus</i> complex midges, and a lab-reared colony has not yet been established. Therefore, this experimental study aims to compare the emergence patterns from field-collected <i>C. obsoletus</i> complex from egg to adult that were exposed to different combinations of temperature and larval substrates (T1: 1% liquid broth (LB) agar at 24 °C; T2: 1% LB agar with dung patches at 24 °C; T3: 1% LB agar at 28 °C). The rearing dishes were kept in an environmental chamber under an 8 h/16 h dark–light regime and 80%–85% humidity. Algae and nematodes were provided as a food source. The average period required to develop from egg to adult was 24 days and varied strongly in each of the conditions (T1: 15–47 days; T2: 14–35 days; T3: 20–37 days). A bias of sex ratio was observed towards the production of males in all three treatments with only 23.9% (T1), 23.5% (T2), and 0% (T3) females. Larval mortality was highest in T3 (25.9%), followed by T2 (8.6%), and T1 (1.8%). All pupae produced adults within 1 to 10 days, and the emergence rates for pupae varied strongly between treatments: 49.5% (T1), 71.6% (T2), and 38.5% (T3). This study shows that the <i>C. obsoletus</i> complex can be reared under laboratory conditions from blood-fed, wild-caught females to emerged progeny. More larval substrates and food sources should be tested with the aim of obtaining a 1:1 sex ratio to bring us one step closer to a viable lab-reared colony.
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