Medical and Veterinary Entomology (2020), doi: 10.1111/mve.12470 The effect of ambient temperature fluctuations on Culicoides biting midges population dynamics and activity in dairy farms: a longitudinal study Y. SAROYA, Y. GOTTLIEB and E. KLEMENT Koret School of Veterinary Medicine, Robert H. Smith Faculty of Agriculture, food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel Abstract. The effect of climatic factors on the presence of Culicoides Latreille (Diptera: Ceratopogonidae) was previously studied. Nevertheless, lack of laboratory rearing data hampers species-specific prediction of weather fluctuations effect on pop- ulation size. To determine fluctuations in population size in the field, we recorded Culi- coides and other Nematocerans in seven Israeli dairy farms over two-years (2011–2012) and analysed the association of their dynamics with fluctuations in ambient temperature and total rainfall. In six farms, the most abundant species were Culicoides imicola Kief- fer and Culicoides schultzei (Enderlein) gp., primarily composed of parous females, and in one farm Culicoides obsoletus (Meigen) gp., mostly nulliparous females, were dom- inant. While the total number of insects was similar in both years, Culicoides numbers were significantly higher in 2012, but appeared later in the season and reached a higher peak. A multi-variable linear regression model demonstrated positive association of C. imicola and C. schultzei numbers with the monthly multi-annual ambient temperature and its specific deviation, but not with monthly rainfall. C. obsoletus populations peaked at spring and sharply decreased when temperature exceeded 20 ∘ C, and were best mod- elled by adding quadratic terms. Weather-specific estimation of population size under field conditions may enable to predict outbreaks intensity of Culicoides-borne viruses. Key words. Culicoides imicola, Culicoides obsoletus group, Culicoides schultzei group, ambient temperature, climate regions, engorged females, nulliparous females, parous females. Introduction In recent years, Culicoides borne diseases such as bluetongue and epizootic haemorrhagic disease frequently affected dairy cattle in Israel (Kedmi et al., 2010; Golender et al., 2016). Most of these outbreaks occur between September and November when Culicoides populations peak. Incidence of such outbreaks is determined by combination of herd immunity (vaccination or previous exposure) (Aharonson-Raz et al., 2017), the number of viremic animals in the herd and the number of Culicoides vec- tors (Gerry et al., 2001; Purse et al., 2006; Mayo et al., 2012). Thus, information on the expected Culicoides population size during their peak season is important for disease control. Correspondence: Yuval Gottlieb, Koret School of Veterinary Medicine, Robert H. Smith Faculty of Agriculture, food and Environment, The Hebrew University of Jerusalem, POB 12, Rehovot, 76100, Israel. Tel.: +972 8 9489633; Fax: +972 8 9489634; E-mail: gottlieb.yuval@mail.huji.ac.il Culicoides population size is determined by fecundity, imma- ture developmental time, adult survival and activity. The influ- ence of temperature on each of these factors is different and distinctive for each Culicoides species (reviewed in Purse et al., 2006), and thus complicates the prediction of their popula- tion size. For example, high temperature can reduce the develop- mental time and gonotrophic cycle period (time from blood meal to oviposition), as well as adult survival (Mullens & Rutz, 1983). Such prediction is also challenged by the lack of laboratory rear- ing data for most vector species. The major species found in dairy farms in Israel are Culicoides imicola, a known Afrotropical vector of Bluetongue virus (BTV) (Mellor et al., 2000) and members of the Culicoides © 2020 The Royal Entomological Society 1