Culicoides occidentalis Wirth & Jones

Culicoides occidentalis Wirth & Jones (Figs. 3A, 4C, 5B, 6A, 8B) Diagnosis. The only species of C. (Monoculicoides) with no more than 70% of the dorsal apotome covered in uniform spicules (Fig. 3A) and bearing three to four clypeal setae (Fig. 4C). Description. Male. Total length = 2.71–3.15 (2.99, 0.196 SD, n=4) mm. Light brown coloration throughout (Fig. 1). Head: Dorsal apotome (DA) roughly 70% covered in uniform spicules decreasing in abundance dorsally (Fig. 3A), DA length = 0.33–0.37 (0.35, 0.021 SD, n=4) mm; DA width = 0.21–0.22 (0.216, 0.004 SD, n=4) mm; DAW/DAL= 0.59–0.65 (0.615, 0.027 SD, n=4), CL–1–H about twice length of CL–2–H, with CL-3-H, with or without campaniform CL-4-H (Fig. 4C); O–2–H, O–4–H separated medially by O–1–H and O–3–H. Thorax: Cephalothorax length = 1.30–1.37 (1.33, 0.031 SD, n =4) mm. Respiratory organ (RO) elongate, slender, 3–4 subbasal pores (Fig. 2B), RO length = 0.39–0.45 (0.42, 0.035 SD, n=4) mm; RO width = 0.04–0.05 (0.043, 0.005 SD, n=4) mm; ROW/ROL = 0.08–0.12 (0.102, 0.019 SD, n=4), D–5–T short. Abdomen: Tergite 1 with long D– 3– I, short D– 2–I, D– 7–I anterior, campaniform D– 4–I, short D– 8–I, and long, thin D– 9–I on short tubercle posteriorly, L– 2–I, L– 3–I short separated medially by long, thin L– 1–I on lateral margin. Chaetotaxy, shagreen of tergite 2 similar to tergite 4, without elongate tubercles, minute L– 2–II, L– 4–II separated medially by long, thin L– 3–II on anterolateral margin. Chaetotaxy, shagreen of segment 3 similar to that of segment 4. Tergite 4 (Fig. 6A) with short D– 2–IV on short tubercle, thin D– 3–IV on elongate, pointed tubercle, D– 5–IV, D– 4–IV, D– 7–IV, D– 8– IV, D– 9–IV in transverse row, arranged medially to laterally, minute D– 5–IV on slightly formed tubercle, D– 4–IV on small tubercle, D– 7–IV on small rounded tubercle, D– 8–IV, D– 9–IV each long on pointed tubercle, D– 8–IV seta thicker than D– 9–IV; lateral tubercles with elongate, apices, L– 1–IV thick seta on small bifurcate tubercle, L– 2–IV, L– 4–IV thick setae, each on elongate bifurcate tubercle, separated by thin L– 3–IV on elongate bifurcate tubercle; sternite 4 with minute V– 5–IV on small rounded tubercle, V– 6–IV thin on pointed tubercle, small V– 7– IV on pointed tubercle, ventral setae in transverse row, shagreen along anterior margins, lateral portion with scattered shagreen. Segments 5 and 6 with similar chaetotaxy, shagreen to that of segment 4. Segment 7 with similar chaetotaxy to segment 4, with reduced lateral shagreen. Segment 8 chaetotaxy with seven sensilla, without lateral shagreen. Segment 9 with anterior shagreen, anterior margin not strongly modified (Fig. 8B). Female. Similar to male other than sexual differences on segment 9 and the following: total length = 2.76–3.20 (2.93, 0.234 SD, n=3) mm, DA–1–H apex extending past ventral margin of DA, DA length = 0.29–0.32 (0.30, 0.015 SD, n=3) mm, DA width = 0.23–0.25 (0.237, 0.012 SD, n=3) mm, DAW/DAL = 0.77–0.79 (0.78, 0.013 SD, n=3), Cephalothorax length = 1.30–1.37 (1.34, 0.035 SD, n=3) mm, RO length = 0.42–0.43 (0.423, 0.006 SD, n=3) mm, RO width = 0.04–0.05 (0.043, 0.006 SD, n=3) mm, ROW/ROL = 0.09–0.11 (0.102, 0.012 SD, n=3). Taxonomic discussion. This species has 3-4 subbasal pores on the respiratory organ and along with C. shemanchuki, are the only members of C. (Monoculicoides) with four subbasal pores on the respiratory organ. We have not observed any specimens of C. sonorensis or C. variipennis, the other members of the C. variipennis complex, with more than three subbasal pores. This could potentially be a useful identifying character within this complex, however, more specimens are needed to confirm this as high variation has been observed in the number of subbasal pores within other species (Lawson 1951). This species and C. sonorensis are the only members of C. (Monoculicoides) examined where some specimens had a 4 th ocular seta, O–4–H (Shults et al. 2016). Of the members of the subgenus with spicules on the dorsal apotome, C. occidentalis has the lowest spicule density (Fig. 3A). Pupae of this species had 1 or 2 extra campaniform clypeal sensilla, CL–3–H and CL–4–H (Fig. 4C). One extra CL sensilla is also present in C. riethi but C. occidentalis is the only species observed with a CL–4–H. Culicoides occidentalis ranges from British Columbia to Baja California, east to Nevada, southeast eastern New Mexico and west Texas. Immatures have been reported from aquatic sites with highly salinity (Wirth & Jones 1957, Holbrook et al. 2000). Material examined: 1 male, 2 females (CNCI), Canada, B.C., Kamloops, alkaline lake, 21.VII.1994, Grogan & McKinnon. 4 males, 4 females, (1 male, 1 female TAMU, voucher series #732; 3 males, 3 females CNCI), Canada, B.C., White Lake, 5 km SW Okanagan Falls, 49°18’27.51"N, 119°138’00.23"W, 4.V.2014, A. Borkent.

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