Culicoides variipennis Wirth & Jones

Shults, Phillip & Borkent, Art, 2018, Pupae of the Nearctic species of Culicoides Latreille subgenus Monoculicoides Khalaf (Diptera: Ceratopogonidae), Zootaxa 4504 (4), pp. 451-472 : 467-468

Culicoides variipennis Wirth & Jones

( Figs. 3D , 7B )

Diagnosis. The only species of C. ( Monoculicoides ) with lateral areas of all abdominal segments mostly bare or without any shagreen ( Fig. 7B ), and lateral tubercles with blunt apices ( Fig. 7B ).

Description. Male. Total length = 2.60–4.15 (3.49, 0.621 SD, n=7) mm. Light brown coloration throughout. Head: Dorsal apotome (DA) roughly 90% covered in spicules of various sizes decreasing in abundance dorsally ( Fig. 3D ), DA length = 0.29–0.38 (0.32, 0.031 SD, n=7) mm; DA width = 0.20–0.25 (0.21, 0.018 SD, n=7) mm; DAW/DAL= 0.58–0.75 (0.663, 0.051 SD, n=7). Thorax: Cephalothorax length = 1.25–1.65 (1.51, 0.150 SD, n =7) mm. Respiratory organ (RO) elongate, slender with 2–3 subbasal pores, RO length = 0.36–0.43 (0.39, 0.023 SD, n=7) mm; RO width = 0.04–0.06 (0.051, 0.009 SD, n=7) mm; ROW/ROL = 0.10–0.15 (0.13, 0.019 SD, n=7). 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 moderate 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. 7D ) 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 short with, blunt apices ( Fig. 7B ), 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 shagreen reduced or absent. Segments 5–7 with similar chaetotaxy, shagreen to that of segment 4. Segment 8 chaetotaxy with seven sensilla, without lateral shagreen. Segment 9 with anterior shagreen, anterior margin not strongly modified.

Female. Similar to male other than sexual differences on segment 9 and the following: total length = 2.96–3.75 (3.33, 0.404 SD, n=4) mm, DA–1–H apex extending past ventral margin of DA, DA length = 0.27–0.28 (0.279, 0.006 SD, n=4) mm, DA width = 0.22–0.24 (0.233, 0.009 SD, n=4) mm, DAW/DAL = 0.80–0.85 (0.834, 0.029 SD, n=4), Cephalothorax length = 1.32–1.55 (1.413, 0.122 SD, n=4) mm, RO length = 0.36–0.42 (0.388, 0.025 SD, n=4) mm, RO width = 0.04–0.05 (0.043, 0.005 SD, n=4) mm, ROW/ROL = 0.10–0.11 (0.109, 0.007 SD, n=4).

Taxonomic discussion. Shults et al. (2016) reported distinguishing features between C. sonorensis and C. variipennis based on the shape of the apices of the lateral tubercles on the abdominal segments, and further illustration of these characters can be found in that study. Those of C. sonorensis are long and slender ( Fig. 7A ), whereas in C. variipennis , they are short and blunt ( Fig. 7B ). In comparison to the other Nearctic members of C. ( Monoculicoides ), these two species seem to represent the extremes of the variation, with the bluntness/elongation of the lateral tubercle apices of the other species falling between these two species. Here we also report the overall reduced shagreen on all abdominal segments in C. variipennis and in particular the lack of lateral shagreen on abdominal segments 4–7 as a diagnostic character state.

This species is known from British Columbia, Alberta, Washington, and Montana to Nova Scotia, and the United States primarily east of the Mississippi river, Texas and Louisiana ( Wirth & Jones 1957; Holbrook et al. 2000; Borkent & Grogan 2009; Grogan & Lysyk 2015; Shults 2015; Jewiss-Gaines et al. 2016). Moderate to large numbers of pupae have been reared and collected from fresh water polluted with manure ( Wirth & Jones 1957, Jamnback 1965). Additionally, specimens have been collected from saltmarshes ( Blanton & Wirth 1979). The pupa of C. variipennis was briefly described by several authors ( Malloch 1915, Thomsen 1937, Fox 1942, Jones 1955, Jamnback 1965, Blanton & Wirth 1979, Weber 2001) but it is difficult to determine whether these descriptions agree with ours as we are uncertain which species of the C. variipennis complex were actually studied by these authors.

The specimens we examined from Vernon, B.C. account for the large amount of size variation seen in fig. 10, as they are much smaller (roughly the size of C. occidentalis ) than the other specimens of C. variipennis examined. The pupae from Vernon key to C. variipennis but have slightly longer lateral tubercles. It is unclear if these measurements and features fall within the normal geographic variation of this species, represent intermediate character states, or even infer a new cryptic species.

Material examined: 3 males, 2 female ( CNCI), Canada, Ontario, Alfred , 30–VI–1985, Dillion & Oliver . 2 males, 2 females ( CNCI), Canada, British Columbia, Vernon, Coldstream Ranch , 19.VII.1994, Grogan & McKinnon . 2 males ( NYSM), USA, Missouri, Petersburg, Boone’s Lick salt spring, 11.III.1955, P.J. Spangler .

Morphometric results

( Figs. 9 , 10 , 11 , Tables 1 & 2)

Morphometric analyses of the Nearctic species of C. ( Monoculicoides ) show general trends among the size of each species ( Figs. 9 & 10 ) as well as sexual dimorphism within the species examined ( Fig. 11 ). Culicoides stigma has a statistically significant smaller respiratory organ in comparison to the length of the cephalothorax (RO length/ cephalothorax length) than all other species of C. ( Monoculicoides ) (ANOVA with Tukey’s, p <0.001). There was no significant difference in this ratio between any other species.

The dorsal apotome of male pupae tend to be longer and narrower than those of female pupae. This is most easily observable in the DA ratio (DAW/DAL) ( Fig. 11 ). Culicoides riethi is the only species examined to show no statistically significant difference in the DA ratio between males and females ( Fig. 11 ) (Student’s t, p = 0.57). All other species examined showed a sexual dimorphism (Student’s t, p <0.05). There is however a sexual dimorphism in the length of the cephalothorax in C. riethi (Student’s t, p <0.05) that does not exist in any other species examined ( Fig. 10 ).

Figures

FIGURE 3. Female, dorsal apotomes, in anterior view. (A) Culicoides occidentalis. (B) C. riethi. (C) C. sonorensis. (D) C. variipennis.

FIGURE 7. Male, lateral and dorsal tubercles of abdominal segments 4, in dorsal view (A) Culicoides sonorensis. (B) C. variipennis.

FIGURE 9. Box plots of measurements of the length of respiratory organs by species. Species ordered by ascending values.

FIGURE 10. Box plots of measurements of the length of cephalothorax by species, separated by sex. Species ordered by ascending values.

FIGURE 11. Box plots of dorsal apotome ratios by species, separated by sex. Species ordered by ascending values.