Corethrella (Corethrella) galba Borkent, 2024

Borkent, Art, 2024, A new species of Corethrella Coquillett (Diptera: Corethrellidae) from Death Valley, California, United States of America, The Canadian Entomologist (e 14) 156, pp. 1-9 : 2-7

Corethrella (Corethrella) galba Borkent , new species

( Figs. 1A–B , 2A–F )

ZooBank Registration number: urn:lsid:zoobank.org:act:B435F33D-63CF-4108-A5D2-45A2DC20C763

Type material. Holotype, female adult on microscope slide, labelled “HOLOTYPE Corethrella galba Borkent ♀,” “ Wildrose Cmpgrd , Death Valley NP, CA, 36° 15' 56.31" N 117° 11' 37.69" W, 10-IV-2022, A. Borkent CD2968” ( CNCI).

Diagnosis. Adult male: Unknown. Adult female: Only extant species of Corethrella in the New World with nearly uniformly light yellowish-brown pigmentation (only some slight darkening near wing base, slight dark patch on katepisternum). Immatures: unknown.

Description. Adult male: unknown.

Adult female (n = 1): Overall pigmentation uniform light yellow ( Fig. 1A ). Head: Outline in anterior view nearly circular ( Fig. 2A ). Coronal suture extending to the dorsal margin of the innermost ommatidia ( Fig. 2A ). One large seta on each side of frons between ventromedial area of ommatidia ( Fig. 2A ). Antennal pedicel with slightly developed more elongate, stout, dorsal, or dorsolateral setae; flagellomeres 1–8 ( Fig. 1B ; others missing), sensilla coeloconica not visible due to damage. Clypeus ( Fig. 2A ) squarish. Mandible with small, pointed teeth. Palpus segment 3 ( Fig. 2B ) swollen apically, 3.7 times longer than wide. Thorax ( Fig. 1A ): Posterior portion of dorsocentral row with single elongate setae situated somewhat lateral to one another. Prescutal suture elongate. Anterior anepisternum divided diagonally by sinuous suture, dorsal portion about equal to ventral portion. Ventral portion of posterior anepisternum not differentiated from dorsal portion, anterior margin slightly more darkly pigmented than posterior margin. Without (?, visibility poor) posterior anepisternal setae, 5 anepimeral setae. Wing ( Fig. 2F ): length = 1.37 mm. Ratio of R 1 /wing length = 0.65. Apex of R 2 basal to apex of M 1. Plain, without pattern of pigmented veins and/or scales; veins (other than wing margin) with only setae. Halter slightly lighter than scutellum. Legs ( Figs. 2C–E ): uniformly pigmented, other than base of hind femur slightly lighter. With only slender setae, lacking scales (except for some in patch of whip-like setae on posterior portion of hind tibia). Apices of fore- and mid-leg fifth tarsomeres undivided, with claws slightly subapical to apical. Claws of each leg equal to those of others; equal on each leg, simple (without inner teeth). Empodia elongate, of intermediate thickness, with five branches along length, apical portion with number of bifurcations (similar to Amaral et al. 2023, Fig. 12C). Abdomen ( Fig. 1A ): Uniformly yellowish brown.

Immatures: Unknown.

Distribution. Corethrella galba is known only from the type locality at Wildrose Campground in Death Valley National Park, California, at an altitude of 1228 m. Specifically, the specimen was swept from shrubs in riparian habitat bordering a small stream originating just southwest of the junction of Emigrant Canyon and Wildrose roads, just west of Wildrose Campground.

Taxonomic discussion. Adult female Corethrella galba key to couplet 32 in Borkent’ s (2008) key to New World species, where it can be distinguished from others in that couplet by its very lightly and nearly uniformly pigmented katepisternum ( Fig. 1A ). It keys out to couplet 37 in Amaral et al.’s (2023) key to New World species, where its nearly uniformly pigmented thorax distinguishes it from subsequent taxa. Within the Nearctic, the adult female (and likely the unknown male) of C. galba will key out to couplet 2 in Borkent’ s (2008) Nearctic key, which can be replaced by the following, also incorporating for the first time the recently described C. kipferi ( Dorff et al. 2022) .

1. Palpal segment three with a uniform diameter (see Borkent 2008, Fig. 33V); thorax nearly uniformly dark brown (see Borkent 2008, Fig. 42D)....................:::................... species near peruviana (see Borkent 2008) (Key Largo, Florida)

–. Palpal segment 3 apically swollen ( Fig. 2B ); thorax nearly uniformly pigmented or with some notable pigmentation):::..........................................2

2. Thorax generally uniformly yellowish brown throughout with a few faint markings ( Fig. 1A )::::::...................................... C. galba (California)

–. Thorax with notable dark pigmentation, at least on the scutum and katepisternum:::::: 3

3. Thorax generally pale with patches of darker pigmentation on the scutum (anterior and lateral) and the dorsal portion of katepisternum (see Borkent 2008, Fig. 40D)::: C. kerrvillensis (Texas)

–. Thorax generally dark with pale sclerites at the base of the wing (see Dorff et al. 2022, Fig. 4 )............................................. C. kipferi (Missouri)

The phylogenetic relationships of the species in the rotunda species group were presented by Borkent (2008) and confirmed by Baranov et al. (2016), who organised the synapomorphies provided by Borkent (2008) into a matrix and analysed these with maximum parsimony and Bayesian approaches. The character numbers that follow are those presented and discussed in Borkent (2008; Fig. 4 ).

Four species have been described in the rotunda group since Borkent (2008), and these are generally congruent with the phylogeny presented by Borkent (2008). The only possible exception is C. yucuman Caldart and Pinho , described by Caldart et al. (2016) but not placed phylogenetically and partially redescribed by Amaral et al. (2023). Based on Caldart et al. ’s (2016) description, this species has synapomorphies 25 and 31–34 and the plesiomorphic condition for 35–38, and therefore placing it as part of a polytomy with C. grandipalpis Borkent, C. kipferi , and ( C. kerrvillensis , ( C. remiantennalis Borkent C. blandafemur Borkent ) and ( C. brevivena Borkent C. globosa Borkent )). However, Caldart et al. (2016) reported that the male of the species had a wing with R 2 shorter than the stem of R 2 3. In addition, the wing of the male of C. yucuman appears to have CuP not extending to the wing margin, although this is questionable ( Caldart et al. 2016, Fig. 3G ). These two features were previously considered to be autapomorphies of C. brevivena ( Borkent 2008; CuP previously considered to be A 1). In C. brevivena , it is both the male and female that exhibit these derived features; this suggests that the short R 2 evolved first in the male was shared thereafter by C. brevivena and C. yucuman and then subsequently was acquired by the female of just C. brevivena . Although Caldart et al. (2016) described the wings as having very narrow scales, Amaral et al. (2023) reinterpreted this character as setae present on the wing veins (character 35). Corethrella yucuman and C. brevivena are the only known species with a katepisternal seta ( Amaral et al. 2023), previously considered an autapomorphy of C. brevivena ( Borkent 2008) and hence a synapomorphy here. Along with the particularly short R 2, this character indicates C. yucuman and C. brevivena are sister species, which is how C. yucuman is placed here. If accurately placed, C. yucuman is missing the two female synapomorphies 37 and 38, interpreted here as reversals (with the possibility of the sexes being misassociated).

Corethrella xokleng Amaral et al. was described by Amaral et al. (2019), who suggested it may be the sister to C. remiantennalis , C. blandafemur , C. brevivena , and C. globosa , but their evidence showed it to form part of a polytomy, including C. kerrvillensis , C. galba , ( C. remiantennalis C. blandafemur ), and ( C. brevivena C. globosa ).

Dorff et al. (2022) placed their new species, C. kipferi , in this phylogeny but, partially because the male was unknown, could provide no further resolution other than to place it as one lineage of a polytomy with each of C. kerrvillensis , ( C. remiantennalis C. blandafemur ), and ( C. brevivena C. globosa ). However, C. kipferi has the plesiomorphic state of character 35 (in Borkent 2008) and actually forms a polytomy with C. grandipalpis, C. yucuman , and ( C. kerrvillensis , ( C. remiantennalis C. blandafemur ) and ( C. brevivena C. globosa )), the original misplacement being my error in that paper.

Most recently, Corethrella pindorama Amaral and Pinho was described by Amaral et al. (2023) and placed as part of a polytomy with C. rotunda Borkent and a group of nine members of the rotunda species group (including C. yucuman and C. xokleng ; and now also including C. galba ).

Corethrella galba is known only as a female and therefore is missing the interpretation of the male features of synapomorphies 32 and 36. The presence of synapomorphies 25, 31, and 33–35 and the plesiomorphic condition for characters 37 and 38 results in C. galba being placed as one lineage of a polytomy with each of C. kerrvillensis , C. xokleng , ( C. remiantennalis C. blandafemur ), and ( C. brevivena C. globosa ). Of these species, C. kerrvillensis is known from the Nearctic and the others are from the Neotropical region.

Because there are no conflicting characters other than the possible loss of character 36 in C. yucuman , a phylogeny presents only the relationships and synapomorphies in Figure 4 .

The holotype is only in moderate condition, partially because it was slightly dry by the time it was removed from the aspirator and preserved in ethanol. Further to this, specimens with pale pigmentation, as is true for other species with similar colouration, are challenging to clear and slide mount, and some collapsing of the antennae, palps, and thorax took place during preparation. Although it is true that specimens left in ethanol over time may become pale, this is not the situation for this specimen, which was seen in the field shortly after preservation and prepared shortly after on a microscope slide.

Bionomics. Because only a single female adult was collected, little can be suggested regarding its bionomics. However, the species belongs to the rotunda species group and, considering that at least two species in that group have hyporheic larvae, it is likely that this species has the same. The only aquatic habitat present at the type locality was a small, barely flowing stream ( Fig. 3A, B ). The remaining 11 species in this group are unknown as immatures, having never been collected by mosquito researchers, who have extensively scoured all conceivable lentic habitats. This furthers the likelihood that all members of this species group have hyporheic larvae.

The female has serrate mandibles, indicating that it is a blood feeder and, as is known in all other Corethrella species to date, likely feeds on male frogs, being attracted by their calls. Six frog and toad species ( Anura ) are known from Death Valley National Park, but only two are common: the red-spotted toad ( Bufo punctatus Baird and Girard ) ( Bufonidae ) and the Baja California treefrog ( Pseudacris hypochondriaca Hallowell ) (Hyladae), with the others restricted to very specific localities in the park more distant from the type locality ( Persons and Nowak 2006, who recorded the latter as the Pacific treefrog). It is unknown which might occur specifically at the type locality, but one or more of these anuran species is the likely host of females of C. galba .

Etymology. The specific epithet, galba (yellow), refers to the overall colour of the female of this species.

Figures

Figure 1. A, Habitus of female C. galba in lateral view; B, antennal flagellomeres 1–8.

Figure 2. Structures of female C. galba: A, head capsule in anterior view; B, right maxillary palpus in anterior view; C, foreleg; D, midleg; E, hind leg; F, wing.

Figure 3. Type locality at Wildrose Campground in Death Valley National Park, California, United States of America: A, overview of riparian habitat; B, area with flowing water.

Figure 4. Phylogeny of the species of the rotunda species group. Numbers refer to those character states presented by Borkent (2008), here listed in their apomorphic state: 25 – wing without patterned pigmentation; 31 – thorax with ventral portion of the posterior anepisternum continuous with dorsal portion and with ventral portion with anterior margin more darkly pigmented than posterior portion; 32 – male antennal flagellomere 8 shorter than both flagellomeres 7 and 9; 33 apex of R2 more basal than apex of M1; 34 – female coronal suture short, not extending ventrally between ommatidia; 35 – wing veins with setae; 36 – male antennal flagellum with one ventral seta in basal whorl of trichoid sensilla more stout and apically expanded; 37 – female antennal flagellomeres 1–3 each very short, with flagellomere 4 moderately short; 38 – female palpal segment 3 length/ width <2.3. The asterisk indicates two synapomorphies: male wing with R2 shorter than the stem of R2 3; katepisternal seta present.