A new, darkwinged species of Pseudochironomus Malloch, 1915 (Diptera: Chironomidae) from Mexico and Costa Rica

Abstract

A new species of Pseudochironomus Malloch, 1915 is described and figured as adult male and female based on material from Chiapas (Mexico) and Heredia (Costa Rica). Pseudochironomus seipi sp. n. can be distinguished from all other species of Pseudochironomus as it has two dark bands across the wing and a small tubercle in mid scutum; all other described species have wings without dark spots or bands, and they all lack scutal tubercle. It can also be separated from other Neotropical species by having 25–30 dorsocentrals in double to triple row; all other described Neotropical species have dorsocentrals in a single row. Including this new species, 10 Pseudochironomus species are described from the Neotropical Region.

Keywords:

• Chironomidae
• Chironominae
• Pseudochironomini
• Pseudochironomus
• new species
• Mexico
• Costa Rica

Introduction

The tribe Pseudochironomini within the subfamily Chironominae was established by Sæther (1977a: 154). The tribe is characterised by having a black comb on the fore tibia, similar to the combs on mid- and hind tibiae, and in the male, the pseudovolsella is generally present. Originally the genera Aedokritus Roback, 1958, Manoa Fittkau, 1963, Megacentron Freeman, 1961, Pseudochironomus Malloch, 1915, Psilochironomus Sublette, 1966, and Riethia Kieffer, 1917 were included in the tribe (Sæther 1977a). However, Psilochironomus is now considered to be a nomen dubium (Spies and Reiss 1996). Later, Andersen (2016) added the genus Madachironomus Andersen, 2016 based on two species from Madagascar to the tribe. However, according to Cranston (2003), the tribe Pseudochironomini might not be monophyletic.

The genus Pseudochironomus was described by Malloch (1915) based on P. richardsoni Malloch, 1915 from Illinois, USA. Pseudochironomus is the most species-rich genus in the tribe. About 11 species are known from the Nearctic Region, and one or two species from the Palaearctic Region (Epler, Ekrem, and Cranston 2013). The Nearctic species were reviewed by Sæther (1977b). From the Neotropical Region, Kieffer (1925) described P. viridis (Kieffer, 1925) from Argentina. Roback (1960) recorded the species from Peru and redescribed the male. Later, Paggi and Rodriguez-Garay (2015) redescribed and figured the male, female, pupa, and larva in more detail based on material from Argentina. Recently Shimabukuro, Pepinelli, and Trivinho-Strixino (2017) and Trivinho-Strixino and Shimabukuro (2018) described eight new Pseudochironomus species from Brazil.

Unnamed specimens of Pseudochironomus have been recorded from Costa Rica, Dominican Republic, Nicaragua, and Mexico (Andersen, Contreras-Ramos, and Spies 2000; Spies, Andersen, Epler, and Heyn 2009; Silva, Wiedenbrug, and Farrell 2015). Below, a new species from Mexico and Costa Rica is described and figured as adult male and female and is the first Pseudochironomus species described from Central America and Neotropical Mexico. However, Watson and Heyn (1992) recorded 11 unnamed species of Pseudochironomus from Costa Rica, so there are several more species to be described from the region.

Material and methods

Prior to examination, the specimens were mounted in Canada balsam following the procedure outlined by Sæther (1969). Morphological terminology follows Sæther (1980). Measurements for the male are given as ranges. Colouration is based on slide-mounted specimens.

The type material is deposited in the Department of Natural History (ZMBN), Bergen University Museum, Norway.

Results

Pseudochironomus seipi sp. n.

(Figures 1–15)

urn:lsid:zoobank.org:act:95A84774–4DBF–4F92–825A–B84A552E5775

Type locality

Mexico, Chiapas, Chintul, Rio Chintul, 17°14.55′N, 93°35.11′W, 180 m above sea level.

Type material

Holotype. ♂ adult (slide mounted) ‘MEXICO, Chiapas, Chintul, Rio Chintul, (trib. Rio Grijalva), Hwy 187, 17°14.55′N 93°35.11′W, 180 m, 20.xi.1996, Contreras, Bueno & Barba leg.’ (ZMBN).

Paratypes. 1 ♀ adult (slide mounted) with same label data as holotype (ZMBN). 1 ♂ adult (slide mounted) ‘COSTA RICA: Heredia, Est. Biol. La Selva, Rio Puerto Viejo, 10.440 N 84.012 W, 19.vi.1986, el. 30 m, Holzenthal, Heyn, Armitage’ (ZMBN).

Diagnosis

The species can easily be separated from its congeners by having two dark cross-bands in the wing and a small tubercle in mid scutum; all other described species have wings without dark spots or bands, and they all lack scutal tubercle. The male can also be separated from other Neotropical species by having 25–30 dorsocentrals in double to triple row; all other described Neotropical species have dorsocentrals in a single row.

Description of adult male

(n = 1–2)

Total length 3.56–3.71 mm. Wing length 1.61–1.79 mm. Total length/wing length 1.98–2.31. Wing length/length of profemur 2.17–2.18.

Colouration. Head, thorax, and abdomen brown. Legs with femur and tibia brown, tarsi lighter brown. Wing hyaline with two dark cross-bands.

Antenna. AR 1.50–1.80. Terminal flagellomere 640–700 µm long.

Head. Temporal setae 18–22, bi- to tri-serial. Clypeus with 19–23 setae. Tentorium 144–150 µm long, 37–41 µm wide. Stipes 135–141 µm long. Palpomere lengths (in µm): 41–45, 62–74, 139–154, 152–168, 203–211. Third palpomere with 2–3 sensilla clavata subapically, longest about 18 µm long.

Thorax (Figure 3). Scutum with weak, median tubercle. Antepronotum with 4 ventrolateral setae. Acrostichals are apparently about 30, very weak, in mainly double row; dorsocentrals 25–30, in double to triple row; prealars 5. Scutellum with 17–20 setae in two rows.

Wing (Figure 1). VR 1.07–1.08. Brachiolum with 1 seta; R with 10–12 setae; other veins and membrane bare. Squama with 9–12 setae.

Figures 1–3. Pseudochironomus seipi sp. n.: (1) male wing; (2) female wing; (3) male thorax.

Legs. Spur of fore tibia 45–49 µm long; spurs of mid tibia 31–35 µm and 39–45 µm long; spurs of hind tibia 41–43 µm and 45–47 µm long. Width at apex of fore tibia 45–49 µm; of mid tibia 49–53 µm; of hind tibia 51–54 µm. Lengths and proportions of legs as in Table 1.

Table 1. Lengths (in µm) and proportions of legs of Pseudochironomus seipi sp. n., male (n = 2).

	fe	ti	ta1	ta2	ta3	ta4
p1	753–842	899–1038	842–964	368–433	310–335	221–237
p2	801–858	825–874	466–507	204–229	163–172	102–110
p3	825–858	882–997	572–613	286–302	237–245	114–123
	ta5	LR	BV	SV	BR
p1	90–106	0.93–0.94	2.50–2.56	1.94–1.95	1.48–1.90
p2	57–65	0.57–0.58	3.82–4.03	3.42–3.49	1.73–2.07
p3	57–65	0.62–0.65	2.28–2.36	2.99–3.03	1.65–1.97

Hypopygium (Figures 4–10). Tergite IX with broadly rounded posterior margin, with subtriangular posterior projection medially ending in two rounded lobes; with 30–35 setae medially, triangular projection with 16–28 setae, apical setae strong and curved. Laterosternite IX without setae. Phallapodeme 108–126 µm long; transverse sternapodeme 83–86 µm long. Gonocoxite 199–213 µm long. Pseudovolsella bluntly triangular, with single, 17–21 µm long seta. Superior volsella pediform, apparently without setae, 90–97 µm long, 33–35 µm wide medially. Inferior volsella bluntly subtriangular, 68–72 µm long, 41–46 µm wide medially. Pars ventralis narrowly leaf-shaped, 65–76 µm long, 12–14 µm wide medially. Gonostylus 117–129 µm long. HR 1.65–1.70. HV 2.88–3.04.

Figures 4–10. Pseudochironomus seipi sp. n., male: (4) hypopygium, dorsal view; (5) hypopygium with tergite IX removed, dorsal view; (6) hypopygium, ventral view; (7) superior volsella; (8) inferior volsella; (9) pseudovolsella; (10) pars ventralis.

Description of adult female (n = 1)

Total length 2.90 mm. Wing length 1.50 mm. Total length/wing length 1.93. Wing length/length of profemur 2.35.

Colouration. Head and abdomen brown, thorax dark brown. Legs with femur and tibia brown, tarsi lighter brown. Wing hyaline with two dark cross-bands.

Antenna. With 5 flagellomeres; AR = 0.53. Length of pedicel and flagellomeres 1–5 (in µm) as: 47; 88; 48; 48; 48; 124. Flagellomeres 1–4 with ring of sensilla chaetica subapically, flagellomere 5 with more extensive sensilla chaetica. Flagellomere 5 with 2 strong setae subapically, longest 66 µm long.

Head. With 13 inner verticals in double row; outer verticals and postorbitals 7. Clypeus with 21 setae. Tentorium 129 µm long, 23 µm wide. Stipes 131 µm long, 35 µm wide. Palp segment lengths (in µm): 43, 49, 103, 127, 213. Third palpomere with 1 sensilla clavata subapically, 12 µm long.

Thorax. Scutum with weak, median tubercle. Antepronotum with 3 ventrolateral setae. Acrostichals apparently about 25, very weak and difficult to discern; dorsocentrals 25, in partly double row; prealars 5. Scutellum with 16 setae in 2 rows.

Wing (Figure 2). VR 1.13. Brachiolum with 1 seta; R with 10; R₁ with 7, and R_4 + 5 with 7 setae in apical 1/3; other veins and membrane bare. Squama with 11 setae.

Legs. Spur of fore tibia 35 µm long, spurs of mid tibia 32 µm and 37 µm long, of hind tibia 35 µm and 40 µm long. Width at apex of fore tibia 46 µm, of mid tibia 48 µm, of hind tibia 51 µm. Lengths and proportions of legs as in Table 2.

Table 2. Lengths (in µm) and proportions of legs of Pseudochironomus seipi sp. n., female (n = 1).

	fe	ti	ta1	ta2	ta3	ta4
p1	645	776	768	327	253	179
p2	686	719	384	163	131	90
p3	760	776	466	237	188	106
	ta5	LR	BV	SV	BR
p1	98	0.989	2.552	1.851	1.11
p2	49	0.534	4.132	3.660	1.31
p3	52	0.600	3.451	3.298	1.76

Genitalia (Figures 11–15). Segment X with 15 setae to each side of the vagina. Seminal capsule ovoid, 73 µm long, not including 11 µm long neck, about 55 µm wide; spermathecal ducts nearly straight. Notum 97 µm long. Dorsomesal lobe 104 µm long from base of the vagina to apex. Gonocoxite IX with 4 setae. Tergite IX with 63 setae. Cercus 145 µm long.

Figures 11–15. Pseudochironomus seipi sp. n., female: (11) genitalia, ventral view; (12) tergite IX and gonocoxite IX, dorsal view; (13) dorsomesal lobe; (14) ventrolateral lobe; (15) apodeme lobe.

Immatures

Larva and pupa unknown.

Distribution

The species is known from Rio Chintul in Chiapas, southern Mexico and from La Selva Biological Station in Heredia, Costa Rica.

Habitat

The species was collected close to streams and rivers in areas with tropical rainforest.

Etymology

The species is named after senior physician Andreas O. Seip, Haukeland University Hospital, Bergen, the orthoped who has looked after my hips and legs, for his strong interest in speciation and taxonomy. The name is a noun in the genitive case.

Discussion

The species can easily be separated from its congeners by having two dark cross-bands in the wing. All other described species are lacking dark cross-bands in the wing. The new species also has a weak tubercle in mid scutum. The generic diagnosis in e.g., Sæther (1977b: 59) and Cranston, Dillon, Pinder, and Reiss (1989: 407) should thus be emendated accordingly: ‘Wing membrane without dark markings, occasionally with two dark cross-bands’ and ‘thorax without tubercle, occasionally with weak tubercle in mid scutum’.

Shimabukuro et al. (2017: 136) demonstrated that several Pseudochironomus species from Brazil have a single row of rather long, thin acrostichals and emended the generic diagnosis accordingly. The new species appears to have a double row of acrostichals, but these are very short and weak and can be difficult to discern.

The new species has 25–30 dorsocentrals in 2–3 rows. Pseudochironomus richardsoni Malloch, 1915 has 59 dorsocentrals in 3–6 rows (Sæther 1977b). The species was described by Malloch (1915: 500) from Illinois and is distributed from Ontario south to California and Florida and has also been recorded from Argentina based on larva and pupa only (Oliver, Dillon, and Cranston 1990; Paggi and Rodriguez-Garay 2015). But apart from P. richardsoni, other Pseudochironomus species described from the New World seem to have dorsocentrals in a single row only.

In the tribe Pseudochironomini, all described genera lack scutal tubercle, and the genus Aedokritus Roback, 1958 is the only genus that has wings with extensive dark marks or bands. In fact, the wing of P. seipi n. sp. is somewhat similar to the wing of Aedokritus platycnemis Edwards, 1931 from Argentina (see Pinho, Dantas, and Hamada 2019: 537). In hypopygial features P. seipi n. sp. is very similar to other Neotropical Pseudochironomus species, so the new species clearly belong to Pseudochironomus. However, more species with scutal tubercle and banded wings might show up when the Neotropical fauna is better studied. So far, the larvae and pupa of the new species are not known, but they might also show aberrant features.

Acknowledgements

I am indebted to Dr Anna B. Seniczak, Bergen, for taking photographs of the wings and thorax.

Disclosure statement

No potential conflict of interest was reported by the author.