Metriocnemus sp.

Eiseman, Charles S., Namayandeh, Armin, Linden, John Van Der & Palmer, Michael W., 2023, Metriocnemus erythranthei sp. nov. and Limnophyes viribus sp. nov. (Diptera: Chironomidae: Orthocladiinae): leafminers of monkeyflowers, speedwells, and other herbaceous plants, with new observations on the ecology and habitats of other leaf-mining Chironomidae, Zootaxa 5249 (1), pp. 41-68 : 54

Metriocnemus sp. “ Oregon ”

( Figs. 7a–f )

Material examined. USA: OREGON: Lane Co., Blue River , 44.1535, -122.328, 3.vi.2022, leg. M. W. Palmer, ex Claytonia sibirica (4 larvae, USNM; 5 larvae, ANC) ; same but ex Myosotis scorpioides (1 larva, USNM) ; same but ex Petasites frigidus (2 larvae, USNM; 11 larvae, ANC) .

Larva (n = 7).

Total length 4.5–6.0, 5.3 mm. Head 288–364, 339 μm long, 429–579, 458 μm wide.

Coloration ( Fig. 5a ). Head capsule dark brown. Occipital margin much darker in contrast to the remainder of the head. Abdomen greenish yellow with a bluish pattern on the 1 st and 2 nd segments.

Head. Antenna short, 5 segmented; antennal segments in μm: 43, 11–14, 3–4, 4–5, 5; 1 st antennal segment L/ W 1.2; ring organ located at mid-section of 1 st segment; AR 1.7–1.8, blade subequal to flagellum; blade 23–25, 24 μm long ( Fig. 5b ). SI trifid with lateral branches shorter, SII-SIII simple ( Fig. 5c ). Labral lamella comb-like ( Fig. 5c ). Premandible dark, with 2 basal and 2 inner teeth, 72–88, 74 μm long; brush well-developed ( Fig. 5c ). Mandible dark, apical tooth shorter than combined width of 4 inner teeth; seta subdentalis narrow reaching the base of basal inner teeth; setae interna with 7 branches, the apex of branches furcate ( Fig. 5d ), mandible 151–170, 161 μm long. Mentum dark, with wide bifid median tooth and 5 pairs of lateral teeth, median teeth sit much lower and are much smaller than 1 st lateral teeth; ventromental plate long running parallel to the lateral edge of mentum, reaching well beyond the base of last lateral tooth; seta submenti just posteriad to mentum aligned with 3 rd lateral tooth ( Fig. 5e ); mentum 94–116, 106 μm long and 110–126, 117 μm wide, ventromental plate 68–77, 74 μm long. Postmentum 132–157, 147 μm long.

Abdomen. Posterior parapods wider than long, bearing around 15 simple dark claws, posterior parapod 157– 221, 174 μm long and 1166–239, 200 μm wide ( Fig. 5f ). Procercus almost as long as wide, bearing 5 apical setae, procercus 17–27, 21 μm long and 18–29, 24 μm wide, apical setae 107–118, 110 μm long. Four wide and conical anal tubules are present, anal tubules 177–234, 205 μm long.

Diagnostic characters. The larva of Metriocnemus sp. “ Oregon ” can be separated from other related species by the combination of the following characteristics: Antenna short, 1 st antennal segment L/ W 1.2, ring organ located at mid-section of 1 st antennal segment, AR 1.7–1.8, blade subequal to flagellum; SI trifid with mid-branch longer; premandible with a well-developed brush; mentum dark, with wide bifid median tooth sitting much lower and are much smaller than 1 st lateral teeth, ventromental plate reaching well beyond the base of last lateral tooth, seta submenti aligned with 3 rd lateral tooth; posterior parapods wider than long, anal tubules semicircular.

Biological notes. Larvae were collected along with leaf mines and larvae of Metriocnemus erythranthei on Claytonia sibirica , Myosotis scorpioides , and Petasites frigidus . The larvae in these samples were not observed closely, but on the Petasites , which was in the spray zone of a dripping rock seep, MWP noted that the dominant species had a dark band in the thoracic segments of the body, evidently referring to Metriocnemus sp. “ Oregon.” On this host, the mines were rather short, and the only larvae seen were window-feeding on the upper leaf surface (i.e., feeding externally and leaving the lower epidermis intact). Only leaves with mines were collected on the other two hosts, but these leaves also included larvae wandering externally. Thus, the degree to which M. sp. “ Oregon ” is a leafminer requires further investigation, and if it does feed in mines, it may be that it only does so within those initiated by M. erythranthei . Along with M. erythranthei and M. eurynotus , the Petasites collection also included two other chironomids: one larva of Boreochlus persimilis (Johannsen, 1926) (Podonominae) and one pupa of Orthocladius (Eudactylocladius) dubitatus Johannsen, 1942 (the adult female apparently emerged after the pupa was placed in ethanol). Boreochlus larvae have been previously reported to inhabit mosses in springs and small streams ( Epler 2001), and Sublette et al. (1998) stated that those of O. dubitatus are probably madicolous (inhabiting thin films or sheets of water in streams, on vertical rock faces, etc.).

Figures

FIGURE 5. Metriocnemus erythranthei sp. nov., pupation on Veronica sp. (a–e), adults (f–g). a. pupa in leaf mine; b. same; c. pupa in stem mine; d. pupal exuviae protruding from leaf mine; e. leaf mine opened to show vacated pupation site, with larval exuviae and gelatinous mass; f. female reared from Erythranthe glabrata; g. male reared from Veronica sp.

FIGURE 7. Metriocnemus sp. “Oregon”, larva (a–c). a. habitus; b. antenna; c. labrum and premandible; d. mandible; e. mentum; f. posterior portion of the larva.