Metriocnemus erythranthei Namayandeh, Eiseman, van der Linden & Palmer 2023, sp. nov.
Creators: name: Eiseman, Charles S.
name: Namayandeh, Armin
name: Linden, John Van Der
name: Palmer, Michael W.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Chironomidae
Metriocnemus
Metriocnemus erythranthei

description: Metriocnemus erythranthei Namayandeh, Eiseman, van der Linden & Palmer sp. nov.
(Figs. 1–5)
LSID: urn:lsid:zoobank.org:act: 524CFBAA-C5C4-48B6-A219-A71614991FB8
Holotype. USA: OKLAHOMA: Woodward Co., Boiling Spring State Park; 2.v.2021, em. 10–11.v.2021, leg. E. LoPresti and K. Toll, ex Erythranthe glabrata (1Ô, USNM).
Paratypes. Canada: BRITISH COLUMBIA: Cowichan Valley, 48.837266, -123.590338, 25.iii.2022, leg. F. McGhee, ex Erythranthe guttata (1 pupa, 1 larva, USNM); USA: CALIFORNIA: Sonoma Co., Bodega Bay, Campbell Cove; 31.v.2019, em. by 3.vi.2019, leg. K. Toll, ex Erythranthe guttata (1 larva, USNM); IOWA: Winneshiek Co., Decorah, Van Peenan Spring at Van Peenan Park, 43.312834, -91.776010, 17.v.2022, em. 22.v.2022, leg. J. van der Linden, ex Veronica sp. (1Ô, USNM); OKLAHOMA: same data as holotype (1Ô, 2♀, 2 pupae, 1 larva, USNM); OREGON: Lane Co., 44.235804, -122.85404, 9.v.2022, em. 14.v.2022, leg. J. Ward, ex Claytonia sibirica (1♀, 1 pupa, USNM); Lane Co., Blue River, 44.1535, -122.328, 3.vi.2022, leg. M. W. Palmer, ex Claytonia sibirica (1Ô, 1 pupa, 1 larva, USNM); same but ex Myosotis scorpioides (1 pupa, USNM); same but ex Petasites frigidus, adults em. 12–20.vi.2022 (3ÔÔ, 2♀♀, 1 pupa, 1 larva, USNM); PENNSYLVANIA: Berks Co., Blandon, 40.461258, -75.88125, 8.v.2022, preserved 14.v.2022, leg. C. Smith, ex Veronica anagallis-aquatica (1 larva, USNM).
Other material examined. USA: CALIFORNIA: Santa Cruz Co., Bonny Doon, 31.x.2012; leg. C.S. Eiseman, ex Erythranthe moschata (1 larva, JHEC); IOWA: Winneshiek Co., Decorah, Twin Springs Park, 43.297623, - 91.815370, 4.iv.2022, em. 6.iv.2022, J. van der Linden, ex Veronica sp. (1Ô, 1 pupa, 1 larva, ANC); same but 6.iv.2022 (2 pupae, 3 larvae, ANC); same location, 17.v.2022, em. 22.v.2022, J. van der Linden, ex Veronica sp. (4ÔÔ, 4 pupae, 1 larva, ANC); OREGON: Lane Co., Blue River, 44.1535, -122.328, 6.iv.2022, leg. M. W. Palmer, ex Erythranthe guttata complex (6 pupae, 12 larvae, ANC); same collection, em. 10–14.iv.2022 (3ÔÔ, 1♀, ANC); same but 28.iv.2022 (16 larvae, ANC); same but 3.vi.2022, ex Stachys cooleyae (8 larvae, ANC); same but 3.vi.2022, adult em. ~ 8.vi.2022, ex Mentha × piperita ssp. citrata (1♀, 1 pupa, ANC); same but 3.vi.2022, adult em. ~ 8.vi.2022, ex Myosotis scorpioides (1Ô, 1 larva, ANC); same but 3.vi.2022, adults em. 12–20.vi.2022, ex Petasites frigidus (1Ô, 11♀♀, 6 pupae, 4 larvae, ANC); Blue River, 44.1507, -122.324, 28.iv.2022, leg. M. W. Palmer, ex Veronica americana (11 larvae, ANC); PENNSYLVANIA: Berks Co., Blandon, 40.461258, -75.88125, 8.v.2022, preserved 14.v.2022, leg. C. Smith, ex Veronica anagallis-aquatica (1 larva, ANC).
Photographed leaf mines. Canada: BRITISH COLUMBIA: Capital Regional District, Langford, Goldstream Provincial Park, 48.483147, -123.551983, 13.viii.2022, L. Ragan, Claytonia sibirica (iNat 130692120); Cowichan Valley, 48.837266, -123.590338, 25.iii.2022, F. McGhee, Erythranthe guttata (iNat 110361786); USA: ALASKA: Sitka Co., Sitka, 57.08361, -135.282176, 15.vii.2021, J. Goff, Erythranthe guttata (iNat 87446898); Sitka Co., 57.123319, -135.313118, 4.viii.2022, M. Goff, Erythranthe guttata (iNat 129592195); CALIFORNIA: Marin Co., Golden Gate National Recreation Area, 37.830228, -122.505225, 12.vi.2022, C. Chang, Erythranthe Sect. Simiolus (iNat 121533464); Napa Co., McLaughlin Preserve, 38.856449, -122.402827, 21.vi.2016, E. LoPresti, Erythranthe guttata (iNat 69586931); Santa Clara Co., San Jose, 37.13310, -121.778717, 29.iv.2022, M. Vonshak, Veronica (iNat 115791054); Sonoma Co., Sebastopol, Morelli Ln, 38.430297, -122.95137, 8.ii.2022, K. Toll, Erythranthe guttata (iNat 106618091); OREGON: Lane Co., 44.153482, -122.329189, 27.iii.2021, M. Palmer, Erythranthe?nasuta (guttata complex) (iNat 109961926); 43.942162, -123.892629, 7.v.2022, J. Ward, Claytonia cf. sibirica (iNat 116020762); 43.637107, -122.617126, 13.vii.2022, J. Ward, Claytonia sibirica (iNat 126161890); Lincoln Co., Cape Perpetua Overlook, 44.287479, -124.110256, 25.vi.2022, J. Ward, Claytonia sibirica (larvae observed, but only empty mines in photos) (iNat 123640622); Linn Co., 44.378202, -122.000636, 22.ix.2022, J. Ward, Erythranthe moschata (iNat 136120938); Marion Co., 44.883958, -122.619387, 7.vii.2022, J. Ward, Claytonia sibirica (empty mines) (iNat 125263360); PENNSYLVANIA: Berks Co., Peters Creek Spring, 27.x.2021, C. Smith, Veronica (iNat 100832107, 100832147, 100832157, 100832185); WASHINGTON: King Co., Vashon, 47.390545, -122.489901, 24.iv.2020, H. Parker, Myosotis (iNat 44625412); same but 3.v.2020 (iNat 52704648, 59353928, 59355328); WISCONSIN: Waukesha Co., Eagle Spring and Fen, 42.924285, -88.468514, 24.ix.2014, D. Carter, Erythranthe geyeri (iNat 893113).
Etymology. The new species is named after Erythranthe (monkeyflowers), one of the plant genera commonly inhabited by the larvae.
Description.
Male (n = 11).
Total length 1.9–2.5, 2.2 mm. Wing 1.8–1.9 mm long and 0.45 mm wide.
Coloration. Head, thorax, legs, tergites, sternites II–VIII, and hypopygium dark brown. Wings, halters, and sternite I greyish.
Head. Antenna with 12 flagellomeres, last flagellomere with 8 sensilla chaetica, second to third segments each with 2 sensilla chaetica, groove starts at third segment, AR 0.9. Eyes bare, with wedge-shaped dorsomedial extension. Temporal setae 32 in several rows. Tentorium with bulging apex, 183–194, 189 μm long (Fig. 1a). Clypeus rectangular, 83–96, 89 μm long and 121–154, 138 μm wide, bearing 26 setae, setae 73–88, 81 μm long. Palpal segment lengths (in μm): 72–76, 74; 51; 129–159, 144; 80–95, 88; 141–167, 154. Third palpomere with 3 sensilla clavata.
Thorax (Fig. 1b). Acrostichals 25–30, 27; dorsocentrals 79–109, 94 in multiple rows; prealars 21–24, 22; scutellars 42–44, 43 in three rows; supraalars 2–3. Antepronotal lobes developed, with a gap, 14–16, 15 lateral setae.
Wing (Fig. 1c). Brachiolum with 10 setae. Squama with 18 setae. Sc with 30–33, 32; R with 32–42, 37 and R 1 with 35–43, 39 setae, R 4+5 with 50–54, 52 setae, and M with 25–28, 27 setae, other veins bare. Costa well-extended, extension 77 μm. R 4+5 ends just above M 3+4. Anal lobe not projecting (Fig. 1c).
Legs. Tibia of all legs with long sparse beard; hind and mid femur with keel. Pulvilli very small. Fore tibia spur 62–72, 67 μm long, mid tibia spurs 34–39, 36 and 33–34 μm long, hind tibia spurs 55–65, 60 and 28 μm long, hind tibia comb with around 12 spines. 2 pseudospurs on ta 1 of mid and hind legs. Lengths and proportions of legs as in Table 1.
Hypopygium (Fig. 1d). Tergite IX with around 14 long setae close to the base of anal point. Anal point short, narrowly triangular, apex rounded; anal point 32–46, 39 μm long and 17–23, 20 μm wide. Virga present, consisting of about 8–9 spines, 38–46, 42 μm long. Sternapodeme nearly straight, 124–136, 130 μm long. Phallapodeme 89–95, 92 μm long. Inferior volsella located anteriorly on gonocoxite, slightly bulging, covered in numerous simple setae. Gonostylus 113–121, 117 μm; crista dorsalis a preapical short triangle. Gonocoxite 231–246, 238 μm long. HR 2, HV 2.5–2.9, 2.7.
Female (n = 5).
Total length 2.8–3.1, 3.0 mm. Wing 1.8–1.9 mm long and 0.6 mm wide.
Coloration. Humeral, anepisternal, preepisternum, and posnotum light brown, remainder same as the male.
Head. Antenna with 5 flagellomeres, last flagellomere 60–73, 67 μm long; last flagellomere with 12 sensilla chaetica, 1 st –4 th segments each with 2 sensilla chaetica, AR 0.3 (Fig. 2a). Eyes bare, with short wedge-shaped dorsomedial extension. Temporal setae 43–50, 47 in several rows. Tentorium with bulging apex, 192–198, 195 μm long. Clypeus rectangular, 101–107, 104 μm long and 149–165, 157 μm wide, bearing 30–36, 33 setae, setae 79–100, 81 μm long. Palpal segment lengths (in μm): 61; 36–42, 39; 122–156, 139; 98–118, 108; 135–181, 158. Third palpomere with 1 sensilla clavata.
Thorax. Acrostichals 34–40, 37; dorsocentrals 105–112, 109 in multiple rows; prealars 27–33, 30; scutellars 50– 54, 52 in two rows; supraalars 5.Antepronotal lobes developed, with a gap, 14–17, 15 lateral setae. Humeral pit small.
Wing (Fig. 2b). Brachiolum with 9 setae. Squama with 19–22, 22 setae. R with 40–57, 50; R 1 with 27–40, 34 setae; R 4+5 with 50 setae, and M with 24–25 setae, other veins without setae. Costa well-extended, extension 45 μm. R 4+5 ends just above M 3+4. Anal lobe not projecting
Legs. Hind-fore tibia with long sparse beard, hind and mid femur with keel. Pulvilli very small. Fore tibia spur 37–41, 39 μm long, mid tibia spurs 31–38, 34 and 30 μm long, hind tibia spurs 45–56, 51 and 25–33, 29 μm long, hind tibia comb with around 15 spines. 2 pseudospurs on ta 1 of mid and hind leg. Lengths and proportions of legs as in Table 2.
Genitalia (Figs. 2c–d). Seminal capsules small, semi-circular, spermathecal ducts without loops, with small bulb (Fig. 2c), seminal capsule 67–68 µm long and 54–67, 61 µm wide. Notum 228–271, 249 µm long. Gonapophysis VIII divided into large ventrolateral and smaller dorsomesal lobe (Fig. 2c). Apodeme lobe distinct. Gonocoxite developed with around 24 setae (Fig. 2d). Tergite IX undivided (Fig. 2d). Cercus pediform, 152–156, 154 µm long, and 60 µm wide.
Pupa (n = 8).
Total length 4.5 mm.
Coloration: Head and thorax brown. Abdomen golden.
Cephalothorax. Frontal setae absent, frontal apotome rugose (Fig. 3a). Antennal sheet without pearls or spines above to pedicels. Thorax rugose, horn absent. Wing sheet nearly smooth, 1.1–1.2 mm long and 0.32–0.39, 0.35 mm wide.
Abdomen (Figs. 3b–c). Tergite I with no posterior row of tubercles and no shagreens. Tergite II with no shagreens, a single row of posterior tubercles; tergites III–VIII with a single row of posterior tubercles; tergites III–VI with anterior crescent-shaped shagreens, becoming more prominent towards segment VI; tergites VII–VIII with shagreens more prominent anteriorly, becoming reduced from mid to posterior regions; tergite IX covered in shagreen (Fig. 3b). Sternites I, II, and VIII bare; sternites III–VII with posterior shagreens; sternite IX bare (Fig. 3c). Anal lobe 233–278, 256 µm long and 159–178, 171 µm wide; with two to three extremely short and hairlike macrosetae, 4.3–4.7, 4.5 µm long. Genital sac shorter than anal lobes, 163–167, 165 µm long and 105–122, 113 µm wide.
Larva (n = 4).
Total length 4.4 mm. Head 327–407, 379 μm long, 234–303, 268 μm wide.
Coloration (Fig. 3d). Head capsule ventrally light brown, dorsally dark brown. Occipital margin much darker in contrast to the remainder of the head. Abdomen yellowish green.
Head. Head L/ W 1.3 –1.5, 1.4. Antenna short, 5 segmented; 1 st antennal segment 1.5–2 × as long as wide; ring organ located at basal ¼ of 1 st segment; AR 1.3–1.5, 1.4, blade longer than the flagellum, blade 25–27, 26 μm long, B 2 6 μm long; antennal segments length in μm: 28–32, 8, 3.4–4, 3, 6–6.6 (Fig. 3e). SI divided into 4 branches, SIISIII simple (Fig. 3f). Premandible dark, with 2 basal and 2 inner teeth, 68–76, 72 μm long, brush developed (Fig. 3f). 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. 3g), mandible 137–149, 141 μm long. Mentum dark, with wide bifid median tooth and 4 pairs of lateral teeth, ventromental plate running parallel to the lateral edge of mentum, reaching the base of last lateral tooth; seta submenti just posteriad to mentum aligned with 2 nd lateral teeth (Fig. 3h); mentum 86–98, 93 μm long and 105–142, 120 μm wide, ventromental plate 47–48 μm long and 10 μm wide.
Abdomen. Posterior parapods well-reduced, much wider than long, bearing around 15 simple claws, posterior parapod 62 μm long and 140 μm wide. Procercus almost as long as wide, bearing 5 apical setae, procercus 19–20 μm long and 22–23 μm wide, apical setae 92–105, 98 μm long.
Diagnostic characters. Metriocnemus erythranthei can be separated from other related species by the combination of the following characteristics: Adult male with AR 0.9; temporal setae 32 in several rows; tentorium with bulging apex; anal point short, moderately wide, and triangular, apex slightly rounded; virga consists of about 8–9 spines; inferior volsella located anteriorly and slightly bulging; crista dorsalis of gonostylus preapical, short and triangular. Adult female with AR 0.9; last flagellomere 67 μm long, last flagellomere/2 nd flagellomere 1.2; temporal setae 43–50 in several rows; seminal capsules small, semi-circular, spermathecal ducts without loops, with small bulb; gonapophysis VIII divided into large ventrolateral and dorsomesal lobe; apodeme lobe distinct; gonocoxite well-developed with around 24 setae; cercus pediform. Pupa with frontal setae absent; frontal apotome rugose; tergites I–II with no shagreens; tergites III–VIII with shagreens; tergites II–VIII with a single row of posterior tubercles. Sternites I, VII, and VIII bare; sternites III–VI with posterior shagreens; sternite IX covered in shagreen. Anal lobe with two to three extremely short and hairlike macrosetae; genital sac shorter than anal lobes. Larva with short antenna; basal antennal segment 1.5–2 × as long as wide; AR 1.4, blade longer than the flagellum; SI divided into 4 branches; premandible with 2 basal, 2 inner teeth and brush; mandible apical tooth shorter than combined width of 4 inner teeth; mentum with wide bifid median tooth and 4 pairs of lateral teeth; posterior parapods wellreduced.
Biological notes (Figs. 4–5). Metriocnemus erythranthei mines leaves of at least three different monkeyflower species: Erythranthe glabrata (Kunth) G.L.Nesom in Oklahoma (Fig. 4a), E. guttata (DC.) G.L.Nesom (or E. guttata complex) in British Columbia, Oregon, and California (Fig. 4b), and E. moschata (Douglas ex Lindl.) G.L.Nesom in Oregon and California (Figs. 4c–d). Mines, probably representing this species, have been photographed in Alaska on E. guttata, as well as in Wisconsin on E. geyeri (Torr.) G.L.Nesom. In Oregon, Iowa, and Pennsylvania, M. erythranthei mines leaves of Veronica americana (Raf.) Schwein. ex Benth. and V. anagallis-aquatica L. (Plantaginaceae) (Figs. 4e–g, 5a–b), and in Oregon it has also been found to feed on Mentha aquatica L. and Stachys chamissonis var. cooleyae (A.Heller) G.A.Mulligan & D.B.Munro (Lamiaceae), all of which, like Erythranthe, belong to the order Lamiales. In Oregon, confirmed hosts also include plants in three additional orders— Asterales (Asteraceae: Petasites frigidus (L.) Fr.), Boraginales (Boraginaceae: Myosotis scorpioides L.), and Caryophyllales (Montiaceae: Claytonia sibirica L.). Larvae and mines have also been photographed on Myosotis in Washington and on Claytonia in British Columbia. Leaf-mining chironomids representing this or a similar species have been found on still other plants in the Pacific Northwest; see the final section of this paper for details.
The leaf mines of M. erythranthei are essentially linear throughout, initially narrow and gradually widening, sometimes becoming somewhat irregular or blotchy toward the end. They are mostly full-depth (all of the mesophyll being consumed, leaving only the leaf epidermises intact), with frass in roughly oval pellets that are scattered at random (Figs. 4a, b, d, f). The larvae are able to exit their mines and establish new ones (Figs. 4c, e, g).
In a thorough review of the literature on North American leaf-mining insects (Eiseman 2022), we found no records of any leafminer occurring on Erythranthe in nature. The only published record involving this host genus is that of Oatman (1959), who conducted greenhouse experiments with the polyphagous fly Liriomyza sativae Blanchard, 1938 (Agromyzidae). He observed mining in E. guttata; a few larvae survived to the point of pupating, but no adults emerged. Were Liriomyza mines to occur on Erythranthe in nature, they would be easily recognizable by the characteristic pattern of frass in strips on alternating sides of the channel. The only previously known leafminer of Veronica spp. in North America is another agromyzid, Phytomyza crassiseta Zetterstedt, 1860. The formation of the puparium (as opposed to a naked pupa) within the leaf is the most obvious feature distinguishing mines of P. crassiseta from those of M. erythranthei. Claytonia likewise has a single recorded leafminer, the Caryophyllales generalist Pegomya flavifrons (Walker, 1849) (Anthomyiidae). The persistent white eggshell at the beginning and the distinctly blotchy ultimate shape will distinguish mines of P. flavifrons from those of M. erythranthei. The other confirmed hosts of M. erythranthei are also mined by various agromyzid species, but all of these produce mines that are more or less confined to one leaf surface and differ in shape and frass pattern (Eiseman 2022).
In the three leaf-mining Cricotopus species, pupation occurs within the mine, but when the adult is ready to emerge, the pupa breaks out of the mine and swims to the water surface (Berg 1950). The habits of M. erythranthei are generally similar. On Erythranthe in British Columbia and on Veronica in Iowa, mines have been collected with pupae inside, each surrounded by a gelatinous mass (Figs. 5a–c, e). In collections of larvae from Claytonia and Erythranthe elsewhere, pupation has taken place outside the mines (at least sometimes in a gelatinous mass), but the leaves had more or less deteriorated by this point. Based on our observations of M. erythranthei on Veronica, the pupa remains in the mine until shortly before emergence of the adult. In one instance the pupal exuviae were found protruding from the mine, with only the tip of the abdomen still inside (Fig. 5d). In another, the exuviae were found loosely adhering to plant material several centimeters from the mine and separated from the mine by a span of water. This suggested that the pupa had broken out of the mine and traveled a short distance through the water in the bottom of the rearing container just prior to the adult’s emergence.
In addition to mining leaves of Veronica, M. erythranthei tunnels in the stems of this host. A larva that was observed and photographed feeding in a Veronica stem (Fig. 4h), and then extracted and examined, was identified as M. erythranthei, and a pupa found in a stem (Fig. 5c) was identified as Metriocnemus sp., although the whereabouts of the latter specimen are unknown. We have also found probable M. erythranthei larvae boring in stems of Claytonia.
The location and details of oviposition remain to be determined, and we do not know how the larvae make their way to the leaves if the eggs are not laid there. Based on the narrowness of some of the mines, we believe that M. erythranthei larvae are leafminers throughout their development, like C. elegans, and unlike C. flavipes which has only been found in leaf mines in the last or penultimate instars (Berg 1950). Unlike all of the known leaf-mining Cricotopus species, M. erythranthei larvae are not restricted to feeding in submerged or floating leaves. Although some occupied mines were found in partially or fully submerged Veronica stems and leaves, the larvae collected from Erythranthe moschata were found in leaves 3 dm or so above the water level in the small stream where the plants were growing. It was misty / lightly raining at the time, which may have allowed the larvae to move higher in the plants than they otherwise would have. The larvae from E. guttata were collected in a forested seep and on a coastal bluff at low tide (K. Toll, in litt.). The E. glabrata plants were at the edge of a concrete, artificial stream channel, forming a mat just above the water level (E. LoPresti, in litt.). The mined Erythranthe plants in British Columbia were on a “seepy slope.” Those in Oregon were on a vertical rock face with seasonal water flow, which was covered with a dense bryophyte layer until a severe wildfire in September 2020 covered the area in ash; the monkeyflowers and associated plants, along with M. erythranthei larvae, appeared in March 2021. One Claytonia -mining larva in Oregon was found in a moist, mossy area of mature conifer forest within 20–50m of a creek (J. Ward, in litt.).
This species evidently has multiple generations per year (i.e., multivoltine). D.L. Wagner (in litt.) reared it in California in the 1980s (the location of these specimens is not currently known), and his collections “spanned the field season (March to November)”. Our observations, and those of others documented in online photographs, indicate that larvae are active by late March in British Columbia and Oregon and are present in late April in British Columbia; in early to mid-May in Oregon, Iowa, Pennsylvania, and Oklahoma; in late May / early June in Oregon and California; in early August in Alaska; and in late October / early November in California and Pennsylvania. Photos show fresh-looking mines in July in Alaska and in September in Wisconsin, but with no larvae visible. In Iowa, Veronica leaves containing M. erythranthei pupae in mines were collected in early April, and an adult emerged from one such pupa within 48 hours after being brought indoors; another pupa was collected in midAugust, and again the adult emerged within 48 hours. Additionally, Metriocnemus larvae, probably of this species, were collected in Veronica leaf and stem mines at a nearby site in late January, with pupae formed indoors by midFebruary. Apparently, M. erythranthei at least partially overwinters as larvae; it is also possible that adults emerge and lay eggs sometime between late autumn and early spring.
description: Published as part of 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, pp. 41-68 in Zootaxa 5249 (1) on pages 43-51, DOI: 10.11646/zootaxa.5249.1.3, http://zenodo.org/record/7685232