Metriocnemus van der Wulp

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 : 56-57

A key to the known fourth instar larval stages of North American Metriocnemus van der Wulp

1. Mentum with 4 small median teeth and 5 pairs of lateral teeth ( Epler 2001: page 7.86, couplet 2(1’))................................................................................................... M. knabi Coquillett, 1904

- Mentum with bifid or simple median tooth and 4 to 5 pairs of lateral teeth........................................ 2

2. Mentum with simple median tooth and 5 pairs of lateral teeth ( Saether 1989: Figure 12G )...... M. ursinus (Holmgren, 1869)

- Mentum with bifid median tooth and 4 to 5 pairs of lateral teeth................................................ 3

3. Mentum with a wide bifid median tooth and 4 pairs of lateral teeth ( Fig. 3h )...................... M. erthranthei sp. nov.

- Mentum with narrow bifid median tooth and 5 pairs of lateral teeth.............................................. 4

4. Median tooth of the mentum is comparatively small, sitting much lower than lateral teeth............................ 5

- Median tooth of the mentum comparatively well-developed, sitting slightly lower or higher than lateral teeth............ 6

5. Basal antennal segment no longer than wide ( Saether 1989: Figure 12B ). Labral lamella and SI simple ( Saether 1989: Fig. 12D ). Median tooth of mentum sunken ( Epler 2001: page 7.86, couplet 3(2’); Orendt & Bendt 2021: page 119, couplet D7; Saether 1989: Fig. 12H ). Anal tubules long and slender ( Saether 1989: Fig. 12J )..................... M. fuscipes (Meigen, 1818)

- Basal antennal segment longer than wide ( Fig. 7b ). Labral lamella comb-like and SI trifid ( Fig. 5c ). Median tooth of mentum not sunken ( Fig. 7e ). Anal tubules short and wide ( Fig. 7f )......................................... M. sp. “ Oregon ”

6. Antenna 4 segmented ( Cranston & Judd 1987: Fig. 4a ). Basal antennal segment L/W> 4. Median tooth of mentum stands higher than 1 st lateral teeth. Setae submenti aligned with the 3 rd lateral teeth of mentum ( Cranston & Judd 1987: Fig. 4c )............................................................................ M. yaquina Cranston & Judd, 1987

- Not with the above combination of characters............................................................... 7

7. Abdominal segments with long setae, each half as long as the segment bearing it.................... M. sp. A Epler, 2001

- Abdominal segments without long setae................................................................... 8

8. Procercus as wide as long or wider than long.AR 1.7–1.8. Basal antennal segment L/W: 2.3 (Th. Bendt & H.K.M. Moller Pillot, in litt.)................................................................................ M. tristellus agg. *

- Not with the above combination of characters............................................................... 9

9. Median bifid tooth of mentum as high as the 1 st lateral teeth ( Saether, 1989: Fig. 6E ). Basal antennal segment L/ W 2.5 –2.6. Head length 0.44–0.45 mm................................................................. M. brusti Saether, 1989

- Median bifid tooth of mentum clearly lower than 1 st lateral teeth. Basal antennal segment L/ W 1.1 –2.4. Head length 0.13–0.47 mm............................................................................................... 10

10. Basal antennal segment L/ W 1.1. AR 0.67. Mandible with 3 inner teeth ( Epler 2001: page 7.162). Procercus with 4 anal setae.............................................................. M. sp. (= Orthocladiinae genus E, Epler, 2001) **

- Not with the above combination of characters.............................................................. 11

11. AR 1.5–1.8. Head length 0.28-0.31 mm ( Saether, 1989)............................... M. albolineatus (Meigen, 1818)

- AR 2.0–2.2. Head length 0.39–0.47 ( Saether, 1989)................................ M. eurynotus (Holmgren, 1883) ***

Figures

FIGURE 3. Metriocnemus erythranthei sp. nov., pupa (a–c), larval (d–h). a. frontal apotome; b. abdominal tergites; c. abdominal sternites; d. habitus; e. antenna; f. labrum and premandible; g. mandible; h. mentum.

FIGURE 4. Metriocnemus erythranthei sp. nov., larvae and leaf mines on Erythranthe spp. (a–d), larvae and mines on Veronica sp. (e–h). a. on E. glabrata; b. on E. guttata; c. on E. moschata (larva establishing new mine); d. on E. moschata; e. larva in newly established leaf mine; f. larva mining leaf; g. larvae in new leaf mines; h. larva in stem mine, with mining in the adjacent petiole.

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 6. Metriocnemus eurynotus associated with Impatiens sp. cotyledons. a. cotyledon with mine containing two larvae; b–f. larvae in mines; g. two larvae in mine; h. three larvae in mine; i. two larvae interacting; j. older larvae feeding externally; k. pupa on cotyledon surface; l. reared adult female.

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.

FIGURE 12. Secondary inhabitants in leaf mines of Metriocnemus erythranthei on Veronica sp. a., larva of M. eurynotus (upper left) and two larvae of M. erythranthei (center and upper right); b., larva of Limnophyes sp. (prob. L. viribus) (lower left) in vacated mine.