Isoperla evanescens Verdone & Kondratieff, 2016

Verdone, Chris J. & Kondratieff, Boris, 2016, A New Species Of Isoperla Banks (Plecoptera: Perlodidae) From The Appalachian Mountains, Virginia & West Virginia, U. S. A., Illiesia 12 (13), pp. 74-85 : 76-83

Isoperla evanescens Verdone & Kondratieff , sp. n.

Vanishing Stripetail

( Figs. 1-19 )

http://lsid.speciesfile.org/urn:lsid: Plecoptera .speciesfile.org: TaxonName:494849

Material Examined. USA - Holotype ♂, Virginia: Bland Co., Wolf Creek, Grapefield Rd., Co. Rd. 614, Stephen Levitt Property , N 37.14702, W 81.26314, 8 June 2016, C. Verdone, B. Kondratieff ( USNM). Paratypes: same data as holotype, ♀ ( USNM); same data as holotype, 4♂, 5♀ ( CSUC); same location, 4 June 2016, C. Verdone, B. Kondratieff, 5♀ ( CSUC); same location, 6 June 2016, C. Verdone, B. Kondratieff, ♂, 2♀ ( CSUC); Wolf Creek, Grapefield Rd. , Co. Rd. 614, USFS Wolf Creek Picnic Area , N 37.18026, W 81.19496, 8 June 2016, C. Verdone, B. Kondratieff, 2♂, 1♀ ( CSUC); same location, 12 June 2016, C. Verdone, B. Kondratieff, ♂, 2♀ ( CSUC); Craig Co., Potts Creek, Hwy 18, Steel Bridge Campground , N 37.59800, W 80.22704, 10 June 2016, C. Verdone, B. Kondratieff, ♂, ♀ ( CSUC); Giles Co., Sinking Creek, Hwy 42, Newport Community Park , N 37.30289, W 80.48522, 10 June 2016, C. Verdone, B. Kondratieff, ♀ ( CSUC). Additional Material: Virginia: Giles Co., Sinking Creek , Rt. 42, Newport Park , N 37.30289, W 80.48522, 21 May 1979, J. Marshall, 2♀ ( CSUC); Grayson Co., New River, Rt. 94 bridge, 3 mi. W of Galax, N 36.64633, W 80.97790, 18 May 1994, B. Kondratieff, F. Kirchner, 2♂, 6♀ ( CSUC); Montgomery Co., Mill Creek, Rt. 785 , N 37.26135, W 80.34054, 1 June 1978, B. Kondratieff, ♀ ( CSUC); same location, 15 April 1980, (emerged 27 April 1980), B. Kondratieff, ♂ ( CSUC); Tom’ s Creek, Rt. 655, N 37.238054, W 80.47339, 11 April 1978, (emerged 11 May 1978), B. Kondratieff, 4♀ ( CSUC); same location, 2 May 1978, (emerged 8 May 1978), B. Kondratieff, ♀ ( CSUC); same location, 2 May 1978, (emerged 12 May 1978), B. Kondratieff, 2♀ ( CSUC); same location, 11 May 1978, B. Kondratieff, ♀ ( CSUC); same location, 28 May 1978, B. Kondratieff, ♂ ( CSUC); same location, 17 May 1979, C. Parker, ♀ ( CSUC); same location, 17 May 1979, Wills, ♀ ( CSUC); same location, 7 May 1981, B. Kondratieff, 2N ( CSUC); same location, 18 May 1979, B. Kondratieff, ♂ ( CSUC); Smyth Co., North Fork Holston River , Rt. 620 , N 36.94099, W 81.44901, 8 May 1982, B. Kondratieff, 7♂, 3♀ ( CSUC); same location, 1 May 1983, B. Kondratieff, 3♂, 2♀, 2N ( CSUC); same location, 11 May 1986, B. Kondratieff, 2♂, 1♀ ( CSUC); Saltville , N 36.88150, W 81.76206, 27 May 1980, R. H. Zimmerman, ♀ ( CSUC); Russell Co., Carr Creek, Co. Rd. 613, Jct. US 58, Bolton , N 36.80438, W 82.19706, 21 May 1993, B. Kondratieff, F. Kirchner, ♂ ( CSUC); Tazewell Co., Little River, at Claypool Hill , N 37.03647, W 81.79749, 21 May 1993, B. Kondratieff, F. Kirchner, ♀ ( CSUC); West Virginia: Summer Co., Indian Creek, Rt. 33, N 37.53020, W 80.80283, 10 May 1982, Burkhardt, 3♂, 7♀ ( CSUC) .

Distribution. USA – VA, WV ( Fig. 21 )

Etymology. The name evanescens is derived from the Latin root word evani meaning “disappearing” or “vanishing” and the Latin adjectival suffix escens meaning “becoming,” or “beginning to” and refers to the seemingly vanishing pigmentation on the proximal portions of the wing veins, head and pronotum of the adult.

Male. Macropterous; forewing length 9.0 - 10.0 mm (N=5). Body length 7.5 - 8.0 mm (N=5). Head and pronotum pale yellow. General body color pale yellow to light brown with light brown markings dorsally ( Fig. 1 ). Dorsum of head unmarked except for dark pigmented ocelli ( Fig. 2 ). Antennal scape pale yellow; flagellum progressively darkened toward apex. Pronotum unmarked; rugosities irregular, raised, pale yellow ( Fig. 2 ). Femora pale yellow on proximal half, light brown on distal half, darkest on dorsal edge, covered with uniformly spaced, short, brown setae ( Fig. 2 ). Tibia yellow to light brown, darkest on proximal dorsal edge, covered with uniformly spaced short, brown setae. Tarsi medium brown. Meso- and metanota mostly pale yellow, light brown on posterior margins. Wings pale; veins pale on proximal half, light brown on distal half. Terga pale yellow, posterior ⅓ light brown, darkest medially, sometimes forming a stripe; terga 1-8 with uniformly spaced brown setae. Posterior ⅓ of tergum 9 with moderately developed patch of sensilla basiconica ( Fig. 3 ). Tergum 10 with a medial, posteriorly directed, pale, spade-shaped marking. Paraprocts short, broadly triangular, slightly incurved ( Figs. 3 , 7 ), scattered setae and sensilla basiconica scattered over dorsal surface, absent on apex; moderately sclerotized on outer margin; tips bluntly pointed and recurved ( Figs. 3 , 7 , 9 ). Cerci pale yellow; terminal segments light brown; cercal segments with a single, long, stout, ventral hair at posterior margins. Sterna pale yellow; sternum 8 with a light brown recessed vesicle, 1.4X as long as wide; evenly rounded and expanded posteriorly, extending to the posterior margin of sternum 8 ( Fig. 4 ). Aedeagus with a stout basal stalk, and ridge of short posteromedial spines. Basal stalk completely encircled by dense golden setae ( Figs. 5-7 ); posteromedial area with a small, thin sclerite bearing ca. 10 short spines that are acutely rounded apically; posterior half of sclerite bearing stout setae ( Figs. 7-8 ); area posterodorsal to basal band with small spinulae; areas posterodorsal and anterodorsal to spine bearing sclerite surrounded by scallop-shaped spine plates ( Fig. 8 ).

Female. Macropterous; forewing wing length 9.5 - 10.5 mm (N=5). Body length 8.6 - 9.2 mm (N=5). Body coloration and morphology similar to male. Sternum 8 with a light brown, broadly triangular, subgenital plate extending approximately ⅔ over sternum 9 ( Fig. 10 ). Sternum 10 with a pair of light brown spots on the posterolateral margins.

Ovum. General shape oblong ( Fig. 11 ); cross section concave ( Fig. 12 ); collar absent; eclosion line absent ( Figs. 11, 12 ). Color light brown. Length 312 - 333 μm, width 248 - 250 μm (N=2). Chorion covered with reticulate, raised, thickened ridges, some not connected; fine punctations present between reticulations ( Fig. 13 ). Micropyles positioned singularly on top of ridges near anterior third of egg body; openings usually expanded, doughnut shaped ( Fig. 14 ).

Male nymph. Body length 6.9 - 7.5 mm, (N=2). Preserved specimen yellow brown with brown markings ( Fig. 15 ). Dorsum of head with a contrasting pigment pattern ( Fig. 16 ); anterior of frontoclypeus unpigmented; anterolateral dark spots near frontoclypeal pale area ( Fig. 16 ); small enclosed pale spot anterior to median ocellus; small, pale, oval interocellar spot anterior to epicranial suture, narrowly open along epicranial Y-stem; interrupting pale spots present on distal edge of lateral ocelli, open along epicranial suture ( Fig. 16 ). Pronotum with dark irregular ring on either side of wide median pale area; a single pale spot within each ring; lateral margins of pronotum pale ( Fig. 15 ). Abdomen with three longitudinal stripes, two wider lateral, one narrow median, each segment with eight dark spots in an anterior transverse row ( Fig. 17 ). Lacinia unidentate ( Fig. 18 ); lacinia tapering evenly from apical tooth and bearing stout marginal setae to near base; medial submarginal setae arranged in a close set row below apical tooth ( Fig. 18A ), no setae on outer surface of apical tooth as in other species of the group; submarginal setae continuous to near base; gaps between setae increase towards base; apical tooth approximately ⅕ as long as palm length. Mandible with 6 teeth and a deep cleft between apical and subapical teeth; most noticeable on dorsum ( Fig. 19 ); dorsal apical tooth flattened, broadly rounded; interior edge serrated, ventral apical tooth acutely rounded ( Fig. 19A ).

Diagnosis. Isoperla evanescens is placed in the I. irregularis group and is the only member of the group currently known to occur east of the Appalachian Plateau Physiographic Province (Woodward & Hoffmann 1991). Isoperla evanescens is superficially similar to I. decepta in general habitus, which also lacks all dark markings on the head, (fig. 12.1, Szczytko & Kondratieff 2015). However, males of the two species are separable by the shape of the paraprocts, vesicle, details of the aedeagus, and pronotal rugosity pigmentation. The paraprocts of I. evanescens are broadly triangular and extend only slightly over the posterior margin of tergum 10 ( Figs. 3 , 7 ); the vesicle is expanded posteriorly ( Fig. 4 ); the posteromedial sclerotized structure of the aedeagus is composed of a thin sclerite bearing setae and ca. 10 short spines ( Fig. 8 ); additionally, I. evanescens lacks dark pigmentation on the pronotum ( Fig. 2 ). Whereas, in males of I. decepta , the paraprocts are elongate and extend ¼ to ½ over tergum 10 (fig. 12.3, Szczytko & Kondratieff 2015); the vesicle is not expanded posteriorly (fig. 12.2, Szczytko & Kondratieff 2015); the posteromedial sclerite of the aedeagus is a lobed structure that is deflected ventrally and is scattered with concentrations of stout sharp spinulae (figs. 12.6, 12.10, 2.11, Szczytko & Kondratieff 2015). Additionally, I. decepta has medium to pale brown rugosities on the pronotum (fig. 12.1, Szczytko & Kondratieff 2015).

Females of I. evanescens can be separated by the unique combination of a pale yellow head in life, whitish in ethanol preserved specimens, pronotum without dark markings, and a broadly triangular subgenital plate ( Fig. 10 ). Whereas, females of I. decepta have medium to pale brown rugosities on the pronotum and the subgenital plate is broadly rounded (fig. 12.4, Szczytko & Kondratieff 2015). Ova of the two species can be separated on the basis of cross sectional shape and the presence of reticulate ridges. The ovum of I. evanescens has a concave cross section and possesses reticulate, raised, thickened ridges ( Figs. 11-14 ). Whereas, the ovum of I. decepta is circular in cross section and lacks reticulate ridges (figs. 12.18, 12.19 Szczytko & Kondratieff 2015). The ovum of I. evanescens is most similar to I. nana (Walsh, 1862) , but can be separated by the presence of inter-reticulate punctations ( Fig. 13 ), which I. nana lacks (figs. 35.13-35.15, Szczytko & Kondratieff 2015).

Several specimens of I. evanescens that are deposited in the C.P. Gillette Museum of Arthropod Diversity had previously been identified as I. dicala Frison, 1942 , which is regionally common and is often sympatric with I. evanescens . Recently collected material of I. evanescens with everted aedeagus has allowed the separation of these two species, which can be confused by the lack of usually dark dorsal head pigmentation. Males of these species without the aedeagus everted can also be separated by the differences in pronotal pigmentation and details of the vesicle. Isoperla dicala has dark pronotal pigmentation and a vesicle that is 3X as long as wide (figs. 14.1, 14.2, Szczytko & Kondratieff 2015). Whereas, I. evanescens lacks pronotal pigmentation and the vesicle is 1.4X as long as wide. Females can be separated by the differences in the pronotal pigmentation and details of the subgenital plate. The subgenital plate of I. dicala usually possesses a medial nipple (fig. 14.5, Szczytko & Kondratieff 2015), whereas I. evanescence lacks it. Eggs of the two species are not similar and can be easily separated by the presence or absence of a collar;

I. dicala possesses a collar (fig. 14.13, Szczytko & Kondratieff 2015), whereas I. evanescens lacks one.

Figures

Fig. 1. Dorsal habitus, holotype male, Isoperla evanescens sp. n., Virginia, Bland Co., Wolf Creek.

Figs. 2-4. Isoperla evanescens, sp. n., holotype male. Virginia, Bland Co., Wolf Creek. 2. Head and pronotum, dorsal. 3. Abdomen and paraprocts, dorsal. 4. Abdomen and vesicle, ventral.

Figs. 5-8. Isoperla evanescens, sp. n., Virginia, Bland Co., Wolf Creek. 5. Aedeagus, lateral: A. anterodorsal lobe, B. dorsal lobe, C. posterodorsal lobe, D. paired posterolateral lobes, E. posteroventral lobe, F. basal setal band. 6. Aedeagus, posterior. 7. Paraproct, posterior. 8. Posteromedial sclerotized structure of aedeagus with ca. 10 short spines and scallop shaped setae, posterolateral, Isoperla evanescens sp. n., Virginia, Russell Co., Carr Creek.

Fig. 9. Male paraproct apex, lateral, Isoperla evanescens sp. n. Virginia, Bland Co., Wolf Creek.

Fig. 10. Female subgenital plate, ventral, Isoperla evanescens sp. n. Virginia, Bland Co., Wolf Creek

Figs. 11-14. Isoperla evanescens sp. n. Virginia, Bland Co., Wolf Creek. 11. Ovum. 12. Ovum, showing concave section. 13. Detail of ovum reticulations and punctuations. 14. Detail of ovum chorion and micropyles.

Fig. 15. Nymphal dorsal habitus, Isoperla evanescens sp. n., Virginia, Smyth Co., North Fork Holston River.

Figs. 16-19. Isoperla evanescens sp. n. Virginia, Smyth Co., North Fork Holston River. 16. Nymphal head, dorsal. 17. Nymphal abdomen, dorsal. 18. Nymphal left lacinia, dorsal: A. submarginal setae. 19. Nymphal left mandible, dorsal: A. dorsal apical tooth and ventral apical tooth.

Fig. 21. Distribution of Isoperla evanescens sp. n. in Virginia and West Virginia.