Isoperla tilasqua : Szczytko & Stewart 2004

Isoperla tilasqua Szczytko & Stewart

(Figs. 2q, 19 a-h, 20 q)

Isoperla tilasqua Szczytko & Stewart 1979, 32:60-61. ♂, ♀, ovum.

Isoperla tilasqua: Szczytko & Stewart 2004, 130(2):236- 237. Larva (reared).

Material examined. TYPES: I. tilasqua Holotype ♂, Oregon: Benton Co., Oak Creek, 13-16/ VI/1968,? collector (NMNH #76346); Paratype ♀, Same as Holotype, 7-10/ VI/1968; Additional Specimens. CALIFORNIA: Siskiyou Co., Sacramento River, Headwater, Mt. Shasta, 29/ V/1967, S.G. Jewett Jr., ♀ (NMNH); OREGON: Benton Co., Oak Creek, Trap 2, 6.5 mi NW Corvallis, 1 mi N Fish Lab 650 feet, 19- 22/ VI/1968, C. Kerst, ♀ (looked more like I. sobria) (NMNH); Clackamas Co., Still Creek, Still Creek Campground, Mt Hood, 10/VI/1955, 17/VI/1967, S.G. Jewett Jr., ♀ (NMNH); Grant Co.,?, Trout Meadows, 5500 feet, 09/VII/1967, J. Baker, ♀ (NMNH); Umatilla Co., Meacham Creek, Upstream (west) of Hwy 84 bridge, 30/V/2008, 22/V/2011, J. Sandberg, Larvae (reared).

Male larva. Body length of mature larva 10–11 mm. Dorsum of head with contrasting pigment pattern and fine dark clothing setae, anterior frontoclypeus margin unpigmented; light M shaped pattern anterior to median ocellus connected to light frontoclypeus area by a median longitudinal light band, its width approximately half the posteromedian portion of the light M shaped pattern, lateral thin arms with nearly parallel margins connected to median light band, directed posterolaterally and extending to antennal bases; posterior ocelli with completely enclosed medium sized light areas along outer lateral margins, extending laterally above epicranial suture in fresh specimens; in older preserved specimens, posterior light brown band becomes faded; interocellar area partially light, an irregular shaped light area connected to posterior head capsule by thin light band; occiput with irregular spinulae band extending from below eye to near median epicranial suture, usually enclosed completely by dark to light brown pigment (Fig. 19a). Lacinia bidentate, total length 978-1012 µm (Figs. 2q, 19e- h, Tables 2-4); submarginal row (A+B) with 4–7 setae, groups A-B interrupted by gap below subapical tooth (SAT) inner margin (Fig. 19g); 2–5 submarginal setae (A) in a close set row beginning at the base of the apical tooth (AT), ending before reaching SAT inner margin, plus 1 thin marginal seta (TMS) adjacent to AT inner margin, sometimes obstructed from view by AT, submarginal setae, or broken, and 1 dorsal seta (DS) located below SAT inner margin, partially obstructed by SAT (Figs. 19 g-h); 1–3 submarginal setae (B) located past SAT inner margin (Fig. 19h); 15–20 marginal setae (C) initially long-stout and widely spaced, last few shorter and closer, blending into and difficult to differentiate from dorsal surface setae (Fig. 19e); 36–62 ventral surface setae (D) scattered below submarginal and marginal setae, ending posteriorly at approximately ¾ the inner lacinia margin length (Fig. 19f); dorsal surface setae (DSS) forming dense, laterally protruding, longitudinal band on and along inner-lateral margin, ending before posterior-most ventral surface setae (Fig. 19f). Galea with 11–19 setae in sparse ventral row, apex with 2–3 setae. Maxillary Palp segments 2–3 with curved, apically rounded setae (Inset, Fig. 19e). Pronotum with large median light area bordered by thick dark comma shaped bands typical of the I. sobria complex, a range of irregular shaped faded light brown areas usually present between the dark commas and fine dark clothing setae distributed evenly except on a few long light rugosites, lateral margins with broad light bands (Fig. 19b). Meso and metanotum with contrasting pigment pattern and fine dark clothing setae (Fig. 19 c). Legs with numerous fine golden clothing setae and scattered erect spines on outer surface of femora, erect spines longest and concentrated along dorsal surfaces; fine silky setae sparse on dorsal surface of femora, numerous and continuous on tibia (Fig. 20q); tibia with faint transverse band near proximal end. Abdominal terga usually with three longitudinal dark stripes; wide light median longitudinal band usually bisected with a median thin faded brown stripe; lateral pair of dark longitudinal stripes about twice as wide as median dark stripe, extending to lateral margins; numerous fine dark clothing setae and erect spines scattered dorsally; posterior margin with scattered long and numerous short spines in a concentrated row (Fig. 19d).

Distribution. Oregon, Washington. Occurrence in California not confirmed.

Diagnosis. Isoperla tilasqua male larvae share the typical comma shaped dark pronotal bands common to the I. sobria complex (Fig. 19b) and have similar numbers of submarginal (A) setae when compared to I. sobria (Table 2). The long, thin apically rounded setae on basal maxillary palpi segments 2–3 (Fig. 19a Inset) are similar to I. baumanni (Fig. 5e Inset). It is distinct from these species by having a partially light interocellar area connected to the posterior margin of head, a continuous light M shaped band above the anterior ocellus, and a relatively thin median longitudinal light band extending from the anterior ocellus to the light frontoclypeus area (Fig. 19a).

Remarks. The Mt. Shasta I. tilasqua female in the NMNH from California may be the first record for the state. The female western Isoperla taxonomy is known, but variations in the length and shape of the subgenital plate are possible. Isoperla sobria females from California and Oregon had elongate subgenital plates with basolateral margins nearly parallel and rounded apical margins. Eight I. tilasqua females reared from Meacham Creek, Umatilla County, Oregon, all had subgenital plates with median invaginations similar to I. gravitans (Fig. 111 in Szczytko & Stewart, 1979), but the lateral margins, similar to I. sobria, were nearly parallel. A reared or recently field collected male will be required to confirm this interesting and possible range extension.