Isoperla bifurcata Szczytko & Stewart

Sandberg, John B., 2011, The Isoperla Of California (Plecoptera: Perlodidae); Larval Descriptions And A Key To 17 Western Nearctic Species, Illiesia 7 (22), pp. 202-258 : 219-222

Isoperla bifurcata Szczytko & Stewart

( Figs. 2d , 6 a-h, 20 d)

Isoperla bifurcata Szczytko & Stewart 1979 , 32:80-84, 86.

Isoperla bifurcata: Bottorff et al. 1990 , 92:299-302. Larva (reared).

Isoperla baumanni Szczytko & Stewart 2002 , 128:2-3. Larva (not reared) = I. bifurcata .

Material examined. TYPES: I. bifurcata , Holotype ♂, OR: Union Co., ~ 6 mi (9.7 km) E Medical Springs, DFTM Proj., Lick Creek, 23/VII/1975, D. Dunster ( NMNH #76343 ) ; Allotype ♀, same location and collector, 30/VI/1976 ( NMNH); Paratype ♂ ♀, same location and collector as Holotype, 23/VII/1975 ( NMNH). Additional Specimens. CALIFORNIA: Butte Co., Butte Creek, Butte Meadows Campground, Humbug Rd., Butte Meadows, 30/III/2007, J. Sandberg, Larvae; Butte Creek, Cherry Hill Campground, Humbug Rd., 9 mi (14.5 km) NE Lomo (Hwy 32), 18/II/2007, J. Sandberg, D. Pickard, Larvae. El Dorado Co., NF Cosumnes River, Headwaters below Singleton Springs, E Grizzly Flat, 22/VI/1987, R. Bottorff, Larvae ( NMNH); NF Cosumnes River, Headwaters below Singleton Springs, E Grizzly Flat, 22/VI/1987, R. Bottorff, Larvae ( CAS). Fresno Co., Huntington Lake, 07/VII/1919, F. Blasdell, ♂ ( NMNH). Plumas Co., Domingo Spring, Domingo Springs Campground, 8.5 mi (13.7 km) NW Chester on Old Red Bluff Rd., 12/VIII/2006, J. Sandberg, J. Slusark, Larvae; 01/X/2006, J. Sandberg, ♂ ♀, Larvae (mature and early instar); 10/XII/2006, Larvae; 20/I/2007, Larvae; 04/II/2007, Larvae; 24/III/2007, Larvae; 22/IV/2007, Larvae (reared); 06/V/2007, J. Sandberg, D. Pickard, Larvae; 19/V/2007, J. Sandberg, S. Hassur, Larvae (reared); 28/V/2007, J. Sandberg, D. Pickard, Larvae (reared); 09/VI/2007, J. Sandberg, A. Richards, ♂, Larvae (reared), Exuviae; 13/VI/2007, J. Sandberg, ♂ ♀, Larvae (reared); 17/VI/2007, ♂ ♀; 07/VII/2007, ♂ ♀; 01/VIII/2007, ♀, Larvae; 16/IX/2007, ♂ ♀, Larvae; 21/IX/2007, ♂ ♀, Larvae; 30/IX/2007, ♀; 03/XI/2007, ♂ ♀, Larvae; 20/V/2008, J. Sandberg, D. Pickard, Larvae; 17/V/2008, Larvae; 13/VI/2008, ♂ ♀; 20& 22/VI/2008, ♂ ♀; 06/IX/2008, ♂ - ♀; 05/VI/2010, Larvae (reared); 03/VII/2010, ♂; Mosquito Creek (East Branch), 0.6 mi (1 km) E of Domingo Springs, 7.9 mi (12.7 km) W of Chester, 04/II/2007, J. Sandberg, Larvae; 01/IV/2007, Larvae; Mosquito Creek (West Branch), 0.4 mi (0.6 km) E of Domingo Springs, 8.1 mi (13.0 km) W of Chester, 04/II/2007, J. Sandberg, Larvae; 24/III/2007, Larvae; 22/IV/2007, J. Sandberg, D. Pickard, Larvae (reared); 19/V/2007, J. Sandberg, S. Hassur, Larvae (reared); 28/V/2007, J. Sandberg, D. Pickard, ♂, Larvae (reared); 13/VI/2007, J. Sandberg, ♂ ♀, Larvae (reared); 01/VIII/2007, Larvae; 11/VIII/2007, Larvae; 16/IX/2007, Larvae; 21/IX/2007, Larvae; 03/XI/2007, Larvae; 17/V/2008, Larvae; 13/VI/2008, Larvae (reared); 20/VI/2008, ♂ ♀, Larvae (reared); 05/VI/2010, Larvae; 03/VII/2010, ♂ ♀. Siskiyou Co., Big Springs Creek, Big Springs Park, Nixon Rd., Mt. Shasta, 13/V/2007, J. Sandberg, D. Pickard, Larvae. Tehama Co., Spring Trib of Gurnsey Creek, Gurnsey Creek Campground, Hwy 36, 2.3 mi (3.7 km) N Hwy 32 Intersec., 26/IV/2010, R. Baumann, B. Kondratieff, A. Richards, J. Sandberg, J. Slusark, Larvae (reared). Trinity Co.,?, Carrville,?/ VI/1913, E.C. VanDyke, ♂ ♀ ( CAS). Tulare Co., Marble Fork Kaweah River, Sequoia Nat. Pk., 24/VII/1907, J. Bradley, ♂ ( NMNH). OREGON: Union Co., Lick Creek, about 6 mi (9.6 km) E Medical Springs, 30/VI/1976, D. Dunster, ♀ ( NMNH).

Male larva. Body length of mature larva 9–11 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 broad median longitudinal light band, lateral thin arms directed posterolaterally, and extending to antennal bases; posterior ocelli with completely enclosed small light areas along outer lateral margins; interocellar area partially light and variable, from completely enclosed by dark pigment to open posteriorly and connected to light area below occipital spinulae band; occiput with irregular spinulae band extending from below eye to near median epicranial suture, enclosed by dark and light brown pigment ( Fig. 6a ). Lacinia bidentate, total length 666–967 µm ( Figs. 2d , 6e- h , Tables 2-4 ); submarginal row (A+B) with 2–4 setae, groups A-B interrupted by gap below subapical tooth (SAT) inner margin ( Figs. 6 g-h); 1–2 submarginal setae (A) the first inserted at base of apical tooth (AT) inner margin, the second when present, located between SAT and AT inner margins, plus 1 thin marginal seta (TMS) adjacent to AT inner margin, sometimes obstructed from view by AT, submarginal setae (A), or broken, and 1 dorsal seta (DS) located below SAT inner margin, partially obstructed by SAT or submarginal setae (B) ( Figs. 6 g-h); 1–2 submarginal setae (B) located past SAT inner margin ( Figs. 6 g-h); 8–11 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. 6e ); 17–38 ventral surface setae (D) scattered below submarginal and marginal setae ending posteriorly at approximately ¾ the inner lacinia margin length ( Fig. 6f ); dorsal surface setae (DSS) forming dense, laterally protruding, longitudinal band on and along inner-lateral margin, ending before posterior-most ventral surface seta ( Fig. 6f ). Galea with 37–50 setae in thick ventral band, apex with 4–6 setae. Maxillary Palp segments 2–3 with curved, apically pointed setae. Pronotum generally light brown, median light area bordered laterally by dark brown pigment and light rugosites; discs each with thin, dark brown comma shaped areas near lateral margins and fine dark clothing setae, lateral margins with broad light bands ( Fig. 6b ). Meso and metanotum with contrasting pigment pattern and fine dark clothing setae ( Fig. 6c ). Legs with numerous fine dark 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 but not continuous on tibia ( Fig. 20d ); tibia with very faint transverse bands near proximal end. Abdominal terga with two distinct longitudinal dark stripes; wide light median longitudinal band occasionally appears bisected by muscle attachment scars; lateral pair of dark longitudinal stripes usually not 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. 6d ).

Distribution. Northern California (Sierra Nevada high elevation springs and creeks), Idaho, and Oregon.

Diagnosis. Male larvae of I. bifurcata are most similar to I. acula and can be separated by having fine silky setae sparse on dorsal surface of femora, numerous but not continuous on tibia ( Fig. 20d ), and abdomen without a distinct median dark stripe ( Fig. 6d ).

Remarks. This species was the lone Isoperla species or occurred with either I. baumanni or I. sobria in small to large, mid-elevation spring creeks in the Sierra Nevada range of California. Emergence was extended at Domingo and Mosquito Springs, Plumas County, and occurred in May–October. An extended summer-fall emergence was also observed for I. laucki .

Figures

Figs. 2a-q. Isoperla lacinia habitus, 40x, Bar = 500µm. 2a. I. acula; 2b. I. adunca; 2c. I. baumanni; 2d. I. bifurcata; 2e. I. denningi; 2f. I. fulva; 2g. I. laucki; 2h. I. marmorata; 2i. I. miwok; 2j. I. mormona; 2k. I. muir; 2L. I. pinta; 2m. I. quinquepunctata; 2n. I. roguensis; 2o. I. sobria; 2p. I. sordida; 2q. I. tilasqua.

Figs. 6a-h. Isoperla bifurcata nymph and ventral maxilla, Mosquito Spring, Plumas County, CA. Submarginal setae groups A and B, Marginal setae C, Ventral surface setae D, Dorsal surface setae DSS, Dorsal seta DS, and Thin marginal seta TMS. White bars = 1 mm, 6e-f 100x, 6g 200x, and 6h 400x.

Figs. 20a-q. Isoperla front right leg habitus, Larvae, 32–40x, Bar = 1mm. 20a. I. acula; 20b. I. adunca; 20c. I. baumanni; 20d. I. bifurcata; 20e. I. denningi; 20f. I. fulva; 20g. I. laucki; 20h. I. marmorata; 20i. I. miwok; 20j. I. mormona; 20k. I. muir; 20L. I. pinta; 20m. I. quinquepunctata; 20n. I. roguensis; 20o. I. sobria; 20p. I. sordida; 20q. I. tilasqua.