Isoperla denningi Jewett, 1955

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 : 222-224

Isoperla denningi Jewett

( Figs. 2e , 7 a-h, 20 e)

Isoperla denningi Jewett 1955, 13: 150.

Isoperla denningi: Szczytko & Stewart 1979 , 32:86-88.

Isoperla denningi: Szczytko & Stewart 2002 , 128:6-7. Larva (not reared).

Material examined. TYPE: I. denningi , Holotype ♂ , CA: Los Angeles Co., Monroe Canyon ?, 4 mi W Tanbark Flats, 21/IV/1950 , H.L. Hanson ( CAS #8583 ). Paratype ♀, same location as Holotype, 21/IV/1950 , H.L. Hanson ( CAS). Additional Specimens. CALIFORNIA: Los Angeles Co., Arroyo Sequit , Mulholland Dr., 1.5 mi (2.4 km) N Hwy 101, S of Solromar, 29/IV/2002 , Larvae (ABL); Elizabeth Canyon Creek , Lake Hughes Rd., ~ 10 mi (16.1 km) E I-5, 1/ V/2002, Larvae (ABL); ~ 0.6 mi (1.0 km) below Prospect Canyon , Winter 2003, Larvae, (ABL); Encinal Canyon Creek, ~ 0.5 mi (0.8 km) above mouth , T1 , 4/ VI/2008, Larvae (ABL); Little Rock Creek , Forest Service Route 5N04, ~ 0.4 mi (0.6 km) below Kitter Canyon Creek , R1 , 15/ V/2008, Larvae (ABL), San Diego Co., Boulder Creek , Boulder Creek Rd., 13.9 mi (22.4 km) N Descanso, 01/ V/2007, J. Sandberg, Larvae; Cañada Verde, Hwy 79 at Pacific Crest Trail, 1.1 mi (1.8 km) S Warner Springs, 10/V/2010, 15/VI/2010 , Larvae (ABL); Carney Canyon Creek , Pamo Valley, 7.5 mi (12.1 km) N Ramona, 12/ V/2010, Larvae (ABL); Cedar Creek , ~ 1.5 mi (2.4 km) above San Diego River, 12/ V/2009, Larvae (ABL); Cold Stream , Hwy 79, 9.9 mi (15.9 km) N Hwy 8, near intersection with Pipeline Fire Rd., 03/ V/2007, J. Sandberg, Larvae; Conejos Creek , at El Capitan Reservoir, 14/IV/2008 , Larvae (ABL); Cottonwood Creek , Downstream of Old Hwy 80 crossing, 04/ V/2007, Larvae (ABL); De Luz Creek , De Luz Murrieta Rd., 2.9 mi (4.7 km) NE De Luz, 16- 17/IV/2010 , J. Sandberg, D. Pickard, Larvae (reared 1 male); Fry Creek , New Fry Creek Campground W side of Canfield Rd., 2.9 mi (4.7 km) N Cty Hwy S 7 (6), 06/ V/2008, J. Sandberg, D. Pickard, Larvae; Japacha Creek , above Hwy 79 crossing, 3.7 mi (5.9 km) S Paso Picacho Campground, 7.9 mi (12.7 km) N Hwy 8, 08/ VI/2010, Larvae (ABL); Pine Creek , Pine Creek Road, 3.9 mi (6.3 km) N Pine Valley off Old Hwy 80, 02/ V/2007, J. Sandberg, Larvae; Pine Valley Creek , ~ 1.6 mi (2.6 km) above Hwy 8, 01/VII/2006 , Larvae (ABL); Pine Valley Creek , ~ 2.3 mi above Secret Canyon Creek, 05/ V/2009, Larvae (ABL); Pine Valley Creek , Below Nobel Canyon Creek, 05/ V/2009, Larvae (ABL); Roblar Creek , 0.36 mi (0.6 km) E Camp De Luz Rd. crossing, Camp Pendleton USMC, 18/IV/2008 , J. Sandberg, Larvae (not reared); San Luis Rey River WF, 1 mi (1.6 km) N Mendenhall Valley , R1 , 28/IV/2009 , Larvae (ABL); San Mateo Creek , San Mateo Canyon , Tenaja Trail crossing at Tenaja Truck Trail & Los Alamos Rd., 05/V/2008, 16/IV/2010 , J. Sandberg, D. Pickard, Larvae (rearing failed); Santa Ysabel Creek , at Hwy 79, 24/IV/2008 , Larvae (ABL); Santa Ysabel Creek , Below Clevenger Canyon Creek, 29/IV/2009 , Larvae (ABL); Stone Creek , 0.41 mi (0.7 km) upstream from S. Stagecoach Lane crossing, 06/ V/2008, J. Sandberg, D. Pickard, Larvae (reared); Sweetwater River , Wildwood Glen Lane bridge, 0.1 mi (0.2 km) W Hwy 79 near Los Terrentos, 04/ V/2007, J. Sandberg, Larvae; Temescal Creek , Pamo Road, 8 mi (12.9 km) N Ramona, N33.17601, W116.85052, 13/ VI/2010, Larvae (ABL); Troy Canyon Creek , near Troy Flat off Kitchen Creek Rd., 3.6 mi (5.8 km) S Sunrise Hwy, 02/ V/2007, J. Sandberg, Larvae; Santa Barbara Co., Jalama Creek , Jalama Rd at railroad crossing, 2.5 mi W of Jalama Ranch, 06/ V/2008, Larvae (ABL); La Brea Creek , FR 10N06 crossing, 3.6 mi (5.8 km) E Hwy 176 intersection,, Larvae (ABL); Ventura Co., Cold Creek , Cold Creek Middle , Duplicate, 03/ V/2010, Larvae (ABL) .

Male larva. Body length of mature larva 11–12 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 usually not connected to light frontoclypeus area, median longitudinal light band thin with parallel margins, lateral thin arms directed posterolaterally, extending to antennal bases; posterior ocelli with completely enclosed small light areas along outer lateral margins; interocellar area variable, usually its entire area lighter than surrounding dark pigment, partially filled with indistinct light brown pigment, extending past posterior ocelli and connected to light area below occipital spinulae band, occasionally interocellar area partially filled with surrounding dark pigment and not connected to light area of posterior head capsule; occiput with irregular spinulae band extending from below eye to near median epicranial suture, partially enclosed by light brown pigment ( Fig. 7a ). Lacinia bidentate, total length 756–1093 µm ( Figs. 2e , 7e- h , Tables 2-4 ); submarginal row (A+B) with 3–4 setae, groups A-B interrupted by gap below subapical tooth (SAT) inner margin ( Fig. 7g ); 1 submarginal seta (A) inserted at base of apical tooth (AT) inner margin, plus 1 thin marginal seta (TMS) adjacent to AT inner margin, sometimes obstructed from view by AT, submarginal seta (A) or broken, and 1 dorsal seta (DS) located below SAT inner margin, partially obstructed by SAT or submarginal setae (B) ( Figs. 7 gh); 2–3 submarginal setae (B) located past SAT inner margin ( Figs. 7 g-h); 9–13 marginal setae (C) initially long-stout and widely spaced, last few shorter and widely spaced, sometimes borne from ventral or dorsal surface or broken with visible sockets ( Fig. 7e ); 11–34 ventral surface setae (D) scattered below submarginal and marginal setae, ending posteriorly at approximately ¾ the inner lacinia margin length and concentrated in apical half, occasionally a few setae located below submarginal row striated ( Fig. 7f ); dorsal surface setae (DSS) usually absent, sometimes last few marginal setae (C) form a short dorsal row ( Fig. 7f – arrow). 15–25 minute scale-like spinulae on and along dorsal inner-lateral margin in basal half. Galea with 35–48 setae in thick ventral band, apex with 4–5 setae. Maxillary Palp segments 2–3 with curved, apically pointed setae. Pronotum with thin, median light area bordered by irregular dark longitudinal bands with adjacent light rugosites; discs each with dark comma shaped lateral areas and fine dark clothing setae restricted to areas of dark pigmentation, lateral margins with broad light bands ( Fig. 7b ). Meso and metanotum with contrasting pigment pattern and fine dark clothing setae ( Fig. 7c ). Legs with numerous fine golden clothing setae and scattered erect spines on outer surface of femora, erect spines longest and concentrated on dorsal surface; fine silky setae numerous and continuous on dorsal surfaces of femora and tibia ( Fig. 20e ); tibia with faint transverse bands near proximal end. Abdominal terga with two distinct longitudinal dark stripes; wide light median longitudinal band bisected with indistinct light brown median pigment band; lateral pair of dark longitudinal stripes not extending to lateral margins; numerous fine light clothing setae and erect spines scattered dorsally; posterior margin with scattered long and numerous short spines in a concentrated row ( Fig. 7d ).

Distribution. Isoperla denningi is the common Isoperla species distributed throughout southern California. Previous northern California records from Fresno, Placer, Tuolumne, Tehama and Trinity counties ( Szczytko & Stewart 1979, 2002) were not confirmed in this study. Larvae and exuviae collected from Secret Ravine Creek, Placer County keyed to I. marmorata .

Diagnosis. The larval male lacinia of I. denningi is distinct from other Isoperla species with 1–4 submarginal (A+B) setae in that the dorsal lacinial surface has no fine setae (must focus down through ventral surface to see) and ventral surface setae (D) are concentrated on the apical half ( Fig. 7f ). The larval dorsal head pigment pattern is striking in this species, which has a well defined median longitudinal light band extending from the median base of the M shaped mark, almost reaching the anterior unpigmented frontoclypeus area ( Figs. 7 a- d).

Remarks. This species was usually the only Isoperla in streams within its range, but co-occurred in a few southern California streams with the following species: I. acula , I. adunca , and I. mormona . Isoperla denningi was the ubiquitous species south of Monterey, Kings, Tulare, and Inyo counties. Emergence occurred in April–June, was lightly extended, and was determined from adult collections and limited rearing.

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. 7a-h. Isoperla denningi nymph, Roblar Creek, San Diego County and ventral maxilla, Jamala Creek, Santa Barbara County, CA. Submarginal setae groups A and B, Marginal setae C, Ventral surface setae D, Dorsal seta DS, and Thin marginal seta TMS. White bars = 1 mm, 7e-f 100x, 7g 200x, and 7h 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.