Isoperla acula Jewett, 1962

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 : 210-214

Isoperla acula Jewett

( Figs. 2a, 3 a-h, 20a)

Isoperla acula Jewett 1962 , 38:18.

Isoperla acula: Szczytko & Stewart 1979 , 32:77.

Isoperla acula: Bottorff et al. 1990 , 92:291-294. Larva (reared).

Material examined. TYPE: I. acula , Holotype ♂ , CA: Fresno Co., 7 mi NE Academy, elev. 800 feet, Dry Cr., 19/IV/1955, D.L. Abell ( CAS #8591 ). Additional Specimens. CALIFORNIA: Amador Co. , Big Indian Creek , 2 km S NF Cosumnes R., Hwy 49, 25/IV/1986 , R. L. Bottorff, Larvae ( NMNH); Big Indian Creek, Hwy 49, 2.9 mi N Plymouth, unnamed rd. xing, 25/IV/2009, J. Sandberg, Larvae; Little Indian Creek , 3

km W Plymouth , 25/IV/1986, R. L. Bottorff, Exuviae ( NMNH); Little Indian Creek , 3 km W Plymouth, 12/V/1987, R. L. Bottorff, ♂ ♀ reared, Larvae ( CAS); Little Indian Creek , 3 km W Plymouth, 12/V/1987, R. L. Bottorff, ♂ ♀ reared ( NMNH). Butte Co.,?, 9 mi N Oroville, 24/IV/1955, S.W. Hitchcock, ♂, Larvae ( NMNH); El Dorado Co. , Cooper Canyon Creek , Rattlesnake Bar Rd. xing, 2.25 mi SE Hwy 49, 30/III/2009, J. Sandberg, Larvae ; Deadman Creek , Church Mine Rd. xing, 2.45 mi SE El Dorado, 30/III/2009, J. Sandberg, Larvae ; J. Sandberg, D. Pickard, 04/IV/2009, Larvae ; 05/IV/2009, Larvae ; 25/IV/2009, Larvae (reared); 10/V/2009, Larvae (reared); 16/V/2009, Larvae (reared); 23/V/2009, ♂ ♀, Larvae (reared); Martinez Creek, Martinez Cr. Rd .,

3.5 mi SE El Dorado, 04/IV/2009, J. Sandberg, D.

Pickard , Larvae ; NF Cosumnes River , Hwy 49 cattle coral, 1.7 mi S Nashville, below confluence w/ MF Cosumnes R., 28/III/2009, J. Sandberg, Larvae; Tributary of NF Cosumnes River , ~ 2 km W Martinez Cr., S El Dorado , 12/V/1987, R. L. Bottorff, 12/V/1987, ♂ ♀, Larvae ( CAS); Tributary of NF Cosumnes River , Union Mine Rd. , 3.4 mi (5.5 km) N Nashville at McNulty Mine Rd. xing, 25/IV/2009, 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 median longitudinal light band, lateral thin arms directed posterolaterally, extending to antennal bases; posterior ocelli with partially enclosed large light areas along outer lateral margins; interocellar area partially light and generally diamond shaped, completely enclosed by dark pigment, light area extending past posterior ocelli, reaching dark pigment below the arms of the epicranial suture; occiput with irregular spinulae band extending from below eye to near median epicranial suture, not enclosed completely by dark pigment ( Fig. 3a). Lacinia bidentate, total length 687– 786 µm ( Fig. 2a, 3e- h, Tables 2-4); submarginal row (A+B) with 4 setae, groups A-B interrupted by gap below subapical tooth ( SAT) inner margin ( Fig. 3h); 1–2 submarginal setae (A), the first inserted at base of apical tooth ( AT) inner margin, the second when present, located between AT and SAT inner margins, plus 1 thin marginal seta ( TMS) adjacent to AT inner margin, sometimes obstructed from view by AT or broken, and 1 dorsal seta (DS) located below SAT inner margin sometimes obstructed by SAT ( Figs. 3 gh); 2–3 submarginal setae (B) located past SAT inner margin ( Figs 3 g-h); 7–9 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. 3e); 28–41 ventral surface setae (D) scattered below submarginal and marginal setae, ending posteriorly at approximately ¾ the inner lacinia margin length ( Fig. 3f); dorsal surface setae ( DSS) continue from last marginal seta (C) as a single, laterally protruding, submarginal row along inner-lateral margin, ending before posteriormost ventral surface setae ( Fig. 3f). Galea with 42–61 setae in thick ventral band, apex with 4–5 setae. Maxillary Palp segments 2–3 with curved, apically pointed setae. Pronotum with median light area bordered (at least partially) by thin, irregular dark bands; discs each with partially to totally enclosed light areas or “windows” and fine dark clothing setae, lateral margins with broad light bands ( Fig. 3b). Meso and metanotum with contrasting pigment pattern and fine dark clothing setae ( Fig. 3c). 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 numerous and continuous on dorsal surfaces of femora and tibia ( Fig. 20a); tibia with faint transverse bands near proximal end. Abdominal terga with three distinct longitudinal dark stripes; wide light median longitudinal band bisected with thin dark median longitudinal stripe; lateral pair of dark longitudinal stripes about twice as wide as median dark stripe, 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. 3d).

Distribution. California: Sierra Nevada foothills.

Diagnosis. Among the male larvae with 2–4 submarginal row (A+B) setae ( Table 2), I. acula is most similar to I. bifurcata ( Figs. 3 a-h, 6a-h). Characters that distinguish this species from I. bifurcata include fine silky setae numerous and continuous on dorsal surfaces of femora and tibia ( Fig. 20a), and abdomen with median longitudinal thin dark pigment band ( Fig. 3d).

Remarks. Isoperla acula co-occurred with I. adunca , Isoperla miwok Bottorff & Szczytko , and I. marmorata in mostly non-perennial and one perennial central Sierra Nevada foothill streams. Emergence occurred in April–May (lasting to early June in wetter years) and life history studies are needed to determine how I. acula , I. adunca and I. miwok cope with shortened surface flow periods. It is suspected that larvae move to hyporheic zones when stream flow ceases in late summer.