Isoperla adunca Jewett, 1962

Sandberg, John B. & Kondratieff, Boris C., 2013, The Isoperla Of California (Plecoptera: Perlodidae); Updated Male Descriptions And Adult Keys For 18 Western Nearctic Species, Illiesia 9 (5), pp. 34-64 : 41-43

Isoperla adunca Jewett

( Figs. 2 a-d)

Isoperla adunca Jewett 1962 .

Holotype ♂, California, Santa Clara County, 5 mi E Mt. Hamilton.

Male. Aedeagus: sclerotized posterior process present; body with one posterobasal and one posteromedian lobe, dorsomedian apex with a pair of rounded lobes, and one anterior lobe ( Fig. 2a ); sclerotized process length approximately 0.25 mm, recurved and rod-like, located below posterior lobes ( Fig. 2a ), and apex clavate in posterior and lateral views ( Figs. 2 a-b). Abdominal terga 8-9, 9, or 9-10: without stout spinulae or long stout setae. Posterolateral margins of at least abdominal segment 8 with scale-like setae clustered in brushes of several setae. Paraprocts: curved dorsally, length if straightened subequal to first and second cercal segments, tapering gradually to blunt apices ( Fig. 2c ). Vesicle: pedunculate, length subequal to width, constricted near base with curved lateral margins, wider and rounded at apex ( Fig. 2d ).

Isoperla adunca ( I. sordida complex) shares similar characters with I. umpqua (known only from Oregon, and a species that should also be included in the I. sordida complex). Both species have a clavate sclerotized process in lateral and posterior views, lack aedeagal spinule patches, possess pedunculate vesicles, and have similar paraproct lengths and shapes ( Table 1 ). Primary differences involve tergal spinulae and two aedeagal characters: I. adunca has 4 lobes and I. umpqua has one; the sclerotized process length is approximately 0.25 mm for I. acula and approximately 0.5 mm for I. umpqua ; and short stout spinulae present on terga 8-9 for I. umpqua only. Lastly, I. adunca wings are tinted and the wings of I. umpqua are hyaline. The I. adunca aedeagus and paraproct shapes differed from those described by Szczytko & Stewart (1979). In the current study, the aedeagus has four distinct lobes in lateral view ( Fig. 2a ) and paraprocts curved dorsally ( Fig. 2c ) vs. aedeagus with only one apical lobe and paraprocts deflected downward ( Szczytko & Stewart 1979, figs. 159-160).

Isoperla adunca , as with I. acula and I. miwok , is usually associated with small intermittent streams of the Sierra Nevada foothills from north to southcentral California ( Bottorff et al. 1990, Sandberg 2011b). The northern most distribution was recently found in Shasta County and the southwestern most distribution of I. adunca overlaps with I. denningi and I. mormona in Ventura and San Diego counties. Records for this species from Alameda and Santa Clara Counties are located in the Coastal Range.

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California typically experiences high variation in precipitation (Haston & Michaelsen 1979) and 2013 is evidencing to be a drought year (http://www.wrc.dri.edu/). Before completing its life cycle, especially in drought years, I. adunca must cope with drying conditions including rapidly warming water temperatures occurring in non-perennial streams. For example, mature larvae of I. adunca were collected on 24 April 2013 from Orestimba Creek (Stanislaus County, 119 m asl) when stream temperatures had already reached 26.94°C (L.E. Serpa, per. com.).

Additional Material Examined. CALIFORNIA, Riverside Co., San Juan Creek, 0.4 mi (0.6 km) N Lion Canyon Creek , 19/ V /2011, larvae, ( ABLC); Santa Clara Co., Tributary to Arroyo Aguague, UCB Blue Oaks Ranch, N37.37189, W121.73289, 06/ V /2012, larva ( ABLC); Shasta Co., Rock Creek, West Redding , 05/ VI /2011, larvae, ( ABLC); Rock Creek, at Iron Mountain Rd ., 04/ V /2009, larvae ( ABLC); Stanislaus Co., Orestimba Creek , 19.3 km E Newman, 37.289°N, 121.22008°W, 24/IV/2013, L.E. Serpa, Larvae, ( JBSC) .

Figures

Figs. 1-2. Adult male characters of Isoperla acula, Deadman Cr., El Dorado Co., CA and I. adunca, Campbell Cr. & Trib., Butte Co., CA, 32-50x. Fig. 1a. I. acula aedeagus, lateral; fine spinule patch (arrow). Fig. 1b. Aedeagus, ventral; fine spinule patches (arrow & inset-posterior view). Fig. 1c. Paraprocts, (black arrow); abdominal spinules (white arrow). Fig. 1d. Vesicle; brush setae (inset). Fig. 2a. I. adunca aedeagus, lateral; sclerotized process (arrow & inset-lateral view). Lobes A: posterobasal, B: posteromedian, C: anterior, D: dorsomedian pair. Fig. 2b. Aedeagus, ventral; sclerotized process (arrow & inset-posterior view). Fig. 2c. Paraprocts (arrow). Fig. 2d. Vesicle.