Isoperla bifurcata Szczytko & Stewart, 1979

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 : 44

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Isoperla bifurcata Szczytko & Stewart


Isoperla bifurcata Szczytko & Stewart

( Figs. 4 View Figs a-d)

Isoperla bifurcata Szczytko & Stewart 1979 .

Holotype ♂, Oregon, Union County, Lick Creek, 6 mi E Medical Springs.

Male. Aedeagus: sclerotized posterior process present; body with one posterobasal lobe, one posteromedian lobe, one large dorsal lobe and one anterior lobe ( Fig. 4a View Figs ); sclerotized process length> 0.5 mm, distal-projecting portion recurved and deeply bifurcate, apices of bifurcate arms with acute points and secondarily barbed ( Figs. 4 View Figs a-c), and length of proximal-attached base ( Fig. 4a View Figs , 1) less than the total length of distal-projecting median arm ( Fig. 4a View Figs , 2), bifurcate arms ( Fig. 4a, 3 View Figs ), and apical tine ( Fig. 4a, 4 View Figs ). Abdominal terga 8-9, 9, 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 combined first and second cercal segments, tapering abruptly to variable blunt to sharp apices ( Fig. 4c View Figs ). Vesicle: pedunculate, length subequal to width, constricted near base with curved lateral margins, wider and rounded at apex ( Fig. 4d View Figs ).

Isoperla bifurcata is most similar to I. fusca Needham & Claassen 1925 , a species not known to occur in California and not included in this study. The vesicle shape for I. bifurcata differed from the previous description. In this study, the pedunculate vesicle length is subequal to width, and rounded at apex ( Fig. 4d View Figs ). In Szczytko & Stewart (1979, fig. 164), the vesicle width appears greater than length and the apex is both described and illustrated as truncate.

The I. bifurcata sclerotized process description and couplet 20 of the key to the males in Szczytko & Stewart (1979) are imprecise. The ambiguity is caused by not clearly defining the “base” character (there are two possible interpretations), and two different proximal-attached “base” lengths are illustrated in lateral view and upside down posterior view in Szczytko & Stewart (1979, figs. 165C & 168, respectively). The written description provides one length character: “arms of apical fork extending same length as base…(figs. 165C & 168)”. Figure 165C (in Szczytko & Stewart 1979) is a lateral view of the process and does not provide a clear view of the apical fork length, but does indicate the entire distalprojecting portion of the sclerotized process is longer than the proximal-attached portion (agreeing with our observations). Only figure 168 in Szczytko & Stewart (1979) provides an accurate view of the “arms of the apical fork” length, illustrating both as half the length of the proximal-attached “base” portion (0.5 times shorter than our observations), and subequal to the “base” of the distal- projecting portion of the sclerotized process (agreeing with our observations). Couplet 20 provides another sclerotized process length character “dorsal arms of sclerotized aedeagal process not extending beyond length of base…(figs. 165C & 168)”. Couplet 20 describes the lengths as they are illustrated in fig. 168 (inconsistent with our observations), but then conflicts with fig. 165C because the dorsal arms (same as “arms of apical fork” above) extend beyond the length of the “base” or proximal- attached portion (agrees with our observations).

The current study addresses this uncertainty by providing updated terminology for the four regions of the I. bifurcata sclerotized process: 1. base, proximal portion attached to aedeagal membrane, bifurcate posteriorly and apically recurved ( Fig. 4a View Figs , 1); 2. median arm, projecting ventrally from aedeagal membrane ( Fig. 4a View Figs , 2); 3. bifurcate arms, extending ventrally from median arm ( Fig. 4a, 3 View Figs ); and 4. short sharp subapical barb and slightly longer apical tine at apex of bifurcate arms ( Fig. 4a, 4 View Figs ).

The total length of the I. bifurcata distal-projecting portion of the sclerotized process (median arm, bifurcate arms and apical tines) ( Fig. 4a View Figs , 2+3+apical tine) is nearly 2 times the length of the proximalattached base ( Fig. 4a View Figs , 1); and the bifurcate arm + apical tine length ( Fig. 4a, 3 View Figs +apical tine) is subequal to median arm length ( Fig. 4a View Figs , 2). Additionally, the length from the ventral barb apex to the apical tine apex ( Fig. 4a, 4 View Figs ) ranged from subequal to less than the bifurcate arm length ( Fig. 4a, 3 View Figs ).

Additional Material Examined. CALIFORNIA, Shasta Co., Hat Creek, Hwy 44, 3 mi (4.8 km) SW Old Station , 16/VII/2011, D. R. Givens, ♂, ♀ ( CSUC); GoogleMaps Siskiyou Co., McCloud River, Hwy 89 Lower Falls Picnic Area 5.5 mi (8.8 km) E McCloud, 41.2402°N, 122.02441°W, 23/ V /2013, J.B. Sandberg, B.C. Kondratieff, 1♂ ( JBSC). GoogleMaps


Departamento de Geologia, Universidad de Chile


California State University, Chico, Vertebrate Museum


Royal British Columbia Museum - Herbarium














Isoperla bifurcata Szczytko & Stewart

Sandberg, John B. & Kondratieff, Boris C. 2013

Isoperla bifurcata

Szczytko & Stewart 1979: 44