Paraleptophlebia strigula ( McDunnough, 1932: 209 )

Burian, Steven K., 2024, Nymphs of the Northeastern Nearctic Species of Neoleptophlebia Kluge, 1997 and Paraleptophlebia Lestage, 1917 (Ephemeroptera: Leptophlebiidae), Zootaxa 5521 (1), pp. 1-65 : 24-25

Paraleptophlebia strigula ( McDunnough, 1932: 209)

Leptophlebia strigula McDunnough, 1932 (original description)

Description of Nymph: McDunnough 1932: 210

Nymphs of P. strigula can be recognized from other members of the northeast Paraleptophlebia that only have posterolateral projections of abdominal segment IX (as in Fig. 4b ) by the segment 1 of maxillary palps only reaching to about the midpoint of the longest crown setae of the galea-lacinia ( Fig. 13 ), segments 2 and 3 of the maxillary palps widest where they meet ( Fig. 13 ) and overall thickness of both segments greater than on other species, tarsal claws with small denticles ( Fig. 16 ); color pattern of abdominal tergites II–VI with a combination short dark lines along the posterior margins of tergites near posterolateral edges and dark diffuse marks at posterolateral corners anterior to gill insertions ( Figs. 14a,b ), and apex of femora with group of 4–5 large, sharp spine-like setae ( Fig. 15a,b ). Most characters seem consistent on nymphs from mid-development to later instars. The description of the nymph of P. strigula by McDunnough (1932) is among the most detailed for any of the northeastern Nearctic species of Paraleptophlebia , but nymphs are frequently misidentified. The maxillary palps of P. strigula are clearly different from those of P. guttata and do not require comparative measurements to distinguish them. Overall the maxillary palps of P. strigula ( Figs. 13, 14a ) are shorter and do not extend out in front of the head as occurs on P. guttata ( Figs. 9a, 10a,b ). McDunnough (1932) describes segments 2 and 3 of the maxillary palps of P. strigula as “distinctly stouter than in guttata ”; which is interpreted to mean that both segments are shorter and wider ( Fig. 13 ) compared to those of P. guttata ( Fig. 9a ). Moreover segments 2 and 3 of the maxillary palps of P. strigula are widest where they meet ( Fig. 13 ). The tarsal claws of P. strigula have small to minute denticles ( Fig. 16 ) that are only clearly visible at high magnification (~400x). The presence of small to minute denticles on tarsal claws is definitive compared to the tarsal claws of P. guttata , which lack denticles, but the extremely small size of the denticles makes them difficult to observe without slide mounting. The color pattern of abdominal tergites II–VI ( Figs. 14a,b ) has been used in several keys ( Burks 1953; McCafferty et al. 2017; Traver 1935) to separate nymphs of P. strigula from those of P. guttata , but in most places the description of this important feature is difficult to interpret. Part of the problem understanding and correctly interpreting this character can be traced back to the original description ( McDunnough 1932), which lacks clarity and emphasizes only details of dark shading on the posterior margins of tergites. No illustrations of this diagnostic feature have ever been published further contributing to the problem interpreting this character. The diagnostic color pattern character of abdominal tergites II–VI is a combination short dark brown (almost black) streaks along the posterior margins of tergites near the posterolateral corners and diffuse dark brown (almost black) marks at the posterolateral corners of each tergite anterior to gill insertions ( Figs. 14a,b ). On some nymphs there is a thin gray line that extends along the posterior margins of tergites II–VI between the larger and more distinctive dark lateral streaks ( Fig. 14b ). The dark diffuse spot in the posterolateral corners of tergites above the gill insertions is usually separated from the lateral dark streak by a thin, pale line ( Fig. 14a ), but occasionally dark shading from the diffuse dark spot spreads into the edge of the dark lateral streak ( Fig. 14b ). The presence of some dark shading on the posterior margins of tergites of some nymphs of P. guttata ( Fig. 10 ; which seems to occur in most populations of P. guttata ) is likely the reason for many misidentifications of P. guttata nymphs as P. strigula . All the specimens of P. strigula borrowed from collections for this study that were previously determined to be P. strigula were determined to be misidentified.Although the abdominal color pattern character is a useful key character, its intrinsic variability, as well as possible confounding variability in P. guttata , relegates it to a supporting rather than a primary role in determining species identity. The legs of P. strigula nymphs are similar to those of P. guttata in the shape and color of segments, but there are some differences in surface and edge setae. Femora have about 10 long, hair-like setae along the ventral edge (most near base) and the dorsal surface has an area of long, thin, spine-like setae extending from base to about midpoint of surface. The dorsal edge of femora has mostly short spine-like setae and a few long hair-like setae. The apical area of the dorsal edge of the femora has a group of 4–5 large, sharp spine-like setae ( Fig. 15a,b ). The outer edges of the tibiae and tarsi have scattered long, hair-like setae, but not forming a distinctive fringe.

Paraleptophlebia strigula is an uncommon (potentially rare) species that is broadly distributed across the northeast Nearctic region with records in 7 of the 14 states and provinces ( Table 2). It has yet to be recorded from NL-I, NL-Lab, NH, NY, RI, VT, and PE. The occurrence of P. strigula in areas which border those with no records suggests that P. strigula should occur in most, if not all, of the states and provinces of the northeast Nearctic region. The lack of records for all mainland areas is likely the result of sampling effort. The lack of records from major islands (NL-I and PE) may reflect actual absences because of the difficulty of dispersal across straits. However, the presence of P. strigula on Martha’s Vineyard, MA ( Whitmore 2008) is interesting because it may represent a relic population that was not the result of dispersal because Martha’s Vineyard was neither covered by ice during the last glacial maxima nor submerged when the surrounding exposed continental shelf habitat was inundated when the sea rose to its present level following the retreat of the glaciers. There is little information on the life history of this species ( McDunnough 1932; Grant et al. 1997), but generally this species seems to emerge from late May to mid-June. This is important because P. strigula nymphs with well-developed forewing pads would not be expected co-occur with similarly developed nymphs of the often-confused species P. guttata (which completes its nymphal development from July into early August). The temporal separation of P. strigula from P. guttata should be helpful in making species determinations. The majority of records of P. strigula are from midwestern states in the Ohio Valley and provinces bordering the Great Lakes (Randoph & McCafferty 1998) indicating that area is likely the core of its continental range. In Canada there are no published records west of southern ON. There are also no records for the southeastern U.S. In Michigan, the record of P. strigula presented by Leonard & Leonard (1962) is likely incorrect because both the description of the male imago and the figure of the male genitalia (i.e., Fig. 77) do not match that of P. strigula . Both the description and accompanying figure are a closer match to the male imago of P. guttata . In the northeast Nearctic region, PA has more records of P. strigula than any other state or province. The statement by Burks (1953) concerning the occurrence of P. strigula in PA is likely based on his study of two male imagos collected in 1948 from Weikert, PA that were deposited in the insect collection of the Illinois Natural History Survey (codes: INHS Ephemeroptera 2948 & 2949). Nymphs have been collected from cool, clean first and second order streams with loose cobble, gravel, and sand substrates. The streams in northwestern PA where P. strigula were collected were slightly basic ( Grant et al. 1997). Most sites did not have high gradient channels occurring mid-network or lower in drainage system position. Habitats apparently suitable for P. strigula are common across the northeast Nearctic region, suggesting that other variables are likely responsible for limiting their uncommon occurrence. With regards to potential effects of climate change, any species that is naturally uncommon, or rare, is potentially at greater risk of range disruption or regional extirpation because they occupy only a fraction of what are apparently suitable habitats and wherever they occur, they usually have low abundance. Even in what could be considered the core of the range of P. strigula it is uncertain as to how they would respond to predicted effects of climate change ( Hicke et al. 2022) on stream habitats.

Figures

FIGS. 1–4: gills and abdominal tergites VIII–X of Neoleptophlebia and Paraleptophlebia nymphs. 1. N. adoptiva gill 4, 2. P. praepedita gill 4, 3a. N. assimilis tergites VIII–X, 3b P. praepedita tergites VIII–X, 3c. P. volitans tergites VIII–X, 3d. P. moerens tergites VIII–X, 4a. N. adoptiva tergites VIII–X, 4b. P. guttata tergites VIII–X.

FIGS. 13–16: mouth- and bodyparts of Paraleptophlebia strigula nymphs. 13. right maxilla (dorsal view) arrow indicates joint between segments 2 and 3 as well as widest point of both segments, 14a. dorsal view of view of the abdomen of three male nymphs, 14b lateral view of abdominal tergites of two male nymphs, 15. foreleg of male nymph, 15b close-up of cluster of long, spine-like setae near the apex of the femur, 16. close-up of foreclaw, arrow indicates inner edge with minute denticles present.

FIGS. 9–12: mouth- and bodyparts of Paraleptophlebia guttata nymphs. 9a. right maxilla (dorsal view), 9b. close-up of dorsal surface of segment 1 of maxillary palp, 10a. dorsal view of view of abdomen of male nymph, 10b. dorsal view of abdomen of female nymph, 10c. lateral view of abdominal tergites of male nymph, 10d. lateral view of abdominal tergites of female nymph, 11. foreleg of male nymph, white circle indicates location of large apical spine-like setae on femur, 12. close-up of foreclaw, arrow indicates inner edge lacking denticles.