Paraleptophlebia debilis ( Walker, 1853: 569 )

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 : 11-12

Paraleptophlebia debilis ( Walker, 1853: 569)

Baetis debilis Walker, 1853 (original description)

Leptophlebia debilis ( Walker, 1853) (combination)

Leptophlebia separata Ulmer, 1920 (invalid renaming)

Description of Nymph: Ide 1930: 210; Gordon 1933: 123; Leonard & Leonard 1962: 70

Nymphs of P. debilis can be recognized from other members of the northeast Paraleptophlebia that have posterolateral projections of abdominal segments VIII and IX (as in Figs. 3b–d ) by the abdominal gills lacking long, hair-like marginal setae ( Fig. 22b ), legs with distinct brown bands on all segments and tibiae with both basal and medial bands but lacks dark brown mark on inner basal edge near joint with femora ( Figs. 24a , 30a–c ), and posterior lateral margins of abdominal sternites with short dark dashes that only become part of brown streaks on sternite IX ( Figs. 31a,b ). Most characters seem consistent on nymphs from mid-development to the final instar. Abdominal gills may appear to lack marginal setae or have a few short, widely spaced marginal setae, which are quite different from the alternate condition shown in Fig. 17 . Brown leg bands are usually distinctive, with only the band on the femora and at the base of the tibiae appearing slightly diffuse on some specimens. The medial brown band on the tibiae is usually distinct even on early instar nymphs. The ventral edge of the femora has only a few short, hair-like setae that are dispersed along the edge, with most occurring close to the base of the edge ( Fig. 25b ). The basal band on the tibiae lacks the more intense dark brown mark that occurs on the legs of P. ontario and it usually completely encircles the leg segment. The dark lateral dashes on the posterior margins of abdominal sternites are sometimes difficult to observe on some smaller specimens and on nymphs that have been in ethanol for a long time. Finally, with regards to separating nymphs of P. debilis from those of P. ontario , differences in the patterns of pale spots on abdominal tergite are also useful. Nymphs of P. debilis have complex patterns of medial and lateral pale spots and some darker marks ( Figs. 30a–c ) that are absent on the mostly brown tergites of nymphs of P. ontario ( Figs. 33a–d ). Further, it was observed that male nymphs of P. debilis had widely separated lateral ocelli ( Fig. 32a ) compared to those of P. ontario ( Fig. 32b ) which had much larger bases and almost met between the compound eyes.

Paraleptophlebia debilis is broadly distributed and common, matching the range of N. adoptiva , with records in 13 of the 14 states and provinces ( Table 2). Only RI currently lack records. The presence of P. debilis in Canada on PE, NL-I and in the U.S. on Martha’s Vineyard (MA) indicates that dispersal to islands is possible and the lack of records from RI is likely the result of sampling effort. The widespread distribution of P. debilis is indicative of its wide habitat tolerances being able to make use of suitable microhabitats in both small first and second order streams and third order rivers ( Burian & Gibbs 1991). Thus, like N. adoptiva and N. mollis , P. debilis is likely secure across its northeastern range with regards to predicted changes in regional hydrology because of climate change ( Hicke et al. 2022).

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. 22–24: gills and legs of Paraleptophlebia nymphs. 22a. dorsal view of lateral gills of P. moerens with gill margins lacking long, hair-like setae, 22b. lateral view of gills of P. debilis with gill margins lacking long, hair-like setae, 23a dorsal view of legs of live P. moerens nymph showing typical brown color pattern without distinct bands, 23b. close-up of foreleg of preserved P. moerens nymph showing uniform brown color, pale areas visible on live nymphs are much less distinct after being preserved, 24a. lateral view of legs of P. debilis showing distinct bands on all leg segments, 24b. lateral view of legs of P. ontario showing partial brown band near apex of femora and dark brown mark on tibiae at joint with femora; dark brown on femora is often diffuse and usually does not encircle the segment.

FIGS. 30a–c: nymphs of Paraleptophlebia debilis. 30a. dorsal view of abdominal color pattern of male nymph from Labrador, Canada, 30b. dorsal view of abdominal color pattern of female nymph from Labrador, Canada, 30c. dorsal view of abdominal color pattern of female nymph from VT, USA.

FIGS. 31a–b: nymphs of Paraleptophlebia debilis. 31a. ventral view of abdominal color pattern of male and female nymphs from Labrador, Canada, arrow indicates dark lateral dashes along edges of sternites (extremely faint on some specimens), 31b. ventral view of abdominal color pattern of female nymph from VT, USA; arrow indicates similar dark lateral dashes but also areas of light brown lateral shading in depressions, lateral shading becomes more distinct on sternites VIII and IX.

FIGS. 17–18: legs, and gills of Paraleptophlebia volitans. 17. dorsal view of abdominal gills with arrow indicating long, hairlike setae along edges of gill filaments, 18a. view of all legs showing presence of distinct bands, 18b close-up of foreleg (dorsal view) showing bands on each leg segment.

FIGS. 25a–c: forefemora of Paraleptophlebia nymphs. 25a. close-up of ventral edge of forefemur of P. ontario showing few short, hair-like setae and stout setae, 25b. close-up of ventral edge of forefemur of P. debilis showing few short, hair-like setae and stout setae, 25c close-up of ventral edge of forefemur of P. moerens showing few short, hair-like setae and stout setae.

FIGS. 33a–c: nymphs of Paraleptophlebia ontario. 33a. dorsal view of abdominal color pattern of male nymph from Pennsylvania, with slight dark gray shading in posterior half of tergites, 33b. dorsal view of abdominal color pattern of male nymph from Pennsylvania, USA with extensive dark gray shading in posterior half of tergites, 33c. dorsal view of abdominal color pattern of male nymph from Illinois USA, that has been preserved in ethanol for 84 years, some gray shading still evident on tergites, 33d. dorsal view of abdominal color pattern of female nymph from Pennsylvania, with slight dark gray shading in posterior half of tergites, shading often less extensive than on male nymphs.

FIGS. 32a–b: heads of Paraleptophlebia nymphs. 32a. dorsal view of the head of male nymph of P. debilis with bases of lateral ocelli widely separated, 32b. dorsal view of the head of male nymph of P. ontario with bases of lateral ocelli touching.