Ditomyia potomaca Fisher

Figs. 3, 5, 19–23, 48 (Map)

Ditomyia potomaca Fisher, 1941: 278. USA: Virginia. HT male (ANSP).

Material examined. CANADA: QUEBEC: Gatineau Park, Black Lake trail W. outflow, 24.V–7. VI.2012, waterfall MT, 45º25’57”N, 75º55’19”W, J.M. Cumming & S.E. Brooks, 3 females (2 SFC, 1 CNCI); USA: CONNECTI- CUT: Fairfield Co., 17 May 1930, A.L. Melander 1 female (allotype) (USNM); MAINE: York Co., West Lebanon, 29 V–11 VI 1990, D.W. Barry, MT, 1 female (UNHC); MARYLAND: Montgomery Co., Glen Echo, 27 April, C.H. Curran, 1 female (paratype) (USNM); MASSACHUSETTS: Middlesex Co., Lincoln, 28–31 May 1982, E. T. Armstrong, Malaise trap, 1 female (USNM); VIRGINIA: Fairfax Co., Holmes Run, ca. ¼ mile NE jct Gallows

Rd & I-495, 38º50’N, 77º12’W, MT, 10 April–7 May 2016, D. R. Smith, 1 female (SFC); Fauquier Co., Phoebe Hall Knipling Outdoor Lab, Bisquit Mtn. Rd., 38.8074ºN, 77.7224ºW, 11–27 April 2016, MT, D. R. Smith & O.S. Flint, 1 female (SFC); Prince William Co., Bull Run Mt. Conservancy, 38º49.484’N, 77º41.362’W, 11–27 April 2016, MT, D. R. Smith & O.S. Flint, 3 males (SFC); Prince William Co., Bull Run Mt. Conservancy, 38º49.484’N, 77º41.362’W, 28 April–19 May 2016, MT, D. R. Smith & O.S. Flint, 1 male (SFC).

Diagnosis. The following characters will distinguish D. potomaca from other Nearctic Ditomyia: Wings hyaline (Fig. 3), antennal flagellomeres pale yellow (sometimes becoming light greyish-brown distally), nearly concolorous with pale yellow pedicel and scape, black spot marking base of each antennal seta strongly contrasting against yellow background color of flagellomere (Fig. 5), mesonotum black to very dark brown (Figs. 5, 19), male terminalia as Figs. 20–22, female terminalia as Fig. 23.

Remarks. Some specimens examined lack yellow bands on abdomen and have all coxae blackish.

Distribution (Fig. 48). Northeastern Nearctic; Canada (Quebec), USA (Maine, Connecticut, Maryland, Massachusetts, and Virginia).

Bionomics. Records indicate the flight period is May through early June. Immature stages and life history are unknown. Marshall (2012: 182) included a photograph of two males competing for a single female on a tree trunk (specimens listed only as Ditomyia, but it appears to be D. potomaca).