Shore Fly

Brachydeutera hebes Cresson

Brachydeutera hebes Cresson, 1926:277.—Williams, 1938:90 [behavior, life history, figures of all stages].—Wirth, 1964:7 [revision].—Tenorio, 1980:293 [revision, figures of thorax, wing, abdomen, male and female terminalia], 338 [description and figures of larvae and puparium].

Brachydeutera argentata of authors.—Howard, 1901:490.—Grimshaw, 1901:49. [Not B. argentata Walker, 1853.]

DIAGNOSIS.—Medium-sized to large shore flies, length 3.60–5.35 mm.

Head: Frons mostly uniformly brown except for olivaceous to greenish area immediately laterad of ocelli; prominent, lateroclinate fronto-orbital bristles 3, anterior bristle only slightly weaker, about 3/4 length of posterior 2. Antenna, ridge of facial carina, border of oral emargination, middle of clypeus, and parafacial area, in lateral view, between eye and oral margin brown, concolorous with frons. Aristal branches 10–12. Facial carina rather sharp, acutely pointed ventrally, extended from ptilinal suture to oral emargination. Lateral margins of facial carina grayish to olivaceous; remainder of face, except as noted above, silvery white. Palpus almost entirely pale, yellowish.

Thorax: Mesonotal chaetotaxy comparatively well developed; bristles as indicated in generic description well developed, setae of main setal tracks larger. Mesonotum mostly brown, with some grayish to olivaceous areas as stripes on either side of acrostichal track, laterad of dorsocentral track, near dorsal margin of notopleuron and extended posteriorly through supra-alar area. Brownish coloration of mesonotum continued ventrally to dorsal ¼ of anepisternum, thereafter abruptly delimited from grayish to bluish gray coloration of ventral portion of pleural areas; anepisternum with brownish coloration continued along posterior margin; anepisternum with dorsomedian circular area silvery white through orientation of microtomentosity. Scutellar ratio 0.73; apical bristles approximate, distance between them less than that between basolateral scutellar bristle and apical one. Anterior notopleural bristle present, nearly as strong as posterior one; katepisternal bristle present. Femora mostly yellowish, apices brownish; forefemur with sparsely microtomentose, extensive blackish area anterodorsally toward base; tibiae mostly brown, yellowish basally, becoming rapidly but gradually darker apically, stramineous to brown; tarsomeres dark brown; male hind tibia lacking patch of ventral, long setae. Wing hyaline, with brownish tinge; R2+3 moderately arched; R4+5, conspicuously arched; costal vein ratio 2.38; M vein ratio 0.80.

Abdomen: Dorsum uniformly dark brown, sparsely microtomentose, slightly subshiny. Male terminalia (Figures 10, 11) as follows: dorsal surface of epandrium in posterior view irregularly concave; epandrial width at dorsum conspicuously extended beyond lateral margins of cerci, lateral margins of epandrium abruptly sinuate with dorsal half very shallowly arched, more or less parallel, thereafter angled inward rather abruptly, then outward to form a small lateral bump; epandrium + surstyli parallel sided to trunculate ventral surface, epandrium + surstyli in lateral view wide, more or less evenly thick, anterodorsal surface rounded to epandrial connection with gonite; gonite thickly developed, posteroventral angle drawn out into narrow process, ventral and anterior surfaces setose.

PRIMARY TYPE MATERIAL.—Holotype male is labeled “Kalihi 2-23 [23 Feb, handwritten] Oahu/E. H. Bryan, Jr Collector/Stagnant water/Kam. School Campus/TYPE 355 Brachydeutera HEBES E.T. Cresson, Jr. [number and species name handwritten, maroon ink].” The holotype is pinned directly, is in good condition, and is in the Bernice P. Bishop Museum.

OTHER SPECIMENS EXAMINED.—HAWAII. Hawaii: Hilo, Jul 1900, H.W. Henshaw (1 USNM); Hualalae, 19 Oct 1963, D.E. Hardy (1, 4 UHH); Laupahoehoe, logging road, 3300 ft [1006 m], 1 Jun 1970, D.E. Hardy (3, 12 UHH); Olaa Forest (upper), Aug 1952–Mar 1968, D.E. Hardy, W. Mitchell, J.A. Tenorio (1, 3 UHH); Paauilo (forest above), 3200 ft [976 m], 6 Aug 1965, D.E. Hardy (6 UHH); Puu Waa Waa Halepiula shed, 20 Jan 1970, 4000 ft [1220 m], in water trough, S.L. Montgomery (1, 2 UHH); Volcano Kiluea, Jun, H.W. Henshaw (2 USNM). Maui: Hanaula, 9 Jul 1968, 4000 ft [1220 m], J.A. Tenorio (2 UHH); Puu Niauniau, Apr 1954, M. Tamashiro (2, 2 UHH). Molokai: Puu Kaeo, Jul 1952, D.E. Hardy, M. Tamashiro (2, 1 UHH, USNM); Wailau Valley, Jul 1952, E. Dresner (1 UHH). Oahu: 13 Jul 1945, Block (3, 6 USNM); 19 Jan 1945, lily pads in pond (1, 1 USNM); Ewa, 1 Apr 1963, light trap, J.W. Beardsley, (1, 2 UHH); Honolulu, 20 Dec 1917–23 Feb 1950, M.S. Adachi (1 3 UHH, USNM); Kaala Makalawena stream, wet bank, 8 Feb 1970, J.A. Tenorio (2 UHH); Kamananui Gulch, 28 Jul 1945, W.W. Wirth (1 USNM); Kaneohe, 13 Mar 1946, W.W. Wirth (1 USNM); Kuliouou Valley, 26 Jan 1945, W.D. Field (2, 8 USNM); Makua, Apr 1951, D.E. Hardy (2 UHH); Mt. Kaala, 22 Aug 1945, 4000 ft [1220 m], puddles in bog, W.W. Wirth (4, 3 USNM); Niu Valley, 5 Jun 1970, S.L. Montgomery (1 UHH); Palolo, 12 Feb 1922, J.F. Illingworth (1 USNM); Poamoho Trail, 9 Nov 1946, W.W. Wirth (1 USNM); Pupukea, 4 Feb 1964, D. Gubler (1 UHH); Waialae, 6 Feb 1916, O.H. Swezey (1, 1 USNM).

DISTRIBUTION.—Apparently endemic to the Hawaiian Islands (Oahu, Kauai, Molokai, Maui, Hawaii, and Kahoolawe).

NATURAL HISTORY.—We quote from the excellent treatment by Tenorio (1980:293, 338), who conducted field studies on this species in Hawaii. He also summarized the work of others.

Williams (1938) gave detailed information on the habits, habitats, life cycle, and immature stages of this species. The adult fly is an excellent water-skater, found most abundant in the lowlands occupying great varieties of quiet pools and other small bodies of water whose bottoms are littered with leaves and other plant parts in various stages of decay. Stagnant pools, some of which have their surfaces covered with scum or algae and which emit a putrid odor, are not uncommon habitats for these flies. At higher elevation, small puddles diverted from streams or those which collect in the rain forests serve commonly as breeding sites for B. hebes. It has also been seen in tree holes filled with water and in artificial containers, such as water tanks or discarded oil drums. On one occasion, in Olaa Forest in Hawaii, I found two fully-grown larvae in a discarded aluminum foil container (4 × 6 × 2 in [10 × 15 × 5 cm]) half-filled with water and rotting leaves; these larvae were subsequently reared to adulthood.

Both as adults and as larvae, these flies are scavengers feeding on microscopic organisms and particles of plant and animal material. The adults occupy the surface of the water, while the larvae concentrate beneath the surface.

The larvae of this species, in one case, were reported to be parasitic by Davis (1959). He observed the larvae “attacking and killing local populations of the liverfluke snail, Lymnaea ollula Gould. ”In laboratory studies, Davis observed six larvae in one snail, and out of 10 adult Lymnaea, three were “consumed” over a period of three days.

The life cycle of this species, based on Williams' studies (1938), may take as little as 14 days: the egg hatches in one day, the larva matures in eight days, and the pupal stage lasts five days. B. hebes is easy to rear in the laboratory from larvae taken in the field.

Hawaiian species, feeds on decaying vegetation and algae in stagnant brackish water.