This is Aulacigaster leucopeza.

I quote from the chapter in the Checklist of the Diptera of the Netherlands:

"Diagnosis. Small, 2-5 mm long flies. Body dark with extensive greyish dusting. Head with ocellar setae reduced, vibrissae present. Antennae with short third segment and short pubescent arista. Wings with distinct subcostal break and less distinct humeral break, cross vein bm-cu absent. (...) Larvae resembling those of Drosophilidae in general appearance but with long respiratory tube on last abdominal segment.

Biology. Larvae living in exuding sap at wounds on both deciduous and coniferous trees. Adults usually found near tree wounds, occasionally attracted to other fermenting fluids or substrates. Adults have been reported to hibernate in sheltered places (cracks and hollows in trees, dry accumulated dead vegetation) in forests.

General references. Papp (1988 [larvae], 1997 [Aulacigaster], 1998d [general]), Teskey (1987a [general])."

The references:
Papp, L., 1988. Periscelis kabuli sp. n. and P. kaszabi sp. n. with notes on larvae and pupae of the families Aulacigastridae and Periscelididae (Diptera). - Acta Zoologica Academiae Scientiarum Hungaricae 34(2/3): 273-284.
Papp, L., 1997. The palaearctic species of Aulacigaster Macquart (Diptera: Aulacigastridae). - Acta Zoologica Academiae Scientiarum Hungaricae 43: 225-234.
Papp, L., 1998d. Family Aulacigastridae. In: Contributions to a manual of Palaearctic Diptera Volume 3 (L. Papp & B. Darvas, eds.): 279-284. Science Herald, Budapest.
Teskey, H.J., 1987a. Aulacigastridae. In: Manual of Nearctic Diptera Volume 2 (J.F. McAlpine, ed.): 891-894. Research Branch Agriculture Canada, Monograph 28, Ottawa.

Anything else? ;-)

Paul

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