Disynopeas Kieffer is regarded as a new synonym to Metanopedias Brues, M. britannicus D. Jackson is conspecific to M. lasiopterae (Kieffer) and thus has to be dropped. Parallelogaster with the type-species P. compressiventris (Ashmead) and Cylindrogaster with the type-species P. tubulosa Brues are established as new subgenera of Platygaster Latreílle. For the genus Gastrotrypes Brues the new tribe Gastrotrypini is established. The two species G. spatulatus Brues and G. caudatus Brues are discussed and Synopeas hungaricus Fabritius is regarded as a new synonym to the latter species. Leptacis tipulae (Kirby) is redescribed and L. scutellaris (Nees) and L. scutellaris Thomson are regarded as its junior synonyms. L. torispinula n.sp. from Austria, Germany, Yugoslavia and Sweden and the remarkable species Platygaster stylatus n.sp. from Burma are discribed. M. lasiopterae, P. (C.) tubulosa, Leptacis? n.sp. Leptacis n.sp. Leptacis torispinula n.sp. and a Synopeas? n.sp. were found mainly on oak logs, where at least the first three species were seen ovipositing into the vascular ducts of the wood. These ducts were inhabited by the gall midge Ledomyia lugens Kieffer. For G. spatulatus and G. caudatus, the host midge is still unknown, but in the Netherlands the gall midge Xylodiplosis praecox (Winnertz) was reared from oakwood on which G. spatulatus had been ovipositing, but no parasites emerged.