AbstractInfestations of an undescribed gall midge species were discovered in Southern Sweden in biomass plantations and nurseries ofSalix viminalisL. Terminal leaf buds are damaged and side shoots subsequently develop. This midge,Dasineura ingerissp.n., closely resembles three other species occurring onSalix: D.terminalis(H. Loew) onS.albaL. andS.fragilisL.;D.iteobia(Kieffer) recorded fromS.capreaL. andS.cinereaL.; andD.schreiteri(Stelter) (= comb.n. forRabdophaga schreiteriStelter) originally found as an inquiline in the galls of another gall midge,Dasineura rosaria(H. Loew), onS.repensL. No qualitative differences in morphology were observed between these four gall midge species, but results of morphometric analyses show significant differences between all of them. In oviposition preference trials, which included host plants of all four midge species,D.ingerislaid eggs mainly onS. viminalis, D.schreiteripreferably onS.repens, andD.iteobiaexclusively onS.caprea.In larval performance trialsD.ingerisproduced many galls onS. viminalis, one gall also onS.caprea, but no galls on eitherS.albaorS.repens.