Several species of resin midges (or pine-pitch midges) have been recorded from species of Pinus in North America. These are all at present referred to the genus Retinodiplosis Kieffer 1912; for reasons given below this genus is here treated as a subjective synonym of Cecidomyia Meigen 1803. At least two species of Cecidomyia have been recorded from jack pine, Pinus banksiana Lamb., in Ontario, Manitoba, Saskatchewan and Michigan (Bradlev (1946), Barker and Wong (1948), anonymous (1946), Prentice and Hildahl (1957, 1958) and Mc-Daniel (1938)); they were sometimes determined as Retinodiplosis sp., sometimes tentatively or definitely as R. resinicola (O.S.). Study of specimens of Cecidomyia from P. banksiana collected during the past three years by officers of the Forest Biology Regional Research Laboratories, Canada Department of Agriculture, has shown that three species of the genus occur on this host. All three are described as new in this paper. C. resinicola (O.S.) 1871, originally described from Virginia pine, Pinus virginiana Mill., was not present in this material nor among Michigan specimens from P. banksiana in the U.S.N.M.; it almost certainly does not occur on P. banksiana.