Abstract
A comparison is made of all the members of the genus Thomasiniana Strand at present known from Rosaceous host-plants, namely T. oculiperda (Rübs.), the Red Bud Borer; T. theobaldi Barnes, the Raspberry Cane Midge; T. crataegi Barnes, the Hawthorn Stem Midge and a hitherto undescribed species from wild blackberry. Although morphologically very similar, each can be readily distinguished in trials on host-plant preference. By this means it has also been shown that there are two strains, favouring apple and rose respectively, within the present species T. oculiperda. Other biological and some morphological evidence is given, supporting the above conclusions, and on this basis the midge from blackberry is put forward as a new species for which the names Thomasiniana fruticosi, sp. n. and “Blackberry Cane Midge” are proposed and a formal description given. The biological and economic status of each species or strain is discussed and a list of the known parasites given.