A preliminary study of the parasites of the Pine-shoot Moth, Rhyacionia buoliana, in England was undertaken at the request of the Dominion Entomologist of Canada.

In all twenty-eight species of primary and secondary parasites were obtained. Thirteen of these species were represented in our material by not more than two specimens and are probably of little economic importance. Of the remaining fifteen, two (Habrocytus and Eutelus) are definitely hyperparasites, and at least two of the Pimplines (P. ruficollis and P. brevicornis) are liable to live as hyperparasites under certain conditions.

The dominant or “key” parasites in this complex appear to be the Braconid, Orgilus obscurator, and two Ophionines, Cremastus interruptor and Omorgus mutabilis. These were shipped to Canada and the first two have become established there.

A brief account is given of the salient facts in the biology of each species and the more important diagnostic characters of the adults are described to facilitate accurate identification, often a very difficult matter.

The mature larvae of the commoner species are described in detail, with the particular object of finding satisfactory specific characters.

Of the common species the majority attack the larva. Pimpla examinator is the only true pupal parasite which is at all common, but Omorgus mutabilis and Orgilus obscurator, although they are essentially larval parasites, frequently remain in their host and complete their development after it has pupated. Four other species, though normally living as larval parasites, may occasionally emerge from the pupa. One egg-parasite, Trichogramma evanescens, was recorded.

None of the common species is confined to R. buoliana, and there is no reason to suppose that the other species, about which less is known, are any more specific. Five of the species reared are new to Great Britain and eighteen constitute new records for this host.