1. In Canada, European holly (Ilex aquifolium) can only be grown successfully in the mild, humid climate of western British Columbia. The sales of cut holly for decorative purposes amount to several hundred thousand dollars annually, and the tree is also in good demand for ornamental planting in public parks and private estates.
2. The most serious pest of holly in this part of the world is the Agromyzid fly, Phytomyza ilicis, or the Holly Leaf-miner, which was accidentally introduced from Europe without its attendant natural enemies. The larvae of this insect produce large unsightly blotches on the leaves which greatly lower the value of the cut foliage. As a rule 75 to 80 per cent. of the leaves are attacked in this manner.
3. Since chemical forms of restraint offered little hope of success, it was decided that the biological method of control should be given a trial. Accordingly, the writer undertook a general survey of the fly and its parasites in England, the results of which are described in the preceding pages. An account of the biological control of P. ilicis will be published in a separate paper at a later date.
4. A general account of the systematics, synonymy, distribution, host relationship, and biology of the holly fly itself precedes the parasite section.