late May–June and leaves a >1 mm emergence hole (exit holes made by parasitoids are much smaller). Effect on the host plant Mining of Ilex aquifolium by P. ilicis has little overall effect on the host plant. A leaf which has been mined may remain present on the host plant for an extended period, usually up to 5 years and exceptionally up to 8. Vacated mines have been shown to host unicellular algae and small mites. Mined leaves are also more likely to be shed by the plant. Predators and parasites Phytomyza ilicis is particularly vulnerable to predation or attack during its larval and pupa stages. The holly leaf miner has frequently been used in ecological studies as a system to study food webs since examination of the leaves can reveal whether the leaf miner has successfully emerged, been killed by a parasitic wasp, or been predated by blue tits. One of the most prominent predators is the blue tit Parus caeruleus, which leaves a characteristic V-shaped tear in the leaf. A 1983 study rejected the hypothesis that less-prickly holly leaves suffered a higher predation rate by tits. In a study of parasitism published in 2000, it was recorded that of a large sample of mines 94 emerged as adult flies and 256 had succumbed to parasitoids. Parasitoids of P. ilicis include the Chalcid wasps Achrysocharoides latreillii, Chrysocharis gemma, Chrysocharis nephereus, Chrysocharis pentheus, Chrysocharis pubicornis, Closterocerus trifasciatus, Pediobius metallicus, Pediobius albipes, Pnigalio minio, Cyrtogaster vulgaris, Sphegigaster pallicornis, Mauleus iligneus, Epiclerus nomocerus, and the Brachonid wasps Opius pulchriceps, and Phaedrotoma pulchriceps. Many of these parasitoids also use the closely related holly-leaf miner Phytomyza ilicicola. An earlier study of parasitism found variable levels of parasitism and predation of P. ilicis between different plants in the same woodland, but as an example of their effect on the success of P. ilicis: from 100 mines on one tree 18.47% succumbed to egg mortality, 41.97% were eaten by birds, 9.83% died due to unknown causes, 2.88% were killed by pupal parasites, and 26.86% were assumed to eclose successfully. Biological control Some of the parasitoids have been introduced as biological control agents to areas where P. ilicis has been introduced. In British Columbia, five species were released on Vancouver Island between 1936 and 1938. Of these, Chrysocharis gemma caused c.90% of the parasitism on Vancouver Island whereas Opius ilicis was responsible for approximately 90% of the