Holly Leaf Miner


This interesting patterning on the leaves of the Holly tree (Ilex aquifolium) is caused by the Holly Leaf Miner (Phytomyza ilicis), a parasitic leaf-mining fly in the Agromyzidae family. Its larvae burrow between the cuticles of Holly leaves, leaving a distinctive trail behind.

The adult female fly lays eggs inside the soft, young leaves using her ovipositor in spring. A maximum of 5 eggs are laid per leaf, although no more than 2 become larvae, so as to avoid competition for food between individual larvae. The species is univolitine, meaning it only has one brood of young each year.

This mining seemingly has no great negative effect on the host plant, presumably because not many larvae are in each leaf, and there is a high mortality rate in larvae. Old mines provide habitats for algae and mites, sheltered from predation by the leaf.

A P. ilicis mine that has been predated by a blue tit (Cyanistes caeruleus).

Holly Leaf Miners are quite vulnerable to predation, largely by blue tits, which leave a characteristic V-shaped tear on the mined leaf. They can also be subject to parasitism by Chalcid and Brachonid wasps. These wasps are parasitoids of P. ilicis, meaning that they eventually kill their host. This serves as population control of P. ilicis, and prevents excessive damage to Holly trees.

The sign of a holly leaf miner larva.

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