Beet leaf miner Pegomya hyoscyami Left: typical damage on a leaf of chard, Right, larva inside peeled-back blister
The larvae of leaf-mining flies feed within leaves between the upper and lower epidermis. In doing so, the larvae create mines that show up as white or brownish discoloured lines or blotches. The pattern of the mine is fairly constant for a particular species of leaf miner. In some species it is a linear tunnel that often twists and turns as the larva moves within the leaf. Other species create irregular blotch mines or a combination of linear and blotch mines. In most species, each larva creates its own mine but the delphinium leaf miner Phytomyza aconiti, beet leaf miner and celery leaf miner have larvae that feed communally, creating large blotch mines.
Leaf-mining flies lay their eggs on or in the foliage of suitable host plants. After hatching, the larvae tunnel through the internal leaf tissues. When they have completed their feeding, the larvae of some species pupate within the foliage but in others the larvae exit the mines and pupate in the soil. Some species have several generations a year. Most species overwinter as pupae.
Role of leaf-mining flies in gardens
Some leaf-mining flies that develop on garden plants cause sufficient damage to their host plants for them to be regarded as pests. In most cases, however, the damage is more of a cosmetic nature and is unlikely to affect the plant’s growth.
Other sources of information
for Leaf and stem mines of British flies and other insects
Spencer, K. A. (1972) Handbooks for the Identification of British Insects Vol 10 part 5g. Diptera - Agromyzidae – out of print but available here
Page text drafted by Andrew Halstead, reviewed by Andrew Salisbury, compiled by Steve Head