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Holly Leaf Miner



P_hollylminer

Holly Leaf Miner

Usually appear in

Spring to Autumn


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Caused By:-     The Larva of Phytomyza ilicis

Description

This pic shows the leaves of Ilex aquifolium with Phytomyza ilicis. There are several Phytomyza leaf miners some of which are particular to certain countries and specific Hollies. Phytomyza ilicis, is a European species and most hollies have some leaves infested with this leaf miner. The damage is unsightly, but usually has little impact on the plant’s growth or vigour. The Holly leaf miner is a small fly whose larva feed inside the leaves. The larva of this fly produces distinctive trails, or mines, in the leaves. Each mine eventually enlarges into a blotch containing one larva or pupa on the outer edge of the blotch where the larva are continuing to feed. The edges of the blotches may be lighter green as the larva continues to feed. If there is only one leaf miner present per leaf it will remain on the plant for its normal period, of about two years. However, if there are several leaf miners per leaf the leaf may fall in the Spring. The adult adult females also causes damage to the leaf as they insert their ovipositors into leaves. If a leaf receives too many punctures, it may become stunted and twisted. There is only one generation of Phytomyza ilicis per year and there are three larval stages in the life cycle of this insect, the last of which overwinters in the leaf. In April and May the larvae pupate, and adult flies begin to emerge in May. The adults only live for two or three days during which time they mate and then begin to lay eggs. The eggs are inserted into the undersides of new leaves which causes tiny, green blisters to appear on the bottom of the leaf. Usually the eggs are laid near the tips of the leaves, close to the midrib. The eggs hatch in about 4 days and the larvae mine into the leaves, remaining there for up to 10 months. Just before each larva pupates, it prepares a circular exit hole covered by a thin layer of leaf cells. Picture from Wikimedia Commons.
See also these other leaf miners APPLE, CEDAR, CELERY, CHRYSANTHEMUM, DELPHINIUM, HOLM OAK, LABURNUM, LEAF, LILAC, SPINACH, PYRACANTHER.


Control

Although the mines are unsightly, this pest can be tolerated as it has little real impact on the health and vigour of a holly and parasites and other beneficial insects are usually effective under natural conditions. The simplest way to control the holly leaf miner is to pick off and destroy all infested leaves before April. Insecticides are unlikely to be effective as the thick, glossy surface of holly leaves means that sprays run off the foliage and do not penetrate to where the larvae are feeding. A systemic insecticide sprayed on the underside of the leaves, which are usually softer than the upper surface of the leaf, may be effective.



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