Holly leaf miner
Encyclopedia
Phytomyza ilicis, the holly leaf miner, is a fly
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...

 whose larvae burrow into leaves of the holly tree (Ilex aquifolium) leaving characteristic pale trails or leaf mines
Leaf miner
Leaf miner is a term used to describe the larvae of many different species of insect which live in and eat the leaf tissue of plants. The vast majority of leaf-mining insects are moths , sawflies and flies , though some beetles and wasps also exhibit this behavior.Like Woodboring beetles, leaf...

. 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
Blue Tit
The Blue Tit is a 10.5 to 12 cm long passerine bird in the tit family Paridae. It is a widespread and common resident breeder throughout temperate and subarctic Europe and western Asia in deciduous or mixed woodlands...

.

Life cycle

Female Agromyzidae
Agromyzidae
The family Agromyzidae is commonly referred to as the leaf-miner flies, for the feeding habit of larvae, most of which are leaf miners on various plants....

 insert an egg in the leaf tissue using an ovipositor
Ovipositor
The ovipositor is an organ used by some animals for oviposition, i.e., the laying of eggs. It consists of a maximum of three pairs of appendages formed to transmit the egg, to prepare a place for it, and to place it properly...

. In the case of Ph. ilicis this poses a problem, because the leaf of the hostplant is unusually tough. Only during the annual flush in April, May, when new leaves unfold, oviposition
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....

 is possible. Oviposition is in the underside of the petiole
Petiole (botany)
In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...

, or the basal part of the midrib. Oviposition induces the formation of a characteristic oviposition scar, enabling an estimate of the number of eggs that has been deposited. The emerging larva tunnels within the midrib, in the direction of the leaf tip. Only around January it enters the leaf blade, and starts making a recognisable leaf mine. Up to three mines may occur on a leaf - often much less than the number of oviposition scars, suggesting that intra-leaf competition has taken place. The adult emerges in late May–June and leaves a >1 mm emergence hole (exit holes made by parasitoids are much smaller).

Distribution

The holly leaf miner is found throughout the holarctic on its host Ilex aquifolium. It is common and widespread in Europe and has been introduced into western Canada and north west USA.
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