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The holly leaf miner : Phytomyza ilicis ~ by Chris

The holly leaf miner : Phytomyza ilicis

Phytomyza ilicis is a (dipteran) fly that lays its eggs in holly leaves.  It is one of the few insects that is able to make use of holly leaves as a food source and somewhere to live (when a larva).  The female fly lays eggs in the holly leaf (near the main veins or midrib – on the underside) using a thin tube or ovipositor.  The eggs are usually laid in early Spring when there are young and ‘soft’ leaves.  Older leaves have a thick and tough cuticle that is far more difficult to penetrate.  The larvae or maggots emerge from the eggs and tunnel their way along the midrib / veins emerging some time later into the lamina or blade of the leaf.  Here they feed on the photosynthetic tissues of the leaf – the palisade and mesophyll layers, creating a leaf mine (see featured image above).  The number of leaf mines per leaf is a maximum of three and often just 1 or two.

After a period of feeding, the larva turns into a pupa.  The pupal stage is one of internal reorganisation [metamorphosis], when the body plan of the insect is ‘redesigned’ (for a picture of the pupal stage see http://www.nhm.ac.uk/nature-online/species-of-the-day/common-species/phytomyza-ilicis/index.html). After a while, an adult fly emerges from the pupa and from the leaf mine via a small hole (less than a millimetre in diameter).  These may be seen on the leaf surface.

The larva may not make it to the adult (imago) stage because

  1. It may be parasitised by the eggs of a wasp – which "eat it", or
  2. It may be eaten by by a blue tit.  If this happens, there is clear evidence that the leaf mine has been pecked at / ripped open and the insect removed (see image).

The holly leaf miner is common throughout Europe.  For further information - see the links below :

Posted in: Flora & Fauna, Pests & Diseases ~ On: 18 January, 2012

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