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Leaf Mining Fly

Agromyzidae

Leaf Mining Fly, Leaf Miner Fly, Leaf Miner Flies

A macroshot of a leaf mining fly from the insect family Agromyzidae on a leaf
Leafminer Fly (34343046680) by Katja Schulz (CC BY 2.0)
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Agromyzidae are a family of Dipteran insects (True Flies). There are roughly 2,500 species in the family, many of which are plant-specific, so will only be able to feed on a particular kind of plant! The larvae feed within the leaf, resulting in meandering lines, galleries or blotches to appear on plant foliage. A small fraction of the group will cause plants to produce galls; a few others will bore into seeds and bulbs.
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Traits

Can be quite difficult to control.
Lots of other things in the garden will eat them!

Appearance

Adults: Adult flies are minute, the largest being only 6mm in length. They tend to be dark coloured (browns and black), with some including yellow markings. They're inconspicuous and rarely seen. It's much easier to identify a species by its larval mines. Larvae: The larvae look like tiny yellow-green translucent maggots, in most cases! Although, they're rarely seen on the leaf surface. Maggots reside inside the leaf, between the two epithelial walls. Each species produces a unique pattern while consuming the inner leaf contents, and this can act as a signature for someone trying to identify what fly it could be. Eggs: The eggs are so tiny, it's impossible to see without a microscope!

Activity

Diurnal

Personality

Order

Diptera

Family

Agromyzidae

Metamorphosis

Complete

Distribution

Worldwide

Biological treatment

Yellow sticky traps are an effective way to monitor fly populations. Alternatively, if you have a large patch, keep a count of the leaves found with mines. Regular monitoring can help with general assessment and decision-making regarding the next steps of action. Rational thinking may avoid unnecessary applications of pesticides and wasted money! Dispose of any leaves that have been mined or have eggs on them, but never dispose of these in compost and food waste bins. Deeply infested leaves can be burnt when the growing season terminates to destroy any persisting pupae. By practising good housekeeping in the garden, e.g. regularly pruning and clearing debris; you'll make your yard less attractive to pests. It's proposed that flies like this dislike strong-smelling herbs, such as lavender, thyme, lemon balm, fennel and basil. Planting these near your vegetable patches won't do you any harm! Another suggestion would be to grow plants beneath an insect-proof mesh. It's advised to rotate crops every year, and by doing so, infection by overwintering pupae will be less likely. Leaf mining flies have an abundance of natural enemies, so ideally, you want these to be controlling your pest populations. It's been found that areas with higher densities of these insects experience less severe symptoms from pests. These can be attracted to your green spaces using a few simple tricks. - Plant an array of indigenous plants, the more diversity, the better! - Install mini-habitats; leave out a pile of logs and sticks, a bucket of water, or, incorporate some climbing plants in the garden. - Reduce your use of pesticides. Using pesticides can harm natural enemies, and this can cause pest populations to increase the following year. When a leafminer infests a plant, one of the best modes of action is to encourage fast growth. Well-established plants that grow quickly can sometimes expel any eggs within the tissue. Crops with insufficient irrigation, water and fertilizer are much more prone to attack than a plant receiving the correct quantities.

Chemical treatment

It's advised only to take chemical action when all other options have been exhausted, and the infestation is considered severe. Insects such as leaf-mining flies have a rapid rate of reproduction. There will always be flies left unaffected by chemical treatments, and this can lead to pesticide resistance. Pesticides containing abamectin, or pesticide 'spinosad', are proposed as the most effective components to fight this pest. Please read instructions carefully, taking care not to spray any plants that are in flower. Such pesticides can still show some degree of toxicity towards wildlife, so should be applied with extreme caution. Tip: some gardeners store mined leaves in a sealed plastic bag. Once the grub inside is fully developed, they emerge from the leaf mine. This is probably the best time to be spraying your plants. If you are planning to eat your harvest, make sure the food plant is listed on the bottle label and follow instructions. If you're ever feeling unsure, you can consult with your local garden centre or ask the wonderful Candide community for assistance!
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