The term leaf miner is an umbrella term for countless types of larval moths, flies, sawflies, and beetles throughout the world, with diets as diverse as any other garden pest.
These larval pests earn the name leaf miner because of their unique feeding habits which leave behind a distinct tunnel as they mine their way through the soft inner tissue of a host’s leaf. Leaf miner eggs are rarely identified by the naked eye because they are exclusively laid between the protective epidermis of a host plant.
While eggs of other sap-sucking insects such as aphids, spider mites, and mealybugs can be readily identified because they are laid on the exterior surface of a host, leaf miners insert their eggs into the soft inner tissue of a leaf so the larvae will immediately have food and protection after hatching.
How to Get Rid of Leaf Miners
- Leaf Miner Distribution: At least 2,700+ known species of larval leafmining insects
- Leaf Miner Host Plants: Nearly any vegetable, fruit, or ornamental commonly grown in greenhouses
- Leaf Miner Damage: Internal tunneling of leaves to feed on sugars and soft tissue
- Leaf Miner Life Cycle: 7 days (in larval stage)
- Leaf Miner Eggs Per Lifetime: ~50-75 eggs
- Leaf Miner Control: Neem oil, citrus leaf miner treatment, Bacillus thuringiensis, pinching by hand
- Leaf Miner Predators: Ants, soldier beetle, store-bought predatory wasps (Diglyphus isaea)
- Most Common Leaf Miner in North America: American Serpentine Leaf Miner (Liriomyza trifolii)
What Do Leaf Miners Look Like?
Leaf miners are easier to identify by the damage caused to the leaves of host plants rather than trying to identify markings based on their physical appearance. Leaf miners are merely the young and insatiable larvae of countless species of flies, moths, and few beetles.
Unlike caterpillars, which are also the young and developing larvae of larger moths and butterflies, leaf miners are much smaller and appear gelatinous, translucent, and maggot-like invertebrates when compared to the adult-looking caterpillar.
Because leaf miners feed and live protected exclusively within the thin walls of a leaf, they are seldom seen with the naked eye. The leaf-mining larva only remains in the leaf for about 7 days as it grows larger and eventually emerges from the leaf as a dark-colored pupa on its way to developing into an adult fly, moth, or beetle.
Leaf Miner Damage
Damage caused by leaf miners is fast, unique, and unmistakable compared to damage caused by any other insect.
Whether it be from adult flies, moths, or beetles, eggs are safely laid within the protection of a leaf so that when the eggs hatch, the vulnerable larvae then have a place to safely feed.
Immediate signs of leaf miner damage are the obvious white tunneling or “mining” that occurs within the leaf from these newly hatched larvae.
Although this damage may seem superficial compared to larger beetles and slugs, it is actually very detrimental because the ravenous leaf miner larvae feed on vital sugars and soft tissue.
The damage caused by various leaf miners is so unique that, more times than not, the exact species can be identified merely by their mining pattern, even if the insect is not spotted with the naked eye.
What Do Leaf Miners Eat?
The term leaf miner is an umbrella term for countless types of larval moths, flies, sawflies, and beetles throughout the world, with diets as diverse as any other garden pest.
Leaf miners can be found in nearly every garden indiscriminately feeding on everything from ornamental flowers to fruits and vegetables including such staples as tomato, pepper, squash, melon, brassicas, and really anything able to be grown in a greenhouse.
Home gardeners are known to regularly find leaf miners in their favorite flowers especially those in the daisy family Asteraceae including sunflower, chrysanthemum, dahlia, zinnia, and marigold. Leaf miners are not large enough to directly consume plant foliage, but rather exclusively feed on the soft inner tissue and sugars of a host plant.
Leaf Miner Eggs
Leaf miner eggs are rarely identified by the naked eye because they are exclusively laid between the protective epidermis of a host plant.
While eggs of other sap-sucking insects such as aphids, spider mites, and mealybugs can be readily identified because they are laid on the exterior surface of a host, leaf miners insert their eggs into the soft inner tissue of a leaf so the larvae will immediately have food and protection after hatching.
Some gardeners claim they can recognize when leafminer eggs have been laid because there will be small, nearly microscopic, puncture wounds on the leaf from where the adult inserted the eggs.
Although the average home gardener may not be able to spot these miniscule puncture wounds, leaf miner eggs hatch in about two weeks and can be easily spotted once they begin feeding.
How to Get Rid of Leaf Miners
Leaf miners can be some of the trickiest insects to remove from the garden because they cannot be found on the exterior of the host plant like so many other pests.
Leaf miners exclusively live within the protective epidermis of their host and are largely unaffected by insecticides sprayed to the exterior of a plant.
The only time that pesticide may be effective on leaf miners is the brief 14-day window before the eggs hatch, if you’re lucky enough to spot the puncture wounds early enough. Directly spraying these puncture wounds will greatly increase the chances of the pesticide from coming in contact with the unhatched eggs.
One of the most effortless ways to kill leaf miners is to simply pinch them within the leaf once you notice they’ve begun to feed. Because leaf miners create a distinct tunneling pattern when feeding, they can easily be crushed between your fingers once you recognize where they are in the mine.
Leaf Miner Treatment
- Citrus Leaf Miner Spray - Imidacloprid-based sprays effective on leaf miners
- Spinosad Spray - Natural soil bacteria effective in treating several garden pests
- Bacillus thuringiensis (Bt) - Store bought spray consisiting of natural soil-borne bacteria
- Organic Neem Oil Spray - 1 tsp neem oil and 1/4 tsp dish soap to 1 quart water
- Castile Soap - 1 tbsp to 1 quart water
- Capsaicin Spray - Soak 6-7 crushed dry peppers in boiling water and spray when cool
- Pinching By Hand - If spotted tunneling a leaf, larval miners can be simply pinched
