The leafminers here are Liriomyza flies, about 1/12 inch long. Their larvae feed inside leaves and leave pale, winding tunnels. Females also puncture leaves to feed and lay eggs, which leaves pale speckles. On most garden plants the damage is cosmetic, and the University of Minnesota says it has little impact on growth. It matters on crops grown for their leaves, such as lettuce and spinach, on long-season tomatoes, and on flowers grown for sale. Wild parasitic wasps usually keep leafminers in check unless broad-spectrum sprays kill the wasps. Under glass, release Diglyphus or Dacnusa. Outdoors, pick off mined leaves early and use row covers.
Mine of a Liriomyza larva in a tomato leaflet, with the frass trail behind it. Photo: pending.
Three Liriomyza species do most of the damage in the US. They are the vegetable leafminer (L. sativae), the American serpentine leafminer (L. trifolii) and the pea leafminer (L. huidobrensis), which UC IPM's lettuce and spinach guides call L. langei. Adults are small flies, mostly black and yellow with clear wings, about 1/12 inch (2 mm) long. Larvae are yellow to orange legless maggots that grow to about 1/10 inch (2.25 mm) inside the leaf.
Not every mine is a Liriomyza. On spinach and chard, broad, irregular blotch mines point to the spinach leafminer (Pegomya hyoscyami), a different fly. The University of Minnesota contrasts its blotches with the winding, snake-like mines of the vegetable leafminer. Trees and shrubs have their own leafminers, among them the citrus leafminer and the boxwood leafminer. Before buying parasitoids, check which leafminer you have. The wasps on this page are sold for Liriomyza, and suppliers' host lists vary.
The damage comes in two kinds. Females puncture the leaf to feed and lay eggs, which leaves round pale speckles, and UF/IFAS calls this slight compared with the mining. The larvae then tunnel between the leaf surfaces, and each mine widens as its larva grows. Heavy mining reduces photosynthesis and makes leafy crops and cut flowers unsaleable. On lettuce, larvae can contaminate the head even after mined leaves are stripped. On tomato, UC IPM says mining early in the fruiting period can cut yield and fruit size and expose fruit to sunburn, and long-season pole tomatoes are the most vulnerable. In one study on squash cited by UF/IFAS, effective insecticides raised yields by 30–60%.
The cycle is fast in warm weather. Eggs are laid inside the leaf, and the larva mines through three instars. Then it cuts its way out and usually drops to the soil to pupate. The vegetable leafminer goes from egg to adult in about 15 days at 86 °F (30 °C). The serpentine leafminer takes about a month at greenhouse temperatures: 14 days at 95 °F and 64 days at 59 °F. UC IPM counts seven to ten generations a year on California tomatoes, and in greenhouses breeding is continuous. In the north, the University of Minnesota says leafminers overwinter as pupae and the adults emerge in April and May. UF/IFAS says the vegetable leafminer cannot survive cold winters, except in greenhouses.
The vegetable leafminer favours the squash, bean and tomato families. In Florida, UF/IFAS lists bean, eggplant, pepper, potato, squash, tomato and watermelon, and Minnesota adds pea, cucumber, beet, onion and lettuce. UC IPM has separate guidelines for leafminers on lettuce, spinach and tomato, and for floriculture crops, where larval mines make plants unmarketable.
The numeric thresholds are all commercial. UC IPM treats lettuce and spinach when there is more than one mine per leaf on average. For tomato, it treats when pupae collected in 12 × 15 inch trays under the plants average 10 per tray per day over 3–4 days. It adds that fresh mines with no pupae mean parasitic wasps are already suppressing the leafminers. For a garden, the University of Minnesota says the damage has little impact on plant growth, so act only on crops grown for their leaves.
Check the older leaves first. Hold a mined leaf up to the light. A larva at the wide end means the mine is active. An empty mine with an exit slit means the larva has gone to pupate. Yellow sticky traps catch the adults. In floriculture houses, UC IPM uses at least one trap per 10,000 sq ft and checks them weekly. Commercial tomato growers count pupae in trays set under the plants, because fresh mines with no pupae mean the parasites are working.
Parasitic wasps are the main control, indoors and out. In the field, native wasps such as Diglyphus begini and Chrysocharis parksi often keep leafminers below economic injury levels on California tomatoes, and UF/IFAS lists several more in Florida. The problem is that UC IPM says the leafminers resist organophosphates, carbamates and pyrethroids, and that outbreaks commonly follow broad-spectrum sprays that kill their natural enemies. Under glass, UC IPM says the commercially available Diglyphus and Dacnusa sibirica are effective. Dacnusa keeps working in cooler conditions, but Koppert says it does not parasitise the vegetable leafminer well.
In a garden, removing mined leaves and keeping the parasites alive does more than spraying. The larvae are protected inside the leaf, and many insecticides no longer work against them.
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
UC IPM PMG Floriculture and Ornamental Nurseries: Leafminers (Tjosvold, Redak & Dreistadt, 01/22)
UC IPM PMG Tomato: Leafminers (Natwick et al., 2013)
UC IPM PMG Lettuce: Leafminers (04/17); PMG Spinach: Leafminers (LeStrange & Koike, 12/09)
UC IPM, Relative Toxicities of Insecticides Used in Tomatoes to Natural Enemies (09/16)
UF/IFAS Featured Creatures (IN507), Vegetable Leafminer, Liriomyza sativae (Capinera)
University of Minnesota Extension, Leafminers (Hahn & Wold-Burkness, reviewed 2023)
Koppert, Dacnusa sibirica species page
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
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