Leafminer, Leafminer Fly, Serpentine Leafminer
Order Diptera, family Agromyzidae
Adults are black and yellow flies that are rarely seen. Larvae are short, pale-green, translucent maggots. Eggs are white and cylindrical.
Adults emerge from overwintering cocoons in the soil in early spring and lay eggs in clusters under leaves. Tiny yellow larvae mine tunnels through leaves for one to three weeks, then pupate for two to four weeks in the leaf before dropping to the soil. Two to three generations a year, more in greenhouses.
Yaupon holly, mums, nasturtiums, and other ornamentals. Beans, beets, cabbage, chard, lettuce, peppers, tomatoes, and other vegetables. They especially like dark vegetables and lamb's-quarter.
Larvae tunnel through leaf tissue, leaving unsightly trails.
Can destroy seedlings but causes only a cosmetic problem on mature plants.
Leafminers have many natural enemies such as hummingbirds. Dacnusa sibirica is a parasitic wasp specific to some leafminers. Beneficial nematodes will attack the pupae in the soil.
Floating row cover on vegetable crops. Neem products or citrus oil products.
Spraying regularly with fish, seaweed, molasses, vinegar, and garlic works well to repel these pests. With organic practices the leafminer never becomes a problem because of its many natural enemies. Where beneficial insects are destroyed by massive spraying to vegetable, cut flower, and greenhouse crops, the leafminers have become almost uncontrollable. A large pecan grove operator told us that the more they sprayed with chemicals, the worse the leafminers got. When they stopped spraying chemical poisons, the leafminers disappeared.