Vegetable Leafminer
Liriomyza sativae Blanchard, Agromyzidae, DIPTERA


DESCRIPTION

Adult - This shiny black fly has variable yellow markings and is 1.0 to 1.8 mm long.

Egg - The white oval egg, about 0.2 mm long, sometimes is visible through the upper epidermis of the leaf.

Larva - The newly hatched larva is nearly colorless and only 0.1 mm long. The fully grown maggot, about 3.0 mm long, has a bright yellow, translucent body, and black mouthparts. Each maggot has a slightly pointed head and a more rounded abdomen.

Pupa - The flattened, segmented pupa is bright yellow at first but gradually turns brown. It is oblong-oval in shape and slightly less than 2 mm long.


BIOLOGY

Distribution - The vegetable leafminer is found from the tropics into the southeastern and southwestern U.S. It occurs at least as far north as Tennessee and Ohio. Since this leafminer has been confused with closely related species for a long time, the extent of its distribution is not known precisely.

Host Plants - Closely related to the serpentine leafminer which feeds almost exclusively on crucifers, the vegetable leafminer infests a wide variety of plants. Some economically important weed and cultivated crop hosts include squash, okra, pea, tomato, bean, cabbage, turnip, potato, tobacco, cotton, radish, spinach, watermelon, beet, pepper, alfalfa, clover, vetch, and plantain.

Damage - Like serpentine leafminers, vegetable leafminers create lightly colored, irregularly winding mines in leaves. The mines are generally S-shaped and may be enlarged at one end. Infested leaves are favorable habitats for invading bacterial and fungal plant pathogens. Also, since heavily mined leaves may have nearly 100% of their mesophyll removed, photosynthetic efficiency is greatly reduced.

Severe infestations may cause the foliage to turn brown and appear burned. Damaging infestations are most likely to occur after crops have been treated weekly with insecticides such as methomyl or carbaryl. These pesticides kill parasitic wasps which normally keep the leafminer populations at acceptable levels.

Life History - Vegetable leafminers feed and breed year round in the southern areas of Florida and Texas. In North Carolina, they overwinter in soil as pupae. Generally, adult flies which emerge in April or May live only 4 to 10 days. After mating, females insert eggs into leaf tissue from the underside of the leaf. Three to 8 days later, eggs hatch and young larvae begin feeding, each one creating its own mine. Although the leafmining stage may last up to 12 days, it is usually completed in 4 or 5 days during summer. Larvae pupate for about 10 days (longer in spring and fall) at the enlarged ends of the mines or in the soil. A new generation is produced approximately every 23 days. At least 5 generations occur each year in southern states. The number is higher in the tropics and under greenhouse conditions.


CONTROL

Practical on a small scale, the removal of infested tomato leaves helps keep leafminer populations at a manageable level. Economically important leafminer damage rarely occurs on cucurbits. Butternut 23 and Cozella are the only squash varieties which show resistance. On vegetable crops other than cucurbits, however, the use of insecticides remains the most reliable method of control. For recommended insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.

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