An adult leafminer is a small, black with yellow markings, critter that looks like a fly – with bumblebee colors. The leafminer goes through four stages of life; egg, larva, pupa, and adult. There are many different species of leafminers, but primarily this focus is on vegetable leafminers, although most leafminers do the same types of damage.
The vegetable leafminer is found from the tropics into the southeastern and southwestern U.S. They can be found 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.
Closely related to the serpentine leafminer which feeds almost exclusively on crucifers, the vegetable leafminer infests a wide variety of plants. Some crop hosts include squash, okra, pea, tomato, bean, cabbage, turnip, potato, tobacco, cotton, radish, spinach, watermelon, beet, pepper, alfalfa, clover, vetch, and plantain.
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.
In warm weather, leafminers may be more active. The life cycle is only 2 weeks long. Eggs are inserted into leaves and larvae feed between leaf surfaces, creating a “mine.” At high population levels, entire leaves may be covered with mines. Mature larvae leave the mines, dropping to the ground to pupate. There can be five to ten generations per year. Development continues all year, the population moving from one host to another as new host plants become available each season.
Leafminers rarely require treatment in home gardens. Small seedlings can be protected by protective cloth. On plants such as cole crops, lettuce, and spinach, clip off and remove older infested leaves. Remove any possible host weeds from the garden that may attract leafminers. Leafminers are often kept under good control by natural parasites. A natural enemy of leafminers are several species of parasitic wasps, which attack and destroy the larvae in the mines. Insecticides are not very effective for leafminer control.
When the gardening season has ended it is a good practice to remove and destroy any left over plant matter or debris, as this will help to control leafminer populations. Burning the left over plant materials is the best option in order to kill any leafminer pupa or larvae that may remain.