Species

Leafminers belong to the order Diptera, family Agromyzidae and, most commonly, genus Liriomyza.

The larval stages of many other insects of orders Diptera (flies), Lepidoptera (moths and butterflies) and Hymenoptera (ants, bees and wasps) can also be considered leafminers because they burrow through leaves in a similar manner.

Host/Site

As their name suggests, leafminers can be found on and around the leaves of plants. The type of plant infested depends on the species of leafminer involved. Crop plants include melons, cucumbers, squash, beans, peas, onions, peppers, tomatoes, eggplants, potatoes, celery, lettuce, and carrots. Ornamental plants include asters, calendulas, chrysanthemum, cineraria, gerbera, baby's breath, snapdragons, gypsophila, and marigolds. Shrubs and trees include birch, holly, rhododendron, and lilac.

Identification

Indicators

Life Cycle

Leafminers lay about 17 eggs per day in the leaf epidermis. They hatch in 2-5 days and are in larval stage for 4-7 days. It is during this stage that they damage plants. The larvae fall from the leaf onto the soil when they are ready to pupate. They reach maturity as flies after 10-15 days as pupae.

Natural Enemies

Parasitic wasps feed on leafminers and several other insects' larvae.

Monitoring

Besides looking for the blistering, blotching, and mines left behind by leafminers, one should look under the leaves of susceptible plants in early spring to check for the presence of their eggs. Yellow sticky cards placed among the leaves of the same plants will attract leafminer eggs and be a good indicator of the size of your leafminer population.

Action Threshold

Leafminer damage is most often cosmetic, but they can cause severe damage to crops, especially during seedling stage. Action should be taken when an infestation exceeds aesthetic standards or immediately when noted on economic crops.

Physical/Mechanical Controls

Pick and destroy infested leaves.

Plastic mulch used around the base of a plant can be effective in preventing larvae from getting into the soil in order to pupate.

Biological Controls

Encourage natural predators such as green lacewings and spiders. Diglyphus isaea, a species of parasitic wasp, has been found to be effective at controlling leafminer infestations. They are commercially available to purchase.

Chemical Controls

Chemical controls for leafminers are not suggested. Not only are they resistant to many insecticides used to try to control them, but they have also been found ineffective due to the larvae being located between the layers of leaves. This location provides a protected cover for the leafminers.

References

"Common Insect and Mite: Leafminers." 2006. WSU Hortsense (Cooperative Extension).18 June 2008.
<http://pep.wsu.edu/hortsense/>.

Delahaut, Karen. "Vegetable Leafminers." 1999. University of Wisconsin Extension. 27 Oct 2008.
<http://www.uwex.edu/ces/wihort/gardenfacts/X1044.pdf>.

Olkowski, William, Sheila Daar and Helga Olkowski. Common-Sense Pest Control: Least-Toxic Solutions for Your Home, Garden, Pets, and Community. Newtown, CT: Taunton Press, 1991.

Spring, Alexandra and Eric Day. "Leafminers." 2006. Department of Entomology, Virginia Tech. 27 Oct 2008. <http://everest.ento.vt.edu/~idlab/vegpests/vegfs/leafminers.html>.