Vegetable leafminer

The vegetable leafminer (Liriomyza sativae) is commonly found in the southern United States from Florida to California and Hawaii, and in most of Central and South America. Occasionally it is reported in more northern areas because it is transported with plant material. It cannot survive cold areas except in greenhouses.

Symptoms
Foliage punctures caused by females during the acts of oviposition or feeding may cause a stippled appearance on foliage, but this damage is slight compared to the leaf mining activity of larvae. The irregular mine increases in width from about 0.25 mm to about 1.5 mm as the larva matures, and is virtually identical in appearance and impact with the mines of the chrysanthemum leaf miner (L. trifolii). Larvae are often easily visible within the mine where they remove the mesophyll between the surfaces of the leaf. Their fecal deposits are also evident in the mines.

Chemical
Foliar application of insecticides is often frequent in susceptible crops Insecticide susceptibility varies greatly both spatially and temporally. Many organophosphate and carbamate insecticides are no longer effective. Insecticides are disruptive to naturally occurring biological control agents, and leafminer outbreaks are sometimes reported to follow chemical insecticide treatment for other insects.

Non-chemical
Some crops vary in susceptibility to leaf mining. This has been noted, for example, in cultivars of tomato, cucumber, cantaloupe, and beans. However, the differences tend to be moderate, and not adequate for reliable protection. Nitrogen level and reflective mulches are sometimes said to influence leafminer populations, but responses have not been consistent. Placement of row covers over cantaloupe has been reported to prevent damage by leafminer. The same study evaluated the benefits of transparent polyethylene mulch, and found no reduction in leafminer populations. Sometimes crops are invaded when adjacent crops are especially suitable, in California, where cotton was an important source of invaders. Weeds are a source of flies, but also a source of parasitoids.