Leafminers are an insect found in gardens, landscaping, and greenhouses whose larvae feed between the surfaces of a plant's leaf often reducing harvested plants due to their infestation. The larvae can often be found on crops such as beans, blackberry bushes, cabbage, citrus trees, lettuce, peppers, spinach, and landscaping flowers and shrubs.
Adults of the leafminer are 1/10 inch long files that are black with yellow stripes and transparent wings. Their appearance is similar to a housefly.
The leafminer larvae are worm-like maggots that are ⅓ inches long with a pale yellow or green body. These pests create tunnels in plant leaves and leave a trail of black fecal matter as they feed.
Older larvae will hibernate in the soil under host plants until spring where they pupae into adults and mating season begins.
Females lay up to 250 eggs below the surface of the leaf that often takes on the form of raised spots to the human eye.
After about 10 days, the eggs hatch, and larvae tunnel under the leaf surface, feeding as they go.
Within 2 to 3 weeks the larvae mature and start the pupate cycle by dropping off of the leaf and digging 2 inches down into the soil below. In another 15 days, an adult will emerge into a fly and begin the next generation life cycle.
To reduce the damage caused by these pests without harming plants or precious pets, natural control is best. Also, pesticides can do more damage by increasing the infestation of leafminers.
Natural control means monitoring plant leaves often. Once you spot tunneling activity, squeeze the leaf at the tunnel with your fingers to destroy any larvae that may be present.
Next, weed out any badly infested leaves since leafminers don't usually damage healthy and mature plants.
Then, invest in floating row covers to prevent adult leafminer flies from laying eggs on plant leaves.
Next, consider using the parasitic wasp, a beneficial insect that can destroy leafminer larva. The wasp is especially beneficial to greenhouses.
Finally, using plastic mulched to cover the soil under plants that have been affected by leafminers can prevent the larvae from reaching the ground to cocoon into an adult.