This is a picture of Leaf Miner.
Many plants are host to different Leaf Miner flies that will lay an egg on the underside of the plant leaf. In cold weather the larvae (the maggot stage) stays dormant and protected in soil. As the weather warms up the larvae emerges and enter into the leaf tissue. Damage from Leaf Miner can restrict plant growth, and one leaf may host up to 6 or more maggots.
The larvae create white or clear tunnels on the leaves as shown in the photo, and leave a black residue that is their fecal matter (frass in gardening terms). The adults are grey or black flies about 1/10th of an inch long and look similar to house flies.
Plants in peril of Leaf Miner include peppers, berry bushes, beans, lettuce and spinach and various bushes, trees and flowering shrubs.
Most common damage is stunting of the plant. Certain bacteria and viruses can enter into existing abandoned tunnels causing defoliation or leaf dropping. The plant yield is compromised and becomes unattractive.
Organic methods of controlling leaf miner work well are are highly recommended, as they are natural and will not harm the beneficial insects found in your gardens.
When you see tunnelling ocurring on leaves in your garden, crush the larvae between your fingers. Pick off any infested leaves.
Be prepared and proactive and you can control this infestation!
Apply 'New World Organics' 100% natural insecticides for best control of this nuisance but disruptive insect/larvae stage.