Facts, Identification & Control
There are a huge number of insects that are grouped as leaf miners. This common name comes from the larval stage of the insect eating and mining inside the leaves of its host plant. This group of insects includes moths, flies, wasps and beetles, so the diversity, appearance and habits of the leaf miner group are extremely variable.
The easiest, most accurate way to identify leaf miners is to look for their damage to host plants. Since the larvae feed within the plant’s leaves or needles, they produce either large blotches or tunnels that wander under the surface of the leaf. Leaf miner damage is easy to see. Leaf miner larvae are very flat, a trait that enables them to adapt to feeding inside a leaf. Feeding larvae eat the green tissue inside the leaf and leave a meandering trail that is covered by a thin case or cover. If there are many larvae feeding on a single leaf, their tunnels may join and give the appearance of large blemishes or spots.
Behavior, Diet, Habits
Leaf miners go through complete metamorphosis: egg, larva (grub), pupa (cocoon) and adult. Adults lay their eggs on the leaf’s surface and the larvae burrow into the leaf. Leaf miner larvae usually spend their entire larval stage inside the host plant’s leaf. Some leaf miners will pupate within the leaf, but most pupate in the soil.
Because of their diversity, leaf miners have a large number of preferred host plants. Among these are vegetables such as cabbage, lettuce, tomatoes, peas and beans, plus flowering plants such as begonias, dahlias, impatiens, marigolds and petunias. In addition, leaf miners will infest trees or shrubs such as evergreens, cottonwoods, elms, aspens, azaleas, boxwoods and birch.
Larval damage normally has little or no effect on plant growth and almost never kills a plant, unless the plant is in the seedling stage of growth. However, extremely large populations of leaf miners may slow plant growth and cause infested leaves to drop before the fall season.
Most leaf miner species have many predators and disease organisms that provide leaf miner population controls. Therefore, applying insecticides is not always the best way to handle a leaf miner problem since conventional insecticides will kill predators as well as leaf miners. If you need help with a leaf miner problem, always seek the advice and assistance of your pest management professional. Some other suggestions to help the homeowner control leaf miners include:
- Covering plants with row covers to prevent the adults from getting access to leaves and laying eggs.
- Remove all leaves infested by larvae.
- Keep plants well watered to help keep them healthy and vigorous.
- For leaf miners, homeowners should use insecticides only as a last resort. However, if using insecticides, always involve your PMP in the application planning and procedures.