Have you ever been out for a hike in the woods or a stroll through your garden and noticed a pattern on the leaves of plants that is out of the ordinary? Kind of like this leaf?
Circuitous pattern on the leaf of a tree seedling. Some leaves below this one have been fed upon, as evidenced by the holes in them.
When I first came across a leaf that looked like this I was shocked and no idea what it could be. The only thought that came to mind was a diseased plant, but that was not the case here. The lines on the leaf above were created by an insect known as the ‘leafminer’.
What are leafminers?
Leafminer larvae become small flies as adults that are only a few millimeters in length. There are over 300 leafminer species worldwide and oftentimes leafminers spread by travelling on imported plants. Host plant preferences vary depending on the species of the leafminer, however, the damages caused are one in the same. Some potential host plants for leafminers include vegetables, dahlias, and ornamentals.
Of the roughly 300 leaf miner species worldwide, these five are considered to be serious pests:
- Vegetable leaf miner (Liriomyza sativae)
- Tomato leaf miner (Liriomyza bryoniae)
- Chickpea leaf miner (Liriomyza cicerina)
- Serpentine leaf miner (Liriomyza huidobrensis)
- American serpentine leaf miner (Liriomyza trifolii).
The Life Cycle of Leafminers
The adult female leafminers create small holes in leaves known as egg spots, which allows them to lay eggs and eat the sap that is released by the plant. Once the larvae hatches from the egg spots, they begin to eat their way into the leaf, leaving extensive lines due to ‘mining’ or eating. Before pupating, the larvae will cut an exit hole in the leaf to fall into the soil below to pupate. From the pupae, an adult leafminer will emerge and be capable of laying up to 160 eggs just 13 days after it emerges. The tunnels created in the leaves by the leafminer cause damage to plants such as dried out leaves, early defoliation, and potential for bacteria to enter via feeding spots.
An adult leaf miner (Link to photo source)
Leafminer Impacts
Overall, leaf miners do not impact plant growth and are important for creating a balance in the forest by contributing to the food chain. However, many leaf miners have become invasive pests which impact both forests and agricultural environments. The vast and rapid growth of leaf miners across the world has caused ecological and economic issues for areas that are heavily impacted. If you see leaf miners in the woods or happen to notice them in your garden, it is important to limit pesticide use. In this case, pesticide use is counterproductive because it kills other insects, including insects that prey on leafminers, allowing the leafminer population to increase. Here is a link to resources about limiting pesticide use.
Natural Alternatives
There are several natural alternatives to pesticides that can be used to deter leafminers. First, try clipping off the leaves that have miners present and be sure to destroy the leaf. After harvesting your crops, till your garden to destroy the pupae and reduce the chances of pupae emerging. Lastly, if all else fails, find some fine mesh netting which can be placed over your crops to keep the flies out. Find out more by reading this University of Minnesota factsheet about leafminers
