Leafminers rarely are abundant enough to injure the plants they infest. However, leafminer injury often is conspicuous and can make plants unattractive. Leafy vegetables, such as spinach, swiss chard or beets, often are considered more heavily injured by leafminers because edible parts are directly damaged. On woody plants, certain leafminers, such as the blackmine blotch leafminer of cottonwood, are a chronic and severe problem in parts of Colorado. Colorado Leafminers Dozens of leafminers occur in Colorado.
Several generations occur during the year.
They are particularly common during the cooler months of the growing season. The yellow and black adult beetle can be found chewing and skeletonizing small areas in the exterior leaf surface from late June through July. They also lay eggs during this period. Later the larvae initiate mines. Its injury is unusual because the older larvae often move out of the mines to fold and web together the leaf.