The Azalea Leafminer, Caloptilia azaleella (Brants), is the larva of a tiny moth (the moth is yellow or golden colored and has purple markings on its wings). It is endemic to Japan but has been introduced worldwide, including most of the United States. Its larvae feed exclusively on the leaves of azaleas and rhododendrons. Although its northernmost range in the Eastern U.S. is described as “north to Long Island, New York,” it has been found near Boston, MA as long ago as 2011, and with a warming climate, could very well be present by now in southern Maine as well. It is also found from Florida to Texas, and in northern California and the Pacific Northwest. It undergoes several generations per year in Florida, three generations in Oregon, and two generations in New York.
The adult wingspread is about 10 to 13 mm. Most of its life as a moth is spent hidden among the leaves of its host plant.
The larvae mine the leaves only for the first half of their larval stage. Once larvae are about a half-inch in length, they emerge from the mines and feed as leafrollers or ‘leaftiers’ where they use silk webbing to roll or fold-up the leaves at the leaf tips or margins, especially on younger leaves near the stem ends. The mines result in brown, blister-like areas and the older larvae chew holes in the rolled-up leaves. Damaged leaves usually turn yellow and drop off, so heavy infestations can thus give rise to very unsightly plants. If the larvae are controlled soon enough, however, the plants may outgrow the initial injury.
As a means of cultural control, one can prune away and destroy infested branches, and strive to keep the plants healthy by keeping them adequately irrigated and fertilized. Healthy plants should be able to tolerate and outgrow the damage. Chemical control is difficult because at all stages, the larvae are protected by the leaf tissue. Also, by the time the injury is noticed, many of the larvae may have already completed their development. A mature larva will pupate inside a freshly rolled-up leaf and emerge as an adult moth in only about a week’s time, unless it’s the final generation in a northern region in which case it will spend the winter as either a last-instar larva or a pupa.
There are at least three known species of parasitoid eulophid wasps (genus Sympiesis) that act as a biological control as well, attacking the pupal stage of the leafminer.
Additional Information (with Photos):
- Azalea leafminer (University of Florida)
- Azalea leafminer (NC State Extension)
- Azalea leafminer (BugGuide.net)