How to Identify and Control Citrus Leafminer

The citrus leafminer (Phyllocnistis citrella Stainton) is a common pest affecting citrus growers worldwide. As its name suggests, this pest creates unsightly tunnels beneath the surface of leaves. Originally from Asia, the citrus leafminer has spread to all major citrus-growing regions due to the widespread cultivation of citrus fruits. In the United States, it was first documented in Florida in 1993 and has since been found in Texas, southern California, and other citrus-producing states.

A member of the Gracillariidae family, Phyllocnistis citrella is a light-colored moth. The tunneling or “mining” of citrus leaves is caused by its larvae. Another closely related pest, the citrus peelminer (Marmara gulosa), mines citrus peels rather than leaves.

While over 30 insect pests affect citrus cultivars, the leafminer is not considered a major threat compared to other leaf-mining species. Studies indicate that while leafminers do not significantly impact the fruit yield of mature citrus trees (over four years old), they can stunt the growth of young trees and nursery stock by reducing the photosynthetic activity of mined leaves. Additionally, the damage they create makes citrus trees more vulnerable to other pests, such as the citrus canker bacteria.

Natural predators help regulate leafminer populations, so careful consideration is needed when using chemical treatments to avoid harming these beneficial insects.

What Are Citrus Leafminers?

Phyllocnistis citrella Stainton, commonly abbreviated as CLM, is a small, silvery-white moth measuring approximately 2 mm in length with a wingspan of around 5 mm. Although visible to the naked eye, its tiny size often allows it to go unnoticed. This delicate moth has wings streaked with brown and white markings, ending in a distinctive black spot on each wingtip.

CLM is nocturnal, most active from dusk to dawn, when mating occurs. During their short lifespan of 2 to 12 days, adult females lay up to 50 eggs on the underside of young citrus leaves, typically near the midrib or veins. The eggs resemble tiny water droplets. A single leaf can be infested by multiple larvae, but older leaves are less vulnerable, as their hardened surfaces make them more difficult for larvae to penetrate.

Life Cycle

Female citrus leafminers lay tiny eggs that take between 4 to 10 days to hatch, depending on weather conditions. Once hatched, the light yellow larvae immediately begin feeding and tunneling beneath the leaf surface. The larval stage consists of four developmental instars: three feeding stages and one non-feeding prepupal stage. Each instar lasts between 10 to 19 days, depending on temperature.

During the final instar, the larva moves to the edge of the leaf and exits the mine, causing a slight curling of the leaf. Within this curl, the larva transforms into a light-brown prepupa before darkening into a pupa. The pupal stage lasts 8 to 20 days before the adult citrus leafminer moth emerges. Mating begins immediately, and the cycle repeats.

The number of leafminer generations per year varies by location. In Florida, one generation emerges approximately every three weeks. In California, there can be seven to eight generations per year, while in Pakistan, an astonishing 16 generations have been recorded. Leafminers are particularly drawn to new leaf flushes for egg-laying. While most citrus damage occurs in late summer and early fall, certain plants, such as California’s coastal lemons, experience continuous flushes of new growth, prolonging the infestation.

Identifying Citrus Leafminer Damage

Leafminer damage is unsightly and often alarming for citrus growers. As citrus leafminer larvae feed on plant tissue, they create shallow, serpentine tunnels just beneath the leaf surface. Interestingly, a larva never doubles back or crosses its own tunnel, and multiple larvae on the same leaf also avoid crossing paths. Their damage coincides with citrus foliage flushing cycles, as newly emerged larvae burrow through young leaves.

As they tunnel, larvae leave behind a trail of frass (excrement), appearing as a thin dark line inside the mines. Leafminers primarily target citrus and citrus hybrids but can also infest orange jasmine (Murraya paniculata) and boxthorn (Atalantia buxifolia). While their feeding can impact young trees, mature trees are largely unaffected, as older foliage becomes too tough for the larvae to penetrate.

Older leaves with mined patterns indicate past infestations where larvae have exited. These tunnels are often necrotic due to plant tissue death.

Control

For mature citrus trees, citrus leafminers rarely cause long-term damage. However, their feeding creates wounds that make trees more susceptible to more serious pests and can hinder the healthy development of young trees. While the damaged flush growth may appear alarming, the best approach is often to leave it alone.

Many natural enemies help keep citrus leafminer populations in check, making it essential to protect beneficial insects, including bees. Using harmful chemicals can disrupt this balance, so it’s important to consider alternative pest management strategies that support a healthy ecosystem.

Organic Control

Horticultural oil, including neem oil, is also sometimes used by commercial and home growers during the flush and sprayed on developing leaves. The oils may help inhibit eggs from hatching.

Continue to spray the leaves for 10-14 days until they have hardened and stop spraying once the temperatures reach above 80°F (27°C). 

Cultural Control

Citrus growers often use sex pheromone sticky traps to monitor citrus leafminer populations, though these traps only attract males. While not effective for controlling infestations, they help estimate pest levels. If you need assistance identifying insects on your sticky traps, you can send them to your local extension office or county agricultural commissioner’s office for analysis.

Hand-picking heavily infested leaves is a common cultural control method to reduce leafminer populations. Discard affected leaves by submerging them in a bucket of soapy water to drown the larvae. However, avoid excessive pruning, as undamaged leaves can still photosynthesize.

Additionally, pruning live branches more than once per season or applying nitrogen fertilizer during a heavy leafminer infestation can encourage excessive flushing, worsening the problem. Vigorous shoots that develop above the graft union of mature trees are particularly attractive to egg-laying adult moths. Removing these shoots can help deter infestations.

Leafminers thrive in optimal conditions of 75 to 80°F (24-27°C) with relative humidity above 60%. In inland California, for example, high summer temperatures naturally suppress populations, whereas cooler coastal environments provide more favorable conditions. With rising global temperatures, this pest has the potential to expand its range, particularly during spring and autumn.

Biological Control

Protecting the natural enemies of the citrus leafminer is crucial for managing infestations. Several species of parasitic wasps, including Ageniaspis citricola and Cirrospilus coachella, play a key role in controlling leafminer populations. These wasps lay their eggs directly inside the leafminer tunnels, and once hatched, their larvae consume the citrus leafminer larvae.

These beneficial wasps typically do not need to be introduced into the environment, as they are already present in many citrus-growing regions. In Florida, for example, natural enemies account for over 50% of citrus leafminer larval mortality, highlighting their importance in maintaining a balanced ecosystem.

Other Insecticidal Controls

It may be overkill to use additional chemical control to manage this pest due to the potential harm they pose to natural enemies of the citrus leafminer. Many of these insecticides are not effective because it is hard to reach under the surface of leaves into the tunnels and make contact with the larvae. 

Frequently Asked Questions