What Is Eating My Citrus Leaves?

Several insects and mites feed on citrus leaves, and the type of damage you see is the fastest way to narrow down the culprit. Serpentine silvery trails mean leafminers; large ragged holes suggest caterpillars or snails; curled, sticky new growth points to aphids or psyllids; and a dull, bronzed appearance often comes from mites too small to see with the naked eye. The good news is that most leaf-chewing pests do cosmetic damage a healthy tree can tolerate, but a few carry diseases that pose a far bigger threat than the feeding itself.

Citrus Leafminer

If you notice winding, silvery-white trails snaking across young leaves, you are almost certainly looking at the work of the citrus leafminer, Phyllocnistis citrella. This tiny moth lays eggs on tender new growth, and the larvae tunnel between the upper and lower surfaces of the leaf, leaving a visible trail of frass inside the mine. The damaged tissue turns silvery or translucent and the leaf edges often curl downward. Leafminers are one of the most widespread chewing pests of citrus worldwide, found in virtually every major citrus-growing region.

A single larva stays inside a single leaf for its entire larval stage, pupating at the leaf margin in a rolled-over flap. Because the insect targets only the youngest, most tender flush, mature leaves are left alone. That means damage tends to appear in waves that coincide with new growth flushes, especially the vigorous summer flush in warm climates. Leafminer populations usually peak in late summer when temperatures are high and trees are pushing out new leaves rapidly.

Despite the dramatic appearance, leafminer feeding alone is rarely fatal. Research on three citrus species found that infestation did not exceed about 10 percent of the total leaf surface of affected plants, and the unaffected green areas of infested leaves maintained normal rates of water transport and photosynthesis.¹ In other words, the tree compensates reasonably well. For mature, established trees, leafminer damage is largely cosmetic. Young nursery trees and newly planted trees are more vulnerable because they have fewer total leaves, so losing photosynthetic area matters more.

Why Leafminer Damage Can Invite Something Worse

The real concern with leafminers is not the tunneling itself but what it opens the door for. The wounds the larvae create are entry points for the bacterium that causes citrus canker, Xanthomonas citri. Studies in Florida showed that leaves damaged by leafminers developed roughly six times more canker lesions than undamaged leaves on the same cultivar when exposed to the bacterium.² In commercial grapefruit and lemon groves surveyed during late July and August, an average of 79 percent of canker-infected leaves had lesions directly associated with leafminer damage, and those leaves carried an average of 36 more lesions per leaf than leaves without mining.²

Brazilian research confirmed the pattern: plants that were inoculated with the canker pathogen after leafminer infestation showed higher disease incidence, greater severity, and shorter incubation periods than plants without insect damage.³ The timing matters: the peak of leafminer activity in summer overlaps with the warm, wet conditions that favor canker spread. If you live in a region where citrus canker is present, managing leafminers is less about protecting leaves and more about reducing the pathways for bacterial infection.

Caterpillars and Swallowtail Larvae

Large, irregular holes chewed out of the leaf margins, or entire young leaves stripped down to the midrib, usually point to caterpillars. Several species of swallowtail butterfly use citrus as a host plant. In tropical and subtropical Asia, the lemon butterfly (Papilio demoleus) is one of the most common citrus defoliators.⁴ In North America, the giant swallowtail (Papilio cresphontes) fills a similar role. The young caterpillars are colored to resemble bird droppings, which can make them surprisingly hard to spot on a leaf.

Caterpillar damage looks alarming because it is so visible: you can lose a noticeable chunk of foliage in a few days. But on a full-size tree with thousands of leaves, a handful of caterpillars rarely cause meaningful harm. For young trees or potted citrus, where every leaf counts, hand-picking is the simplest and most effective control. If you grow citrus in a region with native swallowtails, keep in mind that these are valued pollinators as adults, so spraying mature trees with broad-spectrum insecticides to kill a few caterpillars usually does more ecological harm than good.

The Asian Citrus Psyllid and Greening Disease

Not all citrus leaf damage comes from chewing. The Asian citrus psyllid (Diaphorina citri) is a tiny sap-sucking insect about the size of an aphid that feeds on new growth. Its feeding alone causes leaf curling and distortion of young shoots, which you might confuse with aphid damage. But the psyllid is far more consequential because it is the primary vector of the bacterium behind huanglongbing (HLB), commonly called citrus greening disease, which is considered the most serious disease of citrus worldwide.⁵

Greening disease causes blotchy, asymmetrical yellowing of leaves (sometimes called “yellow dragon” patterning), lopsided bitter fruit, and eventual tree decline. There is no cure. Once a tree is infected, it will gradually become unproductive over several years. The bacterium, Candidatus Liberibacter asiaticus, lives in the phloem, the tissue that transports sugars through the plant. Psyllids pick it up when feeding on an infected tree and inject it into the next tree they visit.

Interestingly, not all life stages of the psyllid transmit the pathogen equally. Research on the insect’s mouthpart anatomy found that while first-instar nymphs have a food canal wide enough to ingest the bacteria, their salivary canal may be too narrow to inject it back into a plant, which could explain why very young nymphs appear unable to spread HLB.⁵ Older nymphs and adults, however, transmit readily. If you spot psyllids on your citrus, the urgency is less about the leaf damage and more about whether they are carrying HLB. In regions where greening is established (Florida, parts of Texas, California’s southern border, much of Southeast Asia and Brazil), any psyllid sighting warrants action.

Aphids on Citrus

Aphids are soft-bodied insects that cluster on the undersides of new leaves and along tender shoot tips. They feed by piercing the leaf and extracting sap, which causes the new growth to curl, pucker, and sometimes become stunted. You will often notice a shiny, sticky residue on the leaves and anything below them; that is honeydew, a sugary waste product aphids excrete, and it frequently develops a black coating of sooty mold.

Several aphid species target citrus. Surveys of aphids landing on adult citrus trees found that Aphis gossypii (the cotton or melon aphid) made up roughly half of all aphids captured, with Aphis spiraecola (the spirea aphid) accounting for about a third, and the black citrus aphid (Toxoptera aurantii) around 11 percent.⁶ What makes this finding unsettling is the sheer scale of visitation: on average, over 37,000 aphids carrying citrus tristeza virus (CTV) visited a single tree during one spring season. Between 19 and 27 percent of landed aphids tested positive for the virus, depending on the species.⁶

CTV causes a range of symptoms from mild decline to rapid death, depending on the virus strain and the rootstock the tree is grafted onto. Trees on sour orange rootstock are particularly susceptible. For backyard growers, the practical message is that aphid control alone will not prevent CTV because the insect visits are so numerous and so brief that even aggressive spraying misses most of them. Using CTV-tolerant rootstocks is a much more reliable defense. As for the leaf curling itself, a strong blast of water from a hose knocks most aphids off young shoots, and natural predators like ladybugs and lacewings usually bring populations under control within a few weeks if you avoid broad-spectrum sprays that kill those predators too.

Mites, Thrips, and Other Less Obvious Culprits

Some citrus leaf damage comes from creatures you cannot easily see without a hand lens. Citrus rust mites (Phyllocoptruta oleivora) are microscopic, feeding on the leaf surface and causing a silvery or bronze discoloration. They are better known for the russeting they cause on fruit rinds, but leaf feeding can reduce photosynthesis and, in heavy infestations, lead to premature leaf drop. Spider mites, particularly the citrus red mite, produce fine stippling on the upper leaf surface and sometimes leave visible webbing on the undersides.

Thrips are another set of tiny pests that scrape the surface of young leaves and petals. Species such as Scirtothrips citri (citrus thrips) and Pezothrips kellyanus (Kelly’s citrus thrips) are widespread in citrus-growing regions.⁴ Their feeding creates a silvery scarring pattern on leaves and can leave distorted, curled new growth. On fruit, thrips damage shows up as a ring of scarring around the stem end.

Then there are the non-insect chewers. Snails and slugs leave large, irregular holes with smooth edges, and you can confirm their involvement by the silvery slime trails on and around the tree. They tend to feed at night, so you may never see the culprit during the day. Grasshoppers and katydids occasionally chew citrus leaves as well, especially in late summer when other vegetation dries out, though they are rarely a persistent problem on citrus.

Telling the Pests Apart by the Damage They Leave

When you find chewed, distorted, or discolored citrus leaves, the damage pattern narrows the suspect list quickly:

Serpentine silvery trails: Citrus leafminer larvae tunneling between leaf surfaces. Typically on the youngest flush.
Large ragged holes or missing leaf sections: Caterpillars (look for frass pellets nearby) or snails (look for slime trails, especially at night).
Curled, sticky new growth: Aphids or psyllids. Check the undersides of young leaves for clusters of small insects. Psyllids hold their bodies at a characteristic 45-degree angle when feeding.
Silvery or bronze discoloration without holes: Mites or thrips. Use a hand lens; if you see tiny elongated insects, they are thrips. If you see almost nothing but the damage is there, suspect mites.
Blotchy yellow mottling, asymmetric between leaf halves: This is less likely a feeding pest and more likely a disease symptom, potentially citrus greening. Get the tree tested.

When To Worry and When To Let It Go

A healthy, mature citrus tree can tolerate a surprising amount of leaf damage without any drop in fruit production. Research showing that leafminer-infested leaves still photosynthesize normally in their undamaged areas illustrates why: the tree has plenty of green tissue to compensate.¹ Cosmetic damage from leafminers, a few caterpillars, or minor aphid curling on a backyard tree is not worth reaching for pesticides, especially since broad-spectrum sprays kill the beneficial insects that keep pests in check.

The situations that do call for intervention are the ones involving disease transmission. If you are in a region with citrus greening, monitoring for and managing the Asian citrus psyllid is critical because no amount of good horticulture can save a tree once HLB takes hold. Similarly, if citrus canker is present in your area, leafminer management during the summer flush can significantly reduce bacterial entry points. In those cases, targeted insecticide sprays timed to the vulnerable new-flush period, or systemic products applied as a soil drench, are the standard approach. For organic growers, spinosad-based sprays and horticultural oils timed to the egg-laying period offer partial control of leafminers.

Soil Drenches, Oils, and Biological Controls

The management strategy depends entirely on which pest you are dealing with and whether disease is a factor. For aphids and psyllids, horticultural oil or insecticidal soap applied to new growth flushes smothers the insects on contact. These products break down quickly and are less harmful to natural enemies than synthetic alternatives. For psyllids specifically, systemic neonicotinoid soil drenches are widely used in commercial citrus to protect young trees during their most vulnerable establishment years, though their effect on pollinators has prompted restrictions in some jurisdictions.

Biological control has a strong track record in citrus. The parasitic wasp Ageniaspis citricola was introduced into Florida and other citrus regions specifically to attack citrus leafminer larvae, and it has become one of the most effective agents keeping leafminer populations below damaging thresholds in many areas. Ladybugs, lacewing larvae, and hover fly larvae are voracious aphid predators. Encouraging these beneficial insects by avoiding unnecessary spraying is one of the most effective long-term pest management strategies for backyard citrus growers.

For caterpillars, Bacillus thuringiensis (Bt) sprays target caterpillars specifically without harming other insects. Apply it to young foliage when you first notice feeding damage; the caterpillars ingest the bacteria on the leaf surface and stop feeding within a day or two. Hand-picking remains the simplest option if you have only a few trees. Snails can be managed with iron phosphate baits scattered around the base of the tree, combined with removing their daytime hiding spots like stacked pots, boards, or dense ground cover right against the trunk.

Nutrient Deficiencies That Mimic Pest Damage

Before you blame an insect, take a closer look at the pattern. Some leaf problems that look like pest damage are actually nutritional issues. Iron deficiency causes interveinal chlorosis, where the leaf turns yellow but the veins stay green, a pattern that can be mistaken for the mottling caused by citrus greening. Zinc deficiency produces small, narrow leaves with yellow blotching between veins, sometimes called “little leaf.” Magnesium deficiency starts as yellowing of the older leaves between the veins, progressing inward from the leaf edge.

The key distinction is that nutrient deficiencies tend to affect many leaves uniformly across a section of the canopy, while pest damage is usually patchy and concentrated on the newest growth (leafminers, aphids, psyllids) or scattered randomly (caterpillars, snails). If you see no insects, no frass, no slime trails, and no webbing, consider getting a soil test or a leaf tissue analysis before treating for pests. Applying the wrong fix wastes time and money, and spraying for insects when the real problem is an alkaline soil locking up iron will not help your tree at all.

1
Tree Physiology / Oxford Academic. Does citrus leaf miner impair hydraulics and fitness of citrus host plants?
2
Florida Entomologist. Exacerbation of Citrus Canker by Citrus Leafminer Phyllocnistis citrella in Florida
3
Fitopatologia Brasileira. Injuries caused by citrus leafminer (Phyllocnistis citrella) exacerbate citrus canker (Xanthomonas axonopodis pv. citri) infection
4
IntechOpen. Ecology, Biology, Damage, and Management of Sucking and Chewing Insect Pests of Citrus
5
PubMed Central. Stylet morphometrics and citrus leaf vein structure in relation to feeding behavior of the Asian citrus psyllid Diaphorina citri, vector of citrus huanglongbing bacterium
6
PubMed Central. Estimation of the number of aphids carrying Citrus tristeza virus that visit adult citrus trees