Citrus Leaf Miner
The infestation can occur at any growth stage and is mainly visible on young leaves. Initial symptoms may be the appearance of deformed, twisted or curled leaves, that however, remain green. A close look reveals serpentine white or gray mine trails between the two leaf epidermis. A thin dark streak or dotted dark line, that corresponds to the larval frass, is visible inside the tunnels, more conspicuous from the underside. Larvae are often found at the end of these tunnels and several of them can be present per leaf. The damage to the leaves can be a source of infection by opportunistic fungi or bacteria. Heavy infestation can also lead to lower photosynthetic rates, resulting in stunted growth, reduced fruit size and quality. In severe cases, citrus leafminer infection can even cause total tree defoliation and eventual death for young trees.
Symptoms are caused by the feeding activity of the larvae of the citrus leafminer, Phyllocnistis citrella. The adults are tiny, brownish or gray moths with heavily fringed wings and a typical dark spot on the top of the front wing. They are mainly active during the cool temperatures of dawn and dusk, early morning and night. In spring, the females lay their eggs on the lower side of leaves. The hatching larvae are translucent greenish or yellow and feed mainly on leaves, even though fruits can also be attacked. They bore tunnels between the two leaf epidermis, resulting in distinctive silvery, serpentine mines. At the end of the larval stage, the leafminer emerge from the mine and enters its pupa stage by curling the leaf around itself. It is a major pest of citrus, found in virtually all major citrus-producing areas. Moreover, the susceptibility to other diseases, such as bacterial canker, is increased.
Predators include the green lacewings of the Neuroptora genus. There is also a wide array of parasitic wasps that attack and feed on the larvae of the citrus leafminer, among others, species of Tetrastichus. Organic insecticides containing spinosad, fish oil resin soap and Pongamia oil may be used as foliar spray applications to control the infestation by citrus leafminer. Neem oil can also be applied to deter the moths from laying their eggs on the leaves.
Always consider an integrated approach with preventive measures together with biological treatments. Insecticides are not entirely effective against infestations of citrus leafminer because larvae are protected by the leaf cuticle. If insecticides are needed, systemic and contact products should be applied when the adults are active. Several products are available as sprays, among others formulations containing imidaclorid, abamectin, tebufenozide, acetamiprid, thiamethoxam, diflubenzuron or spinetoram. Insecticides of the synthetic pyrethroid family were also used against this pest.