Photographer:Jeffrey W. Lotz Affiliation: Florida Department of Agriculture and Consumer Services Source:www.bugwood.org Copyright:CC BY 3.0
Adult Description: Citrus leafminers, Phyllocnistis citrella, are very small moths (2-4mm long) that may be too small to be easily noticed. They have white and silvery iridescent scales on the forewings and black and tan markings and a black spot on each wing tip. The hind wings are white with long fringe-like scales.
Larvae Description: The larvae are very small (1-2mm) and a translucent greenish-yellow and can be found mining inside young citrus leaves. A characteristic of Phyllocnistis citrella is that pupae establish a pupal cell at the leaf margin. The larvae mine on both the upper and lower surfaces of the leaves which causes the leaves to curl up and look distorted. The easiest way to know there is a citrus leafminer present in crops is by the silvery and serpentine “mining” pattern created by the larvae.
Host Plant: All Citrus cultivars and many species in the Rutaceae family. Grapefruit, tangerine and pummelo are most susceptible; but it has also been found on cinnamon, jasmine, mistletoe, some legumes and willow.
Heavy infestations can hinder the growth of newly planted trees or reduce fruit production of mature trees. Foliar and fruit damage is severe when moth populations are high. Although mining usually occurs on leaves, it also can occur on fruit, particularly grapefruit, reducing the market value of produce or making them completely unmarketable. In Florida, Phyllocnistis citrella also helps spread citrus canker because of leaf damage from the mine. Luckily, this moth does not vector citrus canker so does not carrying the bacteria with it into other states. The damage caused by this moth alone makes it a big pest in the citrus industry.
Depending on temperature it can take the citrus leafminer 13 to 52 days to complete a full generation. The adults copulate 14 to 24 hours after emergence and lay their eggs afterwards. A single female may lay about 50 eggs during her lifetime. Larvae emerge from the eggs after 2 to 10 days. The total development time takes 5 to 20 days and larvae go through four instars with the first instar feeding immediately. During the course of larval development, the mines become more visible and larval excrement (frass) forms a central trail within the mine. The third instar usually forms a mine that is directed towards the leaf margin, where it molts into the fourth instar and it forms a silken cocoon within the mine. The leaf curls over the pupal cell. The pupal stage takes 6 to 22 days. Just before adult emergence, the pupa uses a spine on its head to make an opening in the chamber to emerge from. Adults are short-lived (2 to 12 days), nectar-feeding and are most active from dusk to early morning. During the day they rest on the underside of leaves.
The citrus leaf miner was first reported in Florida in 1993 and has spread throughout the whole state. By late 1994, it had spread to Alabama, Louisiana and Texas. It was found in Texas orchards in Hidalgo County and by November 1994 it had spread throughout the southern Texas citrus growing area. In 2000 the moth appeared in southern California presumably from Mexico. Once in California it has started spreading north and now infests citrus orchards in southern and central California.
India and Southern China
U.S. Habitat: Throughout the citrus-growing regions.
U.S. Present: AL, FL, LA and TX
The citrus peelminer (Marmara gulosa), is a small moth that also attacks citrus but it differ from the citrus leafminer because it attacks stems and fruit instead of new growth. Also, the larvae do not leave frass (excrement) trails in the mine and the pupae have decorative ball on its cocoon while the citrus leafminer cocoon’s do not.
In Florida, several species of parasitoids have moved naturally onto this introduced pest, causing up to 90% mortality. One of the most efficient parasitoids is, Ageniaspis citricola, which is responsible for 30% of the mortality. This parasitoid was then introduced into Hawaii in the early 2000s and has provided good control on the islands. Other management techniques are pheromone traps, cultural and chemical control strategies.
Citrus orchards must be chemically treated differently based on age and whether the trees are bearing fruits or not. On young non/bearing trees, soil-applied neonicotinoid insecticides are the most effective chemical controls that prevent mining damage to new growth and do not have a direct impact on natural leafminer enemies. For the insecticides to work the application must be finely timed and not before a large rainfall. For older, bearing trees foliar insecticide sprays focusing on the new flush growth, is the only way to prevent infestation. However, this application is not as effective, because new flush growth is quite unsynchronized; one must try to treat all the peripheral leaves in the canopy. Overall, the foliar sprays should be used immediately following the feather leaf stage.
Avoid pruning live branches more than once a year, so that the cycles of flushing are uniform and short. Once the leaves harden, the pest will not be able to mine the leaves. Do not prune off leaves damaged by citrus leaf miner because undamaged areas of the leaves continue to produce food for the tree. Horticultural oils can be applied to damaged leaves and kill off the moth eggs. These oils are also very effective when applied during peak abundance of the moths.
Traps baited with a pheromone ((7Z-11Z)-7, 11-hexadecadienal) are available for Phyllocnistis citrella and help determine when moths are flying and depositing eggs. Traps are places in citrus trees at chest-height from March through November. Follow the manufacturer's recommendations for maintaining the trap, such as the frequency with which pheromones should be replaced. Use one trap per 5 acres and check the traps weekly for moths. The citrus leafminer is most abundant when citrus is flushing in the summer and fall months. These traps will help you determine when male flights are occurring and when to time insecticide applications, if needed.
Ando, T., Taguchi, K.Y., Uchiyama, M., Ujiye, T., and Kuroko, H. 1985. (7Z-11Z)-7, 11-hexadecadienal sex attractant of the citrus leafminer moth, Phyllocnistis citrella Stainton (Lepidoptera, Phyllocnistidae). Agric. Biol. Chem. Tokyo 49:3633-3653.
Badawy A. 1967. The morphology and biology of Phyllocnistis citrella Staint., a citrus leaf miner in the Sudan. Bulletin of the Entomological Society of Egypt 51:95-103.
Grafton-Cardwell E, Montez, G. 2009. Citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae). Citrus Entomology, University of California.
Johnson SJ, Vaughn A, Bourgeois WJ. 1998. Biological control of the citrus leafminer with Ageniaspis citricola in Louisiana. Louisiana Agric. Summer 1998, pp. 11-14.
Smith JM, Hoy MA. 1995. Rearing methods for Ageniaspis citricola (Hymenoptera: Encyrtidae) and Cirrospilus quadristriatus (Hymenoptera: Eulophidae) released in a classical biological control program for citrus leafminer Phyllocnistis citrella (Lepidoptera: Gracillariidae). Florida Entomologist.