Identification. Adult Liriomyza are between 1/16 and 1/8 of an inch (1-3 mm) in length, yellow and black in color and have one pair of clear wings (Figure 1). Larvae (maggots) are light yellow in color and cylindrical in shape but are not easily observed because they occur inside the leaf tissues. Pupae are oblong in shape and brown in color. It is difficult to distinguish among Liriomyza species but in general, the adult L. trifolii is smaller and relatively more yellow in color than L. huidobrensis. Leafmines are produced by the larvae of both species, but their shape and position on the leaf may also provide clues to species identification. Liriomyza trifolii leaf-mines are more commonly found on the upper leaf surface whereas L. huidobrensis mines mostly occur on the lower leaf surface. Liriomyza trifolii leaf-mines are also narrower and may occur near the leaf margin whereas L. huidobrensis mines are more frequently found near the base of the leaf, often along the middle veins.
Figure 1. Adult Liriomyza spp . Photo credit: Clemson University – USDA Cooperative Extension Slide Series, www.forestryimages.org
Biology and Damage. Adult females feed on leaf tissues by puncturing the leaf surface with their ovipositors and ingesting the liquid cell contents. Females also puncture leaf tissue to lay their eggs and may live for 7 to 10 days. Both feeding and oviposition punctures turn white and damaged foliage looks stippled or speckled. Eggs hatch 2-5 days after oviposition. Each larvae feeds on leaf tissue making a winding tunnel (serpentine leaf-mine) or blotch on the leaf. The leaf-mines become increasingly larger in size as the larvae feed and grow through 3 immature stages (instars). Once feeding is completed, mature larvae cut a slit in the leaf surface, exit the leaf and drop to the ground (or potted soil-mix) where they pupate. Many generations can occur each year as long as temperatures are above 50 °F (10 °C). Egg to adult development may take as little as two weeks at 95 °F (35 °C) or as long as 8 weeks at 60 °F (16 °C). Liriomyza huidobrensis grows best under moderate temperatures (at or bellow 70 °F) while L. trifolii prefers warmer summer temperatures (above 75 °F). Most damage is caused by the larvae. Mined leaves are unattractive and unmarketable (Figure 2). Some damage may be tolerated in crops where foliage is not marketed, such as cut flower and seed production crops. Heavy damage may slow plant growth and cause defoliation.
Figure 2.Liriomyza spp. feeding damage. Photo credit: Alton N. Sparks, Jr., The University of Georgia, www.forestryimages.org
Host Plants. Liriomyza leafminers can attack a large variety of plant species including crops and weeds. Some of the most common ornamental hosts include: Chrysanthemum and Dendranthema (chrysanthemums), Gypsophila (baby’s breath), Dianthus (carnation); Petunia, Tagetes (marigold) and Viola . Many food crop species such as bean, beet, carrot, celery, cucumber, eggplant, lettuce, melon, onion, pea, pepper, potato, squash, and tomato are also leafminer hosts.
Integrated Pest Management. The objective of leafminer management should be to avoid plant damage (high densities of large mines) by integrating cultural practices and control alternatives into an Integrated Pest Management (IPM) program. Successful leafminer IPM involves: minimizing adult movement into the greenhouse, quick and accurate diagnosis to select proper management action, frequent monitoring of populations during conducive periods and using monitoring data to select and time any necessary treatments.
- Sanitation and Exclusion. Eliminate alternate host plants (such as weeds) in and around the greenhouse because they may serve as population sources. Exclude adults by installing greenhouse screens with a pore size of 600 microns or smaller. Carefully inspect and destroy any infested plant material (such as plugs) before it is brought into the greenhouse. Sanitize floors, benches or areas underneath benches, especially in previously infested areas, because these areas may harbor pupae.
- Detection and Monitoring. Small populations are less damaging and more easily controlled. To avoid damage and reduce treatment costs, a significant effort should be placed in detection and monitoring practices. Yellow sticky cards are the best detection method of adult activity. Place one trap per 10,000 square feet (900 m 2) of greenhouse space, making sure they are uniformly distributed across the growing areas. Place traps just above the plant canopy and modify trap height as plants grow. Careful attention should be given to traps placed near doors and vents because these are potential points of entry. A record should be kept of numbers per trap per sampling period and traps should be replaced periodically as they loose stickiness. In addition to sticky traps for detection, leafminer activity on plants should be monitored by looking for feeding and oviposition damage (stippling) and for the presence of small mines on plants. Record numbers of infested plants per area (i.e., number of infested plants per bench) and map any hot spots to focus management efforts. Record keeping his is particularly important in evaluating effectiveness of insecticide applications.
- Quick and Accurate Diagnosis. When insects are detected or plant damage is observed, make sure you are dealing with Liriomyza leafminers before selecting insecticides to apply. Thrips may cause similar stippling damage on foliage but not all insecticides effective against thrips will control leafminers, especially larvae. University and Cooperative Extension specialists are usually available to help with species identification. Save specimens, especially any unusual ones, for accurate diagnosis and future reference.
- Treatment Decision. Sticky traps are effective in detecting adult migration into the greenhouse and population hot spots in growing areas. However they do not necessarily reflect population densities on plants. Use sticky traps to focus plant monitoring efforts. If plant monitoring indicates increasing feeding damage and presence of small mines, treatment may be necessary to avoid plant damage. Treatment may include clipping and destroying infested leaves or plants, when light and localized infestations are detected, and applying insecticides. Small populations may be eliminated by roughing infested plants during regular plant monitoring activities.
- Effective Pest Control Tools. A combination of exclusion, sanitation and pesticides is required for effective leafminer control. Biological control may be effective in certain situations, especially for high valued crops in ‘closed’ greenhouses. There is high variability in host plant susceptibility to leafminers. Group the most susceptible crops or cultivars so they can be more intensively monitored and managed. Avoid continuous cropping of susceptible plant species in greenhouses with a history of infestations. When insecticide use is necessary, good timing of sprays is essential for adequate control. Consider the insect life cycle when selecting insecticide products (Table 1). Contact insecticides like pyrethroids, only control adults because larvae are protected inside leaf-mines. Insect growth regulators only control larvae and work best against early instars. Systemic insecticides such as acephate and the neonicotinoids may need to be applied early, during the active larval feeding period. Repeated applications may be needed to control established populations and achieve appropriate control. Avoid frequent and long term use of insecticides with the same mode of action because this may lead to development of resistant populations. A list of insecticides available to control Liriomyza leafminers in greenhouses is shown in Table 1.
Under certain temperature, humidity, water and shade conditions, pesticides may cause injury to certain plants (phytotoxicity). Generally, apply pesticides during early morning to avoid dew or late afternoon to avoid the hottest part of the day. Water plants 1-2 days before applying a pesticide. Always check the product label for the list of plants that may be injured by the pesticide.
Mention of commercial products is for educational purposes only and does not represent endorsement by Texas Cooperative Extension or The Texas A&M University System. Insecticide label registrations are subject to change, and changes may have occurred since this publication was written. The pesticide user is always responsible for applying products in accordance with label directions. Always read and carefully follow the instructions on the container label.
For more information on Texas insects and Entomology, see http://insects.tamu.edu
Table 1. Insecticide products, listed by mode of action, available for the control of Liriomyza leafminers in commercial greenhouse grown ornamental crops.
Class/ Mode of Action Classification Group 1 |
Common Name |
Trade Name 2 |
R.E.I. |
Manufacturer |
Organophosphate/ Nerve Poison Group 1B | Acephate | Orthene 75 WP |
24 |
Valent |
PT 1300, Orthene TR |
24 |
Whitmire MicroGen | ||
Chlorpyrifos | PT DuraGuard ME |
24 |
Whitmire MicroGen | |
Chlorpyrifos Pro 4 |
24 |
Micro Flo Company | ||
Pyrethroid/ Nerve Poison Group 3 | Bifenthrin | Talstar Flowable, Talstar Nursery Flowable, Talstar Nursery Granular |
12 |
FMC |
Lambda-cyhalothrin | Scimitar CS |
24 |
Syngenta | |
Permethrin | Astro |
12 |
FMC | |
Pyrethrin + Piperonyl butoxide – Nerve Poison Group 3 | Pyrethrin | Diatect II Multipurpose Insect Control |
12 |
Diatect International |
Pyreth-it |
12 |
Whitmire Micro-Gen | ||
Pyrenone Crop Spray |
12 |
Bayer | ||
Neonicotinoid/Nerve Poison Group 4A | Imidacloprid | Marathon II |
12 |
Olympic Horticultural Products |
Marathon 1G |
12 |
Olympic Horticultural Products | ||
Thiamethoxam * | Flagship |
12 |
Syngenta Professional Products | |
Spinosyn/ Nerve Poison Group 5 | Spinosad | Conserve SC |
4 |
Dow AgroSciences LLC |
Avermectin/ Nerve Poison Group 6 | Abamectin | Avid |
12 |
Syngenta |
Insect Growth Regulator/ Juvenile Hormone Mimic- Group 7C | Pyriproxyfen* | Distance |
12 |
Valent |
Pyrrole/ Metabolic Inhibitor Group 13 | Chlorfenapyr * | Pylon | Olympic Horticultural Products | |
Insect Growth Regulator/ Chitin biosynthesis inhibitor Group 15 | Novaluron | Pedestal (suppression only) |
12 |
Crompton |
Insect Growth Regulator/ Chitin biosynthesis inhibitor Group 17 | Cyromazine | Citation |
12 |
Syngenta Professional Products |
Insect Growth Regulator/ Ecdysone agonist/molting disruptor Group 18B | Azadirachtin | Azatin XL Plus |
4 |
Olympic Horticultural Products |
Ornazin 3% EC |
12 |
SePro |
**leafminers not in label; use as appropriate
1 Based on Insecticide Resistance Action Committee International, mode of action classification v. 4.2.1, July 2005.
2 This list does not include all available product formulations, trade names are provided as examples