Leaf mining flies
Order: Diptera
Family: Agromyzidae, Anthomyiidae
Description and life history
The larvae of certain fly species develop within the leaves or needles of host plants. These pests often create different mining patterns, such as serpentine leaf mines that wind in an S-shape and widen gradually as the insect grows, rounded and irregularly shaped leaf mines that form a blotching pattern, and tentiform leaf mines that curve upwards as damaged leaf tissues dry. Some species can produce a combination of these mines.
Quick Facts
- Certain fly species produce larvae that feed within leaves. This behavior produces mines that are visible on the leaf surface and vary in appearance, depending on the species.
- In addition to flies, other types of insects can produce mining injuries in leaves, including moths, beetles, and sawflies.
- While leaf mining insects often produce conspicuous plant injuries, they typically do not significantly affect the health of the plant.
- Scouting plants for feeding injuries or presence of the insects can be an effective monitoring approach, and sticky traps can be used to capture the adults.
- Conserving resident populations of natural enemies along with certain cultural controls can often suppress leaf miner populations to acceptable levels. While not usually necessary, chemical control of some leaf mining insects is possible when applied before egg laying.
Description and life history continued…
Spinach leafminer
The spinach leafminer, Pegomya hyoscyami (Anthomyiidae), can produce mines in the edible parts of certain vegetables. Adults are small flies that measure about 5-7 mm (~1/5-1/3 inch) long and have grey bodies covered with bristles and yellow markings. Mature larvae are yellow or translucent white and measure about 6.4 mm (1/4 inch) long, and the eggs are white and cylindrical. Pupae overwinter in soil until the following spring. After mating, females lay eggs on the undersides of leaves and the larvae hatch about four days later. Newly hatched larvae begin boring into the leaf where they remain until reaching maturity, at which point they exit the leaf and drop to the soil surface to pupate. This pest can produce multiple generations each year, and can attack spinach (Spinacia spp.), beets (Beta spp.), and related herbaceous plants such as lambsquarter (Chenopodium album).
Vegetable leafminers
Several Liriomyza spp. (Agromyzidae) are leaf mining pests of vegetable and ornamental crops. Three species are known to attack vegetable crops in nearby states like Utah, including the American serpentine leafminer (Liriomyza trifolii), pea leafminer (Liriomyza huidobrensis), and vegetable leafminer (Liriomyza sativae). These small flies measure less than 2 mm (<1/10 inch) and have gray or black bodies with yellow heads and markings on the underside. When at rest, the flies hold their wings folded horizontally over the back. The oval eggs are very small and white or yellow in color. Larvae are about the same size as adults and are oval or wedge-shaped, legless, and have dark mouthparts. Newly hatched larvae are often transparent but turn white or yellow as they mature, while pupae are about 1.5-3.5 mm (~1/20-1/7 inch) long and range in color from golden to red or dark brown. Both the larvae and pupae have two spiracles (breathing tubes) present at the posterior end.
These leaf miners overwinter as pupae in soil until emerging as adults the following spring and summer. After mating, eggs are laid inside the leaf and hatch in two to four days under favorable temperatures. Newly hatched larvae begin feeding within the leaf until developing into pupae. Depending on species, pupation occurs within the leaf, on the underside of the leaf, or in soil. Multiple generations are produced each year, and collectively these species have a wide host range including but not restricted to brassicas, cucurbits, legumes, and solanaceous plants.
Injury
Spinach leafminer
Feeding of spinach leafminer larvae produces slender, winding mines on leaves. Severe feeding can result in large white blotches. A single leaf can have up to 100 punctures, inflicted by adults. Leaves with excessive mining are unmarketable and have reduced photosynthetic output. These injuries also increase the risk of secondary infections by plant pathogens.
Vegetable leafminers
Feeding and oviposition sites appear as white stippling injury on the upper leaf surface. Tunneling of larvae within the leaf causes blistering, blotch, or serpentine mines that increase in size as the larva matures. Frass may also be present within mines, and heavy feeding can reduce the photosynthetic output of leaves and cause them to desiccate and drop, resulting in decreased plant health and yields. Serious infestations are most likely to occur later in the season and may be more severe in greenhouse production systems.
Monitoring
Spinach leafminer
Seedlings can be checked frequently for the presence of leaf mines, most of which occur on cotyledons and the first true leaves. Mines may be more visible on the undersides of leaves. Chemical control may be necessary if the leafminer population builds to high levels when seedlings have four to five leaves.
Vegetable leafminers
Detecting adults can be accomplished by inspecting leaves for stippling injury, deploying yellow sticky cards at plant height, or placing a yellow bowl with soapy water near infested crops. Counting the number of mines in leaves with live larvae can provide an estimate of future damage potential, and counting the number of mines with dead larvae can be done to assess treatment efficacy. Management thresholds tend to differ among crops.
Management
Spinach leafminer
It is recommended to avoid planting vegetables near infested fields. Row covers can be deployed over plants to exclude egg-laying females. Infested leaves can be removed and destroyed in home gardens. However, it is important to bag and eliminate infested leaves rather than composting them. Protecting resident populations of natural enemies is recommended to help suppress spinach leafminer populations. To do this, selective pesticides should be chosen when treating other pests.
Vegetable leafminer
Plants that are heavily infested with vegetable leaf miners can be destroyed, or individual leaves infested with larvae can be clipped and destroyed. Increasing the diversity of plants in an area and rotating crops can be helpful since monoculture plantings tend to be more susceptible to infestations. Deploying a floating row cover can physically exclude flies from contacting plants. Fertilizing with excessive nitrogen should be avoided as this tends to facilitate leafminer infestations. Nearby weedy hosts such as American black nightshade (Solanum americanum) or ornamental plants such as chrysanthemum spp. should be removed from the area to eliminate food sources. After the last harvest, remaining plants should be removed to eliminate food sources and crop residues should be plowed to inhibit the development of pupae.
Certain vegetables, such as tomatoes, can tolerate more feeding injury before noticeable yield reductions. Varietal resistance has also been documented in certain vegetables. For example, tomato varieties with curled leaves and shorter fruit maturation periods tend to have lower densities of leaf miners. In addition, there are many generalist predators of vegetable leafminer adults and larvae, including ants, predatory wasps, and spiders, all of which have been shown to help suppress populations of leaf miners. Releasing two species of parasitoid wasp, Diglyphus isaea (Hymenoptera: Eulophidae) and Dacnusa sibirica (Hymenoptera: Braconidae) has been a successful component of integrated pest management programs. Another parasitoid wasp, Opius dissitus (Hymenoptera: Braconidae) is a naturally occurring parasitoid of the American serpentine leafminer in Florida and may be worth further exploration as a biological control agent against leaf mining Liriomyza spp. Conserving resident populations of these natural enemies is highly recommended, as repeated applications of broad-spectrum insecticides are often associated with outbreaks of vegetable leaf miners.
Chemical control targets the larvae of vegetable leaf miners. Since larvae are protected in the leaf, insecticides that can penetrate leaf tissues have shown the greatest management potential, especially when combined with an adjuvant and surfactant. Research suggests that applications abamectin or spinosads can help reduce populations of the American serpentine leafminer. Reductions in mines were most common one to two days after the spray application, while larvae and pupae were suppressed through seven days following the application. It is worth noting that resistance has been documented in areas of California and Florida with intense vegetable production where vegetable leafminers are prevalent. To protect pollinators, applications of broad-spectrum insecticides should be avoided or applied only when there is minimal risk to non-target organisms.
CSU Extension Fact Sheet
References
Camper, M., and W. Cranshaw. (n.d.). Asian Longhorned Beetle in Colorado – Identification of Insects and Damage of Similar Appearance. Colorado State University – Extension. Available https://webdoc.agsci.colostate.edu/bspm/Hexapoda%20(Insects)/Asian%20Longhorned%20Beetle.pdf
Coyle, D., R. Trotter, M. Bean, and S. Pfister. 2021. First Recorded Asian Longhorned Beetle (Coleoptera: Cerambycidae) Infestation in the Southern United State Journal of Integrated Pest Management. 12(1): 1-6. Available https://academic.oup.com/jipm/article/12/1/10/6166961
Hajek, A. 2007. Encyclopedia of Pest Management – Asian Longhorned Beetle: Biology and Control. CRC Press: Taylor & Francis Group. 2: 21-24.
Hu et al. 2009. Ecology and management of exotic and endemic Asian longhorned beetle Anoplophora glabripennis. Agricultural and Forest Entomology. Available http://www.cerambyx.uochb.cz/assets/pdf/hu_et_al_anoplophora.pdf
LaForest, J. 2013. Anoplophora glabripennis. BugwoodWiki. Available https://wiki.bugwood.org/Asian_longhorned_beetle
Meng, P., Hoover, K., and Keena, M. 2015. Asian Longhorned Beetle (Coleoptera: Cerambycidae), an Introduced Pest of Maple and Other Hardwood Trees in North America and Europe. Journal of Integrated Pest Management. 6(1):1-13. Available https://academic.oup.com/jipm/article/6/1/4/788453
Oten, K. 2021. Asian Longhorned Beetle. North Carolina State University – Extension. Available https://content.ces.ncsu.edu/asian-longhorned-beetle
Pimentel, D. 2007. Encyclopedia of Pest Management: Volume II. Cornell University. 21-24.
USANPN. (n.d.). Asian Longhorned Beetle Forecast. USA National Phenology Network. Available https://www.usanpn.org/data/forecasts/Asian_longhorned_beetle#:~:text=Non%2Dnative%20Asian%20longhorned%20beetles,leaving%20perfectly%20round%20exit%20holes.
USDA. 2023. Asian Longhorned Beetle. United States Department of Agriculture – Animal and Plant Health Inspection Services. Available https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/asian-longhorned-beetle/asian-longhorned-beetle
USDA, 2022. Asian Longhorned Beetle Insecticide Treatments. United States Department of Agriculture – Animal and Plant Health Inspection Services. Available https://www.aphis.usda.gov/publications/plant_health/fs-alb-insecticide-treatments.pdf
USDA. 2016. The Asian Longhorned Beetle: An Invasive Tree Pest. United States Department of Agriculture. Available https://www.aphis.usda.gov/publications/plant_health/2016/book-alb.pdf