Elm leaf beetle, Xanthogaleruca luteola
Order: Coleoptera
Family: Chrysomelidae
Description
The elm leaf beetle was first detected in the United States in 1830 and is now present throughout North America wherever elms are planted. It is a particularly important pest of elm trees (Ulmus spp.) in the Western United States and a household nuisance when adults seek shelter during winter months.
Adults are 5-6.5 mm (3/16-1/4 inch) in length and yellow to green with black stripes when actively feeding during warmer weather. The beetles are khaki green while overwintering. The oblong eggs are initially yellow and turn gray near hatching. Newly hatched larvae are small and black, and as they age they turn yellow or green with rows of dark tubercles (projections). When fully grown, larvae are about 8.5 mm (1/3 inch) long. Pupae are orange or bright yellow.
Quick Facts
- Elm leaf beetle is a pest of elm trees during warmer months and a nuisance in homes during cooler months. Feeding by larvae and adults can result in complete defoliation of elms. While adults can invade homes during cooler months, they are only considered a nuisance pest.
- Infestations of elm leaf beetle have declined in most of Colorado. Recent outbreaks tend to occur in the Arkansas River Valley and occasionally in eastern Colorado.
- Healthy elms can tolerate some feeding by elm leaf beetle. When trees are repeatedly defoliated, or when many adults are found laying eggs, applications with certain insecticides can provide control.
Adult elm leaf beetle. Note the yellow body with black stripes, which is the coloration of adults during periods of warm weather. When overwintering, the beetles are dark green. Both larvae and adults feed on leaves and can injure elms, and adults can invade homes when they seek shelter during winter. Image credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Overwintering elm leaf beetles. Note the dark green coloration. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Larvae of elm leaf beetle. Note the yellow bodies and black spots. Image credit: Phil Sloderbeck, Kansas State University, Bugwood.org
Pupae of elm leaf beetle. Note the yellow-orange coloration. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Egg mass of elm leaf beetle. Note the yellow coloration. Eggs can also be gray when they are close to hatching. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Life history and habits
All beetles have four life stages: egg, larva, pupa, and adult. Repeated heavy infestations can diminish tree health and increase host susceptibility to other insect pests and pathogens. In the fall, adults begin seeking overwintering shelter in areas such as woodpiles, loose mulch, garages, attics, piled eaves, and other protected areas. They can also shelter behind walls when entering buildings through cracks or other openings. While overwintering, the beetles do not feed or reproduce but are often active during warm days in the late winter. Feeding resumes the following spring for one to two weeks before females begin laying egg masses on the underside of leaves. Each egg mass contains about 15-20 eggs. Upon hatching, newly emerged larvae tend to feed on young foliage near the egg laying site. Larvae develop through three instars and mature within three to four weeks before migrating to sheltered pupation sites in crevices of tree bark or at the tree base. Adults emerge from the puparium within two weeks and produce a second generation, which feed on leaves from mid-July through September. Adults of the second generation overwinter until the following spring. The density of elm leaf beetle varies between generations, with lower densities commonly observed in earlier generations. English elm (U. procera) is the preferred host, but this pest will also attack Siberian elm (U. pumila), American elm (U. americana), and Chinese elm (U. parvifolia).
Injury
Adults often chew circular holes through leaves. Larvae cause different feeding injuries depending on the growth stage. Young, newly emerged larvae produce pinhole wounds in leaf tissue, while mature larvae consume the entire leaf except for the main veins which results in skeletonized leaves with a brown or white appearance. When abundant, this pest can completely defoliate large elms. While trees can produce new sets of leaves after losing early-season foliage, later generations of elm leaf beetle can attack these newer leaves that generally results in partial defoliation and death of individual branches. Repeated defoliation makes trees more prone to wind breakage and attack by pathogens or other insect pests such as bark beetles or wood borers. Defoliation also reduces the aesthetic value of trees.
Monitoring
Leaves can be inspected weekly beginning in spring for clusters of yellow or gray eggs and larvae. It is recommended that treatment decisions are based on the presence of eggs in the overall stand, rather than individual trees. Chemical treatments should be made immediately when egg densities appear to be peaking, or in the early winter months when high densities of elm leaf beetle are observed.
Prevention
Maintaining tree vigor through adequate irrigation is important, especially in areas with summer drought. Dead or dying branches should be removed, and unnecessary pruning should be avoided. When pruning, it is important to make cuts properly on young trees during late fall and winter. Some elms are resistant to attack by elm leaf beetle, including Accolade, Emerald Sunshine, Frontier, Prospector, most Chinese elms except for Dynasty.
To prevent elm leaf beetles in the household, it is recommended to repair screens, door sweeps, and seal exterior cracks in June or July before beetles attempt to migrate indoors as temperatures drop.
Cultural control
Adequate watering and plant care practices are advised since healthy trees can tolerate some feeding injury. Any beetles discovered in the home can be vacuumed and discarded, which is most effective when beetles are active during warm periods and exposed on windows or walls. Research suggests that Asian elms are more resistant to elm leaf beetle than Siberian or European elms. This pest shows little preference for American elm ‘Valley Forge’. Homestead and Regal elms are highly susceptible to elm leaf beetle but are resistant to the fungal pathogen that causes Dutch elm disease.
Chemical control
In the home, combining prevention with spot applications of insecticides near potential entry sites can be effective. Chemical control is warranted when regular outbreaks occur or when large numbers of eggs are found on leaves. To cut costs and reduce adverse environmental effects, it is recommended that spot treatments of insecticides be applied to areas with high egg densities, rather than preventatively treating all susceptible trees.
Neem-based insecticides containing azadirachtin can act as a feeding deterrent and interfere with the growth of larvae. Trunk injections of imidacloprid or abamectin have been shown to significantly reduce defoliation due to elm leaf beetle and are only necessary on trees with high egg densities. This approach reduces the likelihood of resistance from developing in the population since beetles on untreated trees may repopulate treated areas. For this reason, it is also recommended that the pesticides are rotated since they have different modes of action. The leaves of trees treated with a trunk injection of imidacloprid appear to be toxic to larvae for about a month but display no toxicity after one year. At higher concentrations, soil drenches of imidacloprid have been shown to reduce the severity of feeding injuries one year after the application.
Soil injections of systemic insecticides can also be effective but must be applied in early winter. Other chemical applications for elm leaf beetle management include foliar sprays applied directly to leaves and banding trunks with insecticides to kill larvae before they pupate near the base of the tree.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
Bosu, P., F. Miller, and M. Wagner. 2007. Susceptibility of 32 Elm Species and Hybrids (Ulmus spp.) to the Elm Leaf Beetle (Coleoptera: Chrysomelidae) Under Field Conditions in Arizona. Journal of Economic Entomology. 100(6): 1808-1814. Available https://academic.oup.com/jee/article/100/6/1808/2198754
Elm Leaf Beetle. 2014. Elm Leaf Beetle. University of California – Integrated Pest Management. Available https://ipm.ucanr.edu/PMG/PESTNOTES/pn7403.html
Lawson, A., and D. Dahlsten. 2003. Evaluation of Systemic Insecticides as a Treatment Option in Integrated Pest Management of the Elm Leaf Beetle, Xanthogaleruca luteola (Muller) (Coleoptera: Chrysomelidae). Journal of Economic Entomology. 96(5): 1455-1462. Available https://academic.oup.com/jee/article/96/5/1455/2217857
Lawson, A., and D. Dahlsten. 2003. Implementation of a citywide monitoring program to base treatment decisions on elm leaf beetle abundance. Journal of Arboriculture. 29(1): 34-41. Available https://www.proquest.com/docview/220343195?pq-origsite=gscholar&fromopenview=true&sourcetype=Scholarly%20Journals
Utah State University (n.d.). Elm Leaf Beetle. Utah State University – Extension. Available https://extension.usu.edu/pests/schoolipm/structural-pest-id-guide/elm-leaf-beetle
Valizadeh, B., J. Sendi, A. Zibaee, and M. Oftadeh. 2013. Effect of Neem based insecticide Achook ® on mortality, biological and biochemical parameters of elm leaf beetle Xanthogaleruca luteola (Col.: Chrysomelidae). Journal of Crop Protection Science. 2(3): 319-330. Available https://jcp.modares.ac.ir/article-3-233-en.pdf