Eucalyptus trees are an iconic part of Californias landscape. The famous journalist Harold Gilliam once wrote, “the Eucalyptus seems an indispensable element of this State’s landscapes, as indigenously Californian as the redwoods, the poppy fields, the long white coastal beaches, and the gleaming granite of the High Sierra”. Introduced in the mid-1800s as a fast-growing source of timber, the trees were also used for firewood, oil production, and reforestation. Plantings peaked during the “eucalyptus craze” of the 1870’s and the “eucalyptus boom” of 1907. Eucalyptus were first propagated from seed brought from Australia, as such pests and diseases associated with living trees were not introduced. Eucalyptus remained relatively pest free until the first major pest, the eucalyptus longhorned borer (Phoracantha semipunctata), was introduced in 1984. Since then, several major pests have been introduced with the latest threat to Eucalyptus being the dotted paropsine leaf beetle (Paropsis atomaria). 

The dotted paropsine leaf beetle was first discovered feeding on lemon scented gum (Corymbia citriodora) in Los Angeles in August 2022. This was the first report of the dotted paropsine leaf beetle in North America and has quickly spread throughout Southern California. Currently the beetle can be found throughout Los Angeles, Orange, San Diego, and San Bernadino counties with unconfirmed reports in Ventura County. The beetle has a broad host range, feeding on over 20 Eucalyptus and Corymbia species commonly found in California, including E. camaldulensis (red gum), E. globulus (blue gum), E. polyanthemos (silver dollar gum), E. cladocalyx (sugar gum), and C. citriodora (lemon-scented gum). 

Identifying the Dotted Paropsine Leaf Beetle

The dotted paropsine leaf beetle is a member of the Chrysomelidae family, known for leaf-feeding beetles. Adult beetles are oval-shaped and are about 3/8 of an inch in size. They are easily identified by the yellow and orange markings, along with black spots on their elytra, which stand out against the green Eucalyptus foliage. 

Females lay eggs in a circular cluster of 20-100 around young stems and leaves. When the larvae hatch, they are yellowish in color with black heads and black ends. As they mature through 4 larval instars, they develop black stripes along the top and sides of the body. Larvae have defensive glands on their terminal segments and when threatened will discharge droplets. Mature larvae will drop to the ground to pupate in the leaf litter.

In California, P. atomaria has 2 generations a year and can quickly build up in high numbers, leading to the rapid defoliation of susceptible Eucalyptus species, especially during peak feeding seasons in the spring and fall.

A Comparison to Other Eucalyptus Leaf Feeding Beetles in California

The introduction of the dotted paropsine leaf beetle is part of a larger trend in California, where other eucalyptus-feeding beetles have also been introduced. Two notable examples include Trachymela sloanei and Chrysophtharta m-fuscum.

Trachymela sloanei (Eucalyptus Tortoise Beetle):

• Adults: Dark brown with blackish mottling.
• Larvae: Dark green to reddish brown with a black head. Feed at night
• Damage: This beetle, like the dotted paropsine beetle, feeds on eucalyptus foliage. Its feeding can result in partial defoliation but is not as devastating as P. atomaria.

 

 

Chrysophtharta m-fuscum (Eucalyptus Leaf Beetle):

• Adults: Gray to reddish brown.
• Larvae: Light greenish gray with a black head. Feed during the day
• Damage: Primarily feeds on the leaves and stems causing extensive defoliation. Its feeding behavior is more aggressive than that of Trachymela sloanei, and when left unchecked can defoliate entire branches. 

Dotted Paropsine Leaf Beetle Damage and Management

The dotted paropsine leaf beetle feeds primarily on the foliage of its host trees. Both adults and larvae cause damage by notching the leaves, which can quickly lead to stripping entire branches of their leaves. In severe infestations entire trees are defoliated which can severely weaken the tree. Over time, repeated infestations can cause tree death, particularly in newly planted trees or those that are already stressed due to environmental conditions.

The beetles tend to congregate in high numbers, and during heavy infestations, it’s common to see multiple larval stages and adults clustering on different parts of the tree, as well as on the ground surrounding it. 

Given the similarity between the eucalyptus leaf feeding beetles, the management strategies for P. atomaria will likely align with those used for T. sloanei and C. m-fuscum. These include a combination of cultural, biological, and chemical control methods.

Cultural Control

• Provide proper horticultural care to maintain tree health
• Prune out infested branches and remove fallen leaves that may contain beetle larva

Biological Control 

• Currently there are no known natural enemies feeding on the beetle in California 

Chemical Control 

• Soil drench of a systemic neonicotinoid insecticide
• Foliar sprays of broad-spectrum insecticides such carbaryl or pyrethroids may be effective but are not recommended for eucalyptus in the landscape as blue gum psyllid is under excellent control by beneficials, and these products may disrupt those beneficials

As with many invasive pests, preventing the spread of the dotted paropsine leaf beetle is crucial. To help contain the infestation, avoid transporting infested plant material. Monitoring newly planted eucalyptus trees for signs of beetle damage and inspecting trees regularly can help catch infestations early. The dotted paropsine leaf beetle is just one of several Eucalyptus pests introduced to California, which together require a coordinated and comprehensive pest management approach.

Chris Shogren is an Environmental Horticulture Advisor with UC Cooperative Extension in Los Angeles County. He can be reached at cjshogren@ucanr.edu.