Eucalypt trees have become abundant in the California landscape, but so have the many invasive eucalypt pests that have arrived in California in the last couple decades.

Figure 1. Adult dotted paropsine leaf beetle. Photo by Martin Lagerwey.

In the fall of 2022, yet another invasive pest was added to the hoard of beetles, psyllids, and gall wasps that attack eucalypt trees. The dotted paropsine leaf beetle (Paraopsis atomaria) was found on a lemon scented gum tree (Corymbia citriodora) in Los Angeles County. It was the first report of the dotted paropsine leaf beetle in North America, and it has since become more problematic throughout Southern California. Currently the extent of the spread is unknown.

Like eucalypt trees, the dotted paropsine leaf beetle is native to Australia, where it is known as an abundant pest of at least twenty Eucalyptus and Corymbia species. Some of these tree species are commonly found in California, including the red gum (E. camaldulensis), rose gum (E. grandis), sugar gum (E. cladocalyx), and the silver-dollar gum (E. polyanthemos).

What does it look like?

Adult beetles are about 3/8 of an inch with oval bodies and little beady black eyes (Figure 1). They are tan in color and covered in orangish dots. There are darker spots along the top and edges of the wings. The antennae are straight and become slightly darker toward the tip.

Eggs are laid in a circular cluster around young stems and leaves. They are tan, cylindrical, and are laid in clusters of 20 – 100 eggs. The larvae of the dotted paropsine leaf beetle are yellowish in color with black heads and black ends (Figure 2). As they age, they develop black stripes along the top and sides. When larvae are threatened, they will raise their black back end. They will drop to the ground to pupate.

Figure 2. Larvae of the dotted paropsine leaf beetle. Photo by Pest and Diseases Image Library, Bugwood.org.

Damage and Solutions

Although small, the dotted paropsine leaf beetle and its larvae can cause significant damage to the leaves of a host tree. If they do not eat the whole leaf, they will leave behind distinct notches in the leaves like other eucalyptus leaf beetles. Severe infestations can cause defoliation and eventual death in stressed or young trees.

You can protect Eucalyptus or Corymbia species against insect infestations by providing proper horticultural care. Reducing any water stressors or other environmental stressors will allow the tree to successfully fight off insect infestations.

If you are removing a eucalypt tree or dealing with a severe infestation, consider replanting with a California native or other tree that will not be susceptible to the dotted paropsine leaf beetle and other eucalypt pest. 

Contact your local agricultural commissioner if you suspect you've found this beetle. For more information, please visit the LA County fact sheet regarding the dotted paropsine leaf beetle.

Dead California sycamore tree, next to a healthy tree, killed by fusarium dieback, spread by an invasive shothole borer. Photo by James Jay Farrar.

They may seem too tiny to do much damage to a mature, healthy tree, but invasive shothole borers (ISHB) are responsible for the deaths of tens of thousands of trees in Southern California. These beetles bore into trees and infect them with Fusarium dieback, a fungal disease that kills the trees. Many native California trees like California sycamore, valley oak, and arroyo willow can be killed when invasive shothole borers attack them.

While these pests are currently only found in Southern California, they could spread to many other parts of the state. Limiting the infestation will reduce their impact. Controlling the beetles is difficult but includes regular monitoring of trees to quickly identify sources of beetles, disposing of infested cut wood, and appropriate pesticide treatments.

What can you do to help?

• Don't move firewood around the state. These beetles and other potentially damaging beetles are easily moved on cut wood. Buy it where you burn it.
• Learn more about host trees, symptoms of infestation, and what to do.

UC IPM's new publication, Pest Notes: Invasive Shothole Borers is written by various state experts on this pest and contains everything you need to know about the beetle. Visit the UC IPM website for specific management recommendations, identification of the beetles, and lists of trees affected.

The invasive pest spotlight focuses on emerging or potential invasive pests in California. In this issue, we cover the brown widow spider.

Adult brown widow spider with egg sacs. Photo by Mike Lewis, CISR.

Brown Widow Spider Facts

The brown widow spider became established in Southern California in 2000 and appears to be displacing the black widow in some of its habitats, especially in urban areas. They build their webs in secluded areas around homes and in vegetation. Mature female brown widows are smaller than mature female western black widows. The normal brown widow spider coloration is a mottled mixture of tan, brown, and gray. It has a lengthwise stripe halfway up the back side of the abdomen with two isolated dots in front of it and diagonal stripes on the side. The brown widow spider does have an hourglass, but it is typically orange rather than the vivid red of a black widow. Male brown widows are much smaller than other widow spiders. Like black widows, brown widow spiders make irregular webs of strong silk. The egg sac of the brown widow spider has protuberances of silk all over its surface, resembling a very large pollen grain. The sac is so characteristic that it can be used to confirm that brown widows are present even if the spiders themselves are not seen.

What can you do?

The bite of the brown widow spider is much milder than the black widow so the risk of serious injury from their bite is less. If you spot a brown widow spider in your garden or around your home, manage it as you would any spider. Clear up clutter like wood piles to reduce nesting sites. Check under patio furniture for nesting spiders and sweep down their webs.

For more information on widow spiders, visit http://ipm.ucanr.edu/PMG/PESTNOTES/pn74149.html. 

By Julie Clark, Community Education Specialist III 

Goldspotted borer (GSOB) is a beetle invasive to oaks in California. Infestations have ravaged oak woodlands in San Diego and Riverside counties the last 12 years and in Anaheim Hills, Angeles and San Bernardino National Forests the last few years. Preferred hosts are black oak, canyon oak, coast live oak, and occasionally Engelmann oak.  

Oak woodlands are highly valued ecosystems that support numerous species of fauna. Oak trees serve as the anchor for these systems and support over 5000 insect species, over 105 bird species, 105 mammal species, 58 species of amphibians and reptiles during their respective life cycles. Many beneficial insects rely on oaks to complete their life cycles and do not damage the trees in doing so.  

GSOB bore into the bark of its hosts to lay eggs and rear young. Mature beetles emerge to find new hosts. The adults leave a distinctive D-shape hole in the bark upon exit.  

The insects damage the water and food transfer structures (xylem and phloem) of the tree, causing crown die-back and eventual death in heavily infested (amplifier) trees. Widespread loss of oaks from GSOB has occurred in Idyllwild and San Diego County mountain areas. 

Although GSOB are winged, they do not fly long distance. UC researchers, partners with CAL FIRE and the California Firewood Task Force discovered that several of the infestations throughout Southern California were caused by introduction of firewood imported from infestations in other areas.  

D-shaped GSOB exit holes. Credit: UC ANR 

Ventura County is vulnerable to attack by the beetle and other invasive tree pests that are on watchlists for the area. Best ways of being assured your firewood is safe include purchasing locally source material or selecting kiln-dried or certified firewood. 

For more information: 

https://gsob.org 

www.firewood.ca.gov 

Report suspected GSOB infestation: 

https://ucanr.edu/sites/gsobinfo/What_You_Can_Do/Report_GSOB_Symptoms/