By Eric Middleton PhD, IPM Advisor, University of California Statewide IPM Program and Cooperative Extension, San Diego, Orange, and Los Angeles Counties, for Let’s Talk Plants! September 2024.
A New Eucalyptus Beetle in San Diego County
Eucalyptus trees are everywhere in Southern California, from parks and commercial landscaping to people’s backyards. In the past few years however, a new beetle has arrived that poses yet another threat to eucalyptus growing in the state.
Paropsis atomaria, also known as the Dotted Parospine leaf beetle was first found in Los Angeles County in 2022 and has since been spreading throughout the rest of Southern California. In large numbers, the beetles can defoliate entire sections of eucalyptus trees as they feed on the leaves. Unfortunately, P. atomaria seems to be showing up here in San Diego County in much greater numbers this year and will likely only continue to spread. If you have eucalyptus or corymbia trees, keep an eye out for this new beetle.
Identification
All life stages of Paropsis atomaria are quite distinctive. Adult beetles are around 3/8 in. long and are a tan or yellowish color with numerous small orangish dots across their back. Eggs are laid in clusters at the tip of branches and look like small spiny flowers or pinecones. Young larvae are small with a black head and greenish bodies while older larvae are larger and turn a bright yellow color with dark black heads and black markings along their sides and back. While P. atmoaria look quite distinctive, there are some other eucalyptus beetles that you might mistake for P. atomaria. Take a look at the link here for more information on these other beetles (https://ipm.ucanr.edu/PMG/PESTNOTES/pn74104.html).
Both adult and larval Paropsis atomaria feed on eucalyptus leaves. Because they are often out of sight high in the canopy, one of the best ways to identify an infestation is to look for chewed leaves and for beetle droppings. Parts of the tree canopy may start looking sparse, or you may see partially consumed leaves. As beetle populations grow and both larvae and adults feed, any surfaces below the tree start to become covered with their feces. If you see many small greenish cylinders of feces under your tree, take a closer look for any eggs, larvae, or adults on lower branches to confirm it is P. atomaria.
Management
When it comes to managing this pest, there is still a lot we don’t know. However, there are some steps you can take to help protect your tree.
First, keep your trees well-watered and healthy since robust trees are usually less likely to be targeted by pests and more likely to tolerate any pest damage that occurs. Second, monitor consistently for the presence of beetles so you catch any infestations early. If your tree is small enough, you may be able to pick beetles and larvae off by hand or blast them off with a hose. Mature larvae drop to the ground to pupate in the soil, so covering the ground underneath your tree with a tarp or plastic sheeting may also help to keep beetle populations down (although may also simply be impractical!).
If you do find P. atomaria feeding on your tree, consider how much damage you are willing to tolerate. It may not be worth your time or money to try to get rid of the beetles if you are alright with some defoliation. If you do decide to try to get rid of the infestation, working with a tree care or pest control company will probably yield the best results. Most tree care companies are treating P. atomaria infestations with systemic insecticides like imidacloprid or emamectin benzoate. While we don’t yet know how well these work, it is likely they will help reduce beetle populations, although it may take some time.
Finally, you can always consider replacing your eucalyptus with something that isn’t susceptible to these beetles such as a native Californian tree. Depending on your situation, this may save you effort and time in the long run. Overall, keep an eye out for Paropsis atomaria and the damage they cause. Vigilance will go a long way towards keeping your eucalyptus safe from this pest.
Dr. Eric Middleton is the UCCE Integrated Pest Management advisor for San Diego, Orange, and Los Angeles Counties. Eric is passionate about sustainable agriculture and investigating practical pest management solutions. His goals are to conduct research that is directly applicable to the needs of growers, to promote practices that have less of an impact on the environment, and to share his findings in a way that is accessible to everyone.