by Amy Yuelapwan, Land Restoration Tech
**The beetle shown in the photo above is a full sized adult, with a US penny shown for scale.
The Polyphagous Shot Hole Borer (PSHB) beetle is currently affecting multiple tree species around California. Mountains Restoration Trust (MRT) is monitoring for the PSHB in Calabasas, with the help of the California Resource Conservation District (RCD),. The main species of trees that MRT is monitoring are the Coast Live Oak, Quercus agrifolia, the Valley Oak, Quercus lobata, and the Western Sycamore, Platanus racemosa.
There are test results from University of Riverside that confirm the PSHB beetles found in Calabasas are carrying what’s known as the ‘Fusarium Dieback’ fungal disease. This disease blocks the flow of nutrients through the trees, effectively killing the tree from the inside out.
An impregnated PSHB female travels short distances, from a parent tree to a different tree. When she arrives at a new host tree, she bores in and begins to make galleries, or tunnels, where she will lay her eggs. The offspring are born within the tree and feed on the disease-carrying fungus, Fusarium euwallacea. The life cycle starts all over again when the offspring breed with each other inside the tree and the impregnated females leave to find new tree hosts. This beetle, along with many other types of vectoring beetles (carrying diseases), are closely monitored for their activity because the tree hosts they choose in urban and wild settings are heavily affected. In the worst cases, the trees die completely.
It is a popular theory that the long-experienced drought has severely weakened trees and majorly effects the death of infected trees — so don’t forget to water landscaped trees! The symptoms to look out for are areas of leaf dieback (death of twigs and branches, generally starting at the tips) in the tree canopy, as well as entry/exit holes in the trunk. This is accompanied by discoloration, also called ‘staining.’ There are resources online, but if you suspect that a tree is diseased, MRT and RCD can be contacted for further assistance. RCD also offers citizens the opportunity to monitor their own properties by setting up traps to find potential PSHB beetle activity.
The California Department of Conservation, and the Resource Conservation District can be contacted via the postal service, email, or telephone.
801 K Street, MS 14-15
Sacramento, CA 95814
Phone: (916) 457-7904