Ag Commissioner Update: The Tree of Heaven and Spotted Lanternfly

​You may have heard by now of an invasive insect pest called the spotted lanternfly (Lycorma delicatula). This damaging pest was found in Pennsylvania in 2014 and has established itself in 17 states since then. It is native to Asia, where it lives in balance with population controls such as parasitic wasps and other predators. Here in the United States, no such controls exist, and the population expands rapidly. The spotted lanternfly (SLF) has done serious damage to vineyards. The story of SLF is intertwined with a particular tree species, also endemic to Asia. The tree of heaven (Ailanthus altissima) is a favored host of SLF, and some researchers point to growing evidence of a dependent relationship between the insect and this prolifically spreading tree. Unfortunately, tree of heaven (TOH) was deliberately introduced to the United States in the 1700’s as an extremely hardy and fast-growing ornamental species.

There are many established stands of TOH here in Napa that will provide prime habitat for SLF in the event the pest is introduced here. Some of these TOH populations are directly adjacent to vineyards, increasing the risk of SLF infestation. It is not likely that a weak flyer like SLF would ever expand its range westward through the many geographic barriers it would face. Rather, this pest will likely make it debut into California as a hitchhiker on a plane, in a car, or as egg masses attached to objects in transfer from infested areas. For this reason, California Border Inspection Stations are on high alert to detect SLF egg masses. Because the SLF threat is so severe, the California Department of Food and Agriculture has established an action plan to facilitate rapid response.

The Napa County Agricultural Commissioner’s Office (CAC) has been closely monitoring the SLF/TOH connection and threat potential. Along with plenty of public outreach and education materials, we have been placing SLF detection traps throughout the county since 2020. Very few other counties has actively trapped for this pest. The traps are located in areas of highest risk, including adjacent to vineyards, storage and shipping facilities, rail lines, the airport, and campgrounds. Along with a detection trapping program, we have done a thorough survey of the county, mapping the location of TOH individuals and sapling clusters. This work was made possible by initial grant funding from the State, and on-going funding from the Winegrape Pest and Disease Control District. Napa CAC also inspects all plant material entering the county, along with inspections of materials moved here from high-risk areas. These inspections also look for the egg masses of the Spongy Moth, formerly known as the Gypsy Moth. The Napa CAC will remain vigilant and proactive in facing the double threat of TOH and SLF.

If this information has made you want to take action yourself, we’d like to ask for your help in identifying more TOH specimens for a mapping project that allows us to prioritize locations for detection trapping and outreach. Please participate in our survey to help you identify TOH. 

Take TOH Survey