- Author: Ben Faber
Attend our training to become an invasive shothole borer monitor!
*Results from March 2023 ISHB Monitors Training*
Invasive shothole borers (ISHB) are wood boring beetles that attack many native and non-native trees in Southern California. These beetles bore tunnels into trunks and branches where they grow a fungus they use as food. The fungus causes a disease called Fusarium Dieback. Trees infected with Fusarium Dieback show branch dieback, canopy loss, and may eventually die. Infested trees become sources of beetles that can spread to surrounding hosts. This pest can also spread long distances through infested green waste and firewood, affecting new areas.
How you can help: Get trained, become an ISHB Monitor, and help us gather infestation data! In previous editions of the program, we learned that trained volunteers can identify ISHB-infested trees with 96% accuracy. This high accuracy of volunteer observations allows us to include the data collected through this program directly into the ISHB statewide distribution map. Knowing where beetles have spread will assist scientists, municipalities, and many other conservation agencies plan for management. Also, detecting infestations in their early stages allow for better chances of successful management. Your participation is needed to detect infestations throughout southern California.
Training for Monitors: You can become an ISHB monitor trained by scientists from UC Agriculture and Natural Resources. California Naturalists, Project Learning Tree Educators, and Master Gardeners are especially encouraged to attend, but curious minds of all ages are welcome.
Dates: Online training 7/7/2023. In person dates Ventura County 7/8/2023, Santa Barbara County 7/9/2023, San Diego County 7/14/2023, and Inland Empire (Riverside County or San Bernardino County) 7/15/2023 (specific locations to be determined).
Cost: Free.
Training Requirements:
- Registration is required.
- Attendance to online session is required.
- Attendance to one in-person session is required.
- Completion of the 1-hour free online eXtension Invasive Shothole Borer training is required.
- Monitors must create or already have a free account on iNaturalist.
- After the training, monitors must upload at least 5 observations to the UC ANR ISHB Monitoring Project on iNaturalist using the correct protocols ( UC ANR Invasive Shothole Borer Monitoring Project iNaturalist Guide ).
Note: Past participants of this program may choose not to attend the online session, but in-person session is required. Please make sure you contact us and let us know beforehand if you will not attend the online training.
AGENDA:
Pre-training assignments: before 7/7/2023 Complete 1-hour free online eXtension Invasive Shothole Borer training and make an account on iNaturalist. |
Online session: 7/7/2023 (12pm-2pm) Location: Virtual Zoom meeting. The meeting access information will be sent to registrants prior to training. Speakers will cover how this project fits into the big picture of efforts to manage emerging tree pests in California. There will be a short review of ISHB identification, look-alikes and tree species identification, and then an overview of how to use iNaturalist for this project. |
In person training: Participants may choose which field training to attend, all sessions cover the same material. Attendance at one of the sessions is mandatory. Ventura County 7/8/2023, Santa Barbara County 7/9/2023, San Diego County 7/14/2023, and Inland Empire (Riverside County or San Bernardino County) 7/15/2023 (specific locations to be determined). Speakers will review ISHB symptoms and iNaturalist collection protocols ( UC ANR Invasive Shothole Borer Monitoring Project iNaturalist Guide ), observation of infested trees and filed identification of signs and symptoms, and troubleshooting based on their experiences with the practice observation. |
Deadline for iNaturalist observations: 8/14/2023 After the training, monitors must upload at least 5 observations to the UC ANR ISHB Monitoring Project on iNaturalist using the correct protocols ( UC ANR Invasive Shothole Borer Monitoring Project iNaturalist Guide ) by 8/14/2023. |
Results: end of August 2023 After volunteer data has been evaluated, results will be shared will all participants. See results from March 2023 ISHB monitors training. |
Stay tuned for additional events! |
Registration
Please register here by 7/3/2023.
Contact
Questions or more information about the training can be directed to:
Hannah Vasilis - Statewide ISHB Survey and Trapping Coordinator
![ishb sycamore ishb sycamore](/blogs/blogcore/blogfiles/99973.jpg)
- Author: Beatriz Nobua-Behrmann
- Author: Randall Oliver
- Posted by: Elaine Lander
Two identical looking species of wood-boring beetles, collectively known as invasive shothole borers (ISHB), have killed thousands of trees in Southern California and pose an ongoing threat to California's urban and wildland forests. These beetles, which are not native to the United States, were first identified in Los Angeles County in 2012 and have since spread to six other counties: Orange, Riverside, San Bernardino, San Diego, Santa Barbara, and Ventura.
Beetles, Fungus, and Impact
As the fungus grows, it colonizes the tree's vascular system, blocking transport of water and nutrients. This causes a disease called Fusarium dieback that can kill branches or entire trees. The beetles and their symbiotic fungi have a wide range of suitable hosts, including more than 65 species of trees found in California. The most highly susceptible trees include many of the species commonly used for landscaping, such as sycamores, oaks, cottonwoods, and box elder trees. ISHB beetles attack healthy trees as well as stressed or diseased trees in a variety of urban, suburban, and riparian settings. Visit www.ishb.org to find the full list of reproductive hosts in California.
Female beetles can fly short distances, allowing the pest-disease complex to spread into new areas near already infested trees. Beetles can also be transported in infested firewood and green waste, leading to spread over much greater distances. While beetles have only been identified in Southern California and the Central Coast to date, further spread throughout much of California is possible.
ISHB-infested trees can quickly become public safety hazards. Trees with heavily infested branches can be especially hazardous, since the combined damage of the fungal disease and the beetle's tunneling activity weakens the wood, causing limbs to break and fall. In addition, severely infested trees will become constant sources of beetles that can disperse and infest neighboring trees. Such “amplifier” trees generally need to be removed completely, while more lightly infested trees can be managed or treated without requiring removal. Therefore, early detection and rapid response is the key to controlling ISHB. Substantial recovery in lightly to moderately infested trees has been observed in some areas where amplifier trees have been removed.
Identifying an ISHB infestation
- Beetle entry holes: When the beetles tunnel into trees they make small, perfectly round holes, each about the size of the tip of a medium ballpoint pen (0.8 mm). (Figure 3)
- Additional signs and symptoms: Entry holes are usually accompanied by one or more of the following signs and symptoms, which vary by the tree species: staining, gumming, white powdery exudate, or frass (boring dust).
- Dieback: Dead or wilting branches can be a sign of a severe infestation. If you see dieback on trees, check for entry holes on the trunk or the branch collars.
In addition to visual inspections, traps using quercivorol, a plant-based lure that attracts the beetles over short distances, can help determine the presence and abundance of beetles in an area. Trapping is especially useful for large or inaccessible areas where regular visual inspections of all the trees are not practical. In those cases, trapping can help determine if ISHB is present in the area and can help focus survey efforts on infested trees. Because the lure has relatively low attractiveness, trapping is not an effective control method for ISHB and is only used for detection purposes.
What Can You Do?
- Keep trees healthy. Proper irrigation and maintenance will keep trees strong and help protect them from ISHB and other pests.
- Prune out infested branches. Removing branches that have clusters of 50 ot more ISHB holes would help control this pest. For trees that undergo heavy pruning every year, like avocado trees, removal of all infested branches is recommended. Tools should be disinfected after pruning by spraying them with a solution of 5% disinfecting bleach or 70% ethanol to avoid spreading the fungal disease to other trees.
- Remove severely infested trees. Unfortunately, severely infested trees (with more than 150 entry holes and ISHB-related dieback) are not likely to survive. These trees should be removed as soon as possible, and the stump should be ground to one inch or less. (Figure 4)
- Manage downed wood. Green waste generated by branch and tree removals should be properly disposed.
- Chipping/grinding to one inch or less kills 99.9% of the beetles. If that is not possible, chipping to three inches or less still will kill 98% of the beetles in the wood. In already infested areas, chipped wood can be used onsite as mulch. However, if working on a newly infested area or if the wood chips will be moved to another area, chipping should be combined with solarization or composting to kill 100% of the beetles. If chipping is not an option, logs can also be solarized or kiln dried to exterminate the beetles.Figure 4. California sycamore heavily infested with invasive shothole borers. (Credit: B Nobua-Behrmann, UCCE)
- Solarization involves covering the material with clear plastic tarp and letting the heat from the sun kill the remaining beetles. Chips and beetles should be fully contained by wrapping plastic both underneath and over the material. Chips should remain covered for at least six weeks during the summer months or for at least six months between September and June. The depth of the pile should be no more than 30 inches deep, to ensure even heating.
- Composting, when done correctly, should also kill the remaining beetles in the chips. It is recommended to send infested chips to a professional composting facility that has earned the U.S. Composting Council's Seal of Testing Assurance.
- Prevent the spread. Avoid spreading this pest by not moving firewood or mulch that hasn't been properly solarized or composted. If you must move infested greenwaste (for example, to bring it to a composting facility) make sure the load is tightly covered while in transit.
- Consider chemical control.TreesthatarereproductivehostsforISHB and that show signs of active infestations can be treated with a combination of insecticide and fungicide. The decision to treat a particular tree depends, among other things, on the tree's condition, value, and hazard level. Trees that aren't already infested should be monitored but not treated. There are various chemicaloptionsthatcanbeusedagainstISHB-FD.
- Trunk sprays of a contact insecticide, such as bifenthrin, combined with Bacillus subtilis or tebuconazole (which are fungicides) have been demonstrated to offer some degree of control.
- Systemic soil injections or drenching with the insecticide imidacloprid has also provided control, as has trunk injection with emamectin benzoate (insecticide) combined with tebuconazole or propiconazole (fungicides).
- These pesticides should only be applied by a licenced professional following the instructions on their labels to avoid harming non-target organisms.
Biocontrol options are currently under research. They include the use of natural enemies (such as parasitic wasps from the beetles' point of origin), entomopathogenic fungi (which are fungi that attack insects), endophytes (which are microorganisms that live in the tree that may provide protection) and nematodes. But these biological management options might take time before they are tested and available. Until then, prevention, early detection, and rapid response are our best weapons to keep trees healthy and alive. For more information on invasive shothole borers and their management, visit www.ishb.org.
[Article originally published in the Summer 2021 issue of the Green Bulletin.]
/h2>/h2>/h2>- Author: Ben Faber
Origin and evolution of fungus farming in wood-boring Coleoptera – a palaeontological perspective
David Peris, Xavier Delclòs, Bjarte Jordal https://doi.org/10.1111/brv.12763
A beetle bores a tree trunk to build a gallery in the wood in order to protect its lay. As it digs the tunnel, it spreads ambrosia fungal spores that will feed the larvae. When these bore another tree, the adult beetles will be the transmission vectors of the fungal spores in another habitat. This mutualism among insects and ambrosia fungi could be more than 100 years old --more than what was thought to date-- according to an article published in the journal Biological Reviews.
The study analyses for the first time the symbiotic associations and the coevolution between ambrosia fungi and beetles from a paleontological perspective using the Cretaceous fossil records of these biological groups. Among the authors of the study are the experts David Peris and Xavier Delclòs, from the Faculty of Earth Sciences and the Biodiversity Research Institute of the University of Barcelona (IRBio), and Bjarte Jordal, from the University of Bergen (Norway).
Beetles that grew fungi millions of years before human agriculture
Some termites, ants and beetles developed the ability to grow fungi in order to eat millions of years ago. This mutualism between insects and fungi --one of the top studied symbiosis in the natural field-- is an analogous evolutionary strategy in the farming activities of the human species since the Neolithic revolution.
Understanding the origins of the symbiosis between insects and fungi is a field of interest in several scientific disciplines. Nowadays, the mutualism between ambrosia symbiont beetles and fungi is the cause of forest and crop plagues that cause serious ecological and economic losses "it remains unclear which ecological factors facilitated the origin of fungus farming and how it transformed into a symbiotic relationship with obligate dependency", notes David Peris, first author of the study.
When did the lineage of farming insects begin?
Historically, phylogenetic studies suggest beetle fungiculture started more than 50 million years ago --before other insects-- and some studies dated it back to 86 million years ago. "The symbiotic relationship between fungus and beetles would have probably originated more than 100 million years ago, during the early Cretaceous, in groups of beetles that had gone unnoticed", reveals the expert David Peris.
As part of the study, the experts studied several specimens of worldwide distribution of the biological groups captured in amber from the Cretaceous. Therefore, the origin of ambrosia fungus is older than the main groups of beetles from the subfamilies Scolytinae and Platypodinae --Curculionidae family-- which now grow fungus in tree trunks, as stated by the authors.
"This suggests that these fungi used some other group of insects to spread millions of years ago", notes the researcher. Also, other beetle groups with a similar behaviour to ambrosia beetles --Bostrichidae and mostly Lymexylidae families-- present an older and abundant fossil record that would coincide with the emergence of ambrosia fungi, according to previous studies.
"The most interesting thing --he continues-- is that some studies note the ability to cultivate fungi in some of these current species".
Evolutionary convergence towards an obligate mutualism
The growing process of fungi starts when beetles colonize a new tree trunk or branch. During the Cretaceous, the abundance of fungi and wood-boring beetles facilitated a starting domestication of some groups of fungi. First, the fungal spores were accidentally transported from tree to tree by the wood-boring beetles "until this mutually beneficial association evolved towards a more intimate symbiosis in which fungi were inoculated into to a tree, the fungal mycelia grew and beetle larvae fed from the fungus", notes Bjarte Jordal.
This set of factors, together with the symbionts' high ability to adapt and change, eased the morphological and ecological adaptations of biological groups that converged in an obligated mutualism. That is, a symbiotic relationship between insects and fungi, beneficial for both, which still lasts.
"However, we need more studies on the knowledge of the ecology of the species from the Lymexylidae and Bostrichidae families to get more specific conclusions. Therefore, the discovery of new fossils in cretaceous amber of these groups will certainly help us to better understand the evolutionary history of this symbiotic relationship that still exists nowadays", concludes Professor Xavier Delclòs.
Read on: https://onlinelibrary.wiley.com/doi/full/10.1111/brv.12763
Photo: Invasive Shot Hole Borer tunnels in Box Elder trunk
/h1>![shot hole borer feeding shot hole borer feeding](/blogs/blogcore/blogfiles/83571.jpg)
- Author: Ben Faber
from Dr. John Boland, Dr. Kellie Uyeda researchers, Dr. Jeff Crooks, advisor, Monica Almeida, cartography, Mayda Winter, project management
The Kuroshio Shot Hole Borer (KSHB) is a tiny beetle that invaded San Diego County in 2013. It was first seen in some avocado groves but then in 2015, it became very abundant in the native riparian forests in the Tijuana River Valley. It immediately caused extensive damage to those forests and as it is now also being found in many other sites in southern California, the authorities are extremely concerned that other sites are going to be impacted as badly as the Tijuana River Valley.
Luckily Dr. John Boland was studying the willow trees in the valley in 2015 and he immediately switched his focus to the KSHB's impact in the valley. Here we present a summary of the four main storylines coming out of his intensive five-year study of the beetles in the valley: the KSHB in the valley went through a 5-year boom-and-bust cycle; the KSHB severely damaged the native willow forests in the valley but the forests are now rapidly recovering; the research has uncovered two mysteries about the KSHB – one we think is solved and the other still needs to be solved; and the research has led to a prediction about KSHB's likely impact at other sites in southern California and several management recommendations.
When KSHB (Euwallacea kuroshio) attack a tree, the females drill into the trunk and create galleries of tunnels in the wood by pushing sawdust ‘tailings' out of the entrance hole. They inoculate the tunnel walls with a fungus (e.g., Fusarium sp.), and live in the tunnels eating the fungus and reproducing. Within a few weeks new females emerge, and start another gallery in either the natal tree or a new tree.
The beetles are tiny (~2 mm in length) and seldom seen, however if there are enough of them they can damage and even kill trees via their tunneling activities, which undermine the structure of the tree trunks.
The Tijuana River Valley and the riparian forest
The Tijuana River Valley in San Diego County, California, is a coastal floodplain of approximately 3,700 acres at the end of a 1,730 square mile watershed. The Tijuana River is an intermittent stream that typically flows strongly in winter and spring and is mostly dry in summer. For decades, the Tijuana River has been polluted with sewage and industrial waste as it flowed through the city of Tijuana, Mexico, and when it flows through the Tijuana River Valley it is one of the most polluted rivers in California.
The riparian forest that grows around this river is one of the largest in coastal southern California. The forest is dominated by just two tree species: the black willow (Salix gooddingii) and the arroyo willow (Salix lasiolepis). Both willow species are high on the list of KSHB's preferred hosts.
Annual surveys of infestation rates showed that the KSHB population went through a rapid outbreak and a rapid decline over a five-year period, with the infestation rates peaking in Fall 2016. The early increase in population occurred while the KSHB was attacking the willows in the Wet Forests and the later decrease in population occurred while the KSHB was attacking the willows in the Dry Forests.
The KSHB boom-and-bust is now complete. In fall 2019 it was difficult to find any trees infested with KSHB. While it lasted the KSHB's population explosion was very destructive: it has been estimated that the KSHB infested more than 375,000 willows and killed more than 122,000 willows in the valley.
This boom-and-bust cycle occurred naturally, with no management interventions to control the spread or severity of the outbreak.
Satellite image analyses conducted by Dr. Kellie Uyeda determined spatial and temporal patterns of canopy loss. The normalized difference vegetation index (NDVI), a metric of vegetation health, was calculated for each year from 2015 - 2019.
The remote sensing analyses support the results seen in the ground surveys. First, in the early years of the KSHB infestation, the most dramatic vegetation losses were observed in the Wet Forests and in later years the vegetation losses were observed in the Dry Forests, with lower levels of vegetation loss. Second, the KSHB's impact was greatest in 2016-17 and since then it has been tapering off.
Seedlings
After the KSHB had damaged the adult willows many willow seedlings recruited onto the sunny and moist river beds. Most of the willow seedlings were scattered within the forest, but three large stands of seedlings became established in three units.
A few old willows survived the KSHB invasion and remain as scattered Big Trees. It is likely that they will play an important role in the recovery of willows in the river valley.
Fortunately, the heavily-damaged Wet Forest units recovered considerably, and in some places the forests are almost back to their pre-KSHB condition. However, in other places they have failed to return because of the expansion of the invasive plant arundo, Arundo donax.
We think we know the answer to this mystery:
We think it has to do with the sewage pollution in the river. Sewage contains the most important plant nutrients (nitrogen, phosphorus and potassium) in abundance and so the willows growing in or near the polluted channel water were growing vigorously. The KSHB targeted these fast-growing willows because the sap in these trees was being nutrient loaded in two ways – phloem sap was loaded with sugars from the fast-growing leaves, and xylem sap was loaded with nutrients from the enriched soil. These extremely high nutrient conditions in the wood allowed for the fast growth of the KSHB's symbiotic fungi and ideal conditions for the rapid population growth of the KSHB (the Enriched Tree Hypothesis).
Some kind of link between the environment and shot hole borer impact had been suspected but not previously identified. Hulcr and Stelinski (2017) noted that “in ambrosia beetle research, the role of the environment and preexisting conditions of the trees has not yet been well appreciated, even though it appears to determine the impact of these beetles.” The Enriched Tree Hypothesis directly links the environment (enriched water) and the preexisting condition of the trees (vigorous, fast growing willows) with the impact of the KSHB (tens of thousands of KSHB per host tree, which cause the trunk to snap and the canopy to collapse).
Why are the recovering willows not being re-attacked by the KSHB? The recovering willows in the Wet Forests are forming forests similar to what was present before the KSHB invasion, but the trees are not being substantially re-attacked by the KSHB. Why?
We don't know the answer but suggest these three possibilities: An ‘induced response' of the trees. It is possible that the infested willows have changed their chemistry as a result of the borer attack, and this has increased the resistance of the surviving trees to further borer attacks; overall forest structure. It is possible that the willows, though individually suitable, no longer present a suitable group target for the KSHB; and a disease or predator. It is possible that the KSHB population in the valley is now being kept low by a pathogen, parasite, parasitoid or predator. It will take further research to solve this mystery. But understanding it will provide essential information about the KSHB invasion in southern California and about shot hole borers in general.
Why was the KSHB's impact different in different parts of the valley? The distribution of KSHB within the Tijuana River Valley was not random; they infested and killed willows growing in or near the main channel significantly more than willows growing far from the water. On the wet site the mortality rate was high, and on the dry site the mortality rate was low. Black willow was the most abundant tree species in both sites. Why the difference?
We think we know the answer to this mystery: We think it has to do with the sewage pollution in the river. Sewage contains the most important plant nutrients (nitrogen, phosphorus and potassium) in abundance and so the willows growing in or near the polluted channel water were growing vigorously. The KSHB targeted these fast-growing willows because the sap in these trees was being nutrient loaded in two ways – phloem sap was loaded with sugars from the fast-growing leaves, and xylem sap was loaded with nutrients from the enriched soil. These extremely high nutrient conditions in the wood allowed for the fast growth of the KSHB's symbiotic fungi and ideal conditions for the rapid population growth of the KSHB (the Enriched Tree Hypothesis).
Some kind of link between the environment and shot hole borer impact had been suspected but not previously identified. Hulcr and Stelinski (2017) noted that “in ambrosia beetle research, the role of the environment and preexisting conditions of the trees has not yet been well appreciated, even though it appears to determine the impact of these beetles.” The Enriched Tree Hypothesis directly links the environment (enriched water) and the preexisting condition of the trees (vigorous, fast growing willows) with the impact of the KSHB (tens of thousands of KSHB per host tree, which cause the trunk to snap and the canopy to collapse).
Management recommendations
Do not cut down and remove infested trees thinking that they are going to die. Willows can survive very heavy infestation rates. Remove Arundo in order to improve the riparian forests in the valley. Arundo is degrading the forests and needs to be removed for the willows to fully recover. Continue to plant willows in restoration sites. Use ‘natural restoration' methods wherever you can. When searching for KSHB in other parts of San Diego County search in nutrient-enriched areas, e.g., near storm drain outfalls. In urban forests do not over-fertilize or over-water trees. Nutrient-enriched and fast-growing trees are more vulnerable to KSHB infestation.
This research was funded by the Department of Navy on behalf of the Naval Base Coronado. Funds were managed by the Southwest Wetlands Interpretive Association.
The reports and some of the data analyses were done in collaboration with the Tijuana River National Estuarine Research Reserve.
And Read More: https://trnerr.org/kshb/
![Tijuana willows shot hole Tijuana willows shot hole](/blogs/blogcore/blogfiles/78677.jpg)
- Author: Julie Di Blasio
Invasive shot hole borer (ISHB) infestations have been identified in Ventura County since 2015 but have not significantly spread. Discovery of the pest/disease complex was found in late 2018 in the urban forest of Meiners Oaks. Citizens Journal recently published an article about the removal of a tree that was at risk for amplifying the local infestation and causing potential other community harm.
The Ventura Agricultural Commissioner supervised the removal of the tree, using grant funds for this purpose from CAL FIRE. The box elder was located on private property and considered to be a hazard to extend the infestation.
UCCE Ventura has been collaborating to address ISHB with UC insect, disease, education specialists, Ventura County Agricultural Commissioner, CAL FIRE, US Forest Service, several other agencies and non-government organizations. We are locally active in monitoring and outreach. Ventura County Master Gardeners Invasive Pests Outreach Group augments our work through their efforts to educate the public, firewood users and vendors.
Below is a video produced by California Releaf, a nonprofit organization that works to empower grassroots efforts and build strategic partnerships that preserve, protect, and enhance California's urban and community forests. It's been edited for length.
For more information about ISHB, you can also visit the UCANR website.