Last Thursday on a typical sunny Californian day, I met up w/ researchers, Kirsten Sheehy (UCSB RIVRLAB), Bill Neill (Riparian Repairs) and Noa Rishe (California Department of Parks and Recreation) to romp around Topanga State Park in search of the invasive Cape ivy, Delairea odorata. As soon as we stepped foot onto the Los Leones trailhead we could see the vast entwined vines of this relentless invasive ivy climbing over and smothering all of the native species in its path, hence its nickname- the ‘California kudzu’.
Native to South Africa, Cape ivy was originally introduced into the USA in the 1850s for ornamental purposes due to its pretty green color with lush yellow flowers. However, looks can be deceiving as in some areas this invasive weed has reduced native plant species richness by 36%, and decreased native seedling abundance by 88% (see Alvarez and Cushman 2002). In addition to its detrimental impacts on native plants, this invasive weed also produces many chemical defense compounds (eg. pyrrolizidine alkaloids and xanthones), which make it toxic and unsuitable for foraging by resident mammals; and potentially detrimental to fish survival if substantial amounts of these chemical compounds end up in waterways. Aside from its toxins, this weed can interfere with nesting sites by many riparian-dependent birds. This invasive weed is also quite the ecosystem engineer due to its shallow root system contributing to serious soil erosion problems on hillsides; as well as potentially forming a serious fire hazard due to its dried out foliage hanging over native trees during the dry season.
Thus, there is a dire need to control the spread and growth of this menacing invasive vine. Invasive weeds can be controlled in several manners including herbicide chemicals, mechanical removal (via hand-labor or machines), and biological control. In classical biological control, a pest or weed’s natural enemies (for example, the insect herbivores of Cape ivy) are collected from its geographic place of origin, tested for target specificity and efficacy, and then released into the invaded region.
Successful biocontrol agents can reduce pest populations below threshold levels that cause problems for humans and native species. Once established, biocontrol agents can provide a sustainable, long-lasting management option as biocontrol agents are self-reproducing and self-distributing. Biocontrol agents will not eradicate every target pest or weed individual but this is actually a positive feature as it prevents population crashes of the biological agent and promotes the long term control of the weed. In sensitive or protected regions, biological control and hand-removal of invasive weeds are often the preferred method of control in order to reduce any negative impacts to the surrounding native ecological community.
Hence, last Thursday was quite a monumental day as it marked the first release of the biological control agent for the control of the invasive cape ivy in the greater Los Angeles Region. The biological control agent in this case is the gall-forming fly, Parafreutreta regalis Munro (Diptera: Tephritidae), that has already been approved for release after undergoing intensive testing through the USDA-ARS to ensure that it only targets the invasive cape ivy, in order to prevent any non-target effects on local plants. Similar to its host plant, this gall-forming fly is native to the Cape Province of South Africa and is known to stunt the growth of Cape ivy in both the laboratory and in the field. Thus, it is expected that this biocontrol agent will reduce cape ivy’s ability to spread and climb, both which would reduce the smothering impacts of this invasive weed on native vegetation.
In two weeks from now Kirsten Sheehy and the UCSB RIVRLAB will come back to make sure that the galls are forming on the ivy before removing the cage. Once the galls have formed, these flies are pretty much on their own, continuing the cycle of injecting their eggs into new unsuspecting cape ivy hosts, and forming new galls that promote generation after generation of weed-controlling superheroes. Of course Kirsten will continue to make periodic new releases of adult flies in the SoCal region to increase the genetic variation of this fly to ensure the success of these new populations in the Los Angeles Region. The goals are to establish these super-hero flies in at least one site per coastal county in California to serve as ‘nursery’ sites for future regional releases. San Diego Co. is next up on this lucky-list of biocontrol study sites.
In addition to this beneficial fly, further biological control research on a stem- boring moth, Digitivalva delaireae Gaedike & Krüger (Lepidoptera: Acrolepiidae), is underway via the USDA-ARS (see Mehelis et al. 2015) and is likely to be approved for release in the near future. This stem-boring moth is actually expected to have an even greater impact on controlling Cape ivy, especially if it is combined with the impacts of the gall-forming fly. Once approved, we hope to add this additional superhero biocontrol agent in the SoCal Region in order to reduce the ecological crimes of the invasive Cape ivy villain. Stay tuned for the sequel.
In the mean time, if you would like to learn more, see the contact information, links and research articles below.
Contact Information regarding UCSB RIVRLAB Biocontrol Research:
Dr. Tom Dudley: tdudley(at)msi.ucsb.edu
Kirsten Sheehy: kirsten.sheehy(at)lifesci.ucsb.edu
Alvarez and Cushman (2002). Community-level consequences of a plant invasion: effects on three habitats in coastal California. Ecological Applications. 12(5): 1434-1444. http://marbles.sonoma.edu/users/c/cushman/pdf/alvarez%20&%20cushman%2002.pdf
Mehelis, C.N., Balciunas, J., Reddy, A.M., Van Der Westhuizen, L., Neser, S., Moran, P.J. 2015. Biology and host range of Digitivalva delaireae (Lepidoptera: Glyphipterigidae), a candidate agent for biological control of Cape-ivy (Delairea odorata) in California and Oregon. Environmental Entomology. 44(2):260-276. doi: 10.1093/ee/nvu030.
California Department of Parks and Recreation: http://www.parks.ca.gov/?page_id=21576
UCSB RIVRLAB: http://rivrlab.msi.ucsb.edu/biocontrol/cape-ivy
USDA-ARS, Albany CA:
- Article featuring Drs. Patrick Moran and Scott Portman’s recent releases in the Bay Area: https://baynature.org/article/california-scientists-release-fly-control-landscape-suffocating-invasive-ivy/
Acknowledgements: Additional thanks to Dr. Tom Dudley and Dr. Adam Lambert from the UCSB RIVRLAB and Danielle LeFer from California Department of Parks and Recreation for coordinating this momentous day, and to Dr. Patrick Moran, Dr. Scott Portman, Dr. Angelica Reddy, Dr. Chris Mehelis and additional researchers from USDA-ARS in Albany, CA for all of the rigorous testing of this weed and its biological control agents.