Biological Control
Overview
Plants brought in from other parts of the world arrive without their ‘natural enemies’, the insects and other herbivores that keep them under control back home. Biological control is a method that involves using other living organisms to help control invasive and non-native species. Biological control, as opposed to chemical or mechanical control, reacquaints non-native, invasive pests (such as weeds or insects) with their natural enemies in an effort to provide natural and sustained population reduction. Research in the RIVR lab focuses on evaluating the impacts and efficacy of organisms in aiding the removal of invasive riparian plants. Focal species include plants such as Tamarisk, Arundo donax, Lepidium latifolium, and Phragmites australis, and the newly introduced bagrada bug (Bagrada hilaris).
Tamarisk
Over 300 insects feed on tamarisk in Eurasia, but few native organisms attack it in North America, allowing the weed to spread unchecked. Biocontrol reunites a plant with its natural enemies, selected to exert damage but feeding ONLY on that plant. The tamarisk leaf beetle, Diorhabda elongata, is from central Asia and satisfies those criteria.
Key Dates
Early 1800s – Tamarisk imported from Eurasia for flood control
1970s – overseas exploration beginning in the 1970s resulted in Diorhabda Carinulata being selected as a viable biological control method
- This tamarisk leaf beetle defoliates tamarisk – scraping the foliage and causing it to dry out. after repeated years of exposure to these beetles, tamarisk dies off.This has been shown to be the most effective method for destroying tamarisk in the long-term, as other efforts result in regrowth and reestablishment.
1996 – This species of beetle was approved for field release biocontrol methods by the USDA Animal and Plant Health Inspection Services (APHIS)
- The Tamarisk Biocontrol Project is one of the most intensively studied invasive plant control programs ever undertaken. With over 10 years of testing to ensure Diorhabda was not only effective, but also would not feed on native plants nor crops, the U.S. Department of Agriculture authorized its release, with input from a technical advisory group that included the U.S. Fish and Wildlife Service. While long-term benefits of tamarisk control are anticipated, there is always some risk when releasing a foreign organism. (from virgin river tab on existing website)
1995 – The Southwestern sub-species of Willow Flycatcher (Empidonax traillii extimus) (SWFL) was listed as an endangered species by the USFWS and was reported to use Tamarisk as nesting habitat.
- The primary point of contention surrounding the SWFL was whether or not defoliation of the Tamarisk by the beetle would occur during nesting times, which would expose the SWFL to excessive predators and heat during its late breeding season. (Sogge et al. 2003, 2008). (Dudley & Bean, 2012)
2001- The tamarisk leaf beetles were released in central Utah,
1993-2003 – 10 years of testing on the tamarisk leaf beetle revealed that the larvae only completed their development on the tamarisk trees and did not harm native vegetation.
2006 – Local managers moved the beetles to the Virgin River near St. George in southern Utah.
2010- The beetles were dispersed down the Virgin River, defoliating plants through the Virgin Valley,
2011-2013 – It has been documented that the beetles are capable of tolerating and establishing further south than the original insects released. The beetles contiued moving to the Momon Mesa area in 2011 and in 2012 to Lake Mead
- The beetles are slowly increasing their habitat to a more southeastern extent and now have passed beyond the Virgin River towards the Upper Gila River.
- The beetles became established 250 kilometers north of the border with Mexico.
2014 – The beetles have colonized as far south as Mohave Valley in California
Looking Forward – Current research is being done to determine the range of the tamarisk leaf beetle.
- It is possible that the beetles may colonize to the Colorado Delta of Mexico. Further research is being done to test genetic selection of the adaptation and establishment capacity of the beetle in the Lower Colorado River. (Tom Dudley, U.C. Santa Barbara; Dan Bean, Colorado Dept of Agriculture; Kevin Hultine, Desert Botanical Garden, AZ).
- Monitoring further dispersal and establishment is being achieved through pheromone baited sentinel traps placed along potential colonization sites.
- Tom Dudley is a Collaborator on the 2014 Weaver Proposal for this pheromone based monitoring.
Effects of this Bio-Control Method
Myriad benefits have resulted for the surrounding ecosystems – water savings of 2,500 acre-feet/year from reduced evapotranspiration in northern Nevada, reduced wildfire threats, and positive signs of recovery of native and beneficial vegetation.
Introduction of the beetles has resulted in successful destruction of a large amount of Tamarisk. However, the endangered SWFL began to use Tamarisk as its habitat, and concern grew that as the beetles moved closer to primary SWFL habitat, destroying the Tamarisk would also destroy SWFLs and other bird species. To some degree, the issues of climate change have mooted this conversation as drought and water demands have negatively affected Tamarisk and SWFL populations alike.
In most riparian systems, native populations are sufficiently established to aid in restoration after Tamarisk invasion and reduction, while few riparian systems are too degraded for these native plants to provide habitat for the flycatcher within an appropriate time frame.
The presence of the beetles has created a more balanced ecosystem for birds, with remaining Tamarisk providing more structural complexity to the treescape and the beetles becoming a prominent food source. Due to this, limiting weed treatments is ideal, in order to prevent secondary invasion by other invasive species such as Russian thistle.
Issues
In Arizona, federal regulators funded a media campaign condemning the use of the beetles. However, stopping biocontrol is not the issue at hand, but rather the incorporation of such methods into larger ecosystem dynamics. Promoting native vegetation, both passively and actively, is at the forefront of this dynamic focus.
With a recent turn in focus to water conservation, the tamarisk leaf beetles is receiving increasingly positive attention as people desire the removal of water-intensive tamarisk. However, water savings vary between regions , climates, sub and surface water sources as well as water transport measures.
In 2014, John McCain called upon the USDA and the USDI to have a plan that maximizes the benefits of the beetle’s presence.
Successful restoration requires the diligent monitoring and research into the efficacy of biological control to be coupled with equally effective restoration measures. In the Colorado Basin, this has resulted in two types of revegetation practices – rapid response (short term plantings followed by irrigation, etc. to ensure growth) and sustainable (lending itself more towards improving natural recruitment of plant species)
Arundo Donax
Research in our lab focuses on the diversity, impacts, and augmentative release of Arundo herbivores already present in North America, as well as evaluation of novel insects and pathogens for potential use as biological control agents.
Tetramesa romana
During surveys of Arundo infestations in the southwest US, we detected the Arundo wasp (Tetramesa romana) feeding in Arundo stems in southern California in 2006. This European insect was most likely an accidential introduction in this region, although timing and mode of introduction remain unknown. Currently, the wasp is distributed along the California coast from Santa Barbara County south to Baja California in Mexico, but is continuing to expand its range, as we recently (2013) detected new populations in the Mojave River, Victorville, CA.
Naturalized populations have also been found in Texas, so this species has most likely been present in North America for several decades. Additional insect populations from Europe were evaluated and augmentatively released in Texas by the USDA.
Our Lab continues to track the range expansion and population demographics of T. romana in Arundo stands in the southwest US, and evaluate the direct and indirect effects of wasp herbivory on plants.
Cryptonevra sp.
Chloropid flies (Cryptonevra sp.), native to the Mediterranean region, were also found feeding inside canes in localized populations in the Santa Clara River (Ventura County, CA). Feeding produces characteristic ‘hour glass’ damage at the feeding point, and a ‘witches broom’ effect at the top of canes by stimulating growth of side shoots. Generally these gregarious insects are present at low densities and populations can vary substantially between years.
Melanaphis donacis
The specialist aphid, Melanaphis donacis, was found throughout California (except very northern California) with greatest abundance in coastal Arundo populations. Aphids feed primarily on the apical shoots and less mature, distal leaves, and although reaching high population densities in early spring in some locations, only minor damage was observed on plants in one location. This species is native to the Mediterranean basin.
Cape Ivy
Cape Ivy is the only species in the plant genus Delairea from the family Asteraceae. This promotes the possibility of biocontrol methods that would not harm native vegetation, even species within the Asteraceae family.
Investigations in South Africa have uncovered a moth (Digitivalva delaireae) and a fly (Parafreutreta regalis) that damage Cape Ivy in the native region but to do damage other plants, native or non-native. The Cape Ivy moth causes significant damage to Cape Ivy through leaf- and stem-mining. Studies on the moth revealed that the moth only laid eggs on Cape Ivy and was effective for both morphological varieties (stipulate and exstipulate) that exist in North America through the reduction in plant growth and biomass accumulation. Applications for release of the moth as a biological control method have been approved by the USDA-APHIS Technical Advisory Group on Biological Control of Weeds.
Common Reed
Common reed, Phragmites australis (Cav.), is among the most widespread angiosperms in the world and is found on every continent except Antarctica. Phragmites grows in all aquatic and brackish environments and spreads through both asexual and sexual structures. Rapid expansion of populations in wetlands along the East Coast was previously thought to be driven by human disturbance, but evidence now suggests that a cryptic invasion of an European genotype has occurred in the eastern United States (and some western locations), and this biotype continues to spread across the continent.
Phragmites is represented by three distinct lineages in North America – native P. australis subsp. americanus, which has several dozen distinct haplotypes, an invasive European haplotype, and P.australis subsp. berlanderi, which is of unknown origin. In the southwestern US, we have detected new invasive populations, as well as hybridization between the native and European lineages. Our lab studies the causes and consequences of invasive lineage establishment and hybridization in this arid region.
New Zealand Mudsnail
In the New Zealand mud snail’s native habitats, it is vulnerable to infection by the trematode Microphallus sp.. The potential biological control method that is currently underway at the University of California, Santa Barbara, is the use of the trematode parasite Microphallus sp.. This parasite lives and reproduces in the intestines of ducks and reproduce sexually, with eggs being released through the feces and then consumed by the New Zealand Mud Snail. Inside the snail, eggs hatch and the larvae reproduce asexually result in thousands of cysts forming inside the snail. This trematode uses the snail as only an intermediate host, with the ultimate goal of reaching the intestine of a local water fowl. Snails are infected by the larval stages of the parasite, which multiply asexually and castrate the snail—completely stopping reproduction. Encysted snails also undergo behavioral modification, increasing the chances that the snail will forage near the water’s surface in the morning, the time of day that water fowls hunt (Levri 1998).
The combined effects of parasitic castration and predation may reduce snail densities to tolerable levels. The efficacy of this host-parasite interaction in reducing snail population size, and safety of biological control, must be determined before the costs and benefits of biocontrol can be evaluated.
In 2011, a Sea Grant funded project (Principal Investigators: Tom Dudley and Ryan Hechinger) worked on developing potential biocontrol agents for the New Zealand Mud Snail. We proposed that Classical Biological Control (biocontrol), the introduction of natural enemies from the native region of the pest to suppress the abundance of invasive pest species, is a potentially appropriate means of achieving this goal, and possibly the only effective means of doing so.
This research will provide the information basis regarding efficacy and safety of the intended NZMS biocontrol agent.