Biological control is the most effective, sustainable, economical, and environmentally-sound, approach to controlling arthropods pests, mites, and weedy plants. Its applications can conserve the biodiversity of millions of acres of natural land, protect our food supply by reducing pesticide use on crops, and mitigate the impact of urban pests. Biological control has traditionally been defined as the "the action of parasites, predators, and pathogens in maintaining another organism's density at a lower level than would occur in the absence of the natural enemies" (DeBach 1964). Applied biological control is typically separated from natural biological control and further defined by three main approaches: importation, augmentation, and conservation. These approaches are via human intervention, which has prompted new definitions to surface. A recently proposed definition of biological control by two collaborating project members is “biological control is the indirect positive effect of a biological control agent on humans that is mediated by direct or indirect negative effects of that agent on populations of one or more target species (Heimpel and Mills 2017).

This regional project shows that all three areas of applied biological control remain relevant in the western U.S.  In the importation approach (referred to as classical biological control), exotic natural enemies are imported and released in a new area where the target pest or weed occurs. Research projects that search for effective natural enemies in the pest’s country of origin include years of collaboration with overseas scientists to find a species safe to release; followed by detailed monitoring and evaluation. Augmentation and conservation involve supplementing (or manipulating) natural enemies already in place or modifying the environment, respectively, to improve the effectiveness of biological control. For a given arthropod pest or weed, a pool of natural enemies often exists which consists of vertebrates, invertebrates, and microorganisms.  The fundamental problems of applied biological control are to select an appropriate species or combination of species from this pool that will bring about the desired level of pest suppression, while causing minimal impacts on non-target species.

The landscape of the western U.S. is incredibly heterogeneous, consisting of desert, grassland, shrubland, forest, mountains, and urban habitats. Many of these habitats are under the constant threat of invasive species. This region is also home to the most productive agricultural counties in the country (farm gate) and to over 50% of national organic acreage (USDA NASS 2020). Moreover, biological control is a cornerstone of organic farming, and the production of organic commodities in the U.S. continues to increase. Annual global organic retail sales in 2019 were valued at $117 billion, with the U.S. accounting for 42% ($50 billion) of this market (Willer et al. 2020). In the millions of acres of natural areas and rangeland in the western U.S., biological control is often the only choice to suppress invasive species. Biological control is an increasingly important pest management tactic in extensive low-value per acre areas.

Biological control can result in highly significant benefit:cost ratios. Recently, members of this project synthesized data from biological control programs targeting arthropod pests and discovered that for all studies that included economic data, the mean net present value of a classical biological control program was about $37.3M with an average benefit:cost ratio of 61:1 (Naranjo et al. 2019). They found that conservation biological control options also had significant value, averaging $74/ha. High value fruit orchards under biological control saved producers as much as $22,800/ha. over pesticide programs. Another project member documented a ratio of 50:1 for a mole cricket biological control project (Mhina et al. 2016). While these economic benefits are enormous, the true value of biological control is likely even higher due to external benefits such as reductions in pesticide use and exposure. These reductions lead to improved environmental quality and human health, but have not been consistently considered.

Continued project justification: This regional project involves biological control of arthropod pests and weedy plants. The mission of this project is to facilitate all aspects of applied biological control research and implementation among specialists from the participating institutions and organizations. Because biological control of arthropod pests and weeds is based on many of the same ecological principles, researchers from the two fields benefit greatly from information exchange and research collaboration. The methodologies for controlling arthropod pests and weed plants differ, but the scientific issues (e.g., introduction strategies, genetics of colonization, evaluation of natural enemy impact, etc.) overlap extensively. That some individuals involved in this project conduct research in both arthropod pest and weed systems is further evidence of the conceptual similarities between these two fields.

Stakeholder input justifying this project is based on biological control being of great benefit to agriculture, natural ecosystems, the quality of rural life, and the consumer.  In 2018, the USDA, EPA, DOI and DOD reaffirmed their commitments to pesticide reduction with their National Road Map for Integrated Pest Management (USDA 2018). One of the goals of this document is to encourage development of low-risk suppression tactics, including biological control. It states that reductions in insecticide and herbicide applications should enable farmers and ranchers to reduce production costs, adopt sustainable pest management practices, and reduce the evolution of pest resistance to pesticides. A relevant example of a W5185 project in this area is the ongoing program to suppress the Asian citrus psyllid in California using an imported parasitoid from Pakistan. Since the start of a biological control program in 2011, psyllid densities in urban citrus have declined by over 70%. This has helped to keep some of the largest citrus producing areas in California psyllid-free for more than 10 years (Milosavljevic, I. et al, 2021).

Regardless of the many biological control advances in recent years, appreciably more research is needed due to an unrelenting introduction of invasive pest species (weeds and arthropods), the impacts of climate change, and how natural enemies are affected by pesticides. Additionally, there has been an increase in federal regulations for imported agent non-target testing and release. Genetically-engineered crops continue to add to the challenges in developing biological control tactics.

The following brief summaries will give compelling reasons for this regional project to continue. Classical biological control release programs continue to be rigorously regulated at the Federal level with much of the focus on non-target impacts. Proactive biological control programs, searching for indigenous vs. exotic natural enemies and the increased use of molecular techniques have all been added to the non-target protocols used to determine if a natural enemy will be safe and effective after release.  Further research into the genetics and ecology of colonization is clearly warranted and ongoing. In the future, classical biological control should ideally be able to predict (1) the appropriate species (or biotype) or combination of species (and/or biotypes) to release for control of a target pest in a given situation; and (2) the environmental impact resulting from the introduction of an exotic enemy.  Since 2000, regulations on natural enemy importation and introduction have been enforced by the USDA-APHIS, using guidelines from the North American Plant Protection Organization (NAPPO) that require researchers to provide in-depth studies complete with rigorous data on the non-target effects of biological control agents they wish to release (Mason et al.  2005).  Currently, non-target testing and regulations involved in releasing biological control agents for both weed and arthropod pests continue to be important topics discussed routinely by this workgroup.  We need to develop additional frameworks that evaluate the risks as well as the benefits of potential biological control importations.  When considering benefits, we must think broadly and include not only economic benefits but environmental ones, realizing that these can be multi-faceted. USDA-APHIS-PPQ published their 330 Rule in the past five years, with much input from stakeholders, including W4185.  Our project has always enjoyed the attendance and participation by Federal representatives from all the agencies that affect the movement and regulation of natural enemies.  Our members receive updates routinely via email on many issues that affect biocontrol and when these proposed new regulations debuted they were dispersed via email and thoroughly explained during our annual meeting as a formal presentation.  Many project members have import permits for biological control agents, either existing or pending, and the face to face interaction with USDA-APHIS personnel that this project annually provides has always been invaluable. 

Through international migration, transport, and commerce, human activities have accidentally or deliberately moved plants and animals to new regions, and these events have contributed greatly to the introduction of many species around the globe (Mack et al., 2000).  Invasive species are not only recognized as one of the main drivers of global change (Sala et al., 2000); they often pose an enormous threat to agricultural lands and thus have high economic costs (Pimentel et al. 2005).  Because of their negative consequences, many techniques and strategies have been deployed to control and manage invasive arthropod pests and weedy plants.  When these methods are successful, they can result in long-term reduction in the distribution and abundance of such pests and weeds.  Unfortunately, these efforts are not always successful, and such species proliferate and cause great ecological and economic harm.   The United States Department of the Interior estimated that invasive species was causing $143 million in damage annually to the US (United States Department of the Interior, Invasive Species Strategic Plan. 2021-2025).  Biological control is often the only tool available to control invasive species, especially weeds, when affected habitats involve enormous acreage (Hinz et al. 2019).  Often these areas are home to critical natural habitats and the goal is to preserve biodiversity.  Many collaboratives within this project have continued to work on invasive weeds which impact several states and their overseas cooperators in Europe, who help search for natural enemies, attend the annual meetings to discuss results. But, protecting endangered habitat from invasive species need not involve extensive acreage.  A parasitoid released in Hawaii to mitigate damage by the erythrina gall wasp has proved successful in saving the beloved, native wiliwili tree (Kaufman et. al 2020).  Every approach possible to alleviate the impact of invasive species must be considered and biological control will continue to play an important role.

We continue to increase our understanding of the ecological mechanisms by which a successful natural enemy operates in nature, and why a particular organism is successful in one situation and not in another. Where success has been achieved in classical biological control, the underlying ecological mechanisms are not always clear.  Basic research on augmentation and conservation of natural enemies is also needed.  In augmentation, we urgently need a coherent theory of inundative/inoculative release as well as basic efficacy data in order to more readily incorporate commercially available predators and parasitoids of arthropod pests into IPM systems. The genetics of mass production must be evaluated experimentally so that quality control procedures can improve the final product (Gebiola et al. 2019). Advances in the nutrition of parasitoids and predators are needed.  Continued commitment to conservation of natural enemies is required, including innovative ways of integrating pesticides and cultural controls with natural enemy species.  As IPM programs become more environmentally-friendly, they are using more biopesticides (Bordini et al. 2021) and techniques like Sterile Insect Technique (SIT) or mating disruption chemicals.  In the past five years, W4185 scientists have examined interactions between transgenic crops and biological control species, and these studies will increase as more such crops are approved (Fleischer et al. 2021). 

Global warming has long been accepted as an official threat to our natural and agroecosystems. Climate change and its impact on biological control, predator-prey and host-parasitoid dynamics could impact all three approaches to biological control. NOAA Administrator Rick Spinrad, Ph.D. said “July is typically the world’s warmest month of the year, but July 2021 outdid itself as the hottest July and month ever recorded. This new record adds to the disturbing and disruptive path that climate change has set for the globe.” (NOAA, August 2021).   It will be imperative that scientists watch for the effects of climate change on biological control agents and the arthropod and weed pests that have been kept in check by those agents (Nechols 2021). Recommended actions include conducting surveys for non-target species in areas undergoing climate change, determining tolerances to changes in temperature and precipitation for natural enemies and hosts/prey, incorporating climate data into insect population models, and long-term assessments to document the impact of climate change on non-target species and efficacy of biological control programs. Because climate change will impact both target pests and non-target species, the work will be best-accomplished by grant-funded programs involving interdisciplinary teams of scientists.

Regional, Collaborative Character of Project: Invasive pests continue to arrive in the western U.S., and many of these will become permanently established.  The use of classical biological control will remain a high priority. At the same time, our IPM programs must be continuously evaluated, refined, and adjusted in response to changes in newer and more specific control technologies and production practices. The most effective way to address these new pests that become quickly established and spread to other states is through regional collaboration of state and federal scientists.  Experiment Stations and non-Land Grant institution members to this project accrue timely and relevant benefits to participation.  Regionality is essential to implementing biological control-based solutions to our pest problems for the following reasons: 1) numerous target pests occur in three or more western states or territories; for these pests, the research effort must be coordinated and duplication minimized to effectively utilize very limited resources; 2) regional importation/quarantine facilities are critical for a coordinated response to exotic arthropod pests and weeds. These facilities are finite, there are no plans to expand them in the foreseeable future, and they serve the needs of all states and territories in the region; and 3) interstate exchange of information and exotic species/biotypes is facilitated through a regional approach. Sharing the cost of foreign exploration and quarantine is essential, as is sharing of methodological advances and our knowledge base.  Without a regional project in biological control, the western states and territories will not be able to rapidly share current information on controlling new and existing pest species, many of which have ranges over multiple states.  Additionally, this group discusses emerging pest threats and forms collaborations and networks that anticipate and plan for pest arrival.  Besides state to state (Experiment Station) collaborations, active participants often include scientists from USDA-ARS, USDA-APHIS, USFS, and state departments of agriculture, all of which benefit from rapid information transfer and shared projects. 

Advances in the development of sound ecological theory concerning pest population dynamics, predator-prey interactions, the role of invasion genetics, methodologies for the evaluation and release of natural enemies, and new regulatory policies are all fundamental needs in biological control, along with coordination and cooperation of research for a given pest. For example, theoretical and experimental studies of the actual ecological mechanisms that underpin pest population regulation are being addressed in several states and among pest systems.  In addition, our members and Federal Advisers, serve on key committees that are steering efforts to minimize non-target effects through policy discussions and recommendations

The value of networking that takes place during the 2 day annual meeting of this project cannot be over-emphasized. Without this multistate project, many arthropod and weed pest species will not be targeted for suppression and will cause damage to both agriculture and to natural U.S. ecosystems.  Results produced by the members of this regional project have historically had, and will continue to have, a significant domestic and global impact in the field of biological control.