W1185: Biological Control in Pest Management Systems of Plants
Statement of Issues and Justification
As the human population continues to increase, new demands will be placed on agricultural production and efficiency, and in maintaining environmental quality. This will be especially true for the control of pests in agroecosystems. The broad-scale use of chemical pesticides, the predominant approach used during the past 60 years, is clearly no longer acceptable nor compatible with new trends in agricultural sustainability and land stewardship. Although chemical pesticides have had a beneficial impact on agriculture, their attendant side-effects, such as target pest resurgence, secondary pest outbreaks, pest resistance, and environmental contamination, demand that more ecologically sound methods of pest suppression, such as integrated pest management (IPM), be developed. A move towards a nation-wide increase in the development and implementation of IPM programs has recently been encouraged in a recent USDA IPM initiative strategic plan (USDA 1994).IPM can be defined as the utilization of multiple pest management tactics in a compatible way so as to maintain pest populations at levels below those causing economic injury, while at the same time providing protection against hazards to humans and the environment. Host plant resistance, chemical pesticides, cultural management, and biological control are among the most important pest management strategies used in IPM. For arthropod pests, host plant resistance (where possible) provides one of the most effective and economically feasible pest control strategies upon which the other pest management approaches are integrated. Chemical pesticides are an important pest management tool in IPM, but must be used in a manner that is compatible with other management approaches, particularly biological control. Cultural pest management approaches (e.g., crop rotation, early/late planting, early/late harvesting, trap crops, cultivation and hand pulling of weeds, etc.) have been successfully employed against insect and weed pests in many agricultural settings, with minimal environmental disruption. Biological control has proven to be one of the most effective, environmentally sound, and cost-effective pest management approaches used in pest management. It is anticipated that biological control will play an increasingly important role in IPM as broad-spectrum pesticide use declines in the future.
Biological control is 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). Two types of biological control, natural biological control and applied biological control, are often distinguished. Natural biological control is that brought about by indigenous natural enemies in the native range of a pest species. In contrast, applied biological control is achieved through human efforts or intervention, and consists of three main approaches - - importation, augmentation, and conservation. In the importation approach (generally referred to as classical biological control), exotic natural enemies are imported and released in a new area where the target pest occurs, while 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, consisting of vertebrates, invertebrates, and microorganisms, exists. The fundamental problem in applied biological control is to select an appropriate species or combination of species from this pool that will bring about the desired level of pest suppression with minimal impact on nontarget species. The mission of this regional project is to facilitate research and implementation activities among the participating institutions and organizations in applied biological control.
The proposed project is a revision of regional project W-185 and involves biological control of both arthropod pests and weeds. Because biological control of arthropod pests and biological control of weeds are based upon many of the same ecological principles, researchers from the two fields benefit greatly from the exchange of information and ideas, and in research collaboration. Whereas the methodologies for controlling arthropod pests and weeds may differ, the scientific issues (e.g., introduction strategies, genetics of colonization, evaluation of natural enemy impact, etc.) overlap to a great extent. 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.
IPM programs based largely on biological control will be of great benefit to agriculture, the quality of rural life, and the consumer. Reductions in insecticide, acaricide and herbicide applications should allow farmers and ranchers to reduce production costs and to make adjustments for a more sustainable agriculture. Reduced pesticide use will enhance the quality of rural life through reduction in pesticide contamination of ground and surface water, reduced effects on nontarget species (including wildlife), and increased safety of farm workers and other rural residents. These benefits also accrue at the interface of urban and agricultural environments, where there is increasing opposition to pesticide use. The consumer will be a major beneficiary as average benefit:cost ratio of successful biological control programs is approximately 30:1. The attendant reduction in pesticide residues in food is also desirable, although controversy remains over the extent and public health significance of such residues.
Aside from the obvious benefits to agriculture, quality of rural life, the consumer, and the environment, the proposed research should make major contributions to broader scientific issues as well. The underlying ecological mechanisms concerning the population regulation of arthropods and plants by natural enemies and other factors remain a matter of great theoretical and practical interest. In biological control, a better understanding of such ecological mechanisms is prerequisite to improving our success rate in biological control. The intentional introduction of a biological control agent also can be viewed as a perturbation experiment; as such, it will reveal critical information relevant to the biology of pest invasions. Post-colonization changes in the genetic structure of an introduced agent can provide much needed data on natural selection under field conditions. Natural enemy complexes are comprised of feeding "guilds" which in turn have a characteristic structure. Analysis of the structure of natural enemy guilds can shed important light on general questions in community ecology. Finally, evaluation of successful natural enemies will contribute greatly to the larger question of how a predator and its prey interact and persist over time.
Background Information: Despite many theoretical and practical advances in recent years, our practical and conceptual understanding of success and failure in applied biological control fall short of meeting certain current and future requirements. For example, in classical biological control, the rate of establishment of natural enemies is relatively low in the case of arthropod pests (ca. 34%); further research into the genetics and ecology of colonization is clearly warranted. Classical biological control must also become a more predictive science. We must eventually 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 attendant to introduction of an exotic enemy. Nontarget impacts to plants or insects from biocontrol agents are becoming of increasing concern to conservation biologists, environmentalists, and federal agencies. Hence, documentation of minimal nontarget impact will be of increasing importance in order to foster increased confidence and adoption of biological control in pest management. Where success has been achieved in classical biological control, the underlying ecological mechanisms are not always clear. After 100 years of effort, we still do not fully understand the mechanisms by which a successful natural enemy operates in nature, or why a particular organism is successful in one situation and unsuccessful in another. This holds for natural enemies of both arthropod pests and weeds. Basic research in 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 become a regular practice in the commercial production of natural enemies. Advances in the nutrition of parasitoids and predators are needed. The economic feasibility of augmentation should also be explored. Finally, continued commitment to conservation of natural enemies is required, including innovative ways of integrating pesticides and cultural controls with key natural enemy species. Products of biotechnology designed for pest control must also be assessed and incorporated (where appropriate) into IPM programs.
Recent advances in chemical control of insects, particularly novel modes of action such as insect growth regulators and pheromones, open new opportunities for incorporation of biological control into IPM programs. Few agroecosystems contain a single pest problem and changes in practices to control one pest will often dramatically affect the suppression of others. For example, substitution of a pheromone to control a key pest formerly controlled with broad spectrum insecticides can cause other pests, previously controlled by the insecticide, to become significant problems. The latter pests may be controlled by reverting to the old practices, or by utilizing various aspects of applied biological control. In some cases, such pests may be controlled by careful conservation of existing natural enemies, a tactic formerly impossible when the key pest was suppressed by non-selective pesticides. Conservation may also be supplemented with classical biological control, particularly when secondary pests are of exotic origin.
Biological control is clearly symbiotic with advances in pest control strategies on all fronts, and the need for biological control is ever more important. Our mandate is to incorporate more biological pest suppression into IPM systems. However, a single-minded commitment of our regional and national pest control efforts to this one approach would prove as myopic as our nearly complete abandonment of biological control from 1950-1970, when pesticides were predominantly relied upon. But, to the extent that newer approaches (transgenic crop plants, novel chemistries, etc.) reduce overall pesticide loads in agroecosystems and narrow the range of species killed by toxicants, we will see increased opportunities for biological control.
Regional Character of Project: Exotic pests continue to arrive in the western U.S., and many of these will become permanently established. For such pests, the use of classical biological control should 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.
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. Many examples of regionality in our projects can be found in the tables of Appendices A and B.
Transcending the coordination and cooperation on a given pest is an important shared need for advances in regulatory policy, general methodologies for release and evaluation of natural enemies, and the need to develop sound ecological theory concerning pest population dynamics, predator-prey interactions, and the genetics of colonization in biological control. For example, theoretical and experimental studies of the actual ecological mechanisms that underpin pest population regulation is being addressed in several states and among pest systems.
Revised Project Proposal: The previous W-185 project proposal has been revised to: a) conform to the new guidelines for multistate research projects; b) expand and update five of the 15 objectives; and c) incorporate new target pests.
Conformance to the new guidelines required the addition of two new sections to the main body of the proposal (Measurement of Progress and Results and Outreach Plan, see below) and a great reduction in the overall length of the main text (from 27 pages to 15 pages).
The previous proposal contained 15 objectives classified under four goals:
Goal A: Import and Establish Effective Natural Enemies (Classical Biological Control)Goal B: Conserve Natural Enemies to Increase Biological Control of Target PestsGoal C: Augment Natural Enemies to Increase Biological Control EfficacyGoal D: Evaluate Environmental and Economic Impacts of Biological Control Goals A, B and C represent the three major areas of applied biological control (i.e., the introduction, augmentation, and conservation of natural enemies). Goal D represents another important, yet often neglected, goal of applied biological control, that of evaluation of environmental and economic impacts of biological control. Although we as a community of scientists may experience first hand the fruits of our labor, our accomplishments, and those of our colleagues before us, may go substantially unappreciated because of the relatively slow rate at which pest populations are reduced by the natural enemies (especially in some weed systems). Thus, our purpose in Goal D is to document benefit/cost ratios as well as the positive and negative environmental impacts of biological control. programs. Brief justifications for each of the 15 Objectives above are given in the Methods section. Objectives 2, 4, 7, 14 and 15 have been expanded and updated to accomodate new questions and priorities.
The new target pest species include cape ivy (Delairea odorata) and saltcedars (Tamarix sp., especially T. ramosissima). The target pest groups for this proposal now include aphids, beetles, gorse, true bugs, knapweeds, Lepidoptera, purple loosestrife, saltcedars, sessile Homoptera, spurges, tephritids, thistles, whiteflies, other arthropods, and other weeds (see Appendix A for specific species in each group).
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