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Executive Summary T ITERALLY HUNDREDS OF SPECIES of insects, plant pathogens, rodents, and weeds have become resistant to chemical pesticides. Indeed, re- ~sistance to pesticides is a global phenomenon. It is growing in fre- quency and stands as a reminder of the resiliency of nature. Public health protection efforts have been frustrated sometimes dramatically-by resis- tance in populations of insects and rodents involved in the spread of disease to human populations. Substantial effects of resistance on agricultural pro- ductivity, however, have been limited so far to a few crops and locations because nonchemical tactics and alternative pesticides have generally been available for use. Although scientists recognized resistance of insects to chemical pesticides nearly 76 years ago, the problem became widespread in the 1940s during an era of extensive use of synthetic organic insecticides and acaricides. Research on the phenomenon of resistance progressed slowly over the next three de- cades, despite a steadily growing list of documented cases. In the 1970s three unrelated factors converged, heightening concern around the world and lending momentum to scientific research focused on the genetic, biochemical, and ecological factors associated with resistance. First, entire classes of once highly effective compounds became useless in many major applications because of resistance. The number and diversity of pests displaying resistance increased appreciably worldwide, as did the list of chemicals to which resistance developed. Second, clear limits began to emerge in the ability of chemists to identify and synthesize effective and safe alternative pesticides. The stock of available compounds came to be viewed as a limited resource that could like natural resources be depleted
2 EXECUTIVE SUMMARY through poor management. Third, tremendous progress occurred within sev- eral basic scientific disciplines: scientists experimented with powerful new tools for elucidating the genetic and biochemical modes of action of pesti- cides; understanding of the cellular and subcellular mechanisms by which pests develop resistance grew rapidly; and progress in unraveling the genetics of resistance led to new insights into the defense systems and vulnerability of pests. Scientists began to use these new insights with some encouraging early results to develop more stable and effective pest-control strategies. The combination of these three factors profoundly influenced the thinking of most pest-control researchers, practitioners, and manufacturers. Resistance is spreading at an increasing rate among pests in some crops in virtually all parts of the world. Hard lessons for pesticide manufacturers have accom- panied the economic consequences of resistance. Companies now take very seriously the prospect that resistance may limit the number of years a new product will have to recover the steadily growing costs incurred in its de- velopment, testing, production, and registration. In the United States timely progress in managing resistance is a practical necessity for many farmers struggling to stay profitable in the face of growing international competition. The committee believes that slowing or halting the spread of resistance to pesticides should become a prominent focus in both public and private sectors. A range of activities needs to be pursued, including research, field monitoring and detection programs, education, and incorporation of strategies to manage resistance into international development and health programs. Fortunately, various individuals and groups involved in pest management have pioneered the application of some promising new strategies, and more resources and attention throughout the pest-control industry are being devoted to the ver- ification and dissemination of data on resistance and methods to manage its evolution. The idea and impetus for this project reflect growing concern about re- sistance and the sense that a more systematic and scientific approach is needed to deal with this recurrent problem. In this report we take stock of what is now known about the extent and severity of resistance problems around the world, limiting the discussion primarily to pests of agricultural importance. (Resistance in disease organisms and vectors also is extremely important, but this area has already received considerable attention.) The genetic and biochemical mechanisms of resistance are assessed and emphasis is placed on some of the new biotechnological methods used to study resistance. Application of population biology to the study of resistance is also reviewed. Papers and dialogue presented at the November 27-29, 1984 conference suggest that significant advances in understanding the development of resis- tance can be achieved by researchers in biochemistry, genetics, and theo- retical population biology collaborating with those in applied pest-management disciplines. Such synergism and multidisciplinary cooperation may prove
EXECUTIVE SUMMARY 3 critical in developing, refining, and validating practical management strat- egies that can be adopted to halt or slow down the emergence of resistance or otherwise reduce the severity of its impact. Biotechnology is already providing critical insights into the mode of action of a few major classes of herbicides and is expected to do the same for other pesticides. These and other insights that biotechnology can offer may even- tually make most conventional pesticides obsolete. Under the best of cir- cumstances, however, such breakthroughs are a decade off for the majority of major pests and crops. In the meantime (perhaps indefinitely) pest-control strategies involving some use of chemical pesticides will need to be devel- oped, implemented, monitored, and adjusted to sustain control that is both efficacious and affordable. The nature and properties of new pesticides will also evolve over the next several decades. Most new products will be more selective, less toxic to mammals, and effective at lower rates of application. Many will be chemical analogs of naturally occurring chemicals that control some physiological aspect of development in pest species. Nevertheless, effective management of the propensity of pest populations to develop re- sistance will remain a practical necessity. A second major focus of the symposium and this report is the critical requirement for dealing with resistance now and in the foreseeable future. Resistance is a phenomenon that typically develops rapidly. A pest population just beginning to display resistance may respond favorably to a change in management tactics for only a relatively brief period after detection. Resis- tance can progress within just a few seasons or even within a season to a point at which dramatic changes in control strategies or cropping patterns become necessary. If this narrow window is not exploited, the battle can soon be lost. Two other conclusions surfaced at the symposium and workshops: (1) pest populations that are already resistant to one or more pesticides generally develop resistance to other compounds more rapidly, especially when the compounds are related by mode of action to previously used pesticides, and (2) most pests can be expected to retain inherited resistance to pesticides for long periods. Hence primary reliance on chemical control strategies over the long run will depend on a steady stream of new compounds with different . modes of action that can also meet regulatory requirements and economic expectations an unlikely prospect in many pest-control markets. Throughout the United States and around the world new strategies are being formulated to slow or reverse the onset of resistance during this window of time between the detection of resistance and its often rapid evolution in severity to an unmanageable state. A necessary first step, treated at length in this volume, is the development and use of rapid, reliable methods to detect low levels of resistance in pest populations. Immunology, biochem- istry, and molecular genetics are expected to play a major role in developing
4 EXECUTIVE SUMMARY these methods. Methods also are needed to monitor the spread and severity of a resistance episode over time and space in order to gain an accurate sense of the size of the window and how rapidly it is closing. Data stemming from new assay methods used in resistance detection and monitoring efforts would be extremely valuable in the development of active strategies to manage pesticide resistance. The thinking underlying the use of such strategies is closely related to the philosophy and principles of integrated pest management (IPM). Put simply, management of resistance is an attempt to integrate chemical and nonchemical control practices through a range of tactics, singly or in combination, so that the frequency of resistant members of pest populations remains within a manageable, economically acceptable level. Management of resistance offers great promise as a complementary ex- tension of IPM. The tools and knowledge needed to structure and analyze opportunities to manage resistance are very similar to the information needs of scientists developing, applying, monitoring, and adjusting IPM strategies. Application of theoretical concepts from population biology and the use of general and specific models may provide important new capabilities in pre- dicting the outcome of different sets of pest-management tactics. On the other hand, we see little justification in maintaining the polite fiction that pesticide resistance is solely a technical problem that can be readily overcome with the right new pesticide or an adjustment in the way conventional pesticides are used. For even a single crop or clinical situation, the design, execution, monitoring, and long-term implementation of a pesticide-use program is a major endeavor. Even with careful monitoring, timely research, and enlight- ened product stewardship, the efficacy of many pesticides will prove im- possible to sustain except in a very limited sense and in isolated applications. Problems loom ahead as we are forced to deal with the practical conse- quences of resistance episodes. These problems must be faced and will invariably command the attention of most scientists engaged in pest-control research. Experience has taught us that resistance episodes will flare up like forest fires, sometimes unexpectedly and other times not surprisingly. As scientists and institutions gain expertise and devote additional resources to contend with threatening resistance occurrences, it is critical that steps also be taken, steadily and collectively, to develop a deeper understanding of resistance. New institutional mechanisms and a shared commitment are vitally needed so that the lessons learned in each resistance episode are not lost. Only by learning systematically from mistakes can we hope to avoid making the same mistake elsewhere, or in other crops or for different pests or pesticides. Much of the knowledge needed will be gained more quickly if new forms of collaboration, and closer ties can be forged between applied and academic biology. A concerted effort by research administrators to un- derwrite such collaboration and overcome well-entrenched barriers will
EXECUTIVE SUMMARY s be an important step toward identifying practical solutions to pesticide re- sistance problems. Resistance is a potentially powerful, pervasive natural phenomenon. The development and severity of resistance to pesticides is controlled primarily by human action. Ignorance or a lack of concern in dealing with resistance can set the stage for explosions in pest populations leading to crop failure and reversals in the effectiveness of public health protection programs. Resistance can and must be attacked in a variety of ways. Some scientists and pest-control practitioners will focus on the need for changes in farmers' pest-control practices; some will develop methods to detect and monitor resistance; and others will attempt to find improved institutions to coordinate management of resistant pest populations among various groups of farmers, other pesticide users, and pesticide manufacturers. Some scientists will pursue fundamental work on identifying the molecular and physiological bases of resistance. Progress at one level will help at other levels in understanding the ways organisms manage to overcome external threats like those posed by pesticides. To progress most swiftly and efficiently COmm~'nio.~tinn anal · a_ . .. . .. .. __J ~4,~ ~nrorma~on a~ssem~nat~on are critical needs not adequately met either by public or private institutions. RECOMMENDATIONS Basic and Applied Research Each of these research areas will require moderate or substantial increases in funding, either from new or redirected sources of funds, or both. Some of the needed research can and probably will be undertaken by the private sector. Additional public funding should be supplied through peer-reviewed programs such as USDA's Competitive Grants Program. The following recommendations are not listed in order of priority. RECOMMENDATION 1. More research is needed on the biochemistry, phys- iology, and molecular genetics of resistance mechanisms in species repre- senting a range of pests. Molecular biology, including recombinant DNA technology, should be helpful in isolating and characterizing specific mech- anisms of resistance. The information provided by these investigations is essential to develop tactics to counter resistance, rapid new techniques to monitor and detect the extent of resistance, and novel pesticides (considered in more detail in Chapters 2, 3, and 51. RECOMMENDATION 2. The discovery and exploitation of new "target sites" for novel pesticides should be a key focus as research efforts are initiated that combine traditional research skills with the new biotechnologies.
6 EXECUTIVE SUMMARY The number of modes of action of pesticides in current use is limited and, as a result of resistance, the number of functional pesticides is decreasing for some pests. Pesticide control will remain a necessity in many circumstances, and new compounds will be needed (Chapter 1~. The methods of contemporary biotech- nology should be very useful both in the identification of these target sites and for the production of new pesticides (Chapter 21. RECOMMENDATION 3. Standard methods to detect and monitor resistance in key pests need to be developed, validated, and then applied more widely in the field. Resistance detection and monitoring techniques are essential to early warning systems and in establishing the extent and severity of resistance (Chapter 41. These methods are critical for advancing and evaluating programs to manage resistance (Chapters 3 and 51. Agricultural producers, pesticide manufacturers, and applicators will benefit from better methods to monitor resistance. RECOMMENDATION 4. Concepts and insights stemming from population biology research on pesticide resistance should be used more effectively to develop, implement, and evaluate strategies and tactics to manage resis- tance. Population biology theory has been useful in a retrospective manner in ex- plaining past resistance episodes. It can also be useful in a predictive manner, for the development of optimum operational schemes to manage resistance for each pest-control situation (Chapter 31; RECOMMENDATION 5. The development and testing of a system of resis- tance risk assessment needs to be pursued. The ability to forecast accurately the likelihood of resistance may allow for the extension of the effective life of pesticides and offer insight into how the use pattern of a pesticide should be changed to slow the development of resis- tance. Experts in resistance risk assessment may eventually be able to recognize previously undocumented or unforeseen resistance episodes in time to develop alternative control strategies that halt the evolution of resistance (Chapter 4~. RECOMMENDATION 6. Increased research and development emphasis should be directed toward laboratory and field evaluation of tactics for preventing or slowing development of resistance (Chapter 5~. RECOMMENDATION 7. Efforts should be expanded to develop IPM systems and steps taken to encourage their use as an essential feature of all programs to manage resistance (Chapter 51.
EXECUTIVE SUMMARY Implementation of Detection and Monitoring Techniques for Key Pests and Maintenance of Practices to Manage Resistance 7 RECOMMENDATION 8. It is critical to determine for resistant populations the level of tolerance to the pesticide and the relative fitness of the resistant versus the susceptible portion of the pest population. This information is essential to the development of a sound program for managing the resistant population (Chapter 31. RECOMMENDATION 9. Resistance detection, monitoring, and management organizations should be formed at the local or regional level and assume greater responsibility for education, coordination, and implementation of activities to deal with resistance problems. Resistance monitoring activities are most effective when they are conducted by the people immediately concerned with the problem and most familiar with the specific situation of pesticide use (Chapters 4 and 6~. Building wherever possible on existing initiatives (including NBIAP, the National Biological Impact Assessment Program, organized by the U.S. Department of Agriculture), new institutional mechanisms are needed to coordinate the efforts of different sci- entists working at the local and regional levels on specific crops or pest-control needs. RECOMMENDATION 10. Continuous monitoring programs should be used to evaluate the effectiveness of tactics to manage resistance. Information derived from monitoring programs is essential to evaluate the effectiveness of tactics to manage resistance (Chapters 3 and 41. Continuous monitoring can help protect growers from excessive losses and provide pesticide manufacturers with an early warning that product efficacy may be in jeopardy. RECOMMENDATION 11. Federal agencies should support and participate in the establishment and maintenance of a permanent repository of clearly documented cases of resistance. A bank of information on the incidence of resistance to pesticides will be needed for the rational choice of compounds by users, the planning of programs to manage resistance, and the development of new compounds by industry. This data bank should be broad-based and include information about the incidence and level of resistance for specific pests, the affected geographic regions, and cross-resistance with other pesticides (Chapter 41. RECOMMENDATION 12. Departments of agriculture within each state, in considering whether to request emergency use permits to respond to pest- control needs that have arisen because of resistance to another compound, should seek advice on whether the conditions governing the emergency use
8 EXECUTIVE SUMMARY permit are consistent with validated tactics for the management of resis- tance. The U.S. Environmental Protection Agency, in approving such re- quests, should also consider the consequences for managing resistance, especially when cross-resistance is thought to be a possibility. RECOMMENDATION 13. After consultation with the EPA; university, state, and federal researchers; and industry trade associations, the U.S. Depart- ment of Justice should consider issuing a voluntary ruling that clarifies the antitrust implications (if any) of private sector initiatives to combat resis tance. Such a ruling would alleviate concerns over possible antitrust prosecutions following efforts by private companies working jointly to prescribe directions for use on labels of competing pesticide products. Such jointly developed use directions are sometimes needed to slow the onset of resistance to a family of pesticides or to a single compound sold by different companies (Chapter 6~. RECOMMENDATION 14. The public sector should become more involved in the development of required residue chemistry and other data for minor crop uses. State and federal agencies should consider applying the JR-4 program concept in developing data needed to gain registrations of pesticides with nonagricultural minor uses. Such efforts will help ensure availability of efficacious pesticides for use on minor crops and for nonagricultural uses such as chemical sterilants and roden- ticides (Chapter 61. RECOMMENDATION 15. Activities to manage resistance should not override environmental health and safety responsibilities, which should remain the highest priority mission of regulatory agencies. Appropriate groups, such as the Cooperative State Research Service, the Cooperative Extension Ser- vice, the Public Health Service, and professional societies, should take lead- ership roles in organizing work and educational groups within state, regional, and national IPM programs to implement efforts to manage resistance (Chapter 6~. It is necessary for some organizations to take a leadership role including the establishment of new funding sources and mechanisms to help galvanize re- search pertinent to management of resistance and to initiate new collaboration on projects essential to scientific progress on many key fronts (Chapter 61. RECOMMENDATION 16. A considerable effort should be put into the de- velopment of pest-control measures that do not rely on the use of chemical pesticides. Control of pest populations by combining in cycles the use of old and novel chemical pesticides, as they become available, is unlikely to be a viable long
EXECUTIVE SUMMARY 9 term strategy. There is no biological or evolutionary justification for the prop- osition that pest populations will return to sensitive states in relatively short order following the termination of the use of specific pesticides that brought on resis- tance. Moreover, experience suggests that novel and safe new pesticides will not always appear on the market when needed to replace compounds that have lost their effectiveness due to resistance. * * * We are growing familiar, through unfortunate experiences, with the devel- opment of resistance. We can and should learn from these lessons. It has become apparent that the phenomenon of resistance demands clear, thoughtful, and sys- tematic actions to prevent the loss of valuable pesticides that can contribute greatly to meeting food needs. The day is approaching when effective, affordable alternatives simply will not be available. Then, adjustments that could at times be extremely costly will have to be made in how and where we produce food. Important changes in attitude, commitment, and priority are needed now if we are to slow and eventually reverse the spread of resistance. This report offers guidance on logical steps to get the process under way.