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4 Detection, Monitoring, and Risk Assessment RESISTANCE DETECTION MEANS IDENTIFYING a significant change in the susceptibility of a pest population to pesticides, ideally very soon after the emergence of resistance. Resistance monitoring attempts to measure changes in the frequency or degree of resistance in time and space. Resistance monitoring is most useful when undertaken early in a resistance episode. Monitoring can also be used to evaluate the effectiveness of alter- native tactics that are employed to overcome, delay, or prevent the devel- opment of resistance. In contrast to detection and monitoring of resistance in the field after the fact, resistance risk assessment is predicting the probability of resistance emerging as a result of use of a pesticide in a given use environment. A risk assessment is subject to a varying margin of error and should, in any event, be applied with care. Resistance risk assessments can be made for certain plant pathogens with some precision when the toxicological, epidemiological, and population considerations of the pathogen are well known from previous resistance episodes (Staub and Sozzi, 19841. In such cases, resistance man- agement actions may be taken to prevent resistance before it occurs and is detected in the field. Likewise, there are extensive historical data bases on resistance trends for some insects that make it possible to carry out resistance risk assessments, thereby making it possible to manage resistance by re- stricting the use of certain pesticides, or by managing their application in some specific fashion (Keiding, this volume). More often than not, though, 271
272 DETECTION, MONITORING, AND RISK ASSESSMENT the data base on the resistance potential of a given pest and pesticide com- bination is too limited to allow for resistance risk predictions that are reliable enough for use in devising strategies to manage resistance. Detection, monitoring, and assessment of resistance risk are interrelated. They are generally used during different, sometimes overlapping periods in a resistance episode, and each has a distinctly different objective. A resistance risk assessment may be made when a new compound is proposed for use on a new target pest, or in a new crop or region. A resistance detection program should be initiated when a resistance risk assessment- or common experience- suggests a likelihood of resistance developing. With pesticides involving new chemistry and modes of action, the resistance risk potential will rarely be known. The resistance potential of known products, or of their chemical analogues, often can be assessed with reasonable precision. Once resistance is defected q the ideal program shifts into a monitoring phase. During this phase the spread and degree of resistance are periodically determined. Specific, well-known objectives of these interrelated activities include · Provide an early assessment of the risk for resistance before a pesticide is widely used. · Determine whether ineffective control following applications of a pes- ticide are due to resistance. · Provide an early warning system so that alternative pest-control tactics can be implemented. · Delineate the geographic extent and movement of the resistant species over time. · Validate the effectiveness of resistance management tactics introduced at a specific time and place. · Provide effective crop protection. METHODS AVAILABLE FOR RESISTANCE DETECTION, MONITORING, AND RISK ASSESSMENT Resistance detection and monitoring methods for pest species have in the past been based on classical bioassay techniques (see examples in Keiding and in Brent, this volume; FAO, 1982; Georgopolous, 19821. With these methods, test organisms are exposed to a gradient of pesticide doses or concentrations, and features of mortality, growth, or population abundance are evaluated. More recently, biochemical tests for identifying unique de- toxification enzymes associated with resistant pests have been refined for use in survey of both resistant individuals and populations (Miyata, 19831. Even more recent are immunological tests for resistance based on identifi- cation of detoxification enzymes using monoclonal antibodies (e.g., Dev- onshire and Moores, 1984~. One expected benefit from biotechnology research
DETECTION, MONITORING, AND RISK ASSESSMENT 273 is DNA probes, which may be used to identify specific genetic sequences such as alleles conferring resistance in a pest species. It appears likely that a much greater degree of resolution and more specific identification of re- sistance alleles in pest individuals and populations will be available in the near future. These tools should enable monitoring of resistance much earlier than is currently possible. RESEARCH ON RESISTANCE DETECTION AND MONITORING Research is needed at several levels to determine the speed and degree of resistance that may develop in a given pesticide-use environment (see Chap- ters 2 and 31. At the molecular level, experimental assays in vitro and in viva may be used to compare responses to proposed new compounds with currently used compounds eliciting known (or unknown) resistance mechanisms. Generally, it is assumed that a biochemical mechanism that is genetically conferred is the cause of resistance in most species. At the organismal level, tests with large and diverse populations may be helpful to determine the degree and speed with which resistance may develop in a species. The impacts of a variety of factors on the speed of resistance developing can be studied, including the resistance mechanism, allele dom- in~n~P. ~n`1 fr~.n''~.no.v immigration of sll~centible tones into the system, the '''a'' -- a'' - ''-~ d ~ -''''''-Do rid Jr competitiveness of resistant types, etc. At the population level, the probability of resistance developing under varying ecological conditions and field-use practices may be examined through field tests using the methods employed by pest-control personnel or in trial runs made in conjunction with pest-management operations. In this type of test, problems are often encountered with experimental design, making it difficult to control treatments on highly mobile pests. RECOMMENDATION 1. The following research is needed to evaluate the biological and practical feasibility of resistance detection and monitoring in key pests. · Develop new and improved standard methods to detect and monitor resistance for key pests, where needed. Extensive work in this area has been done by industry and by the World Health Organization (WHO), the Food and Agricultural Organization (FAO), the European Plant Protection Organization (EPPO), the Entomological Society of America (ESA), and other similar organizations. Continued and expanded cooperation is needed. Detection and monitoring methods should be as simple, rapid, accurate, precise, field-adaptable, and inexpensive as possible. Major differences in methods exist among pest types, i.e., insects, weeds, microorganisms, and these differences properly (and sometimes improperly) can influence how
274 DETECTION, MONITORING, AND RISK ASSESSMENT data are interpreted. Monitoring systems need to consider the unique attributes of each pest group and differences among and within species in different geographic areas. · Determine the relationship between detection and/or frequency of resistance as measured by laboratory bioassay tests, and the likelihood and severity of failure of a pesticide under field conditions. Data from resistance monitoring, coupled with field observations, can then be the basis for rational decision making. · Collect and compile baseline susceptibility data for pesticides effec- tive against key pests. An important use of these data will be to estimate doses that kill essentially all susceptible individuals (for example, twice the LDg91. Such doses could then be used for sampling efforts that can quickly detect resistance. The nature of the data needed for different species may vary seasonally over time, geographically, and according to when various pesticides were first introduced commercially. · Develop specialized evaluation methods and statistical procedures for early detection of resistance at low levels, when required. Such meth- ods may differ considerably from routine monitoring methods, and may involve specialized genetic screening tests. · Evaluate new and developing immunological, biochemical, and bio- technological methods for monitoring resistance in the field. Resistance tests for most pests should be directed at the population level; however, assessments of individuals also is possible based on new biochemical and immunological methods that are becoming available. These assessments may prove important for some pests, although many of the currently used bioassays to monitor plant pathogens evaluate individuals (i.e., isolates) rather than populations. · Research on each of the above methods should consider accuracy and precision, cost of collecting samples, previous pesticide histories, environ- mental conditions, and other sources of experimental variation that may affect pest susceptibility. To determine the appropriate size and frequency of a resistance monitoring program, the following should all be considered: sta- tistical levels of accuracy required for detection, time delays involved in mon- itoring, and time required to set resistance management into action. IMPLEMENTATION Where feasible, a resistance monitoring system should be based partly on an areawide, regular survey scheme and should respond to local reports of control failures for key pests throughout their potential range of infestation and economic impact. Once resistance is detected, the scope and extent of the monitoring should be expanded to determine the size, type, and spread of resistance. Ideally, monitoring results will become available on a timely
DETECTION,MONITORING,AND RISK ASSESSMENT 275 basis certainly within a production season-to allow for development and implementation of appropriate management tactics. Levels of resistance that can be reliably detected in the field may vary greatly depending on pest species and the environment in which pesticide is used. Thus, to ensure economical crop protection, it may also be important to take into account the variable periods of time required for a pest to develop resistance, and for resistance to reach a level at which crop production efforts may fail without a change in control strategy and/or chemicals. Examples of pests for which a resistance monitoring program might be ap- propriate and feasible include Be insects Heliothis sp., Spodoptera sp., boD weevil, Colorado potato beetle, alla aphids; mites; the fungal plant pathogens Penicillium sp., Cercospora sp., Botrytis, Monilinia; downy mildews; and cer- tain other pest groups, including selected grass weeds, rodents, etc. Monitoring technologies must be developed to evaluate management strat- egies, validate tactics (Chapter 5), accurately determine critical frequencies for pests under different conditions (i.e., crop, climate, economics), and guide implementation of optimum tactics. At present, some theoretical con- cepts that have been inadequately tested in the field are being advocated for use in resistance management planning. This practice can be dangerous and emphasizes the need to address deficiencies in knowledge through compre- hensive research efforts of applied biologists, population biologists, toxi- cologists, and modelers. Efforts should be made to identify and exploit more systematically the expertise of industry, academia, and public-sector agencies for conducting research and monitoring pesticide resistance. Both the extension service and industry have access to data on geographical extent and degree of resistance development in particular regions. A critical issue that will always need attention is confirming the validity of resistance reports. Industry can assist in eliminating false reports of resistance by rapidly sharing any data that suggest a change in resistance in a given pest population. A major commit- ment on the part of pesticide companies to resistance detection and monitoring and to the communication of their findings will be extremely helpful to any public information and recommendation system. The committee commends those companies that have already demonstrated both a willingness and com- mitment to these goals. RECOMMENDATION 2. Working groups involving both private and public sectors should continuously identify the priority of pests for resistance mon- itoring, based on estimates of economic, environmental, and social costs and benefits. Such working groups should be convened by state agricultural experiment stations, working in conjunction with extension, industry, and university scientists. The involvement and input of grower groups should also be encouraged.
276 DETECTION, MONITORING, AND RISK ASSESSMENT RESISTANCE-RISK ASSESSMENT Resistance-r~sk assessment is carried out intuitively by a wide variety of personnel associated with pesticide discovery, development, or use. Rela- tively few, however, have attempted to present more formal or structured methods for organizing or implementing assessment systems. Exceptions exist including the WHO program for health-related pest insects (Chapter 6), house flies in Danish farms (Keiding, this volume), and with certain highly specific fungicides applied for plant disease control (Staub and Sozzi, 1984~. RECOMMENDATION 3. Research methods and data bases needed to carry out resistance risk assessments need to be developed more fully and system" atically. Components such as historical data bases, detection and monitoring data, resistance models, laboratory selection tests for resistance, and use data could be incorporated into overall systems that can be used to aid in risk-assessment decisions with a higher degree of benefit. IMPLEMENTATION OF RESISTANCE-RISK ASSESSMENT The results of resistance-r~sk assessments should serve as aids to decision- makers and should not be considered conclusive forecasts of the outcome of a resistance episode. The designers of resistance-r~sk assessment programs must ensure that the results of these programs are balanced scientifically and consider species and local differences. Greater communication is needed among all personnel associated with the development, use, regulation, and research on pesticides and pesticide re- sistance. Information systems to monitor resistance currently are maintained by a variety of international, national, and local institutions (e.g., WHO, FAO, USDA, EPA, U.S. Department of Defense, university laboratories, mosquito control districts, pest-management areas). Additional data bases will certainly be developed in the future. There is need to coordinate and share information from these systems to the entire pesticide user community to be used in resistance-r~sk assessment. RECOMMENDATION 4. Appropriate international, federal, state, and local agencies should establish and maintain data bases both to support moni- toring and detection systems and to serve as a repository and clearing house for data on monitoring resistance. The data bases should contain information on pest species, chemical-use profiles, local conditions, resistance mecha- nisms, levels of resistance, test methods, and cross-resistances. Studies are needed on ways to coordinate the diverse resistance data base activities better among these groups and institutions. Both public agencies and pesticide companies should play an expanded role
DETECTION, MONITORING, AND RISK ASSESSMENT 277 in financing activities to monitor resistance and ultimately resistance-risk as- sessment. Industry should concentrate on supporting research and monitoring related to its individual products, while publicly funded institutions should em- phasize activities such as basic research on monitoring methods and disseminating monitoring information on resistance. Moreover, it is critical for the activities and investments of the public and private sectors to be coordinated more sys- tematically and integrated so that the best possible informational data base emerges from a given level of combined resources. Results of resistance-risk assessment programs should be available to the entire pesticide development/user community for evaluation, confirmation, and im- provement over time. RECOMMENDATION 5. Programs should be developed to help decision~mak- ers use information from resistance-risk assessment in pesticide related ac- tivities such as pesticide design, regulatory programs, use directions, and resistance management. Methods and means are needed to share results of resistance-risk assessment programs among all users involved in pesticide production, regulation, and use. REFERENCES Devonshire, A. L., and G. D. Moores. 1984. Immunoassay of carboxylesterase activity for iden- tifying insecticide-resistant Myzus persicae. Pestic. Biochem. Physiol. 18:235-239. FAO (Food and Agriculture Organization). 1982. Recommended methods for the detection and measurement of resistance of agricultural pests to pesticides. Plant Protection Bull. 30:36 71 and 141-143. Georgopoulos, S. G. 1982. Detection and measurement of fungicide resistance. Pp. 24-31 in Fungicide Resistance in Crop Protection, J. Dekker and S. G. Georgopoulos, eds. Wageningen, Netherlands: Centre for Agricultural Publishing and Documentation. Miyata, T. 1983. Detection and monitoring methods for resistance in arthropods. Pp. 99-116 in Pest Resistance to Pesticides, G. P. Georghiou and T. Saito, eds. New York: Plenum. Staub, T., and D. Sozzi. 1984. Fungicide resistance: A continuing challenge. Plant Dis. 68:102 1031. WORKSHOP PARTICIPANTS Detection, Monitoring, and Risk Assessment BRIAN A. CROFT (Leader), Oregon State University KEITH J. BRENT, Long Ashton Research Station WILLIAM BROGDON, Centers for Disease Control THOMAS M. BROWN, Clemson University C. F. CURTIS, London School of Hygiene and Tropical Medicine WILLIAM FRY, Cornell University MAR~oR~E A. HoY, University of California, Berkeley
278 DETECTION, MONITORING, AND RISK ASSESSMENT ALAN JONES, Michigan State University JOHANNES KEIDING, Danish Pest Infestation Laboratory JOSEPH M. OGAWA, University of California, Davis STEVEN RADOSEVICH, Oregon State University CHARLES STAETZ, FMC Corp. T. STAUB, Ciba-Geigy, Ltd., Switzerland ROBERT TONN, World Health Organization, Switzerland MARK WHAEON, Michigan State University