Hoy: Myths of Managing Resistance 385
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Hoy: Myths of Managing Resistance 385 INTRODUCTION TO THE SYMPOSIUM, THE MYTHS OF MANAGING RESISTANCE MARJORIE A. HOY Entomology & Nematology Department, University of Florida, Gainesville, FL 32611-0620 Resistance to pesticides in arthropod pests is a serious and increasingly perplexing problem in Florida, the USA, and the world. Resistance to pesticides already has cre- ated significant economic, ecological, and public health problems in agricultural, household and garden, and medical/veterinary pest management programs. Exten- sive research has been conducted on diverse aspects of pesticide resistance, and we have learned much during the past 40 years. However, to some degree, much of the discussion about ‘resistance management’ has been based on ‘myths’. As an organizer of this symposium, one of my goals was to stress that managing resistance is a formi- dable task that will remain a perpetual pest management dilemma, because resis- tance is a fundamental survival response to stress by arthropods. Five papers were presented in this symposium at the 1994 annual meeting of the Florida Entomological Society, but one manuscript regarding the response by indus- try to resistance could not be published in this series. In the first paper, Gary Leibee and John Capinera assess the impact of resistance to pesticides in Florida and cite examples of resistance that limit pest management options. Julie Scott describes what we currently know about the molecular genetics of ar- thropod resistance to pesticides. The number of genes identified, and the diversity of their effects on the physiology of arthropods, verify that resistance is a normal re- sponse to diverse environmental stresses. ‘Pesticide resistance’ is part of a general stress response with a long evolutionary history. Leah Bauer describes what we know about resistance to various toxins of Bacillus thuringiensis (B.t.) strains. B.t. provides microbial control of an increasingly diverse group of arthropod species and is an increasingly important tool for integrated pest management programs. The deployment of transgenic crop plants containing B.t. toxin genes is likely to be an effective method for inducing resistance in agricultural pests. Despite the diversity of B.t. toxin genes isolated and cloned, cross resistances are common. Thus, B.t. toxin genes are limited resources. Finally, I discuss a variety of resistance management methods and point out that we cannot really avoid resistance—we can only delay its onset. I argue that resistance management needs a paradigm shift that can best be accomplished if we recognize that pest management must be changed from a single-tactic strategy to a multi-tactic mode. Delaying resistance, whether to traditional pesticides or to transgenic plants with toxin genes, will require that we develop truly integrated pest management pro- grams, incorporating all appropriate tactics, including host plant resistance, cultural controls, biological controls, genetic controls, and biorational controls. Pesticides should be reserved for situations in which they perform best—as tools to resolve an unexpected pest population outbreak. Effective, fully-integrated IPM programs will delay resistance because the number and rates of pesticide applications can be re- duced. 386 Florida Entomologist 78(3) September, 1995 PESTICIDE RESISTANCE IN FLORIDA INSECTS LIMITS MANAGEMENT OPTIONS GARY L. LEIBEE1 AND JOHN L. CAPINERA2 1Department of Entomology and Nematology, University of Florida, Central Florida Research and Education Center, Sanford, FL 32771 2Department of Entomology and Nematology, University of Florida, Gainesville FL 32611 ABSTRACT Pesticide resistance in Florida was characterized through a survey and literature review. The survey was conducted in 1994 among public-sector entomologists to de- termine the current and future status, extent, context, pattern, and instances of pes- ticide (insecticide and acaricide) resistance in Florida. Results attested to the impact of pesticide resistance on the management of numerous arthropods in Florida. Twenty-five examples of insecticide and acaricide resistance were cited by survey re- spondents in agricultural, ornamental and landscape, medical and veterinary, or household and structural pests. It remains possible to manage most arthropods by us- ing chemical pesticides, but the current and anticipated lack of efficacious materials threatens current practices in some areas. Trends in extent, context, or patterns of re- sistance were noted as follows: high value crops, frequently treated arthropods, smaller arthropods, and pyrethroids were all considered factors associated with resis- tance. Insecticide resistance and its management were reviewed in depth for the leaf- miner Liriomyza trifolii and the diamondback moth, Plutella xylostella, two major insect pests in Florida for which management options have become severely limited because of insecticide resistance. Both cultural practices (continuous cropping, isola- tion, transport of infested seedlings) and pesticide use patterns (frequent application of broad spectrum pesticides) contributed to L. trifolii and P. xylostella resistance de- velopment. The history of pesticide resistance in these two insects is probably typical of pest resistance in Florida and may portend similar future problems unless depen- dency on pesticides for pest suppression is reduced through adoption of IPM philoso- phy and practices. Key Words: Insecticide resistance, Liriomyza trifolii, Plutella xylostella. RESUMEN La resistencia a los pesticidas en la Florida fue caracterizada a través de una en- cuesta y una revisión de la literatura. La encuesta fue conducida en 1994 entre los en- tomólogos del sector público para determinar el estado presente y futuro, extensión, contexto, patrón e instancias de la resistencia a pesticidas (insecticidas y acaricidas) en la Florida. Veinte y cinco ejemplos de resistencia a insecticidas y acaricidas fueron citados por los que respondieron la encuesta sobre plagas agrícolas, de ornamentales y de jardines, de importancia médica y veterinaria, o domésticas y de otras estructu- ras. Parece posible manejar la mayoría de los artrópodos usando pesticidas químicos, pero la falta actual y anticipada de materiales amenaza las prácticas presentes en al- gunas áreas. La tendencia en la extensión, contexto, o patrones de resistencia fue como sigue: cultivos de alto valor, artrópodos frecuentemente tratados, pequeños ar- trópodos, y piretroides fueron todos considerados como factores asociados con la resis- tencia. Leibee and Capinera: Symposium on Pesticide Resistance 387 La resistenca a los insecticidas y su manejo fueron revisados en profundidad para el minador de las hojas Liriomyza trifolii y para la polilla de la col, Plutella xylostella, los insectos plagas principales en la Florida para los cuales las opciones de manejo se han tornado severamente limitadas debido a la resisitencia a los insecticidas. Tanto las prácticas culturales (cosecha continua, aislamiento, transporte de plántulas infes- tadas) como los patrones de uso de pesticidas (aplicación frecuente de insecticidas de amplio espectro) contribuyeron al desarrollo de la resistencia de L. trifolii y P. xylos- tella. La historia de la resistencia a los pesticidas en estos dos insectos es probable- mente típica para la resistencia de las plagas en la Florida, y podría significar problemas futuros similares a menos que la dependencia de los pesticidas para la su- presión de las plagas sea reducida a través de la adopción de filosofía y prácticas de MIP. Insecticide resistance has had an impact on the management of insect pests in Florida since the mid-1940s following the widespread adoption of synthetic insecti- cides, especially the organochlorines, organophosphates, and pyrethroids. Numerous anecdotal reports exist, wherein consistently effective insecticides have become inef- fective and remained so for several seasons. Such reports have been considered ample evidence of resistance development (Hoskins & Gordon 1956). In fact, Genung (1957) provided strong evidence based on anecdotal reports and data from field efficacy trials for resistance development in the cabbage looper, Trichoplusia ni Hubner, imported cabbageworm, Artogeia rapae (L.), a Liriomyza sp., and leafhoppers, Empoasca sp., at a session of the Florida State Horticultural Society Meeting in 1957 entitled “Sympo- sium-Vegetable Insect Resistance to Insecticides in Florida” (Brogdon 1957). Resis- tance episodes in Florida have also been documented in a number of species with laboratory studies in which concentration-mortality response has been used to com- pare resistant and susceptible strains. Much of this work has been conducted within the last 10 years and involves species such as cabbage looper (Shelton & Soderlund 1983), diamondback moth, Plutella xylostella (L.), (Leibee & Savage 1992a, Shelton et al. 1993, Yu & Nguyen 1992), silverleaf whitefly, Bemisia argentifolii Bellows & Per- ring, (G. L. L. unpublished data), house fly, Musca domestica L., (Bailey et al. 1970, Bloomcamp et al. 1987), German cockroach, Blatella germanica (L.), (Milio et al. 1987, Koehler 1991, Hostetler & Brenner 1994), Liriomyza trifolii Burgess (Keil & Parella 1990, G. L. L. unpublished data), fall armyworm, Spodoptera frugiperda (J. E. Smith), (Pitre 1988, Yu 1992), cat flea, Ctenocephalides felis (Bouche), (El-Gazzar et al. 1986), and citrus rust mite, Phyllocoptruta oleivora (Ashmead), (Omoto et al. 1994). In hopes of providing a better understanding