Entomology at the Land Grant University: Perspectives from the Texas A&M University Department Centenary

24. Driving Forces for Target-Based Insecticide Design in the Twenty-First Century

C  Driving Forces for Target-Based Insecticide Design in the Twenty-First Century
  Department of Entomology Texas A&M University–College Station As we look to the future of entomological research, one valid question is to ask whether synthetic insecticides are going to be used or replaced by other means of pest control in the next century. If we agree that synthetic insecticides are key for the success of modern agriculture and to preserve public health, then, to what extent will insecticides be used? How will new, safer insecticides be developed? This chapter focuses on some factors that will influence insecticide discovery and use in the twenty-first century.       Synthetic organic insecticides currently represent  percent of the active ingredients in the market (Casida and Quistad, ). At the center of our concern as entomologists is the management of insect pest populations in agricultural and urban settings. From the urban perspective, it appears that pesticide use will not only be maintained but also might actually increase at times as pests continue to expand their previously occupied geographical areas . Many of these arthropod pests transmit human diseases, for example, ticks transmit Lyme disease on the East Coast and in the southeastern states of the United States (Linden et al., ). Culex quinquefasciatus Say mosquitoes carrying the West Nile virus are now a recurrent problem in New York and the East Coast of the United States. Malathion is being applied against the vector because the disease can be deadly, and there is no vaccine to prevent it. In Texas C. quinquefasciatus transmit St. Louis encephalitis, a viral disease for which there is also no vaccine. Nuisance arthropods such as the imported red fire ant, Solenopsis invicta Buren, also continue to expand their range in the United States (Mackay and Fagerlund, ). Insecticides are needed against these pests; however, not all types of insecticides are accepted by the public. The public is intolerant of arthropod presence in homes and neighborhoods , and intolerant of insect damage to produce and grains. Paradoxically , the public is also intolerant of the risks associated with insecticide use (Coats, ). The public’s attitude, as reflected in consumer reports, is a driving force in insecticide development.     Many pesticides, and particularly many insecticides, are being taken off the market because of environmental risk concerns and problems associated with insecticide resistance. This loss will most significantly affect public health and small-market commodities for which insecticide choices are limited . Insecticide development for these commodities is virtually nonexistent due to the small market share of these crops reducing product economic feasibility (Casida and Quistad, ). The organochlorinated insecticides DDT, cyclodienes, and related compounds have been eliminated from western markets due to undesirable toxicological effects on nontarget organisms and their high persistence in the environment. Organochlorinated insecticides accumulate in food chains and negatively affect wildlife and human health as endocrine disruptors (Kamrin, ). Compounds such as Mirex have been banned in the United States and most western countries (Kamrin, ). Organophosphates and carbamates are nerve poisons that inhibit the enzyme acetylcholinesterase, and many of these compounds have high mammalian toxicity (Fukuto, ). Several of them are being revised or going to be revised by the Environmental Protection Agency (EPA) and their uses will be further regulated or restricted. The revision by EPA has been prompted by the awareness within the scientific community and the public of the risk of insecticide use to human health, especially for children, the elderly, and agricultural workers, and the potential damage to the environment through ground water contamination and concurrent effects on nontarget species.    -    In addition to regulation, many insecticides are being taken out of agricultural markets because of problems with insecticide resistance. Effective synthetic insecticides are in short supply and need to be used with moderation to prevent development of resistant pest populations. Reliance on specific active ingredients often leads to increases in both frequency and rate of application , which in turn lead to development of insecticide resistance. Thus, when a new compound is registered, resistance management plans are necessary to keep it on the market. In most cases, however, scientists have failed to “manage ” resistance and can only delay or mitigate it (Hoy, ). This has been exempli fied with pyrethroids. Pyrethroids are generally cost-effective products with low mammalian toxicity. However, their excessive use and abuse has developed resistance in major pests including pests of agricultural crops (Luttrell et al., ) and disease vectors. Excessive...