Positive and Negative Aspects of Pesticides

Positive Aspects

Pesticides save lives.

They increase food supplies and lower food costs. They increase profits for farmers.

They work faster and better than other pest control alternatives. Safer and more effective pesticides are continually being developed.

Negative Aspects

Development of genetic resistance reduces the effectiveness of pesticides and leads to the pesticide treadmill.

Pesticides kill natural pest enemies and convert minor pest species into major pest species. Certain persistent pesticides are mobile and can amplify up food chains causing environmental impacts.

There are short-term and long-term threats to human health from pesticide use and manufacture. Source: Adapted from Miller, G. T., Jr. 1991. Environmental Science. Wadsworth, Belmont, CA.

FIGURE 7.7 Linkages in feedback circuits associated with the chemical control of pests. This network creates a cascade of effects when pesticides are used.

FIGURE 7.7 Linkages in feedback circuits associated with the chemical control of pests. This network creates a cascade of effects when pesticides are used.

pesticides leads to higher levels of pest populations due to the development of increased resistance in pests and due to declines in natural pest predators from pesticide toxicity. The circuit is completed when the resistant pests, which are now released from predation, increase thereby requiring the application of even more pesticides. The numbers of arthropod (insects and mites), plant pathogen, and weed species resistant to chemical pesticides has risen dramatically since World War II (Gould, 1991), and there is no easy solution to the positive feedback circuit. In fact, there are a series of these feedback circuits involved in pest management (Figure 7.7), including pesticide manufacturers who advocate use, farmers and other users, and even extending to scientists and the general public whose perspectives on pesticides are often out of phase (van den Bosch, 1978; Winston, 1997). Narcotics addiction has been used as a metaphor for these feedback circuits by several authors to signify the insidiousness of the problem (DeBach, 1974; Ehrlich, 1978). These circuits are actually interacting coevolutionary games or arms races, such as the "Red Queen relationship" (Van Valen, 1973, 1977) from evolutionary theory. A Red

FIGURE 7.8 Energy circuit diagram of the pesticide treadmill concept. Applications of pesticides increase the genetic resistance of the pest population which reduces mortality due to pesticide toxicity.

Queen relationship occurs when any gain in fitness by one species is balanced by losses in fitness by another species. Thus, adaptive success of one species creates selective pressure on the other species to evolve a counter move, which in turn creates selective pressure on the first species, starting the process over again. The Red Queen relationship can occur either between two competing species or between a predator and prey. This kind of coevolution has been named after the Red Queen from Lewis Carroll's Through the Looking Glass because she lived in a land where people had to do all the running they could just to stay in the same place; if they actually wanted to go anywhere, they had to run twice as fast as they could. Other examples of the Red Queen type of evolution are given by Clay and Kover (1996), Hauert et al. (2002), and Stenseth (1979). Exotic species and the natural resource managers who try to control them are being drawn into this kind of coevolutionary circuit and they may have to start working as hard as they can to keep up with one another. Figure 7.8 illustrates some aspects of the pesticide treadmill. Genetic resistance reduces mortality of the pest population due to the pesticide applications and resistance to pesticides increases in proportion to pesticide use in this model. These problems force the farmer to use greater doses of pesticides or different types of pesticides to maintain yield. A similar phenomenon is occurring with the development of drug-resistant pathogens, such as the increasing resistance of bacteria to penicillin and other antibiotics. Whole new strategies of dealing with medical wastes are needed to deal with this growing problem (see, for example, Rau et al., 2000).

Frank Egler's work may stand as a model for the kind of creative research that is needed to deal with the problems of exotic species control. Egler was a consummate plant ecologist (Burgess, 1997) who was committed to understanding and using herbicides as part of his research. He published many papers on herbicide effects (Egler, 1947, 1948, 1949, 1950, 1952b), on overviews of the social ecology of pesticides (Egler, 1964, 1979), and on vegetation management with herbicides (Egler, 1958; Egler and Foote, 1975; Pound and Egler, 1953) along with his collaborator, William Niering (Dreyer and Niering, 1986; Niering, 1958; Niering and

Goodwin, 1958). He developed a new kind of ecology that used herbicides as an experimental tool for applied problems. If exotic plants are to be controlled once they have become established, Egler's work on controlling plant community composition may provide lessons on the selective use of herbicides.

Perhaps some kind of ecosystem management (Agee and Johnson, 1988; Boyce and Haney, 1997; Haeuber and Franklin, 1996; Meffe et al., 2002) will be required for exotic species control. The ecosystem scale was examined by traditional pest ecologists (Haynes et al., 1980; Pimentel and Edwards, 1982) before the concept of ecosystem management arose, but most work in agriculture and forestry has focused on the population scale. Although ecosystem management has been criticized for being a philosophy rather than a set of specific techniques, it does present a different context against which exotic species and pests are judged.

A final topic is the economics of exotic control. Economics involves accounting for costs and benefits of exotic control and determines how much control is possible. Unfortunately, economics of exotics control has been overlooked in most assessments of the problem, so it is difficult to know how much control is possible. Studies are needed which evaluate the costs of control (such as purchases of pesticides and labor costs) and relate them to the relative success of control efforts. That such studies have not been published in the many symposium volumes and other texts on exotics is probably a measure of the preliminary stage of the field. Here again, work on pest control in agriculture and forestry can be a guide for the economics of exotic control. As is usually the case in these situations, it may be cheaper to exclude an exotic from a system (i.e., quarantining) rather than trying to eradicate it once established. Detailed studies must confirm this supposition. Exotic control must find a place among other priorities in the budgets of natural resource managers, and new forms of financing may be required. Economics is a reality for managers whose responsibilities it is to control exotics. Will it be possible to control exotic species with the amount of money available? Is there a risk of getting on a coevo-lutionary treadmill with exotics where more and more money will be required just to maintain levels of invasion? Answers to these kinds of questions will be needed to predict the future of exotics control.

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