Resistance to pesticides

The development of resistance to pesticides is generally considered to be one of the most serious obstacles to effective pest control today. 

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G. P. Georghiou and T. Saito, eds.. Pest Resistance to Pesticides, Plenum Press, New York, 1984. 

G. P. Georghiou and A. Lagunes-Tejeda, The Occurrence of Resistance to Pesticides in Arthropods, FAO, Rome, 1991. 

Selective toxicity is also important in relation to the development of resistance or tolerance to pollutants from two distinct points of view. On the one hand, there is interest among scientists concerned with crop protection and disease control in mechanisms by which crop pests, vectors of disease, plant pathogens, and weeds develop resistance to pesticides. Understanding the mechanism should point to ways of overcoming resistance, for example, other compounds not affected by resistance mechanisms or synergists to inhibit enzymes that provide a resistance mechanism. On the other hand, the development of resistance can be a useful indication of the environmental impact of pollutants. 

Brown, A.W.A. (1971). Pest resistance to pesticides In Pesticides in the Environment, R. White-Stevens (Ed.) Dekker New York, 437-551. 

The speed with which adaptations appear, such as, for example, resistance to pesticides, depends on the pressure of selection. When using pesticides, the pressure is practically 100% and, therefore, new characteristics appear very rapidly, in just 2-3 generations. The speed with which resistance appears depends also on the population size of the target species the larger the population, the more probable that resistance will appear in some members of the first generation. The populations of target species are always large otherwise there would be no reason to try to suppress them. Therefore, in each suppressed population, there will inevitably be more resistant individuals. 

One result of pesticide use is the growth in the number of target species ( pests ) that have become resistant to pesticides. From 1970 to 1984, the number of resistant arthropod species doubled - from 224 to 447. These include 25 species of beetles, mites, and caterpillars that attack... 

The development of resistance to pesticides by insects and herbicides by weeds poses a further ecological barrier for the industry. Industry analysts estimate that pests usually develop effective resistance to any new pesticide in less than ten years. This means new compounds must constantly be researched and run through the EPA registration process to replace those active ingredients that become useless, in addition to those that lose their patents or are banned by the FQPA. 

Georghlou, G. P. Salto, T. Eds. "Pest Resistance to Pesticides", Plenum Press New York, 1983. 

There are serious challenges in certain cropping systems due to the development of insect, disease, and weed resistance to pesticides. As a result, farmers are alternating modes of action of pesticides in order to reduce the development of pest resistance. The use of alternate mode of action pesticides to manage resistant pests varies with different crops and ranges from 30 to 72% of crop acres (Table 32.5). 

Gilpatrick, J.D. 1983. Management of resistance in plant pathogens. Pages 735-767 In "Pest Resistance to Pesticides". G.P. Georghiou and T. Salto, eds. Plenum Press, N.Y. 809 pp. 

Rotating to a cover crop also helps reduce insects and nematode pests, weeds, and plant disease. When a grower doesn t rotate, he is likely to be faced with one or more of these problems. Conventional growers can use pesticides to control these pests rather than rotate. So there is a choice between crop yield (while cover crops are planted) and pesticide use (that can maintain yield but may have toxic effects on the environment), at least in the short run. In the longer run, pests become resistant to pesticides and farmers may be forced to rotate because the crop can no longer be grown in that area. 

I finish this part of my lecture with one more bit of information. Even with the increasing use of synthetic pesticides we still have as many pests as we did when we started in the 1940s, because pests can evolve resistance to the pesticides. This is because pests that can survive the treatment will grow and multiply. In 1991 researchers documented resistance to pesticides in over 500 insects and mites, 270 weeds, and 150 plant pathogens (Bellinger 1996). 

Bellinger, R. G. 1996. Pest Resistance to Pesticides. Clemson University Pesticide Information Program. http //entweb.clemson.edu/pesticid/Issues/pestrest.pdf (accessed June 15, 2006). 

Yamamoto, Eds. Pest Resistance to Pesticides. New York Academic Press, (in press)... 

The environmental protection agencies of most countries have identified agriculture as the largest nonpoint source of surface water pollution. This is a major problem in each country. Pesticides and nitrates from fertilizers are detected in the groundwater in many agricultural regions. Soil erosion is a concern in many countries. Pest resistance to pesticides continues to grow, and the problem of pesticide residues in food has yet to be resolved. All nations are more competitive in international markets than a few years ago. 

But nature is resourceful and adapts to the poisons pumped into the environment. The pest ultimately will develop immunity to the chemical used against it, which creates two problems. Firstly, the temptation is to use the chemicals more frequently to get the same effect. Secondly, another stronger, more effective chemical will ultimately replace the one that no longer works. The process in which pests develop resistance to pesticides is accelerating, which must be worrying for those who are tied into this system. When man competes with nature, it is unlikely that he will win, and likely that he will cause damage in the process. 

Croft, B.A. and Strickler, K., Natural enemy resistance to pesticides Documentation, characterization, theory and application, in Pest resistance to pesticides, Georghiou, G.P. and Saito, T., Eds., New York Plenum Press, 1983, p. 669. 

Georghiou, G.P., The evolution of resistance to pesticides, Annu. Rev. Ecoi Syst., 3,133,1972. 

Georghiou, G.P. and Saito, T., Pest resistance to pesticides., Plenum Press, New York, 1983. 

Mota-Sanchez, D., Bills, P.S., and Whalon, M.E., Arthropod resistance to pesticides status and overview, in Pesticides in agriculture and the environment, Wheeler, W.B., Ed., New York Marcel Dekker, 2002, p. 241. 

Good practice in the use of chemical vector control methods. Vector control measures that make use of pesticides are carried out in accordance with established international norms to ensure that staff, the people affected by the disaster, and the local environment are adequately protected, to avoid creating resistance to pesticides. 

Table 6.6 is provided as a final aid for protective glove selection decisions. Table 6.6 identifies the preferred glove types as well as those not recommended for use with pesticide formulations containing various carrier solvent types. The glove types identified as preferred are those that consistently provide the best permeation resistance to pesticide formulations and undiluted carrier solvents within each chemical classification identified. The glove types identified as not recommended are those that consistently provide very poor permeation resistance. Also note that the recommendations in Table 6.6 are... 

Resistance to pesticides arises primarily through changes in the sensitivity of the site of action or in the metabolism of the pesticide (25,27.28). Many pesticides are activated metabolically. While it is theoretically possible to generate resistance through reduced activation, it seems much more common to observe increased detoxification in resistant strains. In some cases decreased uptake or enhanced excretion also contribute. It is an obvious prerequisite for any type of scientifically-based attempt to combat resistance that the resistance mechanism and its genetic basis must be defined. 

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