Environmental Problems, Their Causes, and Sustainability 1

Figure 23-2 Geographic range of five majorpests in the lower 48 states of the UnitedStates. (Data from U.S. Department of Agriculture)GrasshopperAccording to studies by microbiologistBruce Ames, we consume farmore natural pesticides produced byplants than synthetic ones producedby humans. Ames also contends thatexposure to natural pesticides in foodcauses more cancers than exposureto synthetic pesticides—although neitherexposure poses much risk.Newer pesticides are safer and moreeffective than many older pesticides.Greater use is being made of botanicalsand microbotanicals (Table 23-1).Derived originally from plants, theyare safer to users and less damagingto the environment than many olderpesticides. Genetic engineering is alsobeing used to develop pest-resistantcrop strains and genetically alteredcrops that produce pesticides.Many new pesticides are used atmuch lower rates per unit area than olderproducts. For example, applicationamounts per hectare for many newherbicides are 1/100 the rates for olderones, and genetically engineeredcrops could reduce the use of toxicinsecticides.Pink bollwormWhat Is the Ideal Pesticide?An Ongoing SearchScientists work to develop more effective and saferpesticides, but through coevolution pests find wayscombat the pesticides we throw at them.Scientists continue to search for the ideal pest-killingchemical, which would have these qualities:■ Affect only the target organism■ Not cause genetic resistance in the target organism■ Disappear or break down into harmless chemicalsafter doing its job■ Be more cost effective than doing nothingThe search continues, but so far no known naturalor synthetic pesticide chemical meets all or even mostof these criteria.ranges overlapGypsy mothcaterpillarEuropean red miteBoll weevil23-3 THE CASE AGAINST PESTICIDESWhat Is the Major Problem with UsingPesticides? Insects Have an EvolutionaryAdvantageInsects can rapidly become genetically resistant towidely used pesticides.Opponents of widespread pesticide use believe theirharmful effects outweigh their benefits. They cite severalserious problems with the use of conventionalpesticides.The major problem is that the widespread use ofsynthetic pesticides accelerates the development of genetic522 CHAPTER 23 Pest Management