Environmental Problems, Their Causes, and Sustainability 1

Studies have linked exposure to some pesticidesto childhood leukemia, Parkinson’s disease, immunesystem disorders, and prostate and breast cancer.Some scientists are becoming increasingly concernedabout possible genetic mutations, birth defects,nervous system disorders (especially behavioral disorders),and effects on the immune and endocrine systemsfrom long-term exposure to low levels of variouspesticides (Case Study, p. 416). The pesticide industrydisputes such claims.National Archives/EPA DocumericaFigure 23-5 A crop duster spraying an insecticide on grapevinessouth of Fresno, California. Aircraft apply about 25% ofthe pesticides used on U.S. cropland, but only 0.1–2% of theseinsecticides actually reach the target pests. To compensate forthe drift of pesticides from target to nontarget areas, aircraftapply up to 30% more pesticide than ground-based applicationdoes.Case Study: How Successful Have PesticidesBeen in Reducing Crop Losses in the UnitedStates? Barely Holding the LineA slightly higher percentage of the U.S. foodsupply is lost to pests today than in the 1940s.Studies indicate that pesticides have not been as effectivein reducing crop losses to pests in the United Statesas agricultural experts had hoped, mostly because ofgenetic resistance and reductions in natural predators.David Pimentel, an expert in insect ecology, hasevaluated data from more than 300 agriculturalscientists and economists and come to three majorconclusions.A Superbug Calledthe Silverleaf WhiteflySome pesticides can threaten human health. The WorldHealth Organization (WHO) and the UN EnvironmentProgramme (UNEP) estimate that each year pesticidesseriously poison at least 3 million agricultural workersin developing countries and at least 300,000 in theUnited States. This causes 20,000–40,000 deaths (about25 in the United States) per year. Health officials believethe actual number of pesticide-related illnessesand deaths among the world’s farm workers is greatlyunderestimated because of poor record-keeping, lackof doctors, inadequate reporting of illnesses, and faultydiagnoses.Each year about 110,000 Americans, mostly children,get sick from misuse or unsafe storage of pesticidesin the home, and about 20 die. According tostudies by the National Academy of Sciences, exposureto pesticide residues in food causes 4,000–20,000cases of cancer per year in the United States. Becauseroughly half of all people with cancer die prematurely,this amounts to about 2,000–10,000 premature deathsper year in the United States from exposure to legallyallowed pesticide residues in foods. This is higher thanthe EPA estimate of 3,000–6,000 premature deaths peryear. The pesticide industry disputes these claims.The ideal insect pest would attacka variety of plants, be highly prolificand have a short generationSPOTLIGHT time, have few natural predators,and be genetically resistant to anumber of pesticides.Bad news. The silverleaf whitefly has these characteristics,and farmers who have encountered it callit a superbug. This tiny white insect escaped frompoinsettia greenhouses in Florida in 1986 and hasbecome established in Florida, Arizona, California,and Texas.It is known to eat at least 500 species of plantsbut does not like onions and asparagus and has nonatural enemies. Dense swarms of these tiny insectsattack plants, suck them dry, and leave themwithered and dying.U.S. crop losses from this insect are greater than$200 million a year and are growing. Scientists arescouring the world looking for natural enemies ofthis superbug. Stay tuned.Critical ThinkingWhat is the ecological lesson to be learned fromsilverleaf whitefly?524 CHAPTER 23 Pest Management