CHAPTER 13

Pests and Pest Control

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The need for pest control

Pest: an organism that is noxious, destructive, or troublesome • Pathogens, wild animals, insects, mold, etc.

Agricultural pests: feed on crops, ornamental plants, or animals • Insects, fungi, viruses, worms, snails, rats, mice, birds Weeds: plants that compete with crops, forests, grasses Humans control pests to protect food and health and for convenience • Pesticides helps humans prosper © 2011 Pearson Education, Inc.

The importance of pest control

• Pests destroy 37% of U.S. agricultural production/yr.

• These losses total about $122 billion/yr.

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We are dependent on pesticides

• Changing agricultural technology (monocrops, genetically identical crops) has also boosted yields • Herbicide and other pesticide uses have increased drastically • Leading to a disturbing and unsustainable dependency on them • The following graph shows how pesticide use in the U.S. has doubled in the last 50 years: © 2011 Pearson Education, Inc.

Pesticide use in the U.S.

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Different philosophies of pest control

• Chemical treatment of pests attempts to eradicate or at least decrease pest numbers • • Gives only short-term protection Has highly damaging side effects to other organisms • Ecological control provides long-lasting protection • Based on knowledge of the pest’s life cycle and ecological relationships • May be highly specific to one organism © 2011 Pearson Education, Inc.

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Controlling pests

Ecological control emphasizes protecting people and plants • • Not the eradication of the pest Maintains the ecosystem’s integrity Integrated pest management: combines chemical and ecological control • Controls pests by using all suitable methods to bring about long-term management of pests • • Has minimal environmental impact Used in developing countries that can’t afford pesticides • Used where pesticides pose a health risk © 2011 Pearson Education, Inc.

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Chemical treatment: promises

Pesticides are categorized by the organisms they kill • Insecticides (insects), rodenticides (rats, mice), fungicides (fungi), herbicides (plants) • All can pose hazards to others, including humans Some of the first-generation pesticides like lead, arsenic, and mercury were found to be highly poisonous to humans as well as insects.

Second-generation pesticides like DDT were developed through synthetic organic chemistry. These were promising at first, but then people realized that there were long term consequences… © 2011 Pearson Education, Inc.

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The DDT story

Chemist Paul Müller studied DDT in the 1930s • • • DDT stands for Dichlorodiphenyltrichloroethane It had first been synthesized 50 years earlier It killed flies in his lab • • • As a pesticide, it was extremely successful • Extremely toxic to insects, not immediately toxic to humans or mammals Very cheap Broad spectrum (effective against many insect pests) Persistent (provided long-lasting protection) © 2011 Pearson Education, Inc.

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DDT in war…

It was used to control insect disease carriers • During World War II, it was widely used to control body lice, which carry typhus fever • • In Saipan, it controlled dengue fever It also controlled malaria-carrying mosquitoes, so it was sprayed into ditches of standing water. People sprayed it on window screens and the inside walls of their homes. This is still done today in some regions.

DDT saved millions of lives! • Müller was awarded the 1948 Nobel Prize in medicine © 2011 Pearson Education, Inc.

DDT in peace…

• • • • • After World War II, DDT use skyrocketed In forests, it controlled forest-destroying spruce budworm In salt marshes, it killed mosquitoes It controlled beetles that caused Dutch elm disease It was very effective in controlling agricultural pests • Farmers could ignore crop rotation and destruction of crop residues • • They could grow less resistant, more productive crops They could farm in warmer, moister areas © 2011 Pearson Education, Inc.

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Adverse environmental effects

DDT was widely used from 1940 to 1960 • • 80,000 metric tons in 1962 alone!

Shows the hazards of pesticides In the 1950s and 1960s, many bird species declined drastically • • They were at the top of the food chain (e.g., bald eagle, osprey) DDE (a product of DDT’s breakdown) resulted in thin shelled eggs • Higher doses of DDT and DDE go up the food chain © 2011 Pearson Education, Inc.

Osprey

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Bioaccumulation and biomagnification

Bioaccumulation: many synthetic organic chemicals are soluble in lipids (fats) • They pass through cell membranes into the body’s lipids Organisms can’t fully metabolize or excrete these chemicals • Small amounts accumulate over time to toxic levels Biomagnification: the multiplying effect of bioaccumulation through the food chain • Organisms in the chain have more concentrated amounts of chemicals in their bodies There is no warning until contaminants cause problems © 2011 Pearson Education, Inc.

Biomagnification

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Silent Spring

Silent Spring

(1962) by Rachel Carson documented the effects of the uncontrolled use of insecticides in the U.S.

• If use continued as usual, there might be a spring with no birds • With ominous consequences to humans as well The debate has not ended • Agricultural and chemical industries say the book was unscientific • The book was hailed as a breakthrough in environmental understanding © 2011 Pearson Education, Inc.

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Banning pesticides in the U.S.

DDT was banned in the U.S. in the 1970s • Due to concerns about environmental and long-term health effects Other pesticides were also banned • Due to bioaccumulation and cancer-causing potential Since DDT was banned, bird populations have recovered Today’s debate centers around using DDT to control malaria in developing countries Rachel Carson is credited with stimulating the start of the modern environmental movement • And the creation of the EPA © 2011 Pearson Education, Inc.

Aerial spraying

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Problems of chemical pesticides

• • Development of resistance by pests: chemical pesticides eventually lose their effectiveness • Higher quantities and concentrations must be used • Newer, more potent pesticides must be developed It soon takes more pesticide to get the same results • In 1946, 2.2 lbs of pesticide resulted in 60,000 bushels of corn • In 1971, it took 141 lbs of pesticide to get that amount of corn © 2011 Pearson Education, Inc.

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Evolution at work

Resistance results from the death of sensitive individuals • • The resistant ones survive Insects have enormous reproductive capacity Repeated pesticide applications select for genetic lines that are highly, or totally, resistant to pesticide • Resistance genes can spread rapidly Over 1,000 species of insects, plant diseases, and weeds are now resistant • They may become resistant to other, unrelated chemicals © 2011 Pearson Education, Inc.

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The last Roundup

Extensive use of one pesticide results in resistance The herbicide Roundup (glyphosate) is used on genetically modified corn, soybeans, and cotton • They are herbicide tolerant (HT) HT plants are planted without tilling • Spraying them with glyphosate wipes out weeds Weeds are now resistant to glyphosate • • Farmers must spend more on herbicides Go back to tilling fields, increasing erosion © 2011 Pearson Education, Inc.

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Problems of chemical pesticides:

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resurgence

Resurgence: occurs after a pest has almost been eliminated • The population recovers and even explodes Secondary pest outbreak: small populations of insects that were originally of no concern explode 24 of 25 pest outbreaks in California were due to resurgences or secondary-pest outbreaks • Insects are part of a complex food web • Disturbing the system produces undesirable effects Pesticides often kill more predators of pests than the pests © 2011 Pearson Education, Inc.

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The pesticide treadmill

Trying to eradicate pests with synthetic chemicals does not work Pesticides increase resistance and secondary-pest outbreaks • New and larger amounts of pesticides are used, increasing resistance and secondary-pest outbreaks, and so on This unending cycle is not sustainable © 2011 Pearson Education, Inc.

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Problems of pesticides: acute effects

Pesticides can cause acute and chronic health effects Acute effects affected over 93,000 people in the U.S. in 2007 • Farm workers and employees of pesticide companies Pesticides cause nausea, abdominal pain, shock, respiratory failure, allergic reactions, seizures, pneumonia, coma As estimated 39 million people/yr suffer acute poisoning Most acute cases occur in developing countries • • Untrained users have little information on pesticides Children and families get sprayed, or drink water from contaminated containers © 2011 Pearson Education, Inc.

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Problems of pesticides: chronic effects

Pesticides are applied to fields and orchards • They are also used to protect harvested food Consumers are inevitably exposed to pesticides, which may have chronic effects • Even at low levels Over 20 pesticides may cause cancer and other effects: • • • Dermatitis, nerve damage, birth defects, infertility Disruption of the immune and endocrine systems Parkinson’s disease, low white blood cell counts © 2011 Pearson Education, Inc.

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Endocrine disrupters

Many pesticides interfere with reproductive hormones • Increased breast cancer • Abnormal sexual development Very low levels of chemicals mimic or disrupt estrogenic hormones (potent sexual chemicals) • Farmworkers and herbicide sprayers have low sperm counts or defective sperm The Endocrine Disruptor Screening Program (1999) • It will take decades to test all pesticides in the U.S.

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Alternative pest control methods

Ecological control: controlling pests by manipulating natural factors without damaging the environment or human health • Depends on understanding the pest and its relationship with its host and ecosystem Insects have complex life cycles • Each stage may be vulnerable to abiotic factors, predators, or parasites Four categories of ecological pest control • Cultural control, natural enemies, genetic control, and natural chemical control © 2011 Pearson Education, Inc.

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Cultural control

A nonchemical change of one or more environmental factors • The pest finds the area unsuitable or can’t access its target Cutting lawns too short results in weeds • Keep grass at least 3 in. high Avoid plants that attract pests (e.g., roses) • Plant plants that repel pests (marigolds, chrysanthemums) Hedgerows, fencerows, and shelterbelts provide refuge for pest predators (birds, amphibians, praying mantises, etc.) Plowing or burning crop residues decreases diseases • Mulch in gardens decreases weeds and prevents erosion © 2011 Pearson Education, Inc.

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More cultural controls

By rotating crops (changing crops each year) pests of the first crop can’t feed on the second crop • Controls nematodes in the soil Monocultures are efficient but allow pest outbreaks • Mixing crops and interspersing cultivated and uncultivated strips reduce pests The hardest pests to control are imported from other areas • The U.S. Customs and Border Protection and agriculture departments keep pests out of the U.S.

• Biological materials are prohibited, quarantined, etc.

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Cultural control of pests affecting

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humans

Cultural controls help prevent disease and parasites Proper disposal of sewage prevents water-borne diseases Proper hygiene (combing hair, bathing, clean clothing, clean bedding) prevents head and body lice, fleas, bedbugs Garbage disposal and sealing household cracks and screens prevent roaches, mice, mosquitoes Safe food handling, refrigeration, freezing, and canning prevent spread of disease and rotting Catastrophes and conditions in less developed countries result in sickness and death © 2011 Pearson Education, Inc.

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Control by natural enemies

Four types of natural enemies: predators, parasitoids, pathogens, and plant-eaters Predator beetles prevent hemlock wooly adelgid from killing hemlock trees Mealy bugs and caterpillars in Africa are controlled by parasitic wasps “Green muscle” (a fungus) controls desert locusts Water hyacinth in African lakes is controlled by Brazilian weevils Over 30 weed species are limited by insects © 2011 Pearson Education, Inc.

Parasitic wasps

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Protect the natives

Natural enemies must control the target species without attacking desirable species 1% of the 50,000 plant-eating insect species are pests • 99% are controlled by natural enemies Conservation: protecting natural enemies that already exist • The first step in using natural enemies for control Avoiding or restricting broad-spectrum chemical insecticides allows natural enemies to become reestablished • Controls secondary pests, which become problems after using pesticides © 2011 Pearson Education, Inc.

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Import aliens as a last resort

Effective natural enemies are not always available • We imported pests, but not their enemies Natural enemies are found in their native region • • They must be carefully tested before being released 16% of 313 parasitoid wasp species introduced into North America have attacked native species The cactus moth is now eating native U.S. species • • Threatening desert ecosystems Threatening Mexico’s prickly pear agricultural crops The USDA has released 1,000 pest-controlling insect species © 2011 Pearson Education, Inc.

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Control with sterile males

A natural population is flooded with sterile males The screwworm fly lays its eggs in open wounds of animals • The larvae keep the wound open • Secondary infections can kill the animal Screwworm females mate only once, lay eggs, and then die • Males are raised in the lab and sterilized with radiation • If 100 males are released, there is a 99% chance the female will mate with a sterile male Screwworms, tsetse flies, and others have been eradicated • Saving billions of dollars, and human lives, from disease © 2011 Pearson Education, Inc.

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Strategies using biotechnology

Through genetic engineering, genes from other plants, bacteria, and viruses are put into crop plants Over 280 million acres globally are planted with transgenic crops • Soybeans, cotton, corn One strategy: incorporating the protein coat of a plant virus into the plant itself • The plant becomes resistant to infection by the virus Another strategy: make a chemical (i.e., a specific ribonucleic acid [RNA]) that silences pest’s genes • Interferes with an insect’s RNA and prevents molting © 2011 Pearson Education, Inc.

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Bt

A protein from the bacteria

Bacillus thuringiensis

(Bt) can be put into plants (cotton, potatoes, and corn) • This protein kills larvae from plant-eating insects • But it is harmless to mammals, birds, other insects In 2007, 49% of corn and 59% of cotton were Bt plants • • Enormous exposing insects to this one “pesticide” It is merely a question of when resistance will occur Farmers must plant 20% of their fields in non-Bt crops • Pests in those fields will breed with resistant pests, diluting the resistance genes © 2011 Pearson Education, Inc.

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Integrated pest management

IPM aims to minimize use of synthetic organic pesticides • Includes all sociological, economic, and ecologic factors in crop protection • Crop and pests are seen as parts of a dynamic system The goal is not pest eradication, but keeping crop damage below the economic threshold The EPA’s four-tiered approach to IPM: • Set action thresholds, monitor and identify pests, prevent pests, and control pests © 2011 Pearson Education, Inc.

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The four approaches of IPM

Set action thresholds: identify the point where conditions indicate that some control is needed Monitor and identify pests: experts determine if pests exceed the economic threshold • Extension services, farm cooperatives, or field scouts • Field scouts: trained in identifying and monitoring pests Prevent pests: through cultural and biological controls • Crop rotation, predators, fertilizing, “trap crops” Control pests: selected brands of pesticides are used • Do the least damage to natural enemies of the pest © 2011 Pearson Education, Inc.

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Indonesia

Government policies in developing countries determine whether IPM is used • Governments and agencies subsidize pesticides • Encourage growers to step on the pesticide treadmill Indonesia’s government provided an IPM model to control the brown plant hopper Rice growers switched from heavy pesticide use to light spraying that preserves the predators of the insect FAO workers trained farmers, who in turn trained others • Over 200,000 farmers enrolled in the program © 2011 Pearson Education, Inc.

Brown plant hoppers

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Benefits of the Indonesian program

Economic and environmental benefits of the IPM program have been remarkable The government has saved millions by not buying pesticides Farmers have not had to buy pesticides and equipment Thousand of tons of pesticides have not entered the environment Fish are thriving in the rice paddies Consumers and wildlife have increased health benefits The FAO is sponsoring similar programs in other nations © 2011 Pearson Education, Inc.

Integrated pest management

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Organically grown food

Many farmers are turning away from pesticides, chemical fertilizers, antibiotics, and hormones • For grains, vegetables, and livestock Organic farms are small, using traditional farming methods and diverse crops Organic crops may have lower yields • • • But also lower expenses The soil is richer The product is increasingly in demand © 2011 Pearson Education, Inc.

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Organic food is in high demand

Sales of organics have increased 20%/yr in the last decade • Sales in the U.S. equal $14 billion/yr • Sales worldwide equal $40 billion/yr The major reason for market expansion is concern over health and safety • But the food is also tastier Organic foods are costlier • But are less likely to contain pesticide residues Any pesticide residues come from older, persistent pesticides in the soil © 2011 Pearson Education, Inc.

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USDA organic

Organic Foods Protection Act (1990) • Established the National Organic Standards Board (NOSB) under the USDA The final standards for certifying organic foods prohibits • • • Genetically engineered or irradiated food Fertilization with sludge or chemicals Conventional pesticides, antibiotics, growth hormones Farmers must be inspected to use the USDA’s organic seal If food is at least 95% organic, they can use the seal • But they can not claim to be 100% organic © 2011 Pearson Education, Inc.

Organic foods

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Pesticides and policy

Three concerns involved in pesticide regulation: • Pesticides must be evaluated for intended uses and impacts on human health and the environment • Users of pesticides (agricultural workers) must be trained and protected from pesticide’s risks • The public must be protected from the risks of pesticide residues The Federal Insecticide, Fungicide, and Rodenticide Act • • FIFRA (1947, amended in 1972) Administered by the EPA © 2011 Pearson Education, Inc.

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The EPA and pesticides

Biopesticides: less toxic microbial pesticides • • Bt, plant-incorporated protectants, pheromones Clear the registration process much quicker than conventional pesticides (1 year vs. 3 years) A registered pesticide must carry an EPA-approved label listing the active ingredients, instructions, and risks The EPA works with state environmental agencies • States must show they have adequate regulation and enforcement mechanisms © 2011 Pearson Education, Inc.

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FFDCA

Three agencies are involved in protecting consumers from pesticides on food: • EPA: sets allowable tolerances for residues • • FDA: monitors and enforces tolerances on most foods Food Safety and Inspection Service (USDA): monitors and enforces tolerances on meat, poultry, and eggs The Delaney clause of the Federal Food, Drug, and Cosmetic Act (1938) (FFDCA) • No detectable residue of any pesticide may be on food if it presents any risk of cancer © 2011 Pearson Education, Inc.