Transcript Ch. 13: Pests and pest control

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
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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:
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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
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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
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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…
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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)
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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
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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
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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 thinshelled eggs
• Higher doses of DDT and DDE go up the food chain
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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
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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
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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
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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
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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
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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
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Problems of chemical pesticides:
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
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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
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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
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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
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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
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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
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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
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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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