Chapter 20
Protecting Food
Resources: Pesticides and
Pest Control
•Rachel Carson was a scientist who wrote Silent
Spring in 1962.
•It addressed the growing use of pesticides (DDT) and
their unpredicted effects on song birds.
•Original users of pesticides did not know that the
poisons used to kill insects would accumulate in other
living things and kill them too.
BIOACCUMULATION
Pesticides: Types and Uses
What is a Pest?

A pest is any species that competes
with us for food, invades lawns and
gardens, destroys wood in houses,
spreads disease, or is simply a nuisance
 Most of the time nature takes care of
the pests through natural enemies
(predators, parasites, and disease
organisms)
So what’s a Pesticide?
 Pesticides (also known as
biocides) are chemicals that are
to kill organisms we consider
undesirable

Insecticides

Herbicides

Fungicides

Nematocides

Rodenticides
Above: Worker prepares his vehicle for a day of
pesticide spraying
Coevolution
For almost 225 million years, plants have
been producing chemicals to ward off or
poison herbivores that feed on them…
But, through what is known as
coevolution, the predators overcome
various plant defenses by natural
selection and the plants must develop
new defenses
First Attempts at Pesticides
 Sulfur (early 500 BC)
 Toxic compounds of arsenic, lead, and
mercury (1400’s)

Abandoned in late 1920’s when the
increasing number of human poisonings
increased
 Nicotine Sulfate (1600’s)
 Pyrethrum and Rotenone (mid-1800’s)
Paul Mueller and the
Second Generation
In 1939 Paul Mueller discovered that
DDT, a chemical known since 1874,
was in fact a potent insecticide. DDT
became the first pesticide of the socalled Second Generation Pesticides.
Mueller went on to win the Nobel
Prize in 1948 for his discovery.
Pesticides Today
 Chemists have been developing hundreds
of synthetic organic chemicals for use as
pesticides
 Worldwide about 2.3 million metric tons of
pesticides are used yearly

1 lb for each person on earth

75% in developed countries (Latin America, Asia
and Africa on the rise)

1996 world sales = $30 billion($11 billion: US)
Here in the US
 About 630 different biologically
active (pest killing) ingredients
and about 1,820 inert (inactive)
ingredients are mixed to make
some 25,000 different pesticide
products in the United States
Resistance to pesticides
 Some individuals are genetically immune
to a pesticide.

They survive and pass these genes to their
offspring.
 Pesticides stop being effective.
Pesticide Distribution in US
 Cultivation of two crops

Cotton (55%)

Corn (35%)
 Used about 90% of the insecticides
and 80% of the herbicides applied to
crops in the United States in 1995
Example of Solid Pesticides
More Distribution
 25% of the pesticide use in the United
States is for ridding houses, gardens,
lawns, parks, playing fields, swimming
pools, and golf courses of unwanted
pests
 Average lawn in US = 10x’s more
pesticides per hectare than US cropland
 Each year = 250,000 residents become ill
Biological control

Biological control
(Biocontrol): uses a pest’s
natural predators to control
the pest

Leads to steep reductions in
chemical pesticide use

Cactus moths control invasive
prickly pear cactus

Bacillus thuringiensis (Bt): soil
bacteria that kills many pests
Biocontrol involves risks

No one can predict the effects
of an introduced species.

The agent may become
invasive and harm non-target
organisms.


Cactus moths are eating rare
Florida cacti.
Removing a biocontrol agent
is harder than halting
pesticide use.

The harm done by biocontrol
agents may be permanent.
Some Quick Facts
 Broad-Spectrum agents : toxic to
many species
 Selective or Narrow spectrum
agents : effective against a
narrowly defined group of
organisms
 Pesticides vary in persistence
(length of time they remain deadly
in environment)
The Pros
 Pesticides save human lives: has prevented
premature births due to malaria, bubonic
plague, typhus, sleeping sickness (all carried
by pests)
 Pesticides increase food supplies and lower
food costs: 55% of crop lost before harvest due
to pests
 Pesticides increase profits for farmers: every $1
spent on pesticides yields worth
approximately $4 (although dropped to $2 if
harmful effects)
More Pros
 Pesticides work faster and better than
alternatives: Pesticides can control pests
quickly and at a reasonable cost. Long
shelf life and easily shipped and applied
 Health risks insignificant when compared
to their benefits

Safer more effective pesticides are being
developed
 New pesticides are being used in less rates
per unit when compared to older products
Ultimate Goal of Pesticides
 Kill only the target pest
 Harm no other species
 Disappear or break down into
something harmless after doing its job
 Not cause genetic resistance in target
 Be cheaper than doing nothing
The Cons
 Genetic Resistance: pest organisms develop
resistance to the pesticide after a short
period of being exposed to it
 Broad-Spectrum insecticides kill natural
predators and parasites that may have been
maintaining the population of a pest species
at a reasonable level

Ex. Wolf spiders, wasps, predatory beetles…
Cons continued…
 Because natural predators
can be wiped out; this may
unleash new pests whose
populations the predators
had previously held in
check
In Our Water
 Testing in rivers and
water reveal that
pesticides have
strayed away from
there targets and
found there way
into the waters
Pesticide Treadmill
 As pests become resistant to the
pesticides, sales reps for the pesticide
recommend larger doses or more frequent
application

As a result farmers end up on a pesticide
treadmill where they end up paying more and
more for a pest control program that often
becomes less and less effective
Pesticide Treadmill

Pesticides become less effective over time

Genetic resistance to pesticides develops in pest
species – natural selection

Some individuals have a gene that makes them
resistant to a pesticide, they pass the gene onto
their offspring so that the entire population
becomes resistant

This requires a more frequent sprayings, larger
doses or a switch to new pesticides

Yields have decreased because of pesticide
resistance since second generation pesticides
have come into use
Example of Pesticide Treadmill
In Central America, cotton growers
increased the frequency of
insecticide applications from 10 to 40
times per growing season. Still,
declining yields and falling profits
forced many of the farmers into
bankruptcy
Insecticide
application
Chromosome with
gene conferring
resistance to
insecticide
Survivors
Additional applications of the
same insecticide will be less
effective, and the frequency of
resistant insects in the
population will grow Figure 13.1
Where does it all go?
 Only about 2% of the sprayed insecticide by
air reaches target pests
 Less than 5% of herbicides applied reach
target weed
 Pesticides that don’t reach there target end
up in the air, surface water, groundwater,
bottom sediments, food and other nontarget organisms
Continued
 Still, pesticide waste can
be reduced by using recirculating sprayers,
covering spray booms, and
using rope-wick applicators
DDT
 Banned in 1972 by US
 1980 high levels in peregrine falcon
and the osprey
 EPA found DDT in 99% of the
freshwater fish it tested
 DDT drifts from other countries still
using it

DDT accumulates in fat body
tissues of animals

DDT was not used for
handling weeds

DDT is, persistent, synthetic
organic compound and a
subject to biomagnifications
in food chains
World’s Worst Industrial Accident

Bhopal, India

Occurred December 2, 1984

Union Carbide (a pesticide manufacturer)

MIC (methyl isocyanate) gas leaked

the cooling system malfunctioned and the tank
exploded

Gas affected 30 square miles and an estimated
600,000 people were exposed
Bhopal
 Officially 5,100 people were killed
(probably anywhere from 7,000 –
15,000 died)
 50,000 – 60,000 sustained
permanent injuries, blindness or
lung injuries
The Cause?
Indian government claims it
was caused by company
negligence
The company claims
sabotage by a disgruntled
former worker
Regulation in the US
 All commercial pesticides must be approved by
EPA
 EPA reviews each pesticide
 EPA sets tolerance levels : amount of toxic
pesticide residue that can legally remain on crop
 No longer has to test on birds and fish
 55 active pesticides banned in US, but may be
used and shipped elsewhere
More Regulations
 National Academy of Sciences says that
the federal laws are not adequate
 98% of potential risk of cancer would be
eliminated if pesticide residue on food
eliminated by government
 Approximately $1 Billion spent on
regulating pesticides each year
FIFRA and the EPA

Federal Insecticide, Fungicide, Rodenticide
Act

All commercial pesticides must be approved
for use

The pesticide companies evaluate the
biologically active ingredients in their
products and the EPA reviews the data

When a pesticide is approved for use on fruits
or vegetables, a tolerance level is set that can
legally remain on a crop when a consumer
eats it
1996 Food Quality Protection Act

Requires food to have only reasonable levels
of pesticide tolerance

It requires manufacturers to demonstrate that
the active ingredients in there products are
safe for infants and children

Requires EPA to consider exposure to more
thatn one pesticide when setting pesticide
tolerance levels

EPA develops program to screen ingredients
From Above
 Just one of the
many ways that
pesticides are
being applied are
through aerial
drops of the
chemicals
Other Solutions
 Crop rotations
 Planting times can be adjusted
 Plowing at night (reduces weeds)
 Plant where major pests do not exist
 Switch away from monoculture to
intercropping, agroforestry, and
polyculture
More Solutions

Plants and animals that are genetically resistant to
certain pest insects, fungi and diseases can be
developed
- downside: costly

Biological control: predators and pathogens

300 biological pest control successful in China and
Cuba

Biological Control: non-toxic to humans

Downside: timely
We depend on insects to pollinate crops
 Most insects do not harm agriculture, and
some are absolutely vital.

800 cultivated plant species rely on insect
pollinators.
 Pollination: male plant sex cells (pollen)
fertilize female sex cells

By wind or animals
 Pollinators include:

Hummingbirds

Bats

Insects
Colony Collapse
Disorder

Populations of native
pollinators have plummeted.

Honeybees pollinate more than
100 crops — 1/3 of the U.S. diet.


Recently, introduced
parasitic mites have
devastated hives.
To conserve pollinators:

Reduce or eliminate pesticide
use

Plant gardens of flowering
plants
Even more Solutions…
 Plant toxins

Bt toxin used to kill thousands of strain of
common soil bacterium
 Insect Birth Control (sterile male
approach)
 Aqua heat: spray boiling water on crops
Fish or frankenfish?
FDA weighs altered salmon
Yes… more solutions
 Some crops can be exposed to gamma
rays after harvest

Extends shelf life

Critics say irradiating food destroys vitamins
and other nutrients

Increases death from botulism poisoning

Picowaved stickers on food that has been
Integrated Pest Management (IPM)
 IPM uses multiple techniques to
suppress pests.
Biocontrol
 Chemicals, when necessary
 Population monitoring
 Habitat alteration
 Crop rotation and transgenic crops
 Alternative tillage methods
 Mechanical pest removal

Integrated Pest Management (IPM)
 Each specific crop and its pest(s) are
evaluated
 It requires a mix of biological,
cultivation and chemical practices
 Pests populations are not eradicated,
but carefully managed so that crop
destruction is minimized
IPM
 Biological methods – predators, parasites,
disease organisms, sterilization, sex
attractants, hormones
 Cultivation – vacuuming, planting times,
trap crops, polyculture, intercropping,
agroforestry
 Development of genetically resistant plants,
genetically engineered plants
 Chemical pesticides in small amounts are
used as a last resort
IPM
 Integrated Pest Management
 Goal is reduction of crop damage to
an economically tolerable level

Carefully monitor damage levels of
pests
 When
reached, farmers first use
biological methods
 Small
amounts of insecticides are used
as a last resort
Pesticides in Politics
 Pesticides have
been a big issue
with
environmentally
safe activists. It is a
big topic the EPA
has to deal with