Chapter 20 Pesticides

twoeggfinnishBiotechnology

Dec 14, 2012 (4 years and 8 months ago)

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Chapter 20

Pesticides and Pest
Control

The pros and cons

Beneficial Spiders

Hibernating spiders in China help in rice
and cotton fields

Wolf spiders in undergrowth help
protect cotton and soybeans

Banana spiders in warmer climates
consume household cockroaches

Wolf spider

Banana spider

PESTS

COMPETES WITH US FOR FOOD

INVADES LAWNS AND GARDENS

DESTROYS WOOD IN HOUSES

SPREADS DISEASE

NUISANCE

PESTICIDES (biocides)

Chemicals to kill organisms
undesirerable

Common Types:

1.Insecticides

2.Herbicides (weed killers)

3.Nematocides (roundworm killers)

4.Rodenticides (rat, mouse)

5.Fungicides

Co
-
evolution
between
predator/prey
of
herbivores and plants; the beginning of
chemical warfare 225 million years ago.

Pesticides through time

Sulfur pre 500BC

1400’s, arsenic, lead and mercury,
abandoned in the 1920’s

1600’s, nicotine sulfate, extract from
tobacco leaves

mid 1800’s, pyrethrum (from
chrysanthemum flowers) and rotenone
(from roots of various tropical legumes)


First Generation Pesticides

Natural substances, derived from plants

Also used as insecticides

Natural ways to repel or kill mosquitoes,
ants, cockroaches, flies, fleas and
control weeds (Insecticidal soap, Bt
(bacillus thuringensis), pyrethrum,
rotenone)

Second generation

Paul Muller discovers DDT in 1939, receives
Nobel Prize in 1948 (
dichlorodiphenyl

t
richloroethane
) since then, 100’s of types.

$44 billion of pesticides used worldwide/year

Insecticides, herbicides, fungicides, fumigants
all have a known persistence in the
environment ( see table page 514)

The Case for Pesticides

Save human
lives(malaria, bubonic
plague)

Increase food supplies and lower food
costs

Increase farmers’ profits

Work quickly and more effective

Health risks are low if used correctly

Newer pesticides are more effective and
safer; lower concentrations
needed

Genetically engineered pest resistant
crops being developed

Ideal pest killing Chemical

Kill only the target pest

Harm no other species

Disappear or break down into
something harmless after doing it’s job

Not cause genetic resistance in target
organisms

Be more cost effective then doing
nothing

Insect pests in the US

Grasshoppers Western US;

gypsy moths, NE US;

European red mites, NE, NW US;


pink bollworm and boll weevil, SE and
SW US

Case Against pesticides

Major problems with conventional pesticides

They accelerate
the development of genetic
resistance. Rapid growth rate. Resistance in
less than 10 yrs through
Nat.Selection

Broad spectrum insecticides kill natural
predators and parasites that naturally keep
pests in
check. Pesticide use has not reduced
crop lose in US

Pesticides move with water, air, food,
sediments, other organisms

Some have detrimental effects on wildlife

May threaten human
health(Silent Spring)


US Regulation of pesticides

FIFRA established in 1947, updated in 1972
requires EPA approval for commercial
pesticides; sets tolerance level of biological
agent, and its
residual
on a crop.

EPA has banned
use
56 active pesticide
ingredients since 1972 including chlorinated
hydrocarbon insecticides (DDT),
carbamates
(
Sevin
) & organophosphates
(
malathion
), 2,4,5
-
T and
Silvex

(See pg 514)

Problems with EPA studies

FIFRA required EPA to reevaluate 600
active ingredients in 1972 pesticide
prod. Still today less than 10% have
been evaluated. Expensive

165 active ingredients approved today
causes Carcinogens
, brain tumors,
leukemia….

Fed. Laws regulating pesticide use is
poorly enforced.

Disturbing News

1. 165 of active ingredients approved
are know human carcinogens

2. statistic correlation study of child
hood brain cancer and use of pesticides
in home(flea collars, no pest strips,
roach control baits

3.Yard chemicals and high incident of
muscle cancers in children

Pg. 517

Can regulation be improved?

Better regulation and enforcement and
strengthening of existing pesticide
control laws…

Other ways to control pests…cultivation
rotation, genetic engineering of
resistant crops, biological pest controls,
insect birth control,
phemerones

and
disruptive hormones, hot water, gamma
radiation

Other ways to control Pests

Primary goal of pest control strategy is
to reduce crop damage to an
economically tolerable level.

Economic threshold: point at which the
economic losses cased by pest damage
outweigh cost to apply pesticide.

Problem? To determine when threshold
is reached. Use of pesticide insurance

Other ways to Control Pest

Cultivation practices: rotating crops, adjust
planting times, plant trap crops

Genetic engineering: pest and disease
resistant strains

Biological pest control: natural predators,
disease causing bacterial, parasites to
regulate

Insect birth control: lab raised sterile males

Sex attractants

Hormones to disrupt life cycles

Integrated pest management

Crop and pest are evaluated as part of
the ecological system;
includes
cultivation, biological and chemical
methods applied in proper sequence
and with proper timing

Advantages: reduce pesticide use,
increase crop yield, decrease pollution

Disadvantages: need experts;
microclimate sensitive,
slower, initial
cost is expensive.