Silent Spring
Chapters 7 & 8
Christopher Siess, Jaclynn Chen,
Catherine Flynn
Pests

According to Charles Eton, the key to a healthy community lies in keeping
“the conservation of variety.”

This variety keeps any one species from dominating over the others and
becoming a pest.
We learned in the textbook that an organism’s success in a new
environment is dependent on : predation, disease, competition, and
absence of certain species.


The Japanese beetle thrived in the United States because the U.S. lacked
any species that would prey or compete with it.

Once organisms such as the parasitic wasp Tiphia vernalis were
introduced into the U.S., they controlled the Japanese beetle.
Pests
 Birds such as the woodpecker are natural controllers of
potential pests such as the Engelman spruce beetle.
Once these birds die as a result of insecticide
poisoning, there is no natural protection left to keep the
pests in check.
 The Ten’s Rule- an average of one out of ten
introduced species become established, and one out of
ten established become common enough to become
pests.
Pesticides
 Detrimental insect poisons, pesticides,
have wreaked needless havoc in the
environment harming numerous species
throughout the community.
 Although a single spray will temporary
reduce numbers of pests, they will return,
and a new spraying campaign must take
place.
Pesticides
 Pesticides used unwisely can cause immense
collateral damage.
 In the fall of 1959, 27,000 acres of land in
southern Michigan was sprayed, its purpose to
control the Japanese beetle population.
 What happened was a sharp increase in
respiratory and nervous conditions, and
scourging of the bird and house pet
populations.
Pesticides
 One of the reasons birds and other species
were eradicated was because of direct contact.
The birds came into contact with the poison
when it was dispersed.
 Another reason was because of the food chain.
When infected beetles came to the surface for
their last hours, the birds ate these easy
pickings and became infected.
Pesticides
 A DDT spreading affected a flock of
sheep. In a short time, the sheep
experienced “symptoms of intoxications
almost at once…lost interest in food,
great desire for water, displaying extreme
restlessness, following pasture fence
apparently searching for way out…”
(Carson 94)
Abiotic Factors to
Distribution Restriction
Abiotic Factors
Temperature
Water
Sunlight
Rocks & Soil
Wind
Chain of Infection
Dutch Elm Disease
Introduced in the 1930’s
Is a fungus that spreads
spores that kills Elm trees
Spread by elm bark beetles
Attempted eradication
by pesticides
Collects on tree leaves
Decomposes in soil
Eaten by earthworms
Eaten by Possums,
Squirrels, etc
Eaten by Robins
90% Robin
Population Decrease
Governmental
Interference
 Government officials on many levels
insist that the plainly dangerous poisons
were completely safe to all untargeted
species.
 Budget concerns demanded the use of
less-safe poisons for less expense.
Since Then
 Public attention to pesticide spraying has
increased, as had the demand of the
introduction of natural predators instead
of poisons.
 If a natural predator is determined to not
cause as much havoc as the pest that
was introduced, it shall be attempted to
be established.