Pests and Pesticides

1
Pests and Pesticides
2
Pesticides

• Pesticides are chemicals that are designed to
  kill pests.
• A pest is an organism that humans consider
  harmful or inconvenient.
• E.g. weeds, insects, fungi, rodents

3
Why are pesticides used?

• Pests can destroy crops. This costs farmers
  money. (e.g. estimated that 30 of crops in
  Canada is lost to pests)
• Pests can carry diseases (e.g. mosquitoes carry
  Malaria)

4
4 Types of Pesticides

• Herbicides kills plants
• Insecticides kills insects
• Fungicides kills fungi
• Bactericides kills bacteria

5
History of Pesticide Use

• Pesticides started being used around 500 B.C.
  when sulfur was used to repel insects.
• 15th century arsenic, lead and mercury were
  applied to crops as insecticides
• 1700s farmers started extracting chemicals from
  plants that had developed defenses against
  insects.
• 1939 Paul Mueller discovered that DDT, a
  laboratory made chemical, was an effective
  insecticide

6
2 categories of Pesticides

• Water soluble
• will dissolve and wash away (not persistent)
• can be harmful and affect nervous system of
  organisms
• Fat Soluble
• will dissolve in fatty tissue
• stay in the body
• will be passed on in the food chain
• E.g. DDT

7
Dichloro, Diphenyl Trichloroethane (DDT)

• Pesticide that is suitable for bioamplification/bi
  omagnification
• Has a half-life of 15 years
• That is, every 15 years the amount left in the
  system will be reduced by one half.
• If you use 100 kg of DDT, after 15 years it will
  be reduced to 50 kg, and after another 15 years
  it will be 25 kg, and so on
• NOTE Modern pesticides are designed to last one
  growing season and then break down into less
  harmful substances.

8
Bioaccumulation Bioamplification

• Bioaccumulation
• an increase in the concentration levels of a
  pesticide within the body of an organism over
  time
• Bioamplification/Biomagnification
• a species at a higher trophic level feeds on
  more than one organism below it therefore
  pesticide concentrations tend to increase rapidly
  the higher up the food chain you look

9
(No Transcript)
10
Effects of DDT in Birds

• Shell thinning
• Carnivorous birds, such as peregrine falcons and
  bald eagles, eat other birds, dead animals and
  fish which contain a build-up of DDT
• DDT causes the shells to become too thin to allow
  the large females to sit on the eggs without them
  breaking
• Since eggs are being broken, the overall
  population of these birds is declining

11

• The peregrine falcon almost became extinct in
  Canada because of DDT use.

12

• After DDT was banned in the US and Canada in the
  early 1970s the bird populations began to
  recover.
• DDT bioaccumulates in humans the same as it would
  other animals
• Male birds have also become more feminine as the
  DDT mimics female sex hormones

13
Resistance

• When pests are no longer affected by the chemical
• - particularly for bactericides and insecticides
  because of these pests high reproduction rate
• Some insects have genes that help them survive
  the pesticide application. These pests pass on
  this gene, eventually making the pesticide
  ineffective.

14
Questions

• 1. Not all countries, like Mexico, for example,
  have banned the use of DDT. Since birds migrate
  from winter to summer from one country to
  another, do you think the birds are 100 safe
  from the presence and the effects of DDT? Why?
• 2. DDT is used responsibly in mosquito-infested
  parts of Africa. This saves millions of lives by
  combatting an often lethal disease called
  malaria, which is carried by mosquitoes. Do you
  think there should be a world-wide ban on the use
  of DDT? Explain why or why not.
• 3. How do you think a pesticide like DDT would
  affect the overall biodiversity (the number of
  different types of organisms in an area) in an
  ecosystem?