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Pests & Bioamplification
Foodwebs in Grassland vs. Potato Field
Grassland
Producers
Herbivores
Carnivores
Food web
Potato Field
Pests & Bioamplification
Foodwebs in Grassland vs. Potato Field
Grassland
Potato Field
Producers 50 – 100 different
species of plants
Herbivores numerous species of
insects, rodents, birds,
etc
Carnivores numerous species of
insects, spiders,
snakes, foxes, hawks,
etc
Food web complex with 100s of
species
Pests & Bioamplification
Foodwebs in Grassland vs. Potato Field
Grassland
Potato Field
monoculture of potato
Producers 50 – 100 different
species of plants
Herbivores numerous species of
insects, rodents, birds,
etc
Carnivores numerous species of
insects, spiders,
snakes, foxes, hawks,
etc
Food web complex with 100s of
species
plants. Other plants
considered weeds
few such as Colorado
potato beetle,
considered pests
very few, if any
food web effectively
eliminated
Pests & Bioamplification
Pesticide: a substance used to kill a pest
herbicides kill plants
insecticides kill insects
fungicides kill moulds etc
Pests & Bioamplification
Pesticide: a substance used to kill a pest
herbicides kill plants
insecticides kill insects
fungicides kill moulds etc
Broad-spectrum pesticide: effective against
many types of pests
e.g. DDT is toxic to most insect species
Narrow-spectrum pesticide: effective against
only a few types of pests
e.g. Bt, a modern pesticide from bacteria is
toxic only to caterpillars
Pests & Bioamplification
How pesticides work:
1. Physical harm: diatomaceous earth
scratches the waxy outer coating of insects so
they dehydrate
Pests & Bioamplification
How pesticides work:
1. Physical harm: diatomaceous earth
scratches the waxy outer coating of insects so
they dehydrate
2. Biological harm: some herbicides interfere
with photosynthesis
Pests & Bioamplification
Issues with pesticides:
1. Non-target species: pesticides often kill
species they were not intended to kill
e.g. a broad-spectrum insecticide may kill
predatory insects that normally feed on pests
Pests & Bioamplification
Issues with pesticides:
1. Non-target species: pesticides often kill
species they were not intended to kill
e.g. a broad-spectrum insecticide may kill
predatory insects that normally feed on pests
2. Bioaccumulation: the increasing
concentration of a pesticide as it moves up the
food chain
e.g. DDT is a long-lasting insecticide that
wiped out song bird populations in the 1960s
Pests & Bioamplification
Bioaccumulation:
e.g. DDT leached into a lake from fields
herring gull egg (6.3 ppm)
smelt (0.43 ppm)
(fish)
freshwater shrimp (0.03 ppm)
ppm = parts per million
Pests & Bioamplification
Persistent chemicals: the bioaccumulation
occurred because these pesticides lasted a long
time in the environment and could be passed up
the food chain
-today pesticides are developed to break down
quickly to avoid this buildup
Pests & Bioamplification
Pesticide Resistance: when a species targeted
by a pesticide are no longer affected by it.
-happens by chance mutations of DNA
-once it occurs, these individuals with
resistance produce the most offspring and the
resistance quickly spreads to the entire species
-the more frequently the pest reproduces, the
faster resistance will develop
Pests & Bioamplification
Organic Farming: the system of agriculture that
relies on non-synthetic pesticides and fertilizers
Integrated Pest Management: a system that
uses a combination of physical, chemical, and
biological controls
method
example
biological
control
predatory insects, disease causing microorganisms
altered timing
planting & harvesting to avoid peak pest
populations
crop rotation, avoiding monocultures in the same location
mixed planting year after year
baiting pests
pheromone (sex hormone) baits can be used
to confuse some mating insects