4.4: Pests and Poisons
pg. 138
Key Concepts:
1. Pesticides are used to educe crop losses due
to insects, weeds, and other pests.
2. Pesticides have ecological costs.
Humans are in competition with other organisms for food.
Changing Food Webs
Pests are organism that negatively impact us, can cause
illness or just a nuisance. These pests are truly not pests in
a natural environment, there are only producers, consumers,
and decomposers.
In a food web, each organism plays a specific role and has
many relationships with other organisms. In nature these
relationships are complexes with thousands of organism
involved. In a Agro-ecosystem these relationships are
changed or removed.
Monoculture environments created by farmers are ideal
environments for pests, because there are no predators to
control the pest population.
Controlling Pests
Pesticides: is a substance used to kill a pest.
Pests are controlled and eliminated by chemical pesticides.
The type of pesticide is determined by the type of organism
to be eradicated. Less work is required to kill the pests,
therefore it is considered an effective method.
Herbicide – kills plants
Insecticide – kills insects
Fungicide – kills fungi
How Pesticides Work
Pesticides can impact the structure of the organism
9diatomaceous), interfere with biological processes
(photosynthesis), or damage vital organs of the body.
How Pesticides Are Applied
Pesticides are applied contact, touching the pest to cause
death. Spraying the pesticide is the most common method
of application.
Natural or Synthetic?
Natural pesticides are obtained from nature. Most
pesticides are synthetic, man made chemicals.
Synthetic pesticides are more persistent than natural
pesticides (e.g.: pyrethrum from a chrysanthemum flower),
because they are more water soluble and are washed away
by rain or carried away by the wind.
Alternatives to Pesticides
Organic farming does not require synthetic pesticides and
fertilizers. The farmers accept crop loss to natural pests but
can benefit by the higher prices to balance cost and make
profits.
Check Your Learning:
Questions 1 – 4, pg. 141
Wrap Up:
- The term “pest” is only used to show a relationship
between a type of organism and humans.
- One of the most common ways to control pests is to use
pesticides.
- Pesticides cause physical harm or interfere with biological
processes.
- Some pesticides are delivered by contact, while others are
applied indirectly.
- Persistent synthetic pesticides are more likely to cause
harm to the environment.
- Organic farming is an alternative to using pesticides.