Unit B: Sustainable Ecosystems
4.5: Issues with Pesticides
pg. 135
Key Concepts:
4. Pesticides are used to reduce yield losses from pests, but there are
ecological costs associated with them.
5. Some pesticides and other toxins bioaccumulate in individuals and
biomagnify in food webs.
- Pesticides are used by farmers to protect crops, and are also used to control
populations of insects that may spread disease, which is beneficial to our
society.
- The delivery mechanism can be a problem, the use of aerosols or sprays
will affect their target areas, but can also be carried away by wind to other
locations impacting non-target organisms.
Non-target Species
- Non-targeted species (non-damaging or potentially beneficial) are
sometimes killed by broad-spectrum pesticides.
- As beneficial organisms are killed, farmers must become more dependant
on pesticides.
- The killing of non-targeted organisms is a very serious problem.
Bioamplification
Bioaccumulation: the concentration of a substance, such as a pesticide, in
the body of an organism.
Bioamplification: the increase in concentration of a substance, such as a
pesticide, as it moves higher up the food web.
- Pesticides have the tendency to accumulate in organisms over time. These
are not broken down and eliminated as wastes.
- These pesticides are not water soluble, but are fat soluble, and therefore are
difficult to remove, this leads to bioaccumulation over time in the organism.
- Feeding relationships (food chain) leads to the toxins that are stored in fat
tissue to be passed onto the next trophic level.
- The higher up the food chain the more concentrated the toxin becomes, this
is known as bioamplification.
- As the bioamplification increases the toxic level it has a greater impact on
the organisms.
Figure 3: DDT bioaccumulation up the food chain. Gulls require more food
because they are warm-blood and must maintain their body temperature;
therefore, they accumulate more DDT.
Figure 5: Populations of large predatory birds suffered due to the
amplification of mercury in aquatic ecosystems.
Pesticide Resistance
- When pesticides are used for long periods of time, some target organisms
may become immune or resistant to the pesticide.
- Pests that survive are able to reproduce, and their offspring are also
resistant to the pesticide.
- Organisms that reproduce quickly are more likely to become resistant
through the generations.
Figure 8: Pesticide resistance in is increasing worldwide.
Reducing Our Dependence on Pesticides
Organic Framing: the system of agriculture that relies on non-synthetic
pesticides and fertilizers.
- Pesticides have help to improve food production globally.
- But do the use of pesticides out way the risks of pollution by toxins?
- An alternative to pesticide use is organic farming. No synthetic pesticides
or fertilizers are used.
- Organic farmers rely on ecologically sustainable farming techniques to
protect their crops, such as; Biological control, altered timing, crop rotation
and mixed planting, and baiting pest.
- Although these methods are healthier there are lower crop yields.
- Integrated Pest Management (IPM) is employed to take advantage of all
types of management methods to maximize efficiency, keep costs down and
reduce harm to the environment.
Table 1: Techniques Used by Organic Farmers
Method
Biological
Control
Altering Timing
Crop Rotation
and Mixed
Planting
Baiting Pest
Description
- Predatory insects, mites, and disease-causing microorganisms prey on and infect prey species.
- Examples include parasitic wasps and ladybird beetles
(ladybugs).
- Better timing of planting and harvesting can avoid
peak pest
Populations.
- When farmers do not grow monocultures in the same
location year after year, pest populations do not have the
same opportunities to establish and prosper.
- Pheromone baits can be used to confuse some mating
insects.
Evidence of Learning: Students can …
- assess the impact of human activity in agroecosystems.
- use the terms bioaccumulation and bioamplification to describe the impact
of pesticides.
- describe a variety of ways in which agriculture can impact the
sustainability of an ecosystem.
Check Your Learning
Questions 1 – 11, page140
Summary:
- Non-target organisms may be harmed when pesticides are released into the
air or water.
- Some pesticides and toxins bioaccumulate in the bodies of organisms and
bioamplify up the food web.
- Many Plant and insect pests are becoming increasingly resistant to
pesticides.
- We can reduce our dependence on pesticides by using organic farming or
integrated pest management (IPM) methods.