Lesson
What are pests?
Pests are living organisms that are not wanted around us. They are organisms that people consider to be harmful or inconvenient Examples of pests include unwanted dandelions growing in the lawn; rodents or insects that eat fruits, vegetables or other crop species; micro-organisms that cause disease in forest, fish, or crop resources, etc.
A pest is any organism that we believe is undesirable, has a negative impact on the human environment, or is in competition with human use of a resource, either natural, or cultivated.
What are pesticides?
Pesticides are chemicals designed to kill pests. There have been thousands of pesticides developed to kill pests. More than 500 chemical pesticides are registered for use in Canada alone. There are approximately 2.3 million tons of pesticides used yearly all over the world.
Pesticides are used in the making of such items as carpets, mattresses, paints, and even shampoos. More than 25 % of pesticides are used to get rid of pests in homes, gardens and parks .Pesticides can be grouped into one of four categories:
Categories of Pesticides
1. Insecticide……kills insects……..ex: DDT…….....lingers for 2-15 years
2. Herbicide……...kills weeds………ex: Roundup…lingers for 1-12weeks
3. Fungicide…......kills moulds…….ex: Captan……lingers for days
4. Bactericide…....kills bacteria…..ex: Penicillin….lingers for days
Early Pesticide Use......
Early pesticides included the use of toxic substances such as lead salts, arsenic, or mercury. These substances were generally effective against the intended pest, but also created some environmental problems because they also killed other beneficial organisms, and polluted water and soil resources.
Most early pesticides were non-biodegradable.....meaning that they were not broken down within the ecosystem. As a result, these early pesticides began to accumulate in the environment, contaminating water and soil resources, eventually poisoning humans.
Modern Pesticide Use.......
By the twentieth century, chemists began to develop organic pesticides that were designed to be less toxic to humans and more specific toward the intended pests. Although this was initially believed to be a step in the right direction, humans soon discovered that the organic pesticides also caused unexpected environmental effects.
Bioaccumulation.....
Some of these pesticides were fat soluble. This characteristic lead to a problem known as bioaccumulation. As each organism feeds on one lower in the food chain, the fat soluble pesticide began to be concentrated in ever higher amounts as one moved toward the top of the food pyramid.
Since every organism eats far more than its own body mass in food, the tiny amounts found in each organism in the lower levels of the food web began to accumulate in greater concentrations in species located at higher trophic levels. One example of this problem is illustrated by the damage done to predatory birds as a result of bioaccumulation of DDT. As a result of this problem DDT has been banned from use in North America.
Click here for more information on DDT
Water Soluble Pesticides.....
Unlike DDT which are fat soluble pesticides, newer pesticides are developed that are not stored in fat but are soluble in water. This means that animals can remove these pesticides from their bodies by breaking them down with their liver and excreting them. They are also broken down in soil a lot faster.
Water soluble pesticides do their job in killing pest but they also cause other problems that have to be considered such as:
*Often, more than one application of these pesticides has to be applied to an area because they do not kill all the pests right away. This results in insects becoming more resistant to the pesticide and thus the pesticide does not have such a drastic effect.
*Because they decompose faster in the soil, they don’t last as long and thus may not reach targeted pests. Thus, they have to be applied more often.
* They affect other organisms in the ecosystem besides the pests they are suppose to kill. Thus humans are at risk as well as other plants and animals.
*Bioaccumulation may occur in many different food chains when the dead pests or other non-specific organisms are eaten.
Even though water soluble pesticides cause problems and pose risks to the environment, they are still considered safer than pesticides such as DDT and are the lesser of “two evils”.
Activity
Text Book Reading:
Nelson Science 10 Concepts and Connections: Section 1.11; pages 34-37
Activity 1:
Read Core STSE 1-5:Ecosystem Balance and answer questions that follow
Activity 2:
Complete Questions #1h, #16a, #27a,b page 60-63 of text.
Activity 3:
Read about the Spruce Budworm on page 36 of text and answer questions that follow.
Activity 4:
Read about the Bald Eagle on page 37 of text and answer questions that follow.
Activity 5:
Complete the Understanding Concepts on page 37 of text which is supplemented in the Student Record of Learning page 53-54.
Activity 6:
Complete the Case Study on page 50-52 of the Student Record of Learning.
Activity 7:
Research the effects of the pesticide Btk that is being used in Newfoundland on the Spruce Budworm and Hemlock Looper by visiting the following website:
http://www.gov.nl.ca/env/Env/PollPrev/pesticides/protecting_the_forests.asp
Answer such questions as:
- Why are the Spruce Budworm and Hemlock Looper considered pests?
- What is Btk and what category of pesticide is it?
- Does Btk affect other organisms in the ecosystem?
- What is it’s impact on the environment?
- What is it’s effect on humans?
- Is it water soluble?
- Is the government acting responsible in using this pesticide?
Activity 8:
Complete Black Line Master worksheet s #1.11a and #1.11b
Test Yourself
- Which statement is generally true regarding DDT?
- DDT is not a serious problem since it is biodegradable.
- DDT will kill all the pests it is used against.
- DDT tends to accumulate in the tissues of top predators.
- DDT is water soluble so it is normally excreted in urine
- Which statement best describes the problem associated with
continued use of the same pesticide?
- The pests are completely eliminated from the ecosystem.
- The pesticide kills a greater number of pests with each application.
- The pesticide kills fewer of the pests with each application.
- Pesticides are generally highly specific and rarely harm beneficial organisms.
- Which statement regarding early pesticide use is false?
- Early pesticides made use of heavy metals such as mercury.
- Early pesticides contaminated soil and water.
- Early pesticides were biodegradable.
- Early pesticides were toxic to humans.
- What is the most common problem associated with fat soluble
pesticides?
- They tend to contaminate the ground water supply.
- They are highly specific to a single pest species.
- They are prone to bioaccumulation.
- They must be sprayed more often than water soluble pesticides.
- Which is most likely to contain the highest concentration of
pesticide in its body tissues?
- wheat
- frog eating birds
- frogs
- grasshoppers