Transcript of Biological Control Topic 4-Lesson 1. Introduction The biological control of pests essentially means...
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- Biological Control Topic 4-Lesson 1
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- Introduction The biological control of pests essentially means
making use of the natural enemies of animals or plants to contain
the population of that pest. The cane toad is an example of this
that went horribly wrong.
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- Introduction This control method has been around for over 100
years but has recently become more popular reducing chemical means
of control. Why do you think this is so?
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- From Chemical to Biological In the mid 1900s, farmers almost
totally depended on chemicals for crop protection. This led to
concerns about the environmental effects of such chemicals, their
costs to farmers and the health hazards they posed to workers and
others.
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- From Chemical to Biological Along with the growing concerns
insects were rapidly developing resistance to organic pesticides
which encouraged farmers to use more potent chemicals. Rachel
Carson wrote a book which highlighted the issues relating to the
use of chemicals. This helped motivate people to develop better
means of crop protection.
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- From Chemical to Biological There are however some
disadvantages of biological control: More intensive management and
planning Can take more time Requires a greater understanding of the
biology of the pest and its enemies Results are generally not as
dramatic or quick as pesticides
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- From Chemical to Biological Today most farmers use integrated
pest management strategies to control pests in which biological
control can play a significant role. The major advantages of
biological control over pesticide include: It can be very specific
for a particular pest and no collateral damage sustained More
economical Does not result in public health risks Less danger of
impact on the environment
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- Conditions for Biological Control In order for the biological
control agent to be successful it must be target specific and be
able to survive and reproduce successfully in its new environment.
The most successful cases involved a lot of research before being
used.
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- Conditions for Biological Control The International Union for
the Conservation of Nature (IUCN) has a number of guidelines for
the translocation of living things for the purposes of biological
control. Activity Read the guidelines on page 118 HSC Spotlight
Text together and discuss
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- Types of Biological Control There are three main types of
Biological Control: Classical Augmentation Conservation Classical
Biological Control involves travelling to the pest species' country
of origin, researching its natural enemies, collecting and
introducing these natural enemies to the location where the pest
species is causing problems. This can be very successful (Salvinia)
or very unsuccessful (cane toad).
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- Types of Biological Control Augmentation is trying to increase
the natural enemies of the pest species. This approach requires
continual human management and does not provide a permanent
solution. Conservation involves identifying any factors that limit
the effectiveness of the natural enemies of the pest and changing
these limiting factors to help the beneficial species.
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- Controlling Biologically Several methods of biological control
do not rely on a predator-prey relationship. We are going to look
at a few of such methods: Microbial control Plant immunisation Pest
behaviour-modifying chemicals Genetic manipulation
Immunocontraception
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- Microbial Control This method involves the use of disease
causing bacteria, viruses, fungi or nematodes as control agents.
Careful research is involved to insure the disease acts only on
certain insects or pests. Different methods are used to insure the
target species consumes the agent which will result in them dying
within a few days.
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- Plant Immunisation This method is currently being researched.
It involves microbes or chemicals to raise the level of pest
resistance in plants. For example, genes that naturally produce
toxins in some plants are inserted into new plants, such as cotton,
which results in the new plant naturally producing the toxin which
rejects pests.
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- Genetic Manipulation This involves genetically altering a pest
species DNA and then releasing the altered organisms into the wild.
For example, the male screw worm fly is modified so that they
become sterile preventing the production of offspring.
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- Immunocontraception This involves the use of both microbial
control and genetic manipulation and is currently being trialled on
rabbits in Australia. It involves modifying the DNA of the myxoma
virus to target the eggs and sperm making rabbits infertile.
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- Habitat Rehabilitation: The Bradley Method Rehabilitating
degraded land to restore ecosystems is becoming more practiced
around the world. By reclaiming natural ecosystems from introduced
species and restoring them to their former function is being
carried out by small communities all over Australia.
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- Habitat Rehabilitation: The Bradley Method A method of weed
control developed by sisters Eileen and Joan Bradley in Sydney
(Bradley Method) involves hand- weeding without replanting selected
small areas. This allows each area to be reinhabited and stabilised
by native plants. This has been so successful its being used all
over the world.
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- Habitat Rehabilitation: The Bradley Method This method is
different from conventional weeding approaches. The basis is to
allow the native species to recolonise by tipping the ecological
balance away from the weeds and toward the native species. If you
clear the weeds from heavily infested areas the weeds will only
return. By working a little bit at a time from the best area of
native vegetation towards the weeds, the native vegetation is
favoured and its natural regenerative power will prevail.
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- Case Study: Prickly Pear A successful use of Classical
Biological Control happened in Australia with the eradication of
the introduced prickly pear cactus. This plant was introduced to
Australia in the 1800s as an ornamental garden and hedge
plant.
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- Case Study: Prickly Pear The prickly pear reproduces very
efficiently and rapidly escaped from gardens. Within 100 years of
its introduction it occupied 4 million hectares. By 1925 it
occupied over 125,000 square kilometres of grazing land.
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- Case Study: Prickly Pear In 1920 the Australian Government
built a team to investigate how to solve this growing problem. The
team went to the United States where the prickly pear is native and
researched its natural enemies.
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- Case Study: Prickly Pear Over 13 years this team sent back and
trialled a number of insect species, the most effective was the
larvae of the Argentine Moth (Cactoblastis Cactorum). Cactoblastis
caterpillers bore into the prickly pear and eat them from the
inside out. Within two years of their introduction most of the
prickly pear was eradicated.
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- Homework Read pg 211-213 HSC Spotlight Text Update electronic
vocabulary Complete DOT Point 5.1-5.5
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- Biological Control Topic 4-Lesson 2
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- Activity Read together Case Study: Long Reef pg 120-121 HSC
Spotlight Text Using the Bradley Method, discuss a program to
regenerate the area you studied. (Dot Point 5.11) Start To Think
About pg 121 HSC Spotlight Text
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- Homework Update Electronic Vocabulary Complete To Think About
pg 216 HSC Spotlight Text Complete DOT Points 5.9.2, 5.10