Topic 4-Lesson 1

Biological ControlTopic 4-Lesson 1Introduction 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.

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?

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.

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.

From Chemical to Biological There are however some disadvantages of biological control:More intensive management and planningCan take more timeRequires a greater understanding of the biology of the pest and its enemiesResults are generally not as dramatic or quick as pesticidesFrom 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 sustainedMore economicalDoes not result in public health risksLess danger of impact on the environmentConditions for Biological ControlIn 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.

Conditions for Biological ControlThe 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.

ActivityRead the guidelines on page 118 HSC Spotlight Text together and discuss

Types of Biological ControlThere are three main types of Biological Control:ClassicalAugmentationConservation

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).Types of Biological ControlAugmentation 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.Controlling BiologicallySeveral methods of biological control do not rely on a predator-prey relationship. We are going to look at a few of such methods:Microbial controlPlant immunisationPest behaviour-modifying chemicalsGenetic manipulationImmunocontraceptionMicrobial ControlThis 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.

Plant ImmunisationThis 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.

Genetic ManipulationThis 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.

ImmunocontraceptionThis 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.

Habitat Rehabilitation: The Bradley MethodRehabilitating 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.

Habitat Rehabilitation: The Bradley MethodA 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.Habitat Rehabilitation: The Bradley MethodThis 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.Case Study: Prickly PearA 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.

Case Study: Prickly PearThe 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.

Case Study: Prickly PearIn 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.

Case Study: Prickly PearOver 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.

HomeworkRead pg 211-213 HSC Spotlight TextUpdate electronic vocabularyComplete DOT Point 5.1-5.5Biological Control

Topic 4-Lesson 2ActivityRead together Case Study: Long Reef pg 120-121 HSC Spotlight TextUsing the Bradley Method, discuss a program to regenerate the area you studied. (Dot Point 5.11)Start To Think About pg 121 HSC Spotlight TextHomeworkUpdate Electronic VocabularyComplete To Think About pg 216 HSC Spotlight Text Complete DOT Points 5.9.2, 5.10