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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Biological Control Methods
Imagine your garden is being attacked by pests. Instead of reaching for chemical sprays, what if you could introduce a helpful predator that would eat those pests? That's the basic idea behind biological control! It's a natural way to manage pests by using living organisms rather than chemicals.
Key Definitions:
Chemical pesticides can harm the environment, kill beneficial insects and lead to pesticide resistance. Biological control offers a more sustainable approach that works with nature rather than against it. It's also often more cost-effective in the long run and safer for humans.
Biological control works by introducing natural enemies that will target specific pests. These control agents might eat the pests, parasitize them, or cause diseases that reduce their numbers. The goal isn't usually to eliminate the pest completely but to keep its population at a manageable level.
There are three main types of organisms used in biological control: predators, parasites/parasitoids and pathogens. Each works in a different way to control pest populations.
These organisms hunt and eat the pest species. Examples include ladybirds that eat aphids, birds that eat caterpillars and spiders that catch various insects. Predators typically eat many prey during their lifetime.
These organisms live on or inside the pest, eventually killing it. Parasitoid wasps, for example, lay eggs inside caterpillars. When the eggs hatch, the larvae eat the caterpillar from the inside out.
These are disease-causing microorganisms like bacteria, fungi and viruses that infect and kill the pest. For example, Bacillus thuringiensis (Bt) is a bacterium that produces proteins toxic to certain insect larvae.
Scientists use different strategies when implementing biological control, depending on the situation and target pest:
This involves introducing natural enemies from a pest's native region to control it in areas where it has become invasive. The control agent is expected to establish permanently and provide long-term control. For example, the cactus moth was introduced to Australia to control invasive prickly pear cactus.
This involves releasing additional numbers of a natural enemy that's already present but in numbers too small to be effective. It can be done as a one-time boost (inoculation) or repeated regularly (inundation). For example, releasing more ladybirds into a greenhouse to control aphids.
This approach focuses on protecting and supporting natural enemies that are already present in the environment. Farmers can create habitats like hedgerows or flower strips that provide food and shelter for beneficial insects. They can also reduce practices that harm natural enemies, such as limiting broad-spectrum pesticide use.
In the early 1900s, prickly pear cactus became a major problem in Australia, covering over 60 million acres of land. In 1925, scientists introduced the cactus moth (Cactoblastis cactorum) from Argentina. The moth's caterpillars feed exclusively on prickly pear. Within just a few years, the caterpillars had dramatically reduced the cactus population, clearing millions of acres for agriculture. This is considered one of the most successful examples of biological control in history.
Like any pest control method, biological control has its pros and cons:
Biological control works best as part of an integrated pest management (IPM) approach. IPM combines multiple pest control strategies, including:
By using multiple approaches, farmers can manage pests more effectively while minimizing environmental impact and reducing the risk of pests developing resistance.
Vine weevils can be a serious pest in UK gardens and nurseries, damaging plants by eating leaves and roots. A biological control method involves applying nematodes (Steinernema kraussei) to the soil. These microscopic worms infect and kill vine weevil larvae. They're particularly effective in container plants and can be watered into the soil when conditions are right. This method is safe for humans, pets and wildlife, making it popular with gardeners who want to avoid chemical pesticides.
Here are some common examples of biological control that you might encounter:
Mosquito fish (Gambusia) eat mosquito larvae in ponds and water features. Bacillus thuringiensis israelensis (Bti) is a bacterium that produces toxins specifically harmful to mosquito larvae and is used in water bodies.
Predatory mites control spider mites on plants. Parasitic wasps (Encarsia formosa) control whitefly. These are often sold commercially for use in greenhouses and indoor plants.
Codling moth, which damages apples and pears, can be controlled using pheromone traps and granulosis virus. Nematodes can be applied to soil to control pests that pupate there.
As concerns about chemical pesticides grow, biological control methods are becoming increasingly important. Scientists are discovering new natural enemies and developing better ways to use them. Genetic technologies are also being explored to enhance the effectiveness of biological control agents.
The key to successful biological control is understanding the complex relationships between pests, their natural enemies and the environment. With careful research and application, biological control can help us produce food more sustainably while protecting biodiversity and human health.
For your IGCSE Biology exam, remember to compare biological control methods with chemical methods. Be able to explain the advantages and disadvantages of each and understand how they can be used together in integrated pest management. Know specific examples of biological control agents and how they work.
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