Biological Control of Pests: IELTS Reading Practice Test

This passage traces the development of biological pest control, a method that uses living organisms such as predators, parasites, and pathogens to reduce pest populations. It covers historical examples, the types of organisms used, the risks of introducing non-native species, and comparisons with chemical control. The Cambridge source for this passage is not confirmed; it is classified as a practice passage. You should spend about 20 minutes on Questions 1–13, which are based on the passage below. The passage contains True/False/Not Given questions (Q1–7) and Sentence Completion questions (Q8–13).

Paragraph A 

The continuous and widespread use of chemical pesticides to combat agricultural pests has led to widespread concern about their long-term effects on the environment. Scientists and farmers have therefore looked for other ways to deal with pests. One approach that has attracted considerable attention is biological control, the use of a pest's natural enemies to keep its population at a level where it does no significant damage.

Paragraph B 

Biological control is not a new idea. Chinese farmers used ants to control insect pests in citrus groves as long ago as the third century AD. Modern biological control began in the 1880s, when American entomologists imported the vedalia beetle from Australia to control the cottony cushion scale, an insect pest that was destroying California's citrus industry. The beetle proved to be an outstanding success, and established the principle that a pest's natural enemies could be used to reduce its population to manageable levels.

Paragraph C 

Since then, hundreds of programmes involving the introduction of natural enemies have been carried out around the world. Many have been directed against insect pests, but biological control has also been used against weeds, particularly aquatic weeds. The water hyacinth, for example, was introduced to many parts of the world as an ornamental plant but then became a serious weed, blocking waterways. Biological control agents, insects that fed on the plant, were introduced and succeeded in controlling it in some areas.

Paragraph D 

Animals used in biological control fall broadly into three groups: predators, parasites, and pathogens. Predators kill and consume their prey directly. Parasites generally do not kill their hosts immediately but weaken them over time. Pathogens are disease-causing organisms such as fungi, bacteria, and viruses. A fourth category consists of herbivores, animals that eat plants and are therefore used to control weeds rather than insect pests.

Paragraph E 

The major advantage of biological control over chemical pesticides is that it causes no chemical pollution and has no direct toxic effect on humans. It is also self-sustaining: once a population of natural enemies is established, it will continue to reproduce and control the pest without further intervention. However, biological control is not without risks. Introducing a foreign species into a new environment can have unpredictable consequences, as the introduced organism may attack non-target species or become a pest itself.

Paragraph F 

The classic example of an introduction that went wrong is the cane toad, brought to Australia in 1935 to control beetles in sugar cane crops. The toads failed to control the beetles but spread rapidly across the country, preying on native wildlife and proving extremely difficult to eradicate. This example has made scientists much more cautious about introducing non-native species, and rigorous testing of potential biological control agents is now required before any introduction is approved.

Paragraph G 

Despite the risks, biological control remains an important and growing field. When it works well, it can provide long-term control of a pest at relatively low cost compared to repeated applications of chemical pesticides. The key is careful research to find the most specific and effective control agent available, one that will attack the target pest but leave other species unaffected. Advances in molecular biology are making it easier to identify suitable agents and to predict their likely impact on an ecosystem before they are released.

True/False/Not Given (Questions 1–7)

Do the following statements agree with the information given in the reading passage? Write: TRUE if the statement agrees with the information FALSE if the statement contradicts the information NOT GIVEN if there is no information on this

1. The use of chemical pesticides has caused concern about damage to the environment.

2. The first use of biological control in the modern era took place in Australia.

3. The vedalia beetle is still used in California today.

4. Biological control has been applied to problems caused by plants as well as insects.

5. Pathogens used in biological control kill their hosts immediately.

6. More money is spent on biological control than on chemical pesticides worldwide.

7. Scientists now carry out extensive tests before approving the introduction of a new biological control agent.

Sentence Completion (Questions 8–13)

Complete the sentences below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

8. Chinese farmers were among the first to use a pest's _____ to reduce crop damage.

9. As well as insects, biological control has been used against _____, especially those found in water.

10. Biological control agents include predators, pathogens, herbivores, and _____.

11. Unlike _____, biological control does not pollute the environment or harm humans directly.

12. The cane toad was introduced to Australia to control beetles in _____.

13. Effective biological control can provide _____ of a pest at a lower cost than chemical methods.