Biological control of crop pests
Explain how predators can reduce pest numbers, crop damage and the need for pesticides, and evaluate the limits of the evidence.
On this page
Sources of Food · about 25–35 min
What you need to understand
Predators feed on pest prey, reducing crop damage and the need for pesticides.
Definitions
- biological control
using predators to reduce a population of pest prey
For example: Supporting ladybirds can reduce aphids and the need for pesticide.
Explanation
Biological control uses living organisms to control pests. Here, focus on predators feeding on pest prey: for example, ladybirds eat aphids that feed on crop plants. Fewer aphids can mean less crop damage and less need for a chemical pesticide.
Follow the mechanism: predator feeds on pest → pest population is reduced → less crop damage → less pesticide may be needed. The pest need not disappear completely for the method to help. Calling a treatment “biological” does not show how it works; identify both organisms and their roles.
Biological control also needs evidence and monitoring. A predator must feed on the intended pest, survive in the local conditions and be present at a useful time. It may affect other organisms as well. Do not assume that introducing any predator is harmless or that one season’s results will apply everywhere.
Pause and say it: Predators feed on pest prey, reducing crop damage and the need for pesticides.
Common mistake
Tempting wrong idea: Biological control means spraying a different pesticide.
Why it fails: Biological control requires pest prey to be controlled by predators. Adding a chemical pesticide is a different method.
Use this instead: Biological control uses predators to control pest prey, reducing the need for pesticides.
Worked examples
Modelled example 1
Control an insect pest
Problem
A farmer releases a predator that feeds on a crop pest. Explain how this could reduce crop damage and the need for chemical pesticide.
Study the worked solution
Reason from the evidence
Method
Identify the predator and its pest prey.Reason
The predator reduces the pest population by feeding on its prey.
Working
- The predator feeds on the pest prey.
- Reducing the prey population reduces crop damage.
With fewer pests and less damage, the farmer may need less pesticide.
State the conclusion
Working
This is biological control through control of prey by its predator.
Common misconception 2
Is every pest control method a pesticide?
Learner response
“Releasing ladybirds to eat aphids is pesticide use because both methods reduce pests.” Correct the classification.
Use the mechanism, not only the outcome
View solution step by step
Identify the living interaction
Method
Classify the ladybirds as biological control.Reason
The method uses a predator to reduce its prey rather than applying a chemical pesticide.
Working
predator population → reduced pest-prey population
The fruit-variety and ripening transfer challenge is now in production technology.
Compare benefits and limits
A farm tests two ways to control an insect pest in comparable plots. These are illustrative results from one season; the starting crop, pest population and sampling method are the same.
| Method | Harvested crop / kg per plot | Pest insects per sample | Non-target insects per sample |
|---|---|---|---|
| Chemical pesticide | 48 | 4 | 7 |
| Supported pest predator | 44 | 8 | 25 |
Try it. Which method gave the larger harvest? Which better retained non-target insects in this comparison? Explain why neither result proves that one method is always the better choice. Name a useful follow-up check.
Check the comparison
The pesticide plots produced 4 kg more crop per plot and had fewer pests. The predator plots retained more non-target insects: 25 per sample compared with 7. The choice depends on the production aim and the environmental effects being considered. Repeat comparable plots across seasons, and check whether the predator feeds on the intended pest and affects other organisms. One season does not establish reliability everywhere, and “biological” does not mean “automatically harmless”.
Guided practice
Try it with support
A farmer releases a predator that feeds on a crop pest. Explain the method and why it can reduce pesticide use.
Name the living interaction.
Check the guided answer
Answer: This is biological control: the predator reduces the pest-prey population, so less pesticide may be needed.
Check: Name which organism is the predator and which is its pest prey.
Practise and continue
Practise this
A farmer supports ladybirds, but some aphids remain. Does this alone show that biological control has failed? Explain what further evidence would help.
Need a hint?
Compare pest numbers and crop damage with a similar untreated plot.
Check your answer
No. Reducing pest numbers can reduce damage without eliminating every pest. Compare aphid numbers, crop damage and pesticide use before and after treatment, with matched comparison plots and repeated observations.
The fish-farm comparison is now in production technology
One-minute check
Use a predator–prey example to explain how biological control can reduce crop damage.
Why might some pests remain even when biological control is useful?
Correct this common mistake: “Biological control means spraying a different pesticide.”
Syllabus and review details
- SEC G1 Science 2027 · 2027
Content structure and syllabus content, PDF pages 8–17
Last reviewed: