1.1. Farmers sometimes use biological control to reduce the damage to their crops caused by pests such as insects.

Which of these is an advantage of using biological control over chemical control?

1.2. Aphids are tiny insects that have very sharp mouthparts. They push these mouthparts into the phloem found in stems. They then feed on the phloem contents.

Shipher Wu and Gee-way Lin, National Taiwan University, CC BY 2.5 , via Wikimedia Commons

(i) Name two substances the aphids obtain from the phloem.

(2)

(ii) Explain how aphids feeding from the phloem of crop plants can lead to a reduction in yield.

(4)

1.3. Silverflies and hoverflies are two species of insect whose larvae feed on aphids.

Scientists investigate the feeding behaviour of these species in a laboratory experiment.

This is the scientists’ method.

• Place a single silverfly in a container

• Place a single hoverfly in a separate container

• Keep the containers at 12 °C

• Put 30 aphids in each container

• Count the number of aphids consumed each day for several days

• Determine the mean number of aphids consumed per day

The scientists repeat the method at two higher temperatures.

The graph shows the scientists’ results.

The scientists conclude that the hoverfly is the most effective biological control agent for aphids.

Discuss the scientists' conclusion, referring to information in the graph and the scientists' method in your answer.