Red spider mites are pests that feed on the leaves of apple trees, reducing fruit yield. Scientists investigate using a fungal pathogen as a form of pest management to protect the apple trees. The fungus is sprayed as spores which then germinate and infect the spider mites.
Table 1 shows three experimental treatments:
| Treatment | Site of spraying | Concentration of fungal spores used (million spores/ml) | How long the treatment lasts |
|---|---|---|---|
| Treatment 1 | on the apple leaves | 250 | a few weeks |
| Treatment 2 | on the bark of the trunk | 500,000 | several years |
| Treatment 3 | control (spraying with water) | 0 | — |
Why is the use of the fungus an example of biological control?
How many times more concentrated are the spores in the spray used on the bark compared to the spray used on the leaves?
Table 2 shows the results of the spraying after one year:
| Site of spraying | Red spider mites killed (%) |
|---|---|
| on the leaves | 92.4 |
| on the bark of the trunk | 88.1 |
| control (spraying with water) | 2.5 |
The scientists made the following statement:
"The fungal spores are an effective way to kill the red spider mites. They should be sprayed on the bark of the trunk rather than the leaves."
Discuss why the scientists are correct. Use data from Table 1 and Table 2.
25 exam-style questions on OCR GCSE Biology 6.2 Feeding the human race, covering 6.2.1 Biological factors affecting food security, 6.2.2 Agricultural solutions to growing demand, 6.2.3 Selective breeding, 6.2.4 Genetic engineering, 6.2.5 Steps in genetic engineering, 6.2.6 Benefits and risks of gene technology in agriculture, and 6.2.7 Biotechnological solutions to growing demand. Each one has a worked solution and a mark scheme showing where the marks go.