Fall Armyworm (Spodoptera frugiperda) larvae are major agricultural pests that feed on the leaves of maize plants, severely reducing crop yields and threatening food security. Scientists investigate using a bacterial pathogen, Bacillus thuringiensis (Bt), as a form of biological pest management. The Bt spores are applied to the crops, where they are ingested by the larvae, leading to infection and death.
Table 1 shows three experimental treatments:
| Treatment | Site of application | Concentration of Bt spores used (million spores/g) | How long the treatment lasts |
|---|---|---|---|
| Treatment 1 | Maize leaves | 400 | a few days |
| Treatment 2 | Seed-coating | 1,600,000 | several months |
| Treatment 3 | Control (spraying with water) | 0 | — |
Why is the use of the Bt bacterium an example of biological control?
How many times more concentrated are the spores in the seed-coating treatment compared to the spray used on the leaves?
Table 2 shows the results of the treatments after 12 weeks:
| Site of application | Fall Armyworm larvae killed (%) |
|---|---|
| Maize leaves | 95.8 |
| Seed-coating | 91.2 |
| Control (spraying with water) | 1.8 |
The scientists made the following statement:
"The Bt spores are an effective way to kill the Fall Armyworm larvae. They should be applied as a seed-coating rather than sprayed on 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.