Counts in a pear orchard showed that leaf-eating beetle numbers fell just after an insecticide treatment, then rose over the next month. The number of predatory insects also fell. Tests showed that the beetles remained susceptible to the insecticide, and monitoring found no beetles had entered from outside the orchard. Which is the most likely explanation for the later rise in beetle numbers?
Fewer predatory insects remained to eat the beetles, so more beetles survived and reproduced.
The beetles killed by the spray decayed, releasing mineral ions that made the trees grow more leaves.
With fewer predatory insects, the beetles had less competition for the pear leaves they eat.
The predatory insects killed by the spray became an extra source of food for the beetles.
127 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.