An orchard has apple trees, bees that carry pollen and ladybirds that eat aphids…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
An orchard has apple trees, bees that carry pollen and ladybirds that eat aphids. An outbreak of caterpillars begins. The owner can buy a chemical insecticide that kills most insects, a sachet of Bacillus thuringiensis spores, or a baculovirus that infects one kind of caterpillar.
- Which two choices fit an integrated pest management programme better, and why?
- What may the chemical insecticide do to the other insects of the orchard?
- Why must the Bt spores be sprayed on the leaves?
Need a reminder? The key ideaShow
Biocontrol uses living organisms. Ladybird: aphids. Dragonfly: mosquitoes. Bacillus thuringiensis: caterpillars, by the toxin that is released in the gut of the larva. Trichoderma: plant pathogens. Baculoviruses: insects, narrow spectrum. If a share of the larvae die each day, a number falls to after days. An average is the total divided by the number of plants.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The Bt spores and the baculovirus. Both are narrow spectrum. They attack caterpillars, or one kind of insect, and they leave the bees and the ladybirds alone.
Step 2. (b) It would kill many of the bees and the ladybirds too. The loss of the ladybirds would let the aphids multiply, and the loss of the bees would hurt the pollination of the trees.
Step 3. (c) A larva must eat the spores with a leaf. The toxin is released in its gut and kills it.
Answer: (a) Bt and the baculovirus, because they are narrow spectrum; (b) it also kills useful insects; (c) the larvae must eat the spores.
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