Scientists investigated two different methods for reducing the population of aphids on crop plants in a greenhouse.
In the first method, they sprayed the crop plants with a chemical insecticide.
In the second method, they introduced a predatory glasshouse ladybird as a biological control agent.
They recorded the percentage of the aphid population remaining every 2 weeks for a period of 10 weeks. The results are shown in the table below:
Time after treatment (weeks)Insecticide treatment (%)Biological control treatment (%)010010021545410156258855510804 \begin{array}{c|c|c} \text{Time after treatment (weeks)} & \text{Insecticide treatment (\%)} & \text{Biological control treatment (\%)} \\ \hline 0 & 100 & 100 \\ 2 & 15 & 45 \\ 4 & 10 & 15 \\ 6 & 25 & 8 \\ 8 & 55 & 5 \\ 10 & 80 & 4 \end{array} Time after treatment (weeks)0246810Insecticide treatment (%)1001510255580Biological control treatment (%)1004515854Explain the changes in the percentage of the aphid population remaining over the 10-week period when treated with the chemical insecticide.
Give two advantages of using biological control (predatory ladybirds) rather than chemical insecticide to control the aphid population.
Describe a method that could be used to estimate the population of aphids on the crop plants in a greenhouse.
