Fig. 4.1 shows the structure of a male flower of maize, $\textit{Zea mays}$. Using Fig. 4.1, explain how two features of this flower make it adapted for wind pollination.
The corn borer, $\textit{Ostrinia nubilalis}$, is an insect pest of maize. Its larvae are caterpillars that eat the leaves of maize plants. The adults can fly. Adult corn borers do not feed on maize plants. Much of the maize grown in the USA has been genetically modified so that it produces Bt toxin, which is lethal to insects that feed on the leaves. However, many corn borer populations have now evolved resistance to the Bt toxin. Explain how this resistance could have evolved.
The recessive allele, r, in the corn borer gene gives resistance to Bt toxin. Corn borers that are homozygous for the normal dominant allele R, or that are heterozygous, die when they feed on Bt maize. State the genotype of the corn borers that successfully develop from larvae into adults in fields where Bt maize is grown.
To reduce the number of corn borers that are resistant to Bt toxin, farmers in the USA are required to grow up to 50% of their maize as non-Bt varieties. The non-Bt maize is grown in separate areas, called refuges, close to the Bt maize fields. This is known as the HDR strategy. Almost all corn borer larvae feeding on this non-Bt maize have the genotypes RR or Rr. The HDR strategy assumes that, when these larvae become adults, they will interbreed with the adults developing in the Bt maize fields. Explain how the HDR strategy could reduce the proportion of corn borers that are resistant to the Bt toxin.
The HDR strategy can work only if a high proportion of adult corn borers developing in the Bt fields mate with adult corn borers from the non-Bt refuges. An investigation was carried out to find out how far female corn borers mate with males from their own field, or from outside that field. Several hundred adult male and female corn borers were marked and then released into a maize field that contained no corn borers. After 36 hours, as many corn borers as possible were recaptured from the field and the numbers of marked and unmarked male and female corn borers were recorded. The percentage of marked females that had mated with marked males was also recorded. This was repeated on four more occasions. The results are shown in Table 4.1.
With reference to the two shaded columns in Table 4.1, explain what the results show about the amount of mixing between corn borers from different fields.
With reference to Table 4.1, suggest and explain what the findings of this investigation imply about how effective the HDR strategy is.
With reference to Table 4.1, suggest and explain what the results of this investigation imply about how effective the HDR strategy is.