Outline how genetic engineering produced Bt maize plants resistant to insect attack.
One suggested conservation advantage of Bt maize is that, unlike chemical insecticide sprays, it should leave non-target insects unharmed. When Bt maize was first grown in the USA, scientists were worried that maize pollen containing the Bt toxin could be blown by the wind on to wild plants such as milkweeds, $Asclepias$ spp. Milkweed leaves are eaten by the caterpillars (larvae) of the monarch butterfly, $Danaus\ plexippus$. In 1999, a laboratory experiment investigated the effects on monarch caterpillars of milkweed leaves treated in different ways. Each caterpillar group was given milkweed leaves to feed on for the duration of the experiment. The three treatments were: leaves with no pollen; leaves dusted with pollen from non-Bt maize; leaves dusted with pollen from Bt maize. Fig. 4.1 presents the results of this laboratory experiment.
State the conclusion that can be drawn from Fig. 4.1.
Laboratory findings are not always helpful for predicting what will happen in natural ecosystems. Some scientists expected that increasing the area planted with Bt maize in the USA would reduce the number of monarch butterflies, using the results in Fig. 4.1 as evidence. More monarch butterflies were recorded in 2019 than in 1999, even though the amount of Bt maize grown had more than tripled. Suggest why the predicted fall in monarch butterfly numbers did not happen in the real ecosystem.