Insects in the Lepidopteran group lay eggs on maize crops. The larvae on hatching feed on maize leaf and tender cob. In order to arrest the spread of three such Lepidopteran pests, Bt maize crops were introduced in an experimental field. A study was carried out to see which of the three species of lepidopteran pests was 5 11 most susceptible to Bt genes and its product. The lepidopteran pests were allowed to feed on the same Bt-maize crops grown on 5 fields (A-E). The graph below shows the leaf area damaged by these three pests after feeding on maize leaves for five days. Insect gut pH was recorded as 10, 8 and 6 respectively for Species I, II and III respectively. (a) Evaluate the efficacy of the Bt crop on the feeding habits of the three species of stem borer and suggest which species is least susceptible to Bt toxin. (b) Which species is most susceptible to Bt-maize, explain why? (c) Using the given information, suggest why similar effect was not seen in the three insect species? 


a) From the graph, it is clear that Species III is the most susceptible to Bt maize as it caused the least amount of damage to the leaves. Species I and II, on the other hand, caused more damage to the leaves, indicating that they are less susceptible to Bt maize. Therefore, Species III is the most susceptible, while Species I and II are less susceptible.

b) Species III is the most susceptible to Bt-maize because it has a higher gut pH of 6, which means it has a more alkaline gut environment. The Bt toxin produced by the maize is most effective at this pH, as it can bind to the midgut receptors and cause damage to the gut lining, leading to death of the larvae. In contrast, Species I and II have a lower gut pH, making them less susceptible to the Bt toxin.

(c) The difference in susceptibility to Bt-maize among the three insect species can be attributed to the differences in their gut pH. Species III with a gut pH of 6 is more susceptible to the Bt toxin, while Species I and II with gut pH of 10 and 8 respectively are less susceptible. This difference in gut pH is likely due to differences in the evolutionary history of the species and their adaptation to different food sources. Therefore, the gut pH of an insect species can be an important factor in determining its susceptibility to Bt-maize.

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