Final answer:
The Brown Banded cockroach has yellow stripes on its wings. The increase in Bt toxin resistance in the purple-legged group of insects suggests directional selection, where traits conferring resistance become more prevalent.
Step-by-step explanation:
The question 'which cockroaches have yellow stripes on their wings?' is related to the identification of insect species based on a specific morphological characteristic.
The correct answer to this question is d) Brown Banded cockroaches, as they are known to have yellow stripes on their wings. This question, however, seems to be part of a broader discussion on a population of insects that are showing a division into two sub-groups with different colors on their thorax and legs.
As for the latter part of your question, the observation that the purple-legged group may be increasingly resistant to the Bt (Bacillus thuringiensis) toxin supports the idea of evolutionary processes.
Specifically, it suggests directional selection where an environmental pressure, in this case the Bt toxin, is favoring individuals with certain genetic traits that confer resistance, leading to this trait becoming more prevalent in the population.