Final answer:
The answer to the frass comparison question is 'Both are true', with Anobiid droppings described as powder-like and Lyctid as very fine powdery-like. However, this comparison is between beetles, not termites. The hypothesis about insect color variations leading to Bt toxin resistance is an example of directional selection in evolutionary biology.
Step-by-step explanation:
The direct answer to the question 'How do frass (droppings) differ between Lyctid and Anobiid termites?' is C. Both are true. Anobiid droppings are powder-like while Lyctid droppings are very fine and powdery-like. However, since the question mentions termites but the statement compares frass between Lyctid powderpost beetles and Anobiid beetles, the premise of the question is technically incorrect, as Lyctid and Anobiid refer to types of beetles rather than termites.
Regarding the given reference information on a population of insects with color variations on their thorax and legs, and the hypothesis about the purple-legged group's increasing resistance to Bt toxin, the idea that supports this observation is the concept of directional selection. This evolutionary process occurs when environmental pressures lead to the proliferation of a phenotype within a population that is best adapted to survive under these conditions. In this case, if the purple-legged insects are found to be more prevalent and survive better with exposure to Bt toxin, this could indicate that they have a genetic advantage that confers resistance, supporting the researcher's hypothesis.