To find out which ingredient the cockroaches are refusing, you can carry out a controlled experiment. hydramethylnon is dissolved in oleic acid before being mixed with corn syrup to prepare the poisoned bait, so you should test all three ingredients. suppose you conducted a feeding trial to test each ingredient. in the trial, a set of four agar dishes, three containing all except one ingredient and one with all three ingredients (the control), were weighed and placed 3 cm apart on the kitchen floor in an infested apartment. after two days, the dishes were weighed again to measure food consumption. you then repeated the trial 4 times and averaged the results

The correct options for this question are:

A) Roaches ate about the same amount from the dish with no hydramethylnon as they did from the control dish.
B) Roaches ate about the same amount from the dish with no oleic acid as they did from the control dish.
F) Roaches are refusing corn syrup.

In this scenario (before pesticides were ever introduced to cockroaches) a certain subset of the population was genetically more likely to avoid oleic acid for whatever reason.  Traits like this float throughout populations and contribute to genetic variance.  When pesticides are introduced to the population, cockroaches with the previously neutral trait of oleic acid avoidance were now given a significant boost in regards to their relative fitness.