In households where the traps have been used regularly, the proportion of insect pests that have a natural aversion to eating glucose has increased with each successive generation. The kind of glucose used to bait the traps is one of several different kinds of glucose that occur naturally. Even when only a few individuals out of an entire generation of insects survive the effects of a pesticide, the offspring of those individuals are usually resistant to that pesticide. After the manufacturer of the traps increased the concentration of the pesticide used in the traps, the traps were no more effective in eliminating household insect pests than were the original traps.
A commercial insect trap consists of a small box containing pesticide mixed with glucose, a sweet substance known to attract insect pests. Yet in households where this type of trap has been used regularly for the past several years, recently installed traps are far less effective in eliminating insect pests than were traps of that type installed several years ago. Research scientists have hypothesized that traps in those households decreased in effectiveness because successive generations of the pests developed a resistance to the pesticide in the traps.
Which one of the following, if true, most seriously undermines the hypothesis?