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
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.