Bed bugs might sound like an old-fashioned problem, but now they are back with a vengeance. Fifty years ago, the blood-sucking pests were nearly eradicated in the United States thanks in part to the use of pesticides like DDT. Today, they are creeping over sheets and tormenting sleepers across the country. New York was recently declared America's most bed-bug-infested city in America. In the past, we countered the bed bugs by using pesticides called pyrethrins and pyrethroids. These compounds work by attacking the nervous system. Insects have channels in the membranes of their nerve cells that can be opened to allow sodium into the cells, triggering a nerve impulse. Pyrethrins and pyrethroids alter the nervous system by binding to the sodium channels, locking them in the open position. This allows sodium to pour into the cell continuously, causing the nerve to fire repeatedly and eventually leading to paralysis.

Question

Bed bugs might sound like an old-fashioned problem, but now they are back with a vengeance. Fifty years ago, the blood-sucking pests were nearly eradicated in the United States thanks in part to the use of pesticides like DDT. Today, they are creeping over sheets and tormenting sleepers across the country. New York was recently declared America's most bed-bug-infested city in America. In the past, we countered the bed bugs by using pesticides called pyrethrins and pyrethroids. These compounds work by attacking the nervous system. Insects have channels in the membranes of their nerve cells that can be opened to allow sodium into the cells, triggering a nerve impulse. Pyrethrins and pyrethroids alter the nervous system by binding to the sodium channels, locking them in the open position. This allows sodium to pour into the cell continuously, causing the nerve to fire repeatedly and eventually leading to paralysis.

Todays bed bugs seem to be more resistant to the chemicals. Biologists have determined that mutations are responsible for this resistance. Mutations changing just two of the 2000 amino acids that make up part of the sodium channels would be enough to make an insect 250 times more resistant to a commonly used pyrethroid. These mutations may change the channel so that the insecticide can no longer bind to it effectively.

If bed bugs had never been exposed to DDT in the 1950's and 1960's, how would you expect that to affect bed bugs' resistance to pyrethroids during the last decade?
Responses
A Because bed bugs reproduce so rapidly, resistance to pyrethroids among bed bugs has become a major problem .Because bed bugs reproduce so rapidly, resistance to pyrethroids among bed bugs has become a major problem .
B With the widespread use of DDT, pesticide-resistant mutations became much more common among bed bugs. The bed bugs passed that resistance on to future generations.With the widespread use of DDT, pesticide-resistant mutations became much more common among bed bugs. The bed bugs passed that resistance on to future generations.
C If some of the bed bugs carry the resistance mutations, those insects will be better able to survive and reproduce and will wind up passing the mutation on to their offspring.If some of the bed bugs carry the resistance mutations, those insects will be better able to survive and reproduce and will wind up passing the mutation on to their offspring.
D Without the use of DDT, natural selection would not have favored any mutations that provided protection from pesticides; bed bugs would be more susceptible to today's chemicals.

Answer 1

D Without the use of DDT, natural selection would not have favored any mutations that provided protection from pesticides; bed bugs would be more susceptible to today's chemicals.