Question

cfu - selective pressures
a neighborhood was sprayed with insecticides for a period of several months. initially, the mosquito population decreased sharply, but over time it began to rise again. which statement best justifies the decreased effectiveness of the insecticide?

the insecticide had no effect on the population and the population only decreased because of the season.

the mosquitoes that are resistant to the insecticide survived and passed on their resistant genes to their offspring.

the insecticide was not sprayed for long enough.

the insecticide worked too well which caused the ecosystem to rebound with more mosquitoes.

Explanation:

To determine the best justification, we analyze each option:

• The first option is incorrect as the population initially decreased, showing the insecticide had an effect.
• The second option aligns with natural selection: resistant mosquitoes survived, reproduced, and passed on resistance genes, leading to a resurgent population with decreased insecticide effectiveness.
• The third option is invalid since the spraying lasted months, and the population rebounded, not just due to duration.
• The fourth option is incorrect as ecosystems don’t “rebound” with more mosquitoes due to insecticide over - effectiveness; it’s about genetic resistance.

Answer:

The mosquitoes that are resistant to the insecticide survived and passed on their resistant genes to their offspring.