Scale insects can be serious pests for citrus fruits. Severe infestations of scales result in falling twigs and branches until the affected tree dies. In the early 1900s, California citrus growers sprayed their trees with cyanide gas to kill scale insects. By 1914, some scale insects were surviving the spraying, and eventually the whole population showed resistance to cyanide. Which of the following statements best explains how resistance to cyanide spread in the scale insect population?
A. Insects with a resistance gene survived the first cyanide sprayings and passed the gene to their offspring.
B. Parasites infecting the insect population carried the trait from insects with a resistance gene to insects without a resistance gene.
C. Predators put greater selection pressure on insects with a resistance gene than on insects without a resistance gene.
D. Insects without a resistance gene underwent mutation upon contact with the cyanide to acquire resistance.

Individuals exposed to a damaging factor might mutate and resist the nosive effects. D) Insects without a resistance gene underwent mutation upon contact with the cyanide to acquire resistance.

What is resistance?

The term resistance refers to an inheritable change in the population sensitivity, reflected through the exposure of individuals to damaging factors (insecticides, for instance) that affects the population.

A genetic modification -mutation- might occur in some of the exposed individuals, leading them to survive under the effects of these factors.

Mutated individuals spread this new character in the population, which evolves with the capability of tolerating the element that would normally affect it.

In the exposed example, some of the exposed individuals developed a mutation after the cyanide exposure and got to survive. These individuals could mate and reproduce, transmitting this new resistant character to the following generations.

The correct option is D. Insects without a resistance gene underwent mutation upon contact with the cyanide to acquire resistance

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