Tomato hornworms, a type of caterpillar, were injuring the tomato plants in the fields of two tomato growers. One grower decided to treat his tomato field with a pesticide to kill the hornworms. The other grower decided to use wasps and other insect predators to control the hornworms in her field. A small percentage of the tomato hornworms in each field had an allele that made them resistant to the pesticide when the two treatments began.

Question

If the two farmers continue using their chosen treatments for several years, what effect will the treatments have on the abundance of pesticide-resistant hornworms in each field?

Answer options with 4 options
A.
Neither field will have any hornworms after several years of treatment because either the pesticide or the insects will kill off the hornworms.

B.
Both fields will still have a small percentage of pesticide-resistant hornworms, but the pesticide or the insect predators will reduce the total number of hornworms.

C.
The pesticide-treated field will have no pesticide-resistant hornworms, and the insect-treated field will have a higher percentage of pesticide-resistant hornworms than it did at the beginning.

D.
The pesticide-treated field may have a higher percentage of pesticide-resistant hornworms than it did at the beginning, and the insect-treated field may still have a small percentage of pesticide-resistant hornworms.

Answer 1

The correct answer is:

C. The pesticide-treated field will have no pesticide-resistant hornworms, and the insect-treated field will have a higher percentage of pesticide-resistant hornworms than it did at the beginning.

Explanation:

1. In the pesticide-treated field, the pesticide will effectively kill off the susceptible hornworms. However, the few that are resistant to the pesticide will survive and reproduce. Over time, selective pressure from the pesticide will lead to a decrease in the overall hornworm population, but those that are resistant will become more prevalent as they are the ones that survive and pass on their genes.

2. In the insect predator-treated field, the wasps and other predators will help control the hornworm population, but they are less selective compared to the pesticide. Since the predators will likely still target both resistant and non-resistant hornworms, the resistant population may increase as they survive the predation better than susceptible ones, resulting in an overall higher percentage of pesticide-resistant hornworms compared to the beginning.

Thus, after several years, the pesticide-treated field will gradually lose pesticide-resistant hornworms as they won't survive due to the pesticide's selective pressure, while the insect-treated field will maintain or increase the percentage of resistant hornworms.