The local agricultural official gave the fruit growers of the District 10 Farmers’ Cooperative a new pesticide that they applied for a period of three years to their pear orchards in place of the pesticide they had formerly applied.
Conclusion
The new pesticide is more effective than the old pesticide, at least in the short term, in limiting the loss of fruit to insects.
Evidence
During the three years of using the new pesticide, the proportion of pears lost to insects was way less than during the previous three year period.
Evaluate
We have a Curious Comparison, , and the author's conclusion assumes a Causal Explanation -- the new pesticide is responsible.
We are trained to ask two separate questions: 1. could there be some Alternate Explanation for the Curious Fact? (why else might a lower % of pears have been lost over the last 3 years?)
2. how plausible is the Author's Explanation? (is there any more evidence that would help us believe that the new pesticide is the causal difference-maker?)
Goal
Since this is Strengthen, we would usually want a correct answer to rule out an Alternate Explanation (f.e., fruit loss to insects was not lower than before because there were just fewer insects around those years), or to boost the plausibility of the Author's Explanation (f.e. in the areas of the orchard where we didn't spray the new pesticide, we didn't see a lower proportion of pears lost).
But because this question stem is asking specifically about trees who didn't see a reduction in fruit due to insects, they are driving us specifically into the classic "No Cause, No Effect" plausibility-strengthener.
In order to strengthen the notion that the new pesticide is what caused the reduction in insect damage, we'd love to hear that trees that didn't have a reduction in insect damage weren't sprayed with the new pesticide.