When should samples of control areas be made during the evaluation of insecticides?

Sampling control areas during the evaluation of insecticides is essential for accurately assessing the effectiveness of the treatment. The primary purpose of taking these samples is to determine whether the insecticide applied has had a notable impact on the target mosquito population. By comparing the results from control areas (where no treatment is applied) to those of treated areas, it becomes possible to establish a clear treatment effect.

In this context, control samples serve as a benchmark against which the treated areas can be measured. This comparison helps in understanding the specificity and effectiveness of the insecticide used, as well as its potential side effects on non-target organisms. It also provides robust data that can guide future mosquito control strategies.

The other options do not address the fundamental purpose of sampling control areas in insecticide evaluations effectively. For example, sampling "only when possible" may result in insufficient data for making informed decisions. Focusing solely on applying Mulla's formula doesn't fulfill the broader requirement of establishing a treatment effect. Lastly, while taking samples during peak mosquito populations is beneficial for understanding population dynamics, it doesn't specifically address the necessity of evaluating treatment impacts through control samples.