Step 1 :The null hypothesis is usually a statement of no effect or no difference. In this case, it would be that the mean number of beetles per untreated plant is 9.
Step 2 :The alternative hypothesis is what we are testing for, in this case, that the new formula may reduce this infestation rate. So, the alternative hypothesis would be that the mean number of beetles per untreated plant is less than 9.
Step 3 :Therefore, the appropriate null and alternate hypotheses would be \(H_{0}: \mu=9\), \(H_{1}: \mu<9\).
Step 4 :Final Answer: \(\boxed{a. H_{0}: \mu=9, H_{1}: \mu<9}\)