The frequency of a certain trait in a population of beetles will increase over time if what?

Answer: If the beetle with that trait benefits from it or survives more than other beetles with another trait.

Explanation:

if there is a green beetle and a blue beetle birds are probably going to spot the blue beetle first and eat it but if its a green one it can hide in a leaf and survive more than the beetles with blue color

How does natural selection affect the frequency of traits in a population?

Natural selection only acts on the population's heritable traits: selecting for beneficial alleles and, thus, increasing their frequency in the population, while selecting against deleterious alleles and, thereby, decreasing their frequency. This process is known as adaptive evolution.