Answer:
genetic drift
Step-by-step explanation:
The newly isolated population of beetle would have very different allele frequencies than the main population because of genetic drift.
Genetic drift refers to a change in the frequencies of alleles in a population over generations brought about by pure chance. Genetic drift can cause a bottleneck or founder effect. A bottleneck effect is a temporary decrease in the genetic diversity of a population while the founder effect refers to a decrease in the genetic variability of a new population formed from a small number of individuals that get separated from a larger population.
Hence, the newly formed population of beetles would have lower allele frequencies than the main population due to the founder effect brought about by genetic drift.