Which animal is noted as not being effectively controlled by fumigants?

Voles are noted as not being effectively controlled by fumigants due to their specific biology and behavior. Fumigants are typically gases or vapors that are used to control pests by penetrating spaces and killing pests that breathe in or come into contact with the material. Voles tend to create extensive underground burrow systems which can trap the fumigants and limit their effectiveness. This behavior makes it difficult for the fumigants to reach the voles in sufficient concentrations to achieve control.

On the other hand, ground squirrels, pocket gophers, and rabbits can be more effectively managed with fumigants because their behaviors and burrowing habits allow for better exposure to the treatment, making them more susceptible to the effects of the chemicals used. Each of these animals tends to occupy areas where fumigants can penetrate effectively, leading to higher success rates in controlling their populations.