Pol-line bees have the Varroa Sensitive Hygiene (VSH) trait, which means that nurse bees remove mites from brood cells before they can develop. They are also known for their early season build up, gentle temperament, and resistance to other brood diseases. 

Pol-line bees are more than twice as likely to survive through the winter than standard honey bees. In a study published in Scientific Reports, Pol-line colonies that were given no treatment to control Varroa mites in the fall had a winter survival rate of 62.5 percent, compared to 3 percent for standard bees. 

The USDA releases new Pol-line stock each year to selected queen breeders in the United States. The breeding process involves single-drone insemination, which results in populations where 75% of the workers are directly related to each other. This makes it easier to isolate desired traits.