“If I didn’t have dogs, these bees just wouldn’t be able to move,” she said.

On a recent Friday morning, on the green slopes behind her home here in Jarrettsville, Ms. Preston tossed a toy around for Tukka, a young springer spaniel she had just adopted.

At first glance, it didn’t look like a workday. But that toy had been sealed in a plastic bag with foulbrood, and Ms. Preston was in the early stages of training Tukka on the scent. With any luck, he will join her team before the end of the year.

“You want Foulbrood Bunny?” she asked, throwing the fuzzy gray toy across the field.

Tukka caught the toy in a frenzy, salivating at the smell of it, chewing it with delirious pleasure. “This is what I want to see,” Ms. Preston said.

Soon, she will move on to putting foulbrood inside a small rubber toy and throwing it farther, or in an unexpected direction, to see if Tukka can sniff it out. Then she will hide the scent in the training installation she built exactly for this purpose — tubes mounted close together at various heights on an industrial plastic pallet.

If the exercises are successful, Tukka will learn to find even small traces of the scent, and communicate that to Ms. Preston by pointing with his nose, then sitting down.

She trained Mack the same way, bonding with the dog through games and repetition, building up his confidence and trust, all the while teaching him the basics of his important new job. That training took nine months.