Mounties say in a news release that two locations northwest of Brandon in the rural municipality of Elton are involved.
They say the alleged poisonings are believed to have happened between Aug. 14 and Sept. 3.
Mounties say the bee producers have suffered a substantial financial loss.
Dwindling bee populations have been an increasing concern in the agricultural community, though generally not because of any criminal action.
In recent years, bee populations worldwide have been ravaged by pesticides, parasites and colony collapse disorder, a mysterious phenomenon in which worker bees suddenly disappear.
In California, a record drought has reduced supplies of honey, raising prices for consumers and making it harder for beekeepers to earn a living.
In Ontario, a proposed class-action lawsuit has been launched against two chemical companies that make pesticides widely blamed for massive bee deaths.