There isn’t a perfect spray that permanently stops them, but residual pyrethroid-based insecticides work best as a deterrent. Products with permethrin, cyfluthrin, or bifenthrin are commonly used and can help discourage bees from nesting when applied to bare or lightly finished logs. That said, sprays work best as a preventive, not a cure — keeping logs sealed, stained, and less attractive is just as important as what you spray.