Many dogs are just as allergic to insect bites as people. If your dog was sensitized by being stung once before, a second sting could result in an allergic reaction called "Urticaria" (or hives). Should you notice such a reaction, please bring your dog to the clinic immediately for treatment which could be life saving. Dogs can also get similar reations to food and other contact allergens.
To learn more on how to treat beestings before you get to your veterinarian, click the link.