why can a queen wasp sting many times but a worker bee can only sting once?
It's not true that all stingers have barbs. Wasps, and many other species, don't have barbed stingers, and therefore they can afford to sting you repeatedly without being killed. Worker bees, on the contrary, have a barbed stinger that gets stuck in your skin. 

Although wasps have a more powerful venom than bees, with bees usually the venom sack remains attached to the stinger and will keep pumping venom even after the bee itself has run away and died, causing the sting to be more painful. However, because bees died after stinging, they are less likely to sting you compared to wasps, hornets, yellow jackets and bumblebees.