In general, if at all possible, you should avoid killing ground bees. There are several varieties of bees that live in the ground, and they are all good for the soil. They eat grubs, aerate the soil and pollinate wild flowers. However, if the ground bees inhabit an area where children play or you have allergies, then it may be in your best interest to kill them.
Observe the bees. Ground bees live in a network of tunnels underneath your yard. While you watch them, note where their exit holes are. It won't be as easy to find them at night when you head out to treat them. The best time to watch bees is between 10 a.m. and 3 p.m.
Dust the bee's exit holes and the area around them with an insecticide dust like carbaryl (Sevin is a popular brand) or bendiocarb (Ficam D). Follow the manufacturer's instructions for exact amounts, but a light dusting is usually sufficient.
Pour roughly 1/2 cup of gasoline into each of the bee's holes. This is quite an effective solution, and it really comes in handy if you can't access any of the dust insecticides. However, it may kill some of the surrounding plants.
Plug the bee's holes with mud after you have applied the insecticide of your choice.