A detailed discussion of allergy to insect stings can be found here at the AAAAI website.

If you have had a serious reaction to an insect sting and skin and/or blood tests are positive for allergy to the venom, you have very high risk of a serious reaction to a future sting. Allergy injections with graded doses of the appropriate venom reduces your risk down to normal level.

Starting with a very small dose, insect venom injections are given weekly (or twice a week if you want to shorten the time to reach maintenance) in gradually increasing doses until a maintenance dose of 100 micrograms for each insect is reached. This is the Build Up Phase and takes about 5 to 10 weeks. Thereafter 100 mcg is given every 5 to 6 weeks for about 3 to 5 years, depending upon the severity of your allergy.

100 mcg, by the way, is equal to about two real insect stings.

During the build up phase we will give you upto three step up doses. So you will be in the office for 3 to 4 hours. In the maintenance phase there is only one step and therefore it will take about an hour to get done. The reason it takes that long is because after every dose we need to observe and ensure that you are not having an allergic reaction to the shot. We want you to bring your Epipen with you when you come in for your shots to cover for the remote possibility of an allergic reaction on your way home

Once you reach the full dose your risk of reaction to a field sting is the same as that of any non allergic person. Most patients still carry their Epipen in the insect season for “just in case”. Please feel free to ask any questions you may have and get satisfactory answers before you start these injections.