What do I treat an insect bite with to stop itch?

Antihistamin steroid. Oral or topical antihistamines such as Benadryl (diphenhydramine) or Diphenhydramine will take the sting away quickly but temporarily. The dosing will have to be repeated regularly to maintain effectiveness. Topical steroids such as Hydrocortisone will take a little longer to work but probably, ultimately, will be more effective. You can use both.
Insect bite. If the insect bite is mild, apply a topical cream to ease pain and provide itch relief. Creams containing ingredients such as hydrocortisone, Lidocaine or pramoxine may help control pain. Other creams, such as calamine lotion or those containing colloidal oatmeal or baking soda, can help soothe itchy skin. If you have difficulty breathing go to the er as soon as possible.