Wasp venom is slightly alkaline. However, wasp venom is a complicated mixture of many different chemicals. Attempting to relieve the pain from the sting by neutralizing it with an acid does not have much effect, as only a small number of the harmful compounds in the venom are alkaline.
One of the notable components of wasp venom is the alkaline form of phosphatase. Bee venom contains an acidic form of the same compound. Alkaline phosphatase is an enzyme that assists the other chemicals in venom in destroying cells, but neutralizing it alone does not stop the pain and inflammation caused by the sting.
Some of the other chemicals present in wasp venom include histame, which causes pain and inflammation, phospholipase A, which destroys cell membranes, and acetylcholine, a neurotransmitter that stimulates pain receptors. None of these are notably acidic or alkaline.