Can I be sued if my 18 year old son causes a wreck and his vehicle is in his own name but he is covered under my insurance policy?

What you seem to be describing is the legal theory of "negligent entrustment."  This theory states that the owner of a vehicle may be liable if he/she entrusts their vehicle to someone who may be deemed to be an irresponsible or incompetent driver.  However, since your son was the title owner of the vehicle, then you did not "entrust" the vehicle to him.  The fact that he is on your insurance is irrelevant and is not a legal basis for a claim of negligent entrustment.