Biting Swarm damage is calculated at 1[W]+Wis. If you are using an xbow would that be 1[1d10+Dex]+Wis?
No. [W] refers to the weapon's damage die alone - i.e. 1d10 in this case. That power only deals 1d10 + Wis in damage.
Note that the Basic Ranged Attack's damage line is [W] + Dex. Your dex bonus is added as part of the Basic Ranged Attack, not as part of your weapon's damage die.