bugs!

I stacked my wood on pallets which are on top of 4x6pt to keep it off the ground. Checked on it yesterday and I have termites in the bottom pieces of the stack along with tons of ants. Should I be expecting this? Should I place a tarp between the ground and the 4x6?

First, are the 4 x 6's treated lumber? If you have termites in your woodstack, you may also want to have your home inspected for them. Those buggers are destructive. Is your area prone to termite infestation? If so, you may want to consider pouring a cement pad and using pressure treated wood to keep your stack elevated. Termites live in the ground and need a path to get to the wood they are destroying. They will not get into pressure treated wood. You will want to get this taken care of as soon as you can, before it turns into a major problem. As for the ants, they are attracted to wet wood. Is there alot of moisture present in your woodstack? Is there rotten or punky wood in the stack?

the 4x6's are treated and the wood oak which is still wet from being cut and stacked in the spring.
I have the stack a couple hundred feet from my home to keep from attracting the bugs.
Should I take the stacks apart and restack them on a barrier?

What part of the country are you in (didn't see a location in your profile)? If you are in a moderate climate zone, I would definitely do something. That's just my opinion. Get the infested wood out of your area, put down a treatment and some rubber roofing or other temporary barrier, re-stack the wood and then monitor the wood for activity. If it continues, I would consider a permanent solution, like a pad or a raised shed or something.

The termites might not eat the PT but they will build mud tunnels over the top of it.
If the stack is wet they won't have to return to the ground.

Before restacking it, I'd get some ground treatment soultion, Ive found the Bayer advanced Carpenter ant/termite killer works well mix in 5gal bucket as prescribed and pour around the pile.
If your in a cold enough climate they'll leave and return to the ground and the barrier treatment will keep them from returning.

There are better chemicals that will kill the colony(Termidor) and are relatively comparative in price.

Would a plastic ground cover help?

+1
Bugs eating my hard work would mean "war".
Gravel &/or some landscape cloth under the treated wood may help too.

Yes, and the landscape cloth would allow drainage.

I doubt it.