EXCLUSIVE

America's obsession with hillbillies is spilling over into the adult industry in a BIG WAY ... because sales of redneck-themed porn has nearly TRIPLED in the last two years ... TMZ has learned.

The toothless, backwoods, yokel formula has already proven to be a recipe for success in reality TV -- spawning hits like "Honey Boo Boo," "Duck Dynasty" and "Swamp People" ... in fact, MTV has already announced plans for an upcoming hillbillly-themed reality show.

Now, one of the biggest websites in porn is also recording record sales in the hillbilly/redneck genre (there's a XXX genre for everything) ... and it credits the boom in sales to the bumpkins on the "mainstream" side of the things.

TMZ spoke with a rep for GameLink.com, who tells us the company has seen a 250% increase in Southern, white-trashy porn titles since 2010 ... when the redneck reality shows began to take off.

In fact, we're told prior to the release of the reality shows, hillbilly porn was one of the site's worst-sellers. But now, Southern-themed titles like "Hillbilly Honeys," "Real White Trash" and "Ozark Sex Fiend" are RISING AGAIN ... with no signs of slowing down.