The unknown Wraith beam has only been seen being used once. Major John Sheppard observed it when the Wraith were culling Orin's planet. Just after a dart was seen using its culling beam after it flew over an area a beam formed and started to go up into the sky. The purpose of this beam is unknown. Maybe it's a kind collection beam, so the collected Humans are transported from the darts to the hive. Though seeing as it was on throughout the rest of the culling after it was activated and caused no apparent damage it is most likely not a weapon. (SGA: "Letters from Pegasus")
beam fully formed