The emerald ash borer, an invasive insect that has beleaguered 18 other states including Massachusetts and Connecticut, might now be in New Hampshire. State entomologist Piera Siegert said Friday that a tree in the Concord-area is showing signs of stress indicative of the beetle’s presence. She also discovered what she believes is ash borer larvae, but a federal specialist must confirm her findings. The emerald ash borer, originally from China, has killed millions of ash trees nationwide since being discovered in Michigan in 2002. It’s often spread by people transporting firewood. If the beetle’s presence is confirmed, limits may be placed on the removal of ash logs and firewood from a designated area.