It's worth noting that many citrus relatives can also host HLB/psyllids, including atalantia/severinia, murraya (box orange), and zanthoxylum (hercules club, prickly ash, szechuan/sancho/sansho peppercorn).
That zanthoxylum is in the list suggests there may not be a useful northern limit to HLB, because zanthoxylum is present into Ontario. It's hardier than poncirus.