Obviously, the genetic differences are sufficient to compel different behaviors, no matter what their similarities are.
The fact that they can be induced to breed under laboratory conditions does not negate the fact that they are two different species. Clearly, they are still fairly early in the speciation process. Since they do not naturally interbreed, eventually their genomes will drift far enough apart that interbreeding will become impossible even in lab conditions.
The head louse (Pediculus humanus capitis) is a persistent nuisance, clinging to and laying its eggs in the hair, digging its mouthparts into the scalp and feeding on blood several times a day. The body louse (Pediculus humanus humanus) tends to be larger than its cranial counterpart, and is a more dangerous parasite. It lays its eggs on clothing, takes bigger blood meals, and can transmit relapsing fever, trench fever and epidemic typhus to its human host.
How many physicians would recognize those diseases these days? Around here, most docs younger than 50 misdiagnose the occasional case of bubonic plague I just found the other info interesting and included it. Besides, who knew that lice were racists?
Before Kwell, the generally accepted topical treatment for lice was kerosene. I have no knowledge of its effectiveness. Or that of Kwell, for that matter.