In 1945 Kutter only found a queen on her mating flight and didn't know its host-species. In 1950 and 1967 he discovered and confirmed that the host was L. acervorum.

My mistake about the host stems from Kutter's 1968/9 booklet about the social parasitic ants. On page 54, that you mention, and 55 he only mentions Leptothorax queens and workers and, for the correct host, he says on page 52 and 60 L. acervorum. BUT on page 51, he mentions as host for L. pacis the species T. tuberum, probably an overseen error that I copied for my earlier post. I should have known that that was an error (knowing the other publications.) but didn't pay notice to it.

In his "Liste sozialparasitischer Ameisen" from 1967 he also mentions as host L. acervorum.

All subsequent authors and publications have L. acervorum as host for L. pacis.

Thank you for correcting my error!