I have read the same thing here and there, but there is no definitive proof inbreeding or genetics cause this. I think I saw once that someone mentioned they had some hisser adults that were significantly different in size, yet raised in the same container. That could be genetics, it could also be competition for food (less food would affect overall growth I would think) Still haven't seen any real experiments or results of those done to determine if this is something you could selectively breed or if it is a resource competition issue. Lot's of insects do vary in size in the wild even in the same species. I do suspect it is mainly a food source/climate issue, but that is only my belief. No scientific proof or research to back that up...