During 1919–20 an investigation into the habits of A sterochiton (Aleurodes) vaporariorum, Westw., was being carried out at the Lea Valley Experimental Station, Cheshunt, with a view to controlling its attacks on tomatoes under glass. The station exists for the study of scientific problems connected with the glasshouse industry, and as the staff is small, the work is necessarily confined to strictly economic lines. Points that appear in the course of the investigations cannot be followed to their ultimate conclusion in these earlier years of the station's existence if they seem to be of theoretical rather than of practical importance. The following notes relate to such a problem, which it has been decided to record, though in a very unfinished state.