The green-veined white butterfly, P. napi (Lepidoptera: Pieridae) is a polyandrous temperate species, that has an extensive distribution across Asia, Europe, North America and North Africa. Diapause occurs in the pupal stage and the diapausing pupa eclose as adults in the spring ( Henriksen and Kreutzer, 1982). P. napi is, generally, bi- or-multivoltine in the southern parts of its distribution and monovoltine in the north. Ten female butterflies were collected from the area surrounding Stockholm University on 12th June 2009 and placed in a rearing cage