Observations on green pupae in Papilio machaon L. and Pieris brassicae L.

Observations have been made and experiments performed to investigate the colour of pupae inPapilio machaon L. andPieris brassicae L.InP. machaon brown pupae are nearly always formed except when the pupation site is the foodplant, when nearly half the pupae are green. Switching experiments showed that the sensitive period was just before pupation and that the colour and texture of round foodplant stalks had a significant influence in producing green pupae.In the Cambridge stock ofP. brassicae used all non-diapause pupae are "brown" (including yellowish, ochreous, greyish forms), all diapausing pupae green. The background on which pupation occurred had no significance, nor did the photoperiod immediately preceeding pupation.The colour could, however, be changed by the food used; on artificial diet the pupae are blue or turquoise. This effect could not be reversed by the addition ofβ-carotene to the diet, as might be expected. Attention is also drawn to the fact that at least one pupal colour is known to be genetic, and the possibility that the green/brown relationship with diapause in the CambridgeP. brassicae stock may be due to the rearing conditions used.