The photoperiodic responses of two clones of pea aphid,Acyrthosiphon pisum(Harris), collected on the same day in the same field are compared. The clones differ not only in the photoperiods at which sexuals first appear, but also in the rate of transition from production of one morph to another. When these clones are compared with other pea aphid clones for which data on production of sexuals are available in the literature, further differences in pattern of production of sexuals become apparent. These comparisons further emphasize the need to observe a sample of clones when attempting to describe any aspect of the species characteristics of aphids.