The production of sexual morphs by the greenbug,Schizaphis graminum(Rondani), in response to long scotophases was studied using eight clones of the aphid from one locality in California, one clone from Nebraska (biotype E), and one from Oklahoma (biotype C). The temporal and quantitative differences found in the polymorphism of these clones confirmed that considerable variability in biological traits exists between aphids from local as well as regional populations. The groupings to which the clones could be assigned on the basis of their photoperiodic responses differed from previous groupings based on performance of the clones on different varieties of sorghum.