Chromosome Comparisons of Biotypes of Schizaphis graminum to One Another and to Rhopalosiphum maidis, R. padi, and Sipha flava1, 2

Aceto-orcein-stained squashes of young embryos of the greenbug, Schizaphis graminum (Rondani), proved to be an expedient staining technique for aphid chromosome studies. Embryos averaging about 0.25 mm long provided the best material for study and were found in the greatest quantities from 5-day-old aphids reared at 24°C. Comparison of chromosome sets of 3 biotypes of the greenbug with one another and to those of the corn leaf aphid, Rhopalosiphum maidis (Fitch); the oat bird-cherry aphid, R. padi (L.); and the yellow sugarcane aphid, Sipha flava (Forbes); revealed a different karotype for each genus studied. Total chromosome length comparisons indicated that Biotype A differed statistically from B and C, but Biotypes B and C did not differ. Corn leaf aphid chromosome lengths were significantly different from those of all other aphids studied. Both the oat birdcherry aphid and yellow sugarcane aphid were significantly different from the corn leaf aphid and Biotype C greenbug. The analysis of total chromosome lengths proved unreliable for comparing species with different karyotypes.