Concentration of oak aphids, Myzocallis spp., on irradiated white oaks

In two gradients of gamma irradiation at Brookhaven National Laboratory, white oaks exposed to 10–30 roentgens per 20-hour day are retarded in leafing out. From June 9 to 13, 1969, these oaks under radiation stress were colonized by alate aphids, 61±11 (mean ± Standard Error) Myzocallis tuberculata Richards 13±7 M. discolor (Monell) per 100 leaves. The alates were apparently attracted by the yellowish hue of the retarded foliage, and the initial concentration led to high aphid densities, 500–1600 per 100 leaves, during late June and early July.