"Only two species of s of world-wide distribution are at present known which commonly attack the in numbers sufficient to cause serious injury directly due to their feeding operations. These are are the "potato aphid" (' ) and the "green peach aphid" or "spinach aphid" (' ). A third species, apparently also of world-wide distribution, is often present on the potato, frequenting especially the underside of the lower leaves. This is the "buckthorn aphid" (' Patch); which may, under certain conditions, sometimes cause infestations of a serious nature. All three of these species have been proved to be capable of spreading certain s under experimental conditions; and there can be no logical doubt that they function in the same way in the field. Wherever potatoes are grown for seed purposes these three species of aphids may need to be reckoned with."