The body of the blackmargined aphid is usually yellowish, but it turns black when parasitized. This dark coloration is cause of confusion among some agricultural workers who think they are dealing with the black pecan aphid (Melanocallis caryaefoliae). Even an online extension publication of a university in the southwest shows a parasitized blackmargined aphid in lieu of a black pecan aphid. I know of several instances when insecticide applications were made attempting to control a "black pecan aphid infestation" when in reality, there was a high level of parasitism of blackmargined aphids.