Myzus persicae, known as the green peach aphid, greenfly, or the peach-potato aphid, is a small green aphid belonging to the order Hemiptera. It is the most significant aphid pest of peach trees, causing decreased growth, shrivelling of the leaves and the death of various tissues. It also acts as a vector for the transport of plant viruses such as cucumber mosaic virus (CMV), potato virus Y (PVY) and tobacco etch virus (TEV). Potato virus Y and potato leafroll virus can be passed to members of the nightshade/potato family (Solanaceae), and various mosaic viruses to many other food crops.

Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A typical life cycle involves flightless females giving live birth to female nymphs—who may also be already pregnant, an adaptation scientists call telescoping generations—without the involvement of males. Maturing rapidly, females breed profusely so that the number of these insects multiplies quickly. Winged females may develop later in the season, allowing the insects to colonize new plants. In temperate regions, a phase of sexual reproduction occurs in the autumn, with the insects often overwintering as eggs.