are small insects, Phorodon humuli (Schrank), also known as the Damson-hop aphid, which can have a devastating effect on the hop plant resulting in substantial yield decline and a reduction in cone quality. This is one of the dominant hop pests in the Northern Hemisphere and its impact on a hop yard can result in significant yield loss up to complete devastation of a crop. The aphid overwinters as eggs attached to various Prunus species (i.e., sloe, plum, cherry plum, damson), and in early April, wingless female insects hatch and give birth to an average of four more generations of wingless female aphids. After several generations, winged female arise and migrate to the hop plant when the weather warms above a flight temperature threshold (when minimum daytime temperature is greater than 13°C). They reproduce on the hop leaves and feed on the sap in the phloem strands in the hop leaves, thereby weakening the hop plant and in some cases causing defoliation. Toward the end of August, they migrate back to the Prunus winter host, mate, and lay eggs on or near the buds of the host plant, and these will hatch the following spring. The aphid causes yield declines when high numbers of aphids feed on plant sap during the growing season. Much of the economic damage, however, occurs late in the summer when the aphids enter the hop cone to feed since they are protected from insecticides and can cause heavy damage to the cone. Heavily infected cones appear brown and are prone to shatter during picking and drying. The excreted honeydew from aphid infestation can serve as a medium for sooty mold fungi on hop leaves and cones, and in instances with high levels of mold the hop cones are unmarketable. Furthermore, several viruses can be transmitted by these aphids, including Hop mosaic virus and American hop latent virus, and these may also negatively impact plant health. Control of aphids is often carried out using organophosphates, carbamates, endosulfan, and/or pyrethroid sprays. However, because some of these have been used exclusively for long periods, the Damson-hop aphid has developed resistance to many of these compounds. Use of natural enemies such as ladybird beetles (Coccinellidae), anthocorids, and lacewing and hoverfly larvae has been used successfully by hop growers, provided environmental conditions are more favorable for the predators than for the aphids.