Description and life history
The hop aphid was first reported as a pest of Pacific Northwest hop fields in 1891. Hop aphids are small green (wingless forms) to black (some winged forms) soft bodied insects that suck plant juices. The hop aphid, as do many aphids, has a complicated life cycle. Two seasonal migrations, at least two different host plants, and several aphid forms are involved. Hop aphids overwinter as eggs on plants in the genus Prunus (the primary host). Prune trees are the preferred overwintering host, but peaches and cherry are also used.


The eggs hatch in late march, giving rise to female aphids called stem mothers. The stem mothers give birth to live, wingless females that feed on the overwintering host and give rise to several subsequent generations of similar aphids, before winged females (alatae) are produced. These winged females migrate to hop (the secondary host) plants in May through July. Once on hop plants, these winged females give live birth to wingless females that that feed on hop and reproduce, giving rise to several generations of wingless females. In August and September under the influence of shortening day length these females give birth to winged females that migrate back to the overwintering hosts. After arriving on the overwintering host, winged females give birth to egg laying females (oviparae). Two to three weeks later, winged male aphids produced by wingless females back on the hop plants, will begin arriving on the overwintering host and mate with the egg laying females. The fertilized female will lay the eggs, which survive the winter, around buds, bud scales, or cracks in the bark of twigs and shoots. (back to top)

Winged (top) and wingless (bottom) hop aphids

Damage to hop
Hop aphids can reduce plant productivity through the consumption of water, carbohydrates, and other nutrients transported in the phloem tissues on which they feed. The aphids also excrete a carbohydrate-rich substance known as honeydew. Honeydew serves as a good medium for the growth of sooty mold fungi, the presence of which on hop leaves further reduces the plant productivity. Sooty mold and aphids also contaminate hop cones reducing the quality of the harvested crop. Large infestations can render an entire crop unmarketable.


Hop cone on right has sooty mold damage
In contrast to spider mites, damaging populations of hop aphid are favored by cool, moist climates and are more likely to reach outbreak levels in the hop growing regions of Oregon and northern Idaho. However, if not properly managed, hop aphid is capable of causing serious damage to hops grown in any of the hop-producing regions of the U.S. Hop aphid is also implicated in the transmission of several viral diseases of hop. (back to top)

Hop Aphid Management
Management of hop aphid on hop has relied primarily on the application of appropriately timed pesticides. As is the case with spider mites, low numbers (50-100/leaf) of occurring on hop foliage early in the season can be tolerated. However, even low numbers of aphids in hop cones can result in significant economic loss, and cannot be tolerated after hop plants begin to flower. The reliance on chemical pesticides for control of hop aphid has resulted in a serious problem with the development of resistance to pesticides in European hop growing areas. To date resistance development in has not been a serious problem for U.S. hop producers.

Chemical treatment options are listed in the Pacific Northwest Insect Control Handbook. Because this information changes frequently be sure to check the latest edition of this book, which is available from the University of Idaho Resources for Idaho web page. Be sure to read, understand, and follow label directions. Whenever possible use compounds that are less, or non-toxic to natural enemies in hop fields.

Hop varieties and accessions showing moderate levels of resistance to hop aphid have been identified. To date however, no commercial hop varieties resistant to hop aphid are available for U.S. producers.

Hops have an abundant complement of predators and parasitoids that feed and develop on hop aphid. However, these natural enemies are rarely able to regulate hop aphid below levels that cause economic damage. Establishment of predators and parasitoids attacking hop aphid does not begin until after aphid migrants from overwintering hosts arrive in hops and begin reproducing. Unless climatic conditions are not favorable to reproduction and development, or unless pesticides are applied that limit early season population growth, hop aphid numbers nearly always exceed the regulating capacity of their natural enemies. Progress has been made toward integrating chemical and biological control through the use of systemic, soil applied insecticides that are less disruptive of natural enemy activities.