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Phyllaphis fagi

Woolly beech leaf aphids, Phyllaphis fagi, viewed on fern leaved European beech (Fagus sylvatica 'Asplenifolia') on 6/1/21 in Amherst, MA. Photo: Tawny Simisky, UMass Extension.
Scientific Name: 
Phyllaphis fagi
Common Name: 
Woolly Beech Leaf Aphid
Growing Degree Days (GDD's): 
150-707 GDD's, Base 50F, March 1st Start Date (Source: Robert Childs, UMass Extension.)
Host Plant(s) Common Name (Scientific Name): 
Beech (Fagus spp.) *European beech cultivars only. Does not infest American beech.
European beech (Fagus sylvatica)
Fastigiate beech (Fagus sylvatica 'Fastigiata')
Fern-leaved beech (Fagus sylvatica 'Asplenifolia')
Tricolor beech (Fagus sylvatica 'Roseomarginata')
Weeping purple European beech (Fagus sylvatica 'Purpurea-Pendula')
Insect Description: 

The woolly beech leaf aphid is a highly noticeable but typically not a damaging insect pest of European beech (Fagus sylvatica) and its cultivars. This piercing-sucking insect pest will not feed on American beech. It is often referred to as the woolly beech leaf aphid as the undersides of the host plant leaves are where they are most likely to be found. However, they may feed on host plant leaf petioles, fruit, and fruit stems. This species of aphid is gregarious, and often large groups of them are found on host plant leaf undersides along with large numbers of cast skins (shed exoskeletons following the molting of the insect). The woolly beech leaf aphid is "woolly" because of waxy, white filaments that cover the body - giving the aphids or any surface they coat a white appearance. The woolly beech leaf aphid is widely distributed in North America and found throughout the Northeast (essentially wherever European beech and its cultivars are grown.) These insects overwinter in the egg life stage tucked in bark crevices and near buds. Eggs hatch when spring temperatures warm, often near budbreak. Wingless viviparae (parthenogenetic females that give birth to live young) are pale green and covered with white, waxy wool. Wingless individuals are usually 2.0-3.2 mm long. Winged viviparae (parthenogenetic females that give birth to live young) are dark in color and densely coated in white, waxy wool. Multiple generations per year are possible, and in Europe at least 10 generations per year have been reported, with peak activity by mid-June (Iversen & Harding, 2007). As the insects feed on the host plant leaf undersides, they excrete large amounts of a liquid sugary waste product, known as honeydew. Honeydew can be attractive to stinging insects such as ants, bees, and wasps but also a growing place for fungi such as sooty mold. Sooty mold is often black in color and feeds not on the tree itself, but on the honeydew. The woolly beech leaf aphid is native to Europe, and has been introduced to North America, New Zealand, Australia, China, and Korea. Do not confuse this species of aphid with Grylloprociphilus imbricator (the beech blight aphid). The beech blight aphid is only found on the stems of American beech and is sometimes called the "boogie woogie aphid", owing to the fact that when disturbed, G. imbricator will "dance" and wave their rear ends back and forth in a most entertaining unison.

Damage to Host: 

The woolly beech leaf aphid primarily feeds on the undersides of host plants leaves. Feeding with piercing-sucking mouthparts removes host plant fluids, causing either side of the leaf to turn downward on either side of the midvein, almost creating a pseudo-gall around the insects.  This aphid species creates much honeydew and sooty mold. Huge populations in consecutive years cause little damage to their host plants found in the Northeastern United States, and as such chemical management options for this insect are seldom warranted. In Europe, the host plants are reportedly more severely impacted by woolly beech leaf aphid feeding. 

Monitoring: 

Monitor for the overwintering eggs on twigs near host plant buds, in particular in bark crevices within forked shoots (Kot and Kmiec, 2012). Aphids or cast skins can be monitored for on host plant leaf undersides. Peak activity of this insect may be seen by approximately mid-June.

Cultural Management: 

Syringing aphids (spraying the infested leaves with a strong stream of water from a hose) has often been suggested as a cultural/mechanical management option for these soft-bodied insect pests. This may help reduce their population without the use of insecticides, which could have negative impacts on the natural enemies that often suppress woolly beech leaf aphid populations naturally. Proper planting, site selection, and tree maintenance also help reduce additional host plant stress which can be beneficial when managing insect pests of trees and shrubs.

Natural Enemies & Biological Control: 

In Europe, a species of syrphid fly (Melangyna cincta) is a specialist predator of woolly beech leaf aphids, along with a mirid bug predator (Psallus varians) (Gilbert, 2005). The braconid wasp parasitoids Praon flavinode and Trioxys phyllaphidis are known to parasitize woolly beech leaf aphids in Europe, but are not currently reported from North America. In North America, natural enemies such as lady beetles and others are likely also feeding on woolly beech leaf aphid populations. 

Chemical Management: 

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (eggs) (NL)

Beauveria bassiana (NL)

Bifenthrin (NL)

Carbaryl (L)

Chlorantraniliprole (NL)

Chlorpyrifos (N)

Chromobacterium subtsugae (NL)

Clothianidin (NL)

Cyantraniliprole (NL)

Cyfluthrin (NL)

Cypermethrin (NL)

Dinotefuran (NL)

Emamectin benzoate (L)

Fenpropathrin (NL)

Flonicamid+cyclaniliprole (N)

Tau-fluvalinate (NL)

Gamma-cyhalothrin (L)

Horticultural oil (L)

Imidacloprid (L)

Insecticidal soap (NL)

Isaria (paecilomyces) fumosoroseus (NL)

Lambda-cyhalothrin (L)

Malathion (L)

Neem oil (NL)

Permethrin (L)

Pymetrozine (NL)

Pyrethrins+piperonyl butoxide (L)

Pyrethrin+sulfur (NL)

Pyriproxyfen (L)

Spinetoram+sulfoxaflor (N)

Notes: 

Active ingredients that may be applied systemically include: Abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (eggs) (injection, soil drench), chlorantraniliprole (soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), emamectin benzoate (injection), imidacloprid (soil drench), and neem oil (soil drench).

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations.