Eriosoma americanum

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Superorder	Paraneoptera
Order	Hemiptera
Suborder	Sternorrhyncha
Infraorder	Aphidomorpha
Superfamily	Aphidoidea
Family	Aphididae
Subfamily	Eriosomatinae
Genus	Eriosoma

Scientific Name

Eriosoma americanum

Common Name

woolly elm aphid

Authors: Erica Reid and Laura Timms, Faculty of Forestry, University of Toronto

Identification

The woolly elm aphid (Eriosoma americanum), is a member of the Eriosomatinae (woolly aphid) sub-family. It takes on various appearances depending on its host and its life stage. In its most damaging stage, it is found on Saskatoon roots, and has a pale blue to black wingless body, with a white woolly, waxy coating on the thorax . While occupying American elm, it is wingless with a red-orange body and can be found on the underside of the leaf, often accompanied by small white sticky ‘bubbles’ and/or a white cottony mass . Lastly, in its winged stage it is dark blue to black with clear, black-veined wings .

Hosts

The woolly elm aphid has two primary hosts, on which it feeds at different times of the year. It is specific to the Saskatoon (Amelanchier alnifolia) in late spring through fall, and the American elm (Ulmus americana) during both early spring and late fall .

Geographic Distribution

The woolly elm aphid is a species native to North America, and it can be found wherever both Saskatoon and American elm are established .

Symptoms

Symptoms vary depending on the host. In early May until mid-July, many young aphids (200-1000) can be observed in cottony masses on the underside of distorted American elm leaves . Between July and October, it feeds on the roots of Saskatoon, resulting in above and below ground symptoms . Above ground symptoms include: branch mortality, minimal or entirely lacking spring foliage, discolouration of leaves, and/or early defoliation . Below the ground, blue-white woolly or waxy masses on the roots and or blue-purple soil discolouration can be observed . Unfortunately, symptoms of Saskatoon infestations are sometimes only observable next spring, so it may be too late to take preventative measures .

Damage

The above symptoms are a result of the sucking of sap from the American elm leaves and Saskatoon roots by both the nymphs (juveniles) and adult aphids . Damage to elms is minimal, with a slight decrease in the ability to photosynthesize . However, damage is more severe in Saskatoons, especially young plants, and can lead to stunted growth, minimal berry production and/or mortality . Additionally, while occupying American elm woolly elm aphid excretes honeydew, which is a sticky substance that drops from the leaves coating anything below . While it is harmless to the leaves and vegetation below, honeydew can be a nuisance as it is difficult to remove from property (i.e. cars, lawn furniture) .

Life Cycle

There are multiple generations per year. In early May, female nymphs hatch from eggs that have overwintered on American elm bark and travel to new elm foliage to feed and mature . Once matured they asexually produce a second female generation, which develops wings and flies to its second host, the Saskatoon, in late June. When a Saskatoon has been located, these winged adults asexually produce a second generation of young (>20 individuals) on the underside of the leaves. This generation travels to the roots of the Saskatoon, where they form a large colony through repetitive asexual reproduction . In late August to early September, mature adults develop wings and travel back up to the surface of the soil. They then fly back to American elm trees, where they asexually produce a sexual generation . This generation - the only stage where males and sexual reproduction are present - quickly matures and reproduces. Females lay a single egg which will overwinter, thus completing the life cycle .

Control and Management

As previously mentioned, damage to American elm is minimal and only aesthetic, so infestation control is not essential to protect the health of the tree. On Saskatoons, infestations can be monitored by using yellow sticky traps at the base of the plants to captures aphids migrating to the roots, and/or by digging into the soil near the roots (>10cm deep) which can reveal the characteristic blue-purple soil discolouration associated with infestations. If an established infestation on Saskatoons has been located, there are measures that can be taken to mitigate damage.

Chemical Control The use of chemical insecticides can control woolly elm aphid infestations on Saskatoons and American elm . For Saskatoons, post-berry harvest is the best time for application as no residues will be left on the berries. The roots are protected for twelve months, preventing infestations the following spring . One example is Orthene, which is applied to the soil surrounding young non-fruit-bearing plants. The use of pesticides on fruit-bearing Saskatoons is currently prohibited . Pesticides such as Diazinon, insecticidal soap, and Malathion can be applied to elm leaves in two phases, once before budding and then once again 10-14 days later . Whenever choosing a pesticide to control a pest, consult your local extension office or department of agriculture for the most up to date and accurate recommendations for your area.

Biological Control The utilization of biological agents to control woolly elm aphid is still relatively underdeveloped, however, there is some evidence that fungi and nematodes have the potential to mitigate infestations in both the crown and roots of Saskatoons . Additionally, natural aphid predators such as parasitic wasps, lady beetles, lacewings and hoverflies can help control outbreaks .

Spatial Control Unfortunately, due to their ability to travel far distances in search of their hosts, removal of elm trees in close the proximity to Saskatoons is not sufficient in preventing infestations .

Image Gallery

Infested American elm leaf

More images:

Nymphs and adult producing honeydew while occupying American elm

Winged adult aphid

Root infested with woolly elm aphids

Life cycle of the woolly elm aphid

Stunted growth of young Saskatoon, due to infestation