Fruit IPM Fact Sheet Fruit IPM Fact Sheet
Woolly Apple Aphid
Scientific Name – Eriosoma Lanigerum (Hausmann)
Family – Aphidae
Life Stages
Egg: The cinnamon-colored eggs are oval and measure 0.6 mm by 0.3 mm.
Nymph: The five instars include the adult. The nymphs are reddish brown and covered by a woolly mass of long, waxy fibers.
Adult: The adults are purplish and nearly covered by a woolly mass of long, waxy fibers. The waxy fibers are much shorter on the root-inhabiting forms and give them a whitish, mealy appearance. The males, which are about half the size of the females, are olive-yellow.
Host Range
The woolly apple aphid is a pest of apple, pear, hawthorn, mountain ash and elm. It is
present in all apple-growing areas of the United States and Canada.
Injury or Damage
White, cottony masses cover purplish aphids clustered in wounds on the trunk and
branches of the tree or on large knots on the roots and underground parts of the trunk.
Infested trees will often have many short, fibrous roots. Aboveground colonies develop
around leaf axils on sprouts or on new growth, particularly at abrasions or cuts. They
prevent injured bark of a tree just above the roots; they cause the roots to decay.
The underground aphids do the damage; the ones aboveground cause little damage, especially on larger trees. The injury consists of gall-like formations on the branches and swollen enlargements on the roots. These increase in size from year to year because of the feeding of the aphids. Such galls can form favorable places for fungi to attack. The foliage of infested trees takes on a yellowish appearance. Infested young trees are easily uprooted.
Woolly apple aphids can also transmit apple canker (Pezicula malicorticis)
Factors Affecting Abundance
Woolly apple aphid is generally not a problem in commercial orchards unless
pyrethroids or carbamate insecticides are used repeatedly. These types of insecticides are
very toxic to wasp parasitoids (especially Aphelinus mali) that normally keep aphid
populations under control. Some varieties, such as Northern Spy, are resistant to this
pest. Elm trees in the vicinity of orchards increase the migration of the aphid to apple
trees. The insect is spread by infested nursery stock.
Life History
The aphid spends the winter either in the egg stage or as an immature nymph. The
nymphs hibernate underground on apple roots if elm trees are not nearby. The females lay
eggs in cracks or crevices of elm tree bark in the fall. The eggs hatch in the spring into
wingless, parthenogenetic, viviparous stem mothers. These feed on elm buds and leaves for
two generations during May and June, causing the elm leaves to curl into rosettes. They
then produce a third generation winged form that migrates to apple, hawthorn or mountain
ash. The aphids establish new colonies here, and repeated generations are produced during
the summer. They feed in wounds on the trunk and branches of the tree.
In the fall, winged aphids develop in both the aeril and root colonies. They fly back to elm, where they give birth to males and females. Both males and females are wingless, have no mouthparts and do not grown after birth. A few days after mating, the female lays a single long, dark, oval, cinnamon-colored egg almost as large as her body in a crevice of the bark. These winter eggs hatch in early spring into wingless aphids.
Because of the virtual disappearance of American elm trees, the woolly apple aphid most often lives on apple trees throughout the year. Each group of aphids, small or large, is considered a colony. Aphids are present more nearly year round on the roots than on the tops. The aerial forms are most commonly found on the twigs, water sprouts and callus tissue in wounds, cankers and scars. Wingless females in the aerial colonies may give birth to nymphs at any times in spring, summer or fall. Newborn nymphs are very important in the spread of the woolly apple aphid. They spread either through some mechanical agency or directly by crawling. Birds and insects can also transport aphids.
Any unsettling conditions will produce crawlers, though they are generally more abundant in spring and fall. Crawlers cannot work into and through the soil. In orchards, the swaying of trees in the wind, and organic matter, clods, stones and other objects may provide pathways to the roots. Crawlers begin to infest the roots early in the season. The downward movement can begin at any time when the crawlers are numerous, especially in early summer and fall. Infestations by aerial colonies are not true indications of root infestations over a season without the roots becoming infested.
Monitoring
In the petal-fall/first-cover period, examine abrasions or cuts, particularly on
sprouts or on new growth, for white cottony masses covering colonies of woolly apple
aphids. If numbers warrant treatment, spray during the early season before migration to
the roots occurs.
Control
Some pesticides, such as pyrethroids and carbamates, encourage outbreaks. These should
be used sparingly or be combined with a n aphicide. An application of a summer aphicide
will control woolly apple aphids in tree tops. No control methods for underground aphids
are available.
