Life history (Woolly aphid)

• The entire life cycle is passed on the host tree. Young aphids overwinter in sheltered positions such as in cracks or under loose bark. They are not covered with wool so are inconspicuous at this time.
• In March or April they become active and start to secrete wool from their wax glands.
• Breeding colonies are present by the end of May. In spring and early summer, colonies are found mainly on spurs and branches, especially round pruning wounds.
• Later, the infestations may spread to the young growth, particularly water shoots. They are found on the axils of leaves at first then spread out along the whole length of the shoot.
• A few winged aphids are produced in July and may fly off to infest other trees. Other winged aphids occur in September and produce egg-laying females.
• Although a single egg is produced by each female, there is no further development which can only occur on American Elm (Ulmus amiricana). Thus the life cycle consists essentially of wingless female aphids producing living young.
• Breeding slows down in the autumn and adult aphids die during winter.
• Depending on yearly temperatures, there are approximately 8-12 generations per year.