Spruce Gall Adelgids

Causal Organisms: Adelges cooleyi (Cooley spruce gall adelgid) or other Adelges species (A. lariciatus – Spruce gall adelgid; A. strobilobius – pale spruce gall adelgid) – depending on region

NOTE: There are other species of adelgids that affect other host species

Crops Affected: Spruce, Douglas fir, Larch/Tamarack, depending on species

Life Cycle:

• Aphid-like insects
  • Adelgids are related to aphids, and resemble aphids in many ways, however:
    • They do not have any tail-like appendages (called a cauda)
    • They do not have any “tail-pipes”, known as cornicles
    • Unlike aphids, they do not give birth to live nymphs, only laying eggs
  • Adelgids have a 2-year life cycle
  • Some species alternate between hosts
    • The Cooley spruce gall adelgid (CSGA) alternates between Douglas fir and Spruce
      • In areas where there are no native Douglas firs, the adelgids can complete their life cycle entirely on Spruce
    • The Spruce gall adelgid or Pale Spruce gall adelgid may alternate between Larch/Tamarack and Spruce
  • 1^st Year
    • Winged females move from Douglas fir in summer to Spruce trees to lay eggs
      • Adelgids generally reproduce via parthenogenesis, which is a type of asexual reproduction, which does not require fertilization, however, CSGA does produce males at specific points of their life cycle
      • Eggs hatch into wingless male and female insects, which mate
      • These mated females lay a single egg on the Spruce
      • Nymphs (immature) emerge to feed on Spruce needles, moving to just below the buds at the tips of stems towards the end of the season
        • Nymphs (immature) overwinter
      • 2^nd Year
        • The overwintered nymphs (immature) develop into parthenogenetic adult females
          • These females lay up to 200 eggs
            • Nymphs emerge to feed in the new growth on the buds, which results in gall formation
              • Saliva from feeding causes cell formation, which is what causes gall formation
            • Nymphs feed and develop within the galls
          • Winged parthenogenetic females emerge from the galls to migrate to Douglas fir trees to lay eggs
            • Emerging nymphs overwinter in the foliage of the Douglas fir
          • In the spring, the nymphs develop into either winged or wingless forms, which restarts the cycle
          • Damage to host trees is generally considered cosmetic, rather than damaging

Symptoms:

• Galls are visible on the new growth of trees, although early galls tend to be less conspicuous than mature galls
• The appearance of galls varies with the pest species and the age of the gall
  • Early galls of most species are somewhat reddish-purple, with needles protruding beyond the swollen tissues
  • Early galls of the CSGA are typically 4-6 cm (2-3 inches) in length
  • Early galls of other species are typically shorter (approx. 2-4 cm or 1 inch) in length and resemble a pineapple
    • Galls of other species may have a portion of the stem extending beyond the gall
  • Opening a younger gall will reveal adelgid nymphs and eggs surrounded by a cottony, white material
• Galls may be more frequent on shaded sides of trees

Management:

• The application of registered chemical controls must be extremely specific in terms of timing, to target nymphs prior to entering galls
• Removal of galls will not provide complete control, but may decrease the population somewhat
  • This is impractical on all but smaller trees
• Infestations tend to be very cyclic, with populations controlled or reduced naturally over time
• It is possible that higher pressure applications of water might dislodge and disrupt any nymphs that are present outside of the galls

Spruce Gall Adelgid gall that has been opened – note cavities where nymphs are present