Willow Pine Cone Gall Midge

Causal Organism: Rabdophaga strobiloides

Crops Affected: willow species

Life Cycle:

• Single generation per year
• Insect is a midge, which is a small, two-winged fly
• Adults emerge in the spring as the leaves are starting to flush
  • They mate and the females lay eggs singly on young leaves
• Light orange-coloured larvae hatch from the eggs and move to the developing branch tips or developing growing points (these may be terminal [end] or axillary [side branch] growing points)
  • Larvae bore through the base of the leaves into the cavity of the growing point
  • Feeding by the larvae stimulates the formation of the hard, pinecone-like, gall
  • Larvae remain inside the gall until they reach maturity in late September
    • It is possible that the larvae will overwinter inside the gall
  • Damage by the insect is not significant and does not seriously harm the host
    • Higher levels of infection can reduce the aesthetic value and appearance of the tree
  • The galls represent shelter for other insects

Symptoms:

• Conspicuous pine cone-like galls are prominently displayed on the tips of branches, or at a side branch junction of a branch
• The galls tend to be golf ball-sized
• Galls persist long after the insect matures and leaves

Management:

• Galls can be removed from the plant by pruning when they are observed
  • To reduce insect pest populations, the removal would have to be done on new galls, as older galls will be vacant
• No other management is required

Willow branch with a Pine Cone Gall on the terminal bud