Insect of the Month - Willow Pine Cone Gall Midge

  Hort Snacks - November 2016
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 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 larvae hatch from the eggs and move to the developing branch tips or developing growing points (may be terminal or axillary growing points)
    • Larvae bore through base of the leaves into the cavity of the growing point
    • Feeding by larvae stimulates the formation of the hard, pine cone-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 don’t seriously harm the host
    • Higher levels of infection can reduce the aesthetic value and appearance of the tree
  • The galls represent shelter for a number of other insects
  • Conspicuous pine cone-like galls are prominently displayed on the tips of branches
  • Galls tend to be golf ball sized
  • Galls persist long after the insect matures and leaves
Willow branch with a Pine Cone Gall on the terminal bud
Willow Pine Cone Gall caused by a small midge
Taking apart the gall reveals a tiny white larva at the exact centre of the mass of woody "leaves" that comprise the gall
Tiny white larva in the centre of the gall
Photos by Robert Spencer

  • Galls can be removed from the plant by pruning when they are observed
    • Removal would have to be done on new galls in order to reduce populations, as older galls will be vacant
  • No other management is required
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on October 31, 2016.