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
Symptoms:
  • 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

Management:
  • 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.