Citrus gall wasp endangers productivity in gardens as well as in commercial orchards, especially in Western1 and South Australia2. So recognizing and controlling it are important tasks since it spreads easily.

What are they?

Many of our more persistent garden pests are not native to Australia but citrus gall wasp is definitely an Aussie grown garden variety pest. Originally, this native wasp was limited to Queensland and northern New South Wales and its preferred host was native finger limes.  But citrus gall wasp Bruchophagus fellis has rapidly adapted to the wider variety of citrus fruits now on offer.  Since the 1990’s it has successfully migrated from Queensland, through NSW and can now be found as far south as Melbourne where it is virtually endemic in the iconic back yard lemon tree.

Plants affected

All citrus especially lemons and grapefruit.

Damage Caused

The wasp larvae grow within the citrus stems until late summer when gardeners start to notice unsightly galls appearing on their trees.  These galls or calluses are formed in response to the presence of the feeding larvae. Galls cannot be ‘cured’ or reversed.  Old galls are unsightly but are also empty as the adult wasp will have left through the tiny exit holes.  Developing galls can be removed but this may also mean the loss of developing fruit at the end of the infected stem. Citrus gall is more damaging to younger citrus trees than older trees.

Control Methods

Controlling citrus gall wasp can be difficult but damage can be minimised by:

  • Avoiding high nitrogen fertiliser in spring as this promotes soft sappy growth – just perfect for the egg laying stage.  Feed trees in late autumn and early winter instead.
  • Removing all newly formed galls that don’t show signs of exit holes before mid-winter – “Prune in June”.  Old galls have already been exited.  Prune only a maximum of 1/3 of the tree to avoid stressing it too much.
  • Preventing the wasps from maturing within galls that don’t show exit holes in winter by slicing off part of the gall on one side.  Don’t slice all around the surface of the gall as this will ringbark the branch.
  • From mid-August, hanging yellow sticky traps with a chemical attractant inside to trap emerging adult wasps. The yellow is an attractant and the sticky coating makes it impossible for the wasp to escape.  Remember to twist the top so that the chemical is released. Since beneficial insects may also be attracted to this trap, do not leave on after November as the wasps are no longer about and even small birds may become trapped.
  • Destroying infected stems by burning or bagging.




Pic 1, 2 & 3: Elaine Shallue, SGA