Citrus Gall Wasp

picture by Elaine Shallue.SGA

Latest Update 13th April 2020.

Citrus Gall Wasp

•  I don't have citrus gall wasps in my garden, at least not yet.
• They are native to Queensland in Australia and have been migrating southward for many years.
• They have become a significant pest in Melbourne, but I have been lucky so far and they have not yet infested my plants.
• Gall wasps are very small, only about 3mm in their adult form.
• Their larvae feed on the soft tissue and sap inside the branches of citrus trees.
• To achieve this the adult wasps mate in spring and the female inserts her fertilised eggs into the tissue of the sappy young stems of citrus trees. All citrus are affected, but grapefruits and lemons are especially vulnerable.
• When the wasps eggs hatch, the larvae begin to feed inside the young stems of the tree, and in late summer, the tree responds by developing hard swellings (galls) around the infested sites. Each gall contains many wasp larvae
• The juvenile wasps pupate over winter inside the galls, and emerge in the following spring as adult wasps to complete the cycle.
• They are poor fliers and are likely to reinfest the same tree in which they were gestated, but they can be blown by the wind to infect plants further away.

Details

• Binomial name:                                     Bruchophagus fellis.
• Family:                                                 Eurytomidae.

Why Citrus Gall Wasps are pests. 

• Each gall is home to many juvenile wasps, and when they emerge, they have the potential to reinfest the tree with many more galls the following year.  
• If uncontrolled, they can infest the whole tree deforming it and reducing its vigour.

Pest Control

• The gall provides very effective protection for the juvenile wasps against synthetic and organic pesticides. The only effective measure against them is to remove the gall and dispose of it in a sealed plastic bag in the garbage bin before the adult wasps emerge.
• Small holes in galls are a sign the wasps have emerged from their winter home. If the galls are intact and have no holes, the pupating wasp is still inside.
• Unfortunately, early removal of galls may conflict with harvesting fruit growing on the branch affected.
• Some fruit loss may be necessary, but if you can keep the number of infestations under control, fruit losses may not be significant.
• The use of chemical fertilisers, especially ones containing lots of nitrogen will result in rapid growth of sappy branches which are particularly vulnerable to the female wasp's ovipositor. Home made compost and compost tea, which toughen the plant's tissue could be a significant deterrent, and could be the reason I have been unaffected so far.