Citrus Gall Wasp (Bruchophagus fellis) is an insect native to the coastal regions of south-east Queensland and north-eastern New South Wales. Its native host is the Australian Finger Lime, Citrus australasica.
Over the last century it has taken a liking to cultivated citrus and has spread well out of its native range. It is now found across southern Australia, all the way into south-west Western Australia.
The Citrus Gall Wasp itself is a tiny insect that is not usually seen. What you will see are the woody galls that grow in response to the feeding of Citrus Gall Wasp larvae.
Prevention is always better than cure, and you are more likely to be able to achieve that if you are out and about in your garden regularly (see How to Prevent Citrus Gall Wasps Appearing).
Regular monitoring of your citrus trees will ensure that a major infestation of Citrus Gall Wasp doesn’t happen. All treatments are way more effective if you can catch an infestation in its early stages. This is especially so for Citrus Gall Wasps.
A tree with many large galls has either been pruned too heavily at the wrong time, or it has been neglected. If you keep at this pest and you encourage your neighbours to do the same, you will get on top of it.
A few galls here or there can be pruned off if you wish. Try to do this around April. If you leave it till winter you may just encourage a whole lot of soft growth in spring which is a magnet for Citrus Gall Wasps. If you leave it even later the wasps may emerge before you get to it!
A new method you might try is shaving off one side of the gall with a sharp blade or a kitchen peeler to expose the contents of the gall. This will dry out and kill any larvae inside. You only need to do one side though – if you shave all the way around the gall you will ringbark that stem.
Once you have pruned gall affected branches, give the tree a good feed with Yates Thrive Natural Citrus & Fruit Organic Based Pelletised Plant Food to help it recover.
Citrus Gall Wasps are native insects which cause large grotesque woody galls to form on citrus plants. The galls form in response to Citrus Gall Wasp larvae feeding inside the soft new growth of citrus plants.
Citrus Gall Wasp adults are shiny brown-black wasps about 2.5 mm long.
Citrus Gall Wasp larvae are white legless grubs about 3 mm long. You won’t see larvae unless you cut open a gall.
Citrus Gall Wasps go through a life cycle of complete metamorphosis: egg, larva, pupa, adult. All stages of this life cycle, except the adult stage, occur within the woody gall on the citrus plant. There is only one generation per year.
Adult citrus gall wasps emerge from their woody galls during spring. In south-eastern Queensland and north-eastern New South Wales emergence occurs from mid-September to early November. In southern Australia emergence occurs sometime between mid-October and mid-December depending on the climate.
The wasps mate, and females begin laying eggs on the same day as emergence. Female wasps lay their eggs into the bark of soft new growth twigs. They are capable of laying about 100 eggs over their life of about two weeks. Several females may lay their eggs into the same twig at the same time.
Eggs hatch after about two weeks and the larvae burrow into the bark. A sheath of soft tissue develops around the larva initially, but by late December woody tissue begins to form. Then the twig swells and begins to develop the characteristic gall. Large galls may contain hundreds of larvae.
Larvae live inside this gall in individual cells for several months, after which they pupate, and eventually emerge as adults the following spring. Emerging wasps leave characteristic pinprick size holes in the woody galls. Citrus Gall Wasps are poor fliers and short lived so they mate and begin egg laying almost immediately, often into the same tree.
Citrus Gall Wasp is a pest of all cultivated citrus varieties, with lemons and oranges being the most seriously affected. Its native host, the Australian Finger Lime, is becoming increasingly popular in cultivation, and will definitely be a target for Citrus Gall Wasps.