Aug 272014
 

(Photograph by Bulleen Art & Garden)

Citrus gall wasps (Bruchophagus fellis) are small (3mm) shiny black wasps native to northern Australia. There they have natural predators (two parasites) which keep the number of gall wasps under control. As the wasps have gradually moved south (thought to be via the movement of infected citrus trees), they have appeared in many areas without their natural predators, and consequently have exploded in numbers and caused considerable damage.

The wasps have a preference for the native limes, as well as lemons, oranges and grapefruits. Mandarins are less affected, and cumquats are unaffected as they are not from the citrus genus. Adult wasps emerge in spring, often timing emergence with the onset of a flush of new growth. After mating, the female immediately lays her eggs into the soft new season flush. Eggs hatch after 2 – 4 weeks and the young larvae burrow into the soft bark. Distinctive woody galls form around the larvae during summer. The new generation emerges the following spring, completing the year-long life cycle. Adult wasps live for only one week after emergence.

Control

This is difficult in Melbourne as at this stage predator release is not possible (as happens in Queensland). Best practice at the moment includes placing sticky traps into the trees around spring to catch emerging wasps and prevent them mating and laying eggs into the new growth. Adult wasps don’t fly far. They can be moved good distances by wind, but will tend to re-infect the tree they emerged from. Hence traps are useful to prevent re-infection. Remove galls before spring, wrap and place in your rubbish bin (NOT your greenwaste bin). You can also reduce the amount of soft spring flush growth by fertilising over late autumn or winter. Use a balanced fertiliser rather than a highly nitrogenous one.

Karen Sutherland from Edible Eden Design in Melbourne has released a 6 minute video on controlling citrus wasp – makes a good quick summary of latest best practice on control of Citrus Gall Wasp.

(Photograph by Bulleen Art & Garden)

Protect the bees, birds and butterflies from your sticky trap.

Physical traps are one of the few tools that we have to help prevent the infestation of our citrus trees by the citrus gall wasp. Unfortunately, these traps are non-selective and can also catch other species including bees, butterflies and even birds. The level of bycatch can be reduced through the use of a physical barrier that will still allow the citrus gall wasp through but not species larger than the size of the holes in the mesh.

Below is a basic barrier anyone can build that requires minimal equipment and materials.

(Photograph by Bulleen Art & Garden)

Materials you need

  • Aviary mesh (make sure the holes are small enough to block bees and butterflies)
  • 10 cable ties
  • Hook
  • 2 jar lids
Tools you need

  • Drill
  • 7mm drill bit
  • Wire cutters
  • Scissors

Step 1
Drill 6 holes in each of the lids.

(Photograph by Bulleen Art & Garden)

Step 2
Cut the mesh so that the width is just larger than the circumference of the jar lids and about 25mm taller than the height of the gall wasp trap.

Step 3
Roll the mesh into a tube.

Step 4
Slip the tube into the inside edge of the jar lids and use 4 cable ties to hold in place. This is the bottom of your barrier cage. The middle 2 holes will help with drainage.

(Photograph by Bulleen Art & Garden)

Step 5
Use a cable tie to hold the two long edges together forming a secure tube.

(Photograph by Bulleen Art & Garden)

Step 6
Loop a cable tie through the 2 centre holes in the top of the top jar lid and attach the metal hook to the outside and the plastic hook on the top of the gall wasp trap on the inside. Tighten the cable tie so they don’t fall off.

(Photograph by Bulleen Art & Garden)

Step 7
Twist open the pheromone lure in the yellow sticky trap.

Step 8
Place the trap inside the cage and using the 4 holes and cable ties, secure the top lid to the mesh cage.

Step 9
Cut off the excess length from the cable ties.

Step 10
Hang the bycatch barrier and trap in your citrus tree.

Related Factsheets

  • Elizabeth_Jane_au

    Save Our Citrus (Melbourne) says to avoid using the traps because they also trap beneficial insects. There’s more info on the campaign to save Melbourne’s lemon trees on their website:
    http://www.saveourcitrusinfo.org/

  • Elizabeth_Jane_au Hi Elizabeth. As outlined above we are not aware at this stage that natural predators are present in sufficient numbers in Melbourne to effectively control Citrus Gall Wasp, however to be certain I have referred the matter to an expert. We use IPM technologies as our consultants for the Integrated Pest Management systems we use here at BAAG, and Angelica from IPM has kindly agreed to research this for us and get back with a comment on this page in the next few days.

  • Elizabeth_Jane_au

    julian_BAAG Elizabeth_Jane_au 
    Hi Julian, thanks for your reply. I don’t know that they are suggesting that predators of the gall wasp will be trapped; I took it to mean beneficials in a broader sense of the word. The traps I’ve observed have been covered in dead insects, mostly not citrus gall wasps.
    For myself, with five citrus trees, I’ve decided the traps represent too much plastic in any case. I’ve followed the other suggestions on the save our citrus website, and look forward to seeing how my trees fare over the coming year.

  • Elizabeth_Jane_au julian_BAAG

    Hi Elizabeth, 

    You are right that sticky traps can catch both pest and beneficial species. It is up to you whether you are prepared to risk trapping some beneficials or not. 

    I think that hanging sticky traps within the canopy of citrus trees for the short period during which adult citrus gall wasps are active is a relatively targeted use of sticky traps, and may well be justified if you find that you are trapping significant numbers of the pest. The impact on beneficial insects can be minimised by making sure that the traps are removed as soon as the adult citrus gall wasps cease to be active. 

    There are natural parasites (wasp parasitoids) of citrus gall wasp that provide excellent levels of control in northern Australia, where the citrus gall wasp comes from. Unfortunately this pest has escaped is natural parasites down here in Melbourne. I have spoken to a citrus biological control expert about the current distribution of the parasites, and he confirmed that they are not established in the Melbourne region. Our climate may not be suitable for them to ever establish here, and even if we were to try to introduce them, experience from other regions in Australia shows that it takes 6-10 years for them to get established enough to begin to provide control. This is because they have only one generation per year, and so population growth is slow.

    So, yes, sticky traps catch both pests and beneficials, but if citrus gall wasp control is a priority, and you decide to try the traps, then you needn’t worry that you might be trapping the key natural enemies of the citrus gall wasp. Unfortunately they simply aren’t here.

  • Elizabeth_Jane_au julian_BAAG
    Hi Elizabeth, you may be right. The layout was just a little misleading to me… the line “Avoid using ‘sticky’ yellow traps as they also kill beneficial insects” is directly followed by “Two similar sized parasitic wasps, Megastigmus brevivalvus and M. trisulcus, are predators of the Citrus Gall Wasp” and on first reading we all read it as saying that the sticky traps catch the beneficial wasp predators as well as the wasps. 

    Best of luck with whatever method you choose to follow, I hope you have a bumper citrus crop!

  • MW74

    Hi guys.
    I’m really interested in what pheromone you are using to attract Gall Wasp to a trap.
    As a technical agronomist involved in the industry and government funded control and management program in the Riverland (SA) and Sunraysia (VIC) I am yet to here of a pheromone being isolated that target Citrus Gall Wasp.
    The chief entomologist from NSW DPI who is also involved in this program is yet to isolate a Gall Wasp specific pheromone either.
    This is an extremely difficult pest to control and we have undergone numerous trials over many years. You are correct that the parasitoids which can help control Gall Wasp in the gall are currently struggling to establish themselves in the southern part of the country but that is only part of the problem. Queensland has also has Gall Wasp explode over the last 3 years despite naturally occurring parasitoids being present and well established. It has adapted to all major citrus varieties now so Lemons are far from the only variety being infested.
    Regards,
    Matt

  • Hi Matt,
    Thanks for your question. Gall wasps are indeed a difficult pest to control. The gall wasp traps we have here are the GoNatural Insectrap, the ingredients of the attractant are not listed on the label, but you can contact the supplier HTC International Pty Ltd on 1300 292 818 or though their website http://www.gonaturalgardening.com.au for the information you require. Hope that helps.

  • MW74 Hi Matt,
    The MSDS for the GoNatural Insectrap lists the attractant as Ammonium Bicarbonate Food Grade