Angela Ascertains

“Know thy enemy, and you shall prevail.” – Sun Tzu.

If you’ve had the pleasure of owning a lemon tree or a citrus tree of some variety in Australia, you may also have had the displeasure of encountering the stink bug – or the bronze orange bug. (Click here for bug pics.)

These pesky stink bugs suck on the saps of young leaves, drain the life out of the tree, and turn fruits bitter. This video by Trish Restante is very informative, she recommends to deal with the eggs in winter using horticultural oil and hand-pick or vacuum in summer.

My tree had hundreds of stink bugs because I had regrettably neglected it this year, and when I looked just the other day I was alarmed at the amount of bugs on the trees and its condition. I was fueled by an immediate desire to get rid of them, so I pulled out my laptop.

Part 1: About Bronze Orange Bug – Stink Bugs in Australia

As with any war, one starts by understanding the enemy. I learnt that bugs start out as eggs of 2mm in a cluster. When they hatch they are small green bugs with thin shell, they cluster around the eggs until their shells are a bit more resistant then they start venturing out (Ref 0).

When startled, touched or squashed, the stink bug ejects an acidic liquid about 61cm or 2 feet from its body. Younger bugs eject liquid from the rear, while adult bugs spray from both sides (Ref 2). The liquid is:

• Bad for vertebrates and birds do not like to eat them;
• Liquid can cause blindness when it gets into the eyes;
• Liquid will stain skin and is hard to wash off.

As the bronze orange bug grows, its shell changes to orange and eventually to black hardened exoskeleton when they are adults. Adult shells are “armoured” and “pestisides are useless against them” (Ref 3). A full-fledged stink bug also gains the ability to fly.

On a hot day, you can find the bugs on underside of the leaves or at the base of the tree to escape from the heat.

I found countless suggestions across reddit and Chinese forums, wikis, videos and even Taiwan government pest-control brochures. I’ll review the methods here, but for my successful strategy on clearing hundreds of bugs on my grown tree, see: War on Stink Bugs (2).

PART 2: Finding what works for Controlling Stink Bugs

1. Pest Oil – effective on younglings but not on adults

A gardener sprayed Yates pest oil on my tree, but one application wasn’t enough. The pesticide works by smothering young bugs (asphyxiation and coating), but does not work well against adults.

The same applies to neem oil, homemade dish soap + olive oil and alcohol spray, and vinegar and salt spray. These only kill young bugs. Videos on youtube show that it takes 1-5 minutes to kill a bug and requires 3-5 sprays. It is likely the died through suffocation. Definitely remember to wear masks and goggles, and don’t stand under the trees since the bugs will spray acid when startled!

With sprays, it is important to be mindful of the ingredients you are using when you are spraying and their strength, otherwise you may affect the tree or soil. With pesticides, check ingredients carefully if you are harvesting the fruits.

One interesting thing is home-made spray is most likely not good enough for destroying eggs (Leokim did an egg effect comparison). Further study could be made about pest oil effectiveness on eggs.

2. Shake the branch or knock the bugs off into a bucket of soapy water – low effectiveness due to capture method

This was one of the most widely circulated methods and it is easy to see the appeal, knocking the bug into water which contains soapy water and they die quite quickly. Also, because we dispose of it on our own turf, we don’t offload the bugs to somewhere else and stink up my bin.

As a matter of fact, soapy water is very effective at killing the bugs, especially if they are dumped in an ocean of it. So that’s a 100% kill rate. However, how effective is shaking the branch and knocking the bugs into the bucket? I decided to find out.

It was a fine morning, and I placed a medium-sized open container with water under the lemon tree. The bugs were relaxing and not disturbed. Knowing the bugs were not good swimmers, I used plain water instead of soapy water. If I didn’t need to use detergent, I could just bury the bugs and use the water in the garden.

My friend had fashioned a thin, long bamboo stick for me, and I stood about a metre away in my rain coat, glasses and gloves. I shook the branches gently and no bugs fell out of the tree. They simply adjusted their positioning around the branches.

I then attempted to knock some down, and that was a disaster. No bugs fell, and they were startled. I could smell the putrid gas. I smacked the bugs and shook the branches more insistently, and at last a few started to fall. About five bugs fell, two into the bucket and three onto the ground, two flew off the branch and one circled behind me. The smell was too strong so I retreated strategically. It was very clear from my preliminary experiment that this method was not what it was touted to be! This was just one small branch, and I had a hundred branches I needed to clear.

This debunks a lot of myths surrounding this method, and proves that the success rate really depends on the capture method. Essentially:

1. Shake branch gently: 0% effectiveness
2. Knock it off the branch: 20% effectiveness
3. Net with long handles wrapped with plastic bags: probably also 20% effective rate
4. Tongs with plastic bags & hand-pick with gloves: 100% effective but annoying
5. Vacuum: 100% effective, set-up is annoying

Thus, this is why I decided to go with vacuum for my ultimate method.

The next day, when the bugs were enjoying their day, I went to check on the container. Surprisingly, two were dead inside. This meant that a plain ocean of water is enough to drown the bugs! However, I am unsure how long it took for them to die. Any scientists reading this blog, I would be very appreciative if further research was done on this!

3. Spray strong pesticides

This can only work with pesticides that target saps where the bugs feed from, and may impact the fruit! However, it is a very effective method if you use the right pesticides!

4. Propane Torch method – don’t do this even if it seems satisfying

Satisfaction level is very high for this method as it is an instantaneous kill and the bugs just drop. I have seen this method in a video used directly on the branch, or used in combination with the fact that bugs will congregate at the base of the tree on a hot day then directly torching them at the base.

After talking with my gardening friend and doing more research, I abandoned this idea. Lethal heat for bugs is 60 °C or prolonged exposure to 50 °C, which is basically the same temperature for the trees. At 60 °C, the cells take damage and die. A propane torch is 1100 °C. The tree would suffer irreversable damage. Of course, the damaged leaves might be able to renew next year, and any fruit yield is gone, but if the tree bark is damaged the tree could die.

5. Wasp Spray – Interesting Idea

This is an interesting comment left on reddit by an Australian user, apparently it kills the bugs quickly. I checked Bunnings and they sell long range wasp sprays which can shoot up to 6m, way beyond the range of the bug’s acidic spray.

I did not try this, but if I did my considerations would be:

• Toxicity of the spray
• Effect on fruit
• The stink bug is much bigger than the wasps, so it might not be as effective
• Spraying technique
• Cost. Apparently 400g goes out very quickly, so to spray a whole tree would be very, very expensive and you also need to hit multiple targets, unlike a wasp nest. However, this could be a very good option when there are few bugs.

6. Bug-trap and Peppermint Methods for American Stink Bugs

Subject: This is mainly for the home-invading Brown marmorated stink bugs which gets inside of home over winter in the US.

1. Stink bug traps with a light underneath
   • How it works: These stink bugs are attracted to light, will land on or fall into the traps and can’t get out, or walk along surface with pesticides
   • Links:
     • https://www.youtube.com/watch?v=AZxkmmImRIc&ab_channel=DannerCronise
     • https://www.youtube.com/watch?v=v8l8r-O14Aw&t=57s&ab_channel=FOX47News
   • My thoughts: not sure if the Australian bronze orange bugs are as attracted to light at night, hope a scientist can test this out. However, since it is outdoors, light will attract a bunch of other insects as well, i.e. mosquitos, moths, etc.
2. Stink bug deterrent spray with peppermint oil + sealing house
   • Subject: mainly US stink bug again
   • How it works: preventing from getting inside the house
   • Links:
     • https://www.youtube.com/watch?v=1baiMyqMXrA&t=361s&ab_channel=StoneyRidgeFarmer
   • My thoughts: not useful for Australian bronze orange bugs as it is in open air, unsure if bug has olfactory receptor. There are various reddit forums and videos from US that use pepermint, detergent and alcohol spray. Some have written that this is very effective at deterring or killing them, however, further studies or actual video footage would further strengthen the case. Since these bugs are in houses and not on fruit trees, it can be a good method (note pepper mint oil might irritate pets!).

7. Diatomaceous earth for stink bugs

This one I know for a fact can work. Diatomaceous earth food grade is ultra fine and can be used to line the entry point of the house to physically destroy the bug. The particles stick to the exoskeletons of bugs and dehydrate them.

It is deep see particles and breakdown naturally. The only risk with this one is if crystalline silica contained in diatomaceous earth is breathed in is NOT GOOD for the human, and can cause silicosis or other respiratory issues. The food-grade diatomaceous earth is low in crystalline silica and considered safe for humans – but still, be careful!

The application problem with this one is that particles need to be brushed in a tree unlike in the US where you can line the household surfaces with it. There will be a lot of wind/rain which can easily displace it. What I think would be worth doing is lining the base of the tree before a very hot day, so when they crawl around it will dehydrate the bugs completely.

8. Electricity – futuristic

I was thinking long and hard about how to get rid of the bugs without hurting the trees, and I moved onto fantasizing about a bug zapper stick. However, I was again faced with the same problem as the bamboo stick. First I needed to make good contact with the bug. Due to the bug’s hard shell, the best place to make contact with the bug would be its legs, making it more difficult. Secondly, a high enough voltage and amps is required to kill or maim the bug instantly. This was going to be a lot higher than a regular bug swatter and needs to be purpose-built.

PART 3: Disposing After Capturing Bronze Orange Bugs (trigger warning: yuck!)

The question about disposing is a delicate and unpleasant matter which I will expand on quickly right now.

A lot of methods that was shared online doesn’t really explain how the bugs are disposed of afterwards, but here are a few shared by forum users:

1. Handheld vacuum
   • put vacuum in freezer (??), empty the vacuum, bug in bag, bin the bag.
   • pros: simple
   • cons: questionable freezer usage, bug incapacitated but may still survive, when crushed it will just release horrid gas, bug may populate landfill area
2. Bagged/bagless vacuum
   • empty the vacuum, bug in bag, freeze bug, bin the bag or burn the bag.
   • pros: disposal on own turf
   • cons: bug could escape/release smell when put into bag, burning creates acrid-smelling smoke
3. Soapy water bucket
   • flush down the toilet
   • pros: bug already dead before disposal, simple
   • cons: small risk of clogging the toilet if in large numbers

Combining the research above, I came up with:

1. My first idea
   • capture in vacuum bag, place bag in larger plastic bag to prevent smell escaping, leave in the Aussie sun for 4 hours and use heat to kill, bin it
   • As a precaution, I could also add some vinegar and alcohol swaps in the bag prior to bagging the bugs. Theoretically, they would be in a really bad environment and would die off.
   • pros: relatively easy, bug dead before disposal
   • cons: not sure if the fumes/heat is enought to kill bugs
2. My modified idea
   • Capture in vacuum chamber, hot water to kill bugs, bury bugs in soil as fertilizer.

Further research suggestions:

1. Does alcohol fumes or vinegar fumes kill stink bugs? What is the concentration required?
2. The bug’s acidic spray also creates fumes, in confined spaces, could this be lethal to the bug too? What if a lot of them are setting it off?

Now, I’m ready to take on the stink bugs! For the equipment and process, continue to read War on Stink Bugs 2!

References:

Ref 0:

leokimvideo, 2023. Stink Bugs 18 Day Egg Study Flamethrower Vs Detergent What’s The Best Pest Control. YouTube. Available at: https://www.youtube.com/watch?v=F2rS7s5eSiI [Accessed 4 January 2025].

Ref 1:
Wu, C.Y. (2021). 【昆蟲擾西上課了！】荔枝椿象真的有這麼可怕嗎？一起來認識牠！Tessaratoma papillosa. [YouTube video] Available at: https://www.youtube.com/watch?v=5ydoTzYSk-Y [Accessed 4 Jan. 2025].

Ref 2:
Bug Spray (2021). How to Control Citrus Tree Pests: How to Get Rid of Stink Bugs. [YouTube video] Available at: https://www.youtube.com/watch?v=D7Wf_fkVh1c [Accessed 4 Jan. 2025].

Ref 3:
Restante, T. (2022). Informative prevention: Bronze Orange Bug. Best and Easiest Method to Control These Bugs on Citrus Trees. [YouTube video] Available at: https://www.youtube.com/watch?v=D-zSR3tLSXo [Accessed 4 Jan. 2025].

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