If there is one garden pest that knows how to announce its arrival, it is the Bronze Orange Bug. You might spot strange orange insects crawling over your Lemon tree or notice tender new shoots beginning to wilt. Quite often though, your nose gets there first.
Bronze Orange Bugs are large sap sucking insects that attack citrus trees. They are also commonly called Stink Bugs thanks to the powerful and thoroughly unpleasant smelling defensive liquid they release when disturbed.
The liquid is not just smelly either. It is caustic and can irritate skin and eyes badly, which means this is one garden pest that deserves a little respect. Gardening gloves are good. Eye protection is even better.
The good news is that a Bronze Orange Bug infestation is much easier to manage when you catch it early. Regular checks through Winter, Spring and Summer can save you from dealing with a tree full of large, grumpy adults later.
Table Of Contents
- What Is A Bronze Orange Bug?
- How To Identify Bronze Orange Bugs
- The Bronze Orange Bug Life Cycle
- What Damage Do Bronze Orange Bugs Cause?
- How To Control Bronze Orange Bugs Naturally
- What About Sprays?
- How To Prevent A Major Infestation
- Are Bronze Orange Bugs Dangerous To People?
- Why You Should Start Looking In Winter
- Protecting Your Citrus All Year Round
Botanical name
Musgraveia sulciventris
Common name
Bronze Orange Bug, Stink Bug
What Is A Bronze Orange Bug?
The Bronze Orange Bug is a native Australian insect and a member of the true bug group, Hemiptera. Like other true bugs it has specialised piercing and sucking mouthparts that allow it to feed on plant sap.
Its original host plants include native citrus species such as Finger Lime (Citrus australasica) and Desert Lime (Citrus glauca). Unfortunately for backyard gardeners the Bronze Orange Bug has also developed quite a taste for cultivated citrus.
It is most strongly associated with coastal Queensland and New South Wales although its range has expanded. Bronze Orange Bugs have now been reported farther south in New South Wales, in some inland citrus growing areas and in Victoria.
They may attack:
- Lemons
- Limes
- Oranges
- Mandarins
- Grapefruit
- Pomelo
- Kumquat
- Native citrus
Basically, if it is citrus, they are interested.
How To Identify Bronze Orange Bugs
One of the confusing things about bronze orange bugs is how dramatically their appearance changes as they develop.
A gardener finding tiny green bugs under the leaves in Winter and enormous bronze insects in the same tree during Summer could quite reasonably assume two completely different pests had moved in.
They haven’t. Same bug. Different outfit.
Eggs
Bronze Orange Bug eggs are bright green and around 2.5 mm across. They are usually laid on the underside of leaves in remarkably tidy batches of 14.
The eggs are often arranged in four rows following a 3, 4, 4, 3 pattern. Considering the trouble they are about to cause, the organisational skills are almost admirable. A female can lay several batches during the season.
Young Nymphs
The first stage nymphs are small, rounded and pale green at around 5 mm long. They usually remain clustered near their empty egg cases shortly after hatching. At this first stage they do not feed.
Second stage nymphs are around 7 mm long. They are pale green, somewhat translucent and flatter in shape. These young nymphs disperse through the tree and seek protected places beneath leaves, particularly where foliage overlaps.
Older Nymphs
As Bronze Orange Bugs grow they pass through several more nymph stages. Third stage nymphs are around 10 mm long and pale green, often with darker edging. Fourth stage nymphs reach around 15 mm and begin changing from green to yellow or orange.
The fifth and final nymph stage can reach around 20 mm. These bugs may be spectacularly bright orange before becoming more greenish grey as they mature. Unfortunately their fashion sense is considerably better than their manners.
Adults
Adult bronze orange bugs are large shield shaped insects around 25 mm long. Their colour ranges from bronze brown to almost black.
Adults have fully developed wings and can fly. You will often find them feeding on fresh citrus growth, flowers, young fruit and fruit stalks. During hot weather they may also gather together on the trunk.
Older nymphs and adults can release their characteristic defensive fluid when threatened. The identification table below gives you a quick reference for telling the different stages apart.
| Life Stage | Approx. Size | Colour And Appearance | Where To Look |
|---|---|---|---|
| Eggs | About 2.5 mm | Bright green and usually arranged in neat batches of 14 | Undersides of citrus leaves, often on newer growth |
| First Stage Nymph | About 5 mm | Rounded and light green | Clustered near recently hatched egg cases |
| Second Stage Nymph | About 7 mm | Pale green, semi transparent and flattened | Under leaves and between overlapping foliage, particularly during Winter |
| Third Stage Nymph | About 10 mm | Pale green and often edged with black | Fresh citrus growth as activity increases in Spring |
| Fourth Stage Nymph | About 15 mm | Green changing to yellow or orange with visible wing buds | New shoots, flowers and young fruit |
| Fifth Stage Nymph | About 20 mm | Bright orange at first then becoming greenish grey with obvious wing buds | Young shoots, fruit and flower stalks |
| Adult | About 25 mm | Large, shield shaped and bronze brown to almost black | New growth, flowers, fruit and sometimes clustered on the trunk during hot weather |
The Bronze Orange Bug Life Cycle
Understanding the Bronze Orange Bug life cycle gives you a considerable advantage when it comes to control.
There is generally one generation each year. Adults begin mating in late Spring although the timing of egg laying varies with climate.
In Queensland, eggs are commonly laid from Spring into early Summer. In New South Wales, egg laying tends to occur later from around mid Summer into early Autumn. The eggs usually hatch after about seven to ten days depending on temperature. Newly hatched first stage nymphs remain clustered around their empty egg cases before moulting.
After another week or two they develop into second stage nymphs and spread through the citrus canopy. These small green nymphs commonly spend Winter tucked away on the undersides of leaves and in protected areas where foliage overlaps.
When temperatures rise in Spring and citrus trees begin producing fresh new growth, the nymphs become active again. They move onto those tender new shoots to feed then progressively moult through the remaining stages until they reach adulthood.
This gives gardeners a very useful window of opportunity. Finding a group of small green nymphs during Winter is considerably easier than tackling a collection of 25 mm flying stink bugs several months later.
What Damage Do Bronze Orange Bugs Cause?
Bronze Orange Bugs feed by piercing plant tissue and sucking sap. Unfortunately their favourite targets are exactly the parts of your citrus tree you would prefer they left alone.
They commonly feed on:
- Tender new shoots
- Young leaves
- Flower stalks
- Developing fruit
- Fruit stalks
Feeding can cause young shoots to wilt, brown and die back. Flowers may fall before fruit develops and small fruit can drop from the tree. The worst damage is generally caused by the larger nymphs and adult bugs during Spring and early Summer when citrus trees are actively producing fresh growth, flowers and young fruit.
Their defensive liquid can also scorch foliage.
A handful of Bronze Orange Bugs is unlikely to destroy a mature citrus tree. A large infestation left unchecked can cause significant damage and seriously reduce your crop.
How To Control Bronze Orange Bugs Naturally
For backyard citrus, physical removal is one of the simplest ways to manage Bronze Orange Bugs. Bug on tree. Bug off tree.
There is one important rule before you begin. Protect yourself. Wear safety glasses or goggles, long rubber or waterproof gloves, long sleeves and closed shoes. Avoid standing directly underneath the insects while you are removing them.
Large nymphs and adults can squirt their defensive liquid surprisingly accurately and getting it in your eyes is something you only need to experience never.
Remove Small Nymphs Early
Winter is an excellent time to inspect the undersides of citrus leaves. Look particularly closely where leaves overlap or create sheltered pockets inside the canopy. Second stage nymphs often gather in these protected areas while overwintering.
Small groups can be picked off while wearing gloves. Leaves carrying young nymphs can also be removed. This is one of those gardening jobs where ten minutes now may save you a much less pleasant battle later.
Knock Bugs Into Soapy Water
For larger nymphs and adults, place a bucket containing water and a small amount of detergent beneath the affected branch.
Gently shake or knock the insects into the bucket. Another option is to carefully hold the bucket beneath a branch and dip or shake the branch over the water. Return a few days later and check again. Dense citrus foliage provides plenty of hiding places, so one patrol rarely catches every bug.
If your citrus inspection turns into a general garden potter, you can also browse the Gardening Tools collection at The Curious Gardener Shop, including Australian Made recycled hand tools for all those other little jobs that mysteriously appear once you walk outside.
Use A Vacuum With Caution
Some gardeners use a vacuum cleaner to collect bronze orange bugs from larger trees. It can work although I certainly would not volunteer the good household vacuum.
Their defensive liquid smells dreadful and may stain or damage the equipment. If you are going down the vacuum route, an old machine with a disposable bag is a considerably more sensible candidate.
Check For Eggs
During the egg laying season, inspect the undersides of leaves for those distinctive green clusters. Before destroying them, take a closer look.
Tiny beneficial wasps in the genus Anastatus can parasitise bronze orange bug eggs. Parasitised eggs lose their normal bright green appearance and become greyish. Assassin bugs and robber flies will also prey on bronze orange bugs.
Not every insect wandering around your citrus tree is therefore a villain. Some are actually helping with pest control free of charge, which seems only fair considering how much gardening costs us already.
What About Sprays?
Small backyard infestations can often be managed through monitoring and physical removal, particularly when Bronze Orange Bugs are discovered early. There are registered contact insecticides available for Bronze Orange Bug control on citrus including pyrethrum based products.
A current home garden option is OCP eco-pyrethrum PLUS, which contains pyrethrins and canola oil and is registered for Bronze Orange Bug control on fruit trees. Contact sprays need to reach the insects directly to work effectively.
Always read the current product label before using any garden pesticide and make sure the product is registered for both the pest and the plant you are treating. Follow application directions, withholding periods and safety instructions carefully.
Even products derived from natural ingredients can affect beneficial insects, so spraying the entire garden simply because you spotted three stink bugs is probably overkill.
For backyard citrus I would start with regular monitoring and physical removal then use a registered targeted treatment when numbers become difficult to manage.
How To Prevent A Major Infestation
You probably cannot convince bronze orange bugs that your citrus trees are suddenly unappealing. You can stop a small population from quietly turning into a full blown stink bug convention.
A few good habits make a big difference:
- Check beneath citrus leaves during Winter for groups of small green nymphs
- Inspect fresh growth regularly during Spring
- Look for orange later stage nymphs as temperatures rise
- Check beneath leaves for egg clusters during the laying season
- Inspect trunks and major branches during hot weather when adults may gather
- Remove manageable numbers as soon as you find them
- Avoid unnecessary broad spectrum pesticide use that may kill natural predators
- Keep citrus trees reasonably accessible so you can inspect the canopy
Consistency is far more useful than waiting until the tree is covered in adults and declaring war.
Are Bronze Orange Bugs Dangerous To People?
Bronze Orange Bugs are not aggressive insects and they are not interested in chasing gardeners around the backyard. Their defence system is the problem.
Older nymphs and adults can eject a pungent caustic liquid when disturbed. This secretion can burn or irritate skin and can cause severe eye irritation. Always wear eye protection and gloves when removing bronze orange bugs.
If the liquid gets into your eyes, rinse immediately with plenty of clean water. Seek medical advice if significant irritation, pain or vision problems occur. It is also sensible to wash any exposed skin promptly if it comes into contact with the secretion.
The citrus tree will survive while you fetch your goggles. Your eyeballs are considerably harder to replace.
Why You Should Start Looking In Winter
Most gardeners first notice bronze orange bugs when the insects are large, bright orange, bronze or almost black and sitting rather conspicuously on new Spring growth. By then the bugs have already been living in the tree for months.
Winter is the sneaky gardener’s advantage. Turn over citrus leaves and look carefully through sheltered areas of the canopy. Pay particular attention to overlapping foliage where small green nymphs can hide.
Finding a handful of overwintering nymphs during Winter can mean far fewer large bugs to deal with in Spring and Summer.
Protecting Your Citrus All Year Round
Bronze Orange Bug control is not especially glamorous. It involves peering underneath leaves, wearing goggles and occasionally standing beside a bucket full of soapy stink bugs wondering exactly when gardening became this weird.
Still, a little vigilance is considerably better than watching your Lemon tree lose fresh shoots, flowers and developing fruit.
Learn what the different life stages look like. Check your citrus through Winter, Spring and Summer. Deal with Bronze Orange Bugs while they are still small and leave beneficial insects to get on with their work wherever possible.
Your citrus will be healthier, your fruit crop should be happier and hopefully you can enjoy your Lemon tree without being sprayed by something that smells like it crawled out of Satan’s compost bin.
Frequently Asked Questions About Bronze Orange Bugs
Bronze Orange Bugs are attracted to citrus trees where they feed on tender new growth, flowers and developing fruit. Healthy citrus can still attract them, so finding bronze orange bugs does not necessarily mean there is something wrong with your tree.
Winter and early Spring are the best times to control bronze orange bugs because the nymphs are smaller, less mobile and easier to remove. Dealing with them early also helps prevent large numbers of adults appearing later in Spring and Summer.
A small number of bronze orange bugs is unlikely to kill a healthy mature citrus tree. A heavy infestation can cause significant damage to new shoots, flowers and young fruit and may greatly reduce your citrus crop.
Adult Bronze Orange Bugs have fully developed wings and can fly between citrus trees and neighbouring gardens. The younger nymph stages cannot fly which is another good reason to tackle them before they reach adulthood.
