What's it look like?
Often you detect the presence of these horrid critters by their smell before you actually see them. They're commonly known as stink bugs for obvious reasons. They look different at the different stages of their development.

They range from almost transparent green discs of about 1cm diameter at early nymph stage, onto a soft orangy-yellow, 1 ½ - 2cm round bug at late nymph stage with a characteristic black dot on their back.

As an adult they are about 2 ½ cm with a metallic brown to black hard shield and they are squirt putrid smelling spray when attacked. This spray can cause skin irritation so be careful, and don't forget to wear goggles or glasses if your intending to catch a few of these guys.

What it attacks
All citrus plants, including some Australian native citrus.

What to do before it arrives
Treat these bugs during winter with a soap spray on the underside of the leaves. Eggs and young nymphs are present at this time and if you control in winter you keep the pest population down when it comes to mid-summer and autumn. The eggs are little white spheres, laid on the underside of leaves for protection and are always found in groups of 4 lines.

What to do if you already have problems
You'll know you have these bugs if you don't see them first because they affect the trees in a number of ways. The bugs suck on flowers and fruit stalks causing them to drop off. So look for lots of small fruit fallen on the ground below (although sudden changes nutrient and watering levels can also do this). You may also see some wilting and browning of new shoots.

The best way to deal with the bugs is manual removal if there aren't too many. Using gloves and a pair of goggles, knock them off into a bucket of boiling water or onto the ground and take out your aggressions by stomping on them with heavy boots very therapeutic! Beware they will fight back so be prepared with long sleeves and pants for protection from that horrid spray.

Otherwise, convince the neighbours that you have gone completely insane and take to your citrus trees with a vacuum cleaner. Suck them straight off for a clean crisp finish!!

For further information:

Plant bugs
... Bronze orange bug, Musgraveia sulciventris, is a common and serious pest of coastal citrus trees ... and burn human skin and eyes. The bronze orange bug's only host is citrus. ...
http://www.agric.nsw.gov.au/reader/2941

Explore: How do I control pest bugs such as Bronze Orange Bugs?
... How do I control pest bugs such as Bronze Orange Bugs ... Bronze Orange Bug Fact File - Wildlife of Sydney, Australian Museum ...
http://www.austmus.gov.au/explore/faqs/bronze_orange_bugs.htm

Bronze Orange Bug - Musgraveia sulciventris
Bugs that we found in the Brisbane area, Queensland, Australia. ... We only found one species in this family. Bronze Orange Bug - Musgraveia sulciventris ... 4th instars Nymph, 15mm. The Bronze Orange Bug nymphs reassemble as leaves ...
http://www.geocities.com/brisbane_bugs/BronzeOrangeBugs.htm

Explore: My citrus tree is covered in brown or orange bugs. What are they?
If your bugs are broad (up to 2.5 cm long) and are bronze to nearly black with a prominent black patch on their abdomen, they are Bronze Orange Bugs. ... Bronze Orange Bug Fact File - Wildlife of Sydney, Australian Museum ...
http://www.austmus.gov.au/explore/faqs/citrus_tree.htm

Amgrow Gardenking, Australia - Problem Solver
... Bryobia Mite. Bronze Orange Bug. Cabbage Moth ... Grasshoppers. Green Vegetable Bug. Harlequin Bug ...
http://www.gardenking.com.au/range.htm

Natural Pest Control - Green Harvest
... Black spot - rose. Bronze orange bug ... Spined Citrus Bug. Stored Food Pests ...
http://www.greenharvest.com.au/pestcontrol2