This is a stink bug nymph. This guy can’t fly and neither can his young sibling who is green and well camouflaged. They hatch in the citrus trees from eggs left by their larger flying parents who are either green or black. The green ones live on the fruit and so kind of stand out against a bright orange peel. I’ve never seen them on any tree other than our citrus. I think they are pretty loyal to their food source.
I’ve looked online and these pests seem impossible to deter. The only way to deal with them is seek and destroy. This we do with a rake. Within 2 minutes of this snap being taken, Mr. Nymph was in stink bug heaven.
If left alone, they can decimate a tree. Last weekend we went to a local nursery and saw an orange tree teeming with nymphs and almost leafless. They suck the sap from new shoots. So far we’ve kept on top of them and the damage is viturally nill. They arrived about 3 weeks ago and we’ll see how long they stick around.
Laura Rittenhouse's Gardening Journal 
I am enjoying your blog. I am a transplanted Yank from Alabama but now living in Cairns. My garden and travel is my passion after I retired from Social Work. I have so much growing but your life appears positively enviable and at least you don’t sweat so much in Sydney. Very sticky today in the wet tropics. I found your site when I googled Monstera plant. I’ll follow your posts and hope to learn and glean some of your knowledge! Thoroughly enjoyed my visit.
Thanks, it’s nice to hear people enjoy this – I sure have fun writing it. I lived in the tropics (Darwin) for 18 months and didn’t last a full day without sweating. I’m not convinced I’d ever get used to it. I much prefer temperate climates and so does my garden!