We don’t seem to have a lot of pest issues here at the Choko Tree, but we do have a yearly battle with bronze orange bugs (AKA stink bugs). Bronze orange bugs are a wide ranging pest of citrus trees on the east coast of Australia from central NSW to SE Queensland. They are a native, feeding on native citrus like the finger lime and desert lime, and when other citrus species were imported they were pleased to move straight across to them too!
Description/lifecycle
The bronze orange bug goes through several stages of nymphs before becoming adults. First off the eggs are small spheres about 2.5mm in diameter laid on the underside of the citrus leaf. These hatch into light green circular nymphs. As they move through their life cycle, the light green nymphs get larger until they reach the fourth or fifth instar which is the last stage before adulthood. At this stage they are oval, bright orange bugs which can be easily noticed. When they reach adulthood they are black, can fly and reproduce, resulting in the next generation of bugs.
Damage/signs of infestation
Initially it can be difficult to identify an infestation when the bugs are in their small, light green stages, but they become obvious when they reach their orange stage. They are a sap sucking insect and tend to infest new growth on the trees in spring and their activities can result in this new growth turning brown/black and dying back. They can also cause flower and fruit drop. The irritating, smelly liquid the bugs produce can also result in wet patches on the leaves and fruit resulting in brown spots of dead tissue. The distinctive smell the bugs produce can also be an indicator of an infestation. A severe attack can result in a sick looking tree and reduced yields.
Prevention
Look for the eggs and squash them before they have a chance to hatch and net the trees after they have been cleared of eggs.
Controls
Manual removal – this is the one we practice here. I use pliers or gloved fingers, because the smell substance they secrete is also an irritating chemical which can cause your fingers to look like you have been smoking for the past 40 years and if it gets in your eyes, will sting like hell!! If you go the manual removal route always wear eye protection, goggles are better than glasses. This is an important point, particularly if they are above you when you are trying to remove them, their aim is good.
Once removed I place them in a container of water which has a bit of washing detergent or soap so the water wets them out and they drown quicker. If the weather is hot (39⁰C or above), they will tend to congregate around the base of the tree, facilitating manual removal. If you want to make things a bit quicker you can use a vacuum cleaner, just make sure that this won’t cause any problems with in the household, and require a replacement vacuum cleaner to be bought because the original is contaminated.
Manual removal is easiest before the bugs reach the adult (black) stage, because after that point not only are they capable of laying eggs but can also avoid you by flying away, although in most cases they don’t seem to fly far.
Predators – From what I see around here, there is not much in the way of wildlife interested in snacking on bronze orange bugs with the exception, many years ago, of watching a black-faced cuckoo shrike sample some from our orange tree. My exhortations for him (or her) to come back and bring their friends unfortunately fell on deaf ears.
There is a species of wasp that parasitises the eggs and the assassin bug will predate bronze orange bugs given the chance but, again, we do not seem to see many of either around here.
Sprays – a pyrethrum based spray will work but it is broad spectrum and will also kill other beneficial insects like lady bugs and arachnids like spiders. I have read that using eco-oil in the winter to control other pests has resulted in a lower incidence of bronze orange bug in the spring, possibly due to destruction of over-wintering eggs. Spraying a solution of soft soap 2% - 2.5% in water in later winter to early spring will kill young nymphs, reducing infestations later in the season.
A friend has told me she uses a 50:50 mix of vinegar and water as a pest spray and this seems to work fairly well, driving them off or killing them.
