Hemiptera : Tessaratomidae

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Image above: Adult Bronze Orange Bug
(image courtesy of Elise Dando)

Bronze Orange Bug (Musgraveia sulciventris) is a native insect that may occur on citrus trees in home gardens. It was once limited to coastal SE Queensland and northern NSW, but has now spread to the far south coast of NSW near Bega, as well as some inland citrus growing areas of Queensland and NSW.

The native food plants of Bronze Orange Bug include finger lime (Citrus australasica) and desert lime (Citrus glauca), and over time the bug has adapted to feed on most varieties of cultivated citrus.

Bronze Orange Bugs are notorious for their chemical defence system, and their colonies have a strong, unpleasant smell. They are one of several bugs that may be called ‘stink bugs’.

Best Treatment for Bronze Orange Bugs

Sap-sucking pests such as Bronze Orange Bugs can become a serious problem on poorly maintained citrus trees. The secret to pest control is to keep an eye on your plants, so that you can spot pest incursions early. Regular monitoring, along with the prevention and control methods outlined here, will ensure that a major infestation of Bronze Orange Bugs does not occur on your citrus trees.

While you are performing regular garden tasks, such as watering, that is a great time to check your citrus trees for Bronze Orange Bugs. For this to work you will need to know what Bronze Orange Bugs look like (see Description).

Prevention is always better than cure. There are a number of measures that you can take to prevent or minimise damage by Bronze Orange Bugs (see How to Prevent Bronze Orange Bugs Appearing). If you find adult bugs or late stage nymphs on your citrus trees you could pick them off by hand - but beware their defence system (see Description).

Whatever control method you choose for Bronze Orange Bugs, you need to be persistent and try to tackle the pest early in its life cycle. Bronze Orange Bugs cause the greatest damage as late stage nymphs and adults. Try Yates Nature's Way Citrus & Ornamental Spray, an organically certified insecticide for control of insect pests on fruit trees, including Bronze Orange Bug.

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Image above: 5th instar of Bronze Orange Bug

What are Bronze Orange Bugs

Bronze Orange Bug is a member of the bug family Tessaratomidae. It is a native sap-sucking insect which has taken a liking to cultivated citrus plants. Bronze Orange Bug is rarely a problem in commercial orchards, but can be a significant problem in home gardens.

Description

Adult Bronze Orange Bugs are large shield-shaped insects about 25 mm long and are bronze to nearly black in colour.

Eggs are bright green and about 2.5 mm in diameter. Eggs are laid in batches of 14 – usually in four neat rows in a pattern of 3,4,4,3.

First stage (instar) nymphs are globular, about 5 mm long, and light green in colour. Second stage nymphs are pale green, semi-transparent flattened insects about 7 mm long. Third stage nymphs are also pale green, usually edged with black, and are about 10 mm long.

Fourth stage nymphs change from green to yellow/orange in colour and are about 15 mm long. Fifth (and final) stage nymphs are bright orange initially but change to green/grey in colour later, and are about 20 mm long. Fourth and fifth stage nymphs have noticeable wing buds.

Late instar nymphs and adult Bronze Orange Bugs spray a well-aimed pungent and caustic defensive liquid when threatened. The fluid can burn skin and sting eyes to the point of temporary blindness. The defensive fluid will also stain your skin a yellowy/brown colour. Always wear gloves and eye protection when handling Bronze Orange Bugs.

Life Cycle

Bronze Orange Bugs develop through a life-cycle of gradual metamorphosis – egg, nymph, adult.

Female bugs lay their egg clusters on the underside of leaves, mostly on new growth, from spring to early summer in Queensland, and mid-summer to early autumn in New South Wales.

Eggs hatch after about a week to 10 days depending on the temperature. First stage nymphs do not feed, but are gregarious and the nymphs usually remain clustered near their empty egg cases.

After a week or two the tiny nymphs moult into the second growth stage and disperse throughout the canopy of the host tree, seeking protected sites on the underside of leaves and especially where leaves overlap. The second stage nymphs overwinter in this manner, until they become active in spring - which coincides with new flush growth on the citrus trees. The nymphs move to the new shoots to feed on them and then moult into the third stage.

The nymphs moult progressively through the next two stages, feeding continuously, and eventually reach adulthood. Adults begin mating in late spring and egg laying commences – each female may lay up to four batches of eggs. There is only one generation per year.

Plants Impacted by Bronze Orange Bug

All varieties of citrus including:

  • Lemon
  • Lime
  • Orange
  • Mandarin
  • Grapefruit
  • Pomelo
  • Kumquat

Symptoms of Bronze Orange Bug

  • Bugs suck sap from young shoots, and from fruit and flower stalks, causing shoots to wilt and flowers and fruit to drop.
  • The worst damage is caused by late instar nymphs and adults in spring and early summer.
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Image above: Adult Bronze Orange Bug
(image courtesy of Elise Dando)

How to Prevent Bronze Orange Bugs Appearing

Monitor

  • Look for clusters of eggs on the underside of leaves during summer. Check to see if they have been parasitised (see Natural enemies). Squash egg clusters (if they are not already parasitised) as you find them.
  • Look for groups of second stage nymphs on the underside of leaves.
  • Look for later stage nymphs and adults on shoots and young fruit.

Prevent

  • Pick off second stage nymphs in winter where they cluster on the underside of leaves.
  • Pick off large nymphs and adult bugs as soon as you see them. You can drop any bugs you find into a bucket of soapy water to drown them.
  • Wear gloves and eye protection when handling Bronze Orange Bugs to avoid their defensive fluid.

Natural enemies

  • Tiny wasps (Anastatus) parasitise bug eggs. Parasitised eggs lose their normal bright green colour and become greyish. If in doubt, collect some eggs on a leaf and put it in a jar in your kitchen and see what hatches. If little wasps hatch out you can release them into the garden. If Bronze Orange Bug nymphs hatch you can squash them and then check your tree for other eggs and first stage nymphs, and squash them too (see Beneficial Wasps).
  • Assassin bugs and robber flies are predators of Bronze Orange Bugs, but have little effect on large infestations of the bugs.

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