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Number 10
Revised February 1993
By Charlma Phillips, Principal Forest Health Scientist

These bugs belong to the family Pentatomidae. They are often called "stink" bugs as some species produce a powerful odour when handled. Many shield bugs are pests, for example the Green Vegetable Bug, Nezara viridula, but some are predators of other insects.

The predatory shield bug most commonly found on eucalypts is Oechalia schellenbergii. This is a very mobile insect that feeds on a wide range of caterpillars and larvae (immature stages) of moths, beetles, sawflies and weevils. It is a very BENEFICIAL insect and plays a vital role in the control of many pest insects. For example, it is often seen on grapevines where it is important in the control of the Grape Vine Moth, Phalaenoides glycine. Unfortunately, like other beneficial insects, this insect is easily killed by chemical sprays and therefore it is essential that sprays be used in a responsible fashion, preferably as a last resort.

Description

 
Adult(Above): Oechalia schellenbergii is a medium sized insect, approximately 10-12mm in length. It is a mottled browny/grey in colour and can be easily recognised by the sharp spines on either side of the thorax. Females are larger than males.

Eggs: The eggs are black with an "eyelash" like fringe around the top.

Nymphs: Immature stages are called nymphs. They are brightly coloured black and red and resemble the adults in shape but do not have spines or wings. They remain black and red, though in changing patterns, throughout the nymphal stages, becoming browny/grey on moulting to the adult stage.

 
Eggs of Oechalia schellenbergii – a predatory bug

 
Newly hatched nymphs Oechalia schellenbergii

Life History

Adult bugs can be found from spring, through summer to autumn ie from about October through until April/May. This is the time of year when their food supply of caterpillars etc is most abundant.
Eggs are laid in batches on or under leaves. There may be up to 50 eggs in each batch with the average number being 18. After they hatch the young nymphs remain huddled about the egg batch for 2-3 days before moving off. Older nymphs are solitary.

Habits

Predatory bugs kill their prey by sucking out the body contents through a long, stout proboscis (or beak). Once a bug detects a caterpillar it extends its proboscis and pushes it into the caterpillar which may thrash around in an attempt to dislodge the bug, but the bug is rarely deterred. Adult bugs are often seen with caterpillars or other larvae impaled on their beaks. On average, 8 prey are eaten in the nymphal stage and 12 in the adult stage making a total or 20 individuals eaten by each bug in its lifetime. Adult bugs are quite shy and will fly off or hide at the slightest disturbance.

Summary

When to look: October to May, but adults may be present at other times.

Where to look: On leaves and twigs.

What to look for: Look for black fringed eggs on leaves.
Look for small red and black nymphs
Look for mottled browny/grey adults with sharp spines on each side.

NOTE: This is an extremely beneficial insect.

For further information contact PIRSA Forestry
 

Disclaimer: While this publication may be of assistance to you, the government of South Australia and its officers do not guarantee that it is without flaw of any kind or is wholly appropriate for your particular purpose. The Government therefore disclaims all liability for any error, loss or other consequence that may arise from you relying on any information in this publication.