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Tryphocaria acanthocera
Number 18
Revised October 1993
By Charlma Phillips, Principal Forest Health Scientist

The Bulls-eye borer, Tryphocaria acanthocera, is a species of longicorn beetle. It is also known as the Marri Borer. It feeds on a wide range of eucalypts and is distributed throughout southern Australia. In Western Australia it was first recognised as a problem in 1967 in 30-35 year old Karri trees. It is now found in many plantations and also in regenerating eucalypts. In Victoria, two species, T. acanthocera and T. mastersi, have been responsible for the death of trees in plantations, while in Tasmania, T. mastersi is the main species causing problems.

In South Australia, several species have been recorded but of these T. acanthocera is causing the most concern in eucalypt plantations. Adults have been found emerging from four year old trees which, as the life cycle is of two years duration, means that these trees were initially attacked at age two. This is earlier than any previously recorded attacks.

Description

Adult Bulls-eye borers (Pictured below) are typical longicorn beetles with long narrow bodies and very long antennae (hence the name longicorn). They are 30 to 45 mm in length, head and thorax reddish to dark brown in colour and wingcovers straw coloured with reddish brown markings. The antennae are long, in males much longer than the body, and have spines at intervals along their length. A distinguishing feature of the Bulls-eye borer is the presence of a curved spine on each side of the thorax.

Larvae are typical longicorn beetle larvae, large, fleshy and cream in colour. They may be 70mm or more in length with well defined segments and no legs. The head is large and flattened with reddish-brown chewing mouthparts and reddish-brown markings on the prothorax (behind the head).

Pupae (Pictured below) are approximately 37 mm in length and cream in colour with course hairs. The wing buds can be clearly seen.

Eggs are elongated, round to oval in shape and approximately 6 mm in length. They are a pale greenish white in colour.

Life History

Adult beetles fly at dusk in summer (December, January and February). They rest during the day under bark or in crevices. Little is known of the mating and oviposition (egg laying) behaviour. However, it is known that eggs are laid in cracks in the bark, usually low down near the base of the tree.

On hatching, larvae tunnel through the bark into the sapwood and then into the heartwood. They tunnel upwards, following an erratic path, often entering the sapwood again and by the time they are fully grown the tunnels extend 4-5m or more. The larvae then tunnel out through the sapwood to excavate a circular groove, in the shape of a slightly oval bulls-eye, just under the bark. They then tunnel downward again from the centre of this bulls-eye, into the heartwood for approximately 25-30 cm and form a pupal chamber. This tunnel is tightly packed with sawdust. The pupal chamber is formed in April or May but the larvae do not pupate until October or November. Adults emerge in December and January.

The whole life cycle takes two years.

Damage

The Bulls-eye borer is an important pest as it attacks growing trees. The resulting damage may cause considerable economic losses, as fungus which grows in the excavated tunnels, stains the wood and may result in the timber being downgraded or discarded as waste.

It was originally thought that only relatively old trees were attacked.

It is now known that trees in all stages of growth are attacked but that young trees, approximately 30 cm in diameter are preferred. Adult beetles have been found emerging from four-year-old trees and as the life cycle takes two years, these trees would have been attacked at age two when trunk diameters were much smaller than 30 cm.

It is also thought that adult beetles are attracted to drought stressed trees and to fertilised trees. There is a higher concentration of nitrogen in such trees which makes them attractive to insects.

It is not easy to detect the presence of Bulls-eye borer larvae in trees but there are some signs to look for. There may be sawdust around the base of the tree or caught in the bark or in spiders webs on the trunk. There may also be some bleeding on the trunk ("kino" bleeding). The most characteristic sign is the presence of a bulls-eye (pictured above) approximately 2-4m off the ground. The bulls-eye is often difficult to find as there is usually only a slight split in the bark to indicate its whereabouts. The picture below shows damage to tree by a single bulls-eye borer larva over its 2 year life cycle.

Control

There is no satisfactory method of control for these insects. Chemical control is not possible because of the difficulty of getting the chemical into the region of the tree attacked by the larvae. However, it is possible to reduce numbers by removing infested trees. Silvicultural practices such as thinning, reduce water stress and thus trees are healthier and less susceptible to attack.

There is little known about parasites and predators. Black cockatoos feed on the larva but the cockatoos themselves do considerable damage to the trees, tearing at the bark and trunk to reach the larvae.

Summary

When to look:  All year

Where to look:  Look on the tree trunk

What to look for:  Look for sawdust on trunk or around the base of the tree
Look for "kino" bleeding or sap running down the trunk
Look for cracks in the bark and a bulls-eye on the trunk, 2-4m off the ground. The bulls-eye may be covered by bark - there may be only a small split in the bark which sounds hollow when tapped. Peeling back the bark will reveal the bulls-eye.

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.