Exotic longhorn beetles

Adults

• Adults are a typical elongate longhorn beetle (cerambycid) shape.
• They are shiny black and have white spots on their back.
• Their body length ranges from 20–37mm. Females are larger than males.
• Their antennae have whitish blue rings and are longer than their bodies (1.7–2 times length of body for males and 1.2 times length of body for females).

Eggs

• Eggs are similar in shape to rice grains (oblong), 5–7mm long and creamy white.
• Each egg is laid singly under the bark of the lower trunk, a low branch or an exposed root.
• Eggs turn a yellowish brown before hatching.

Larvae

• Larvae are elongated and cylindrical in shape.
• They are creamy or yellowish white legless grubs with an amber-coloured diffuse band behind the head and black mouthparts.
• They range from 10–60mm in length (young to mature larvae).

Pupae

• Pupae are off-white to yellowish in colour.
• They have legs and long coiled antennae and are 24–38mm long.
• They are usually surrounded by wood shavings.

Plant stage and plant parts affected

• All stages of plant growth (seedlings to mature trees) can be affected.
• Exotic longhorn beetles can feed on leaves, the plant stem or trunk, branches and roots.

Plant damage

Severe infestations of the wood-boring larvae can damage a tree’s vascular tissue, structurally weakening the tree. During severe winds and storms, affected trees are more likely to drop branches or fall over. These trees are also predisposed to attack by secondary pests or diseases.

Feeding by the adult beetles can cause defoliation and shoot damage. Damage to fruit shoots can reduce fruit production, leading to economic loss.

There are a number of native longhorn beetles in Australia. Of these, only Glenea spinifera (13–25mm long) is dark blue with white spots. However, Glenea spinifera does not have the banded pattern on its antennal rings.

Read more about common wood-boring beetles of trees and timber in Australia.

Exotic longhorn beetles attack over 100 woody plant species, especially hardwoods. These species include alder, apple, ash, avocado, birch, blueberry, citrus, elm, fig, guava, lychee, maple, mulberry, pear, plane tree, poplar, oak, olive, stone fruit, robinia, roses and willow.

Native Australian plants such as Acacia decurrens (green wattle), Acacia mearnsii (black wattle), Allocasuarina verticillata (drooping she-oak), Casuarina equisetifolia and C. stricta (coast she-oak) can also be affected (EPPO Global Database).

• Newly emerged adults feed on leaves, petioles and bark of host trees for 10–15 days before mating.
• They are active during the day. Adults usually survive for about a month.
• Egg-laying commences a week after mating, usually on susceptible host tree trunks about 60cm above the soil.
• Each female lays 30–70 eggs. They lay them singly under the bark.
• Depending on environmental conditions, the eggs hatch after 1.5–2 weeks.
• Larvae initially feed on the inner bark layer in branches and the trunk, moving deeper into the heartwood and sapwood as they mature.
• As the larvae feed, they form tunnels or galleries in tree trunks and branches. Frass (larval waste products) and sawdust accumulate near the original oviposition holes and at the base of infested trunks and branches.
• Larvae continue feeding and growing for several months before pupation.
• Pupation occurs in chambers in the heartwood.
• After emerging from their pupae, adult beetles emerge from circular holes that are 10–20mm in diameter.
• Depending on climatic and feeding conditions, there is usually a generation every 1–2 years.

Economic impacts

Exotic longhorn beetles have the potential to cause significant damage to a number of tree crops including apple, avocado, citrus, pear, stone fruit and tree nuts. Production nurseries may also be affected.

In forestry plantations, this pest can cause yield reduction. Timber may be downgraded, reducing its value, and export markets for timber products may be disrupted.

Overseas, the cost of removing, treating and destroying affected urban street trees has also been significant.

Environmental impacts

Some Acacia, Allocasuarina and Casuarina species are known to be hosts for exotic longhorn beetles. However, for all Australian native species the true host range for exotic longhorn beetles is unknown. Australian native forests and bushland could be impacted.

Long-distance spread of longhorn beetles can occur through the movement of eggs, larvae, pupae and adults in woody planting material, such as nursery stock or bonsai plants. Spread can also be via timber, timber products and wood used in pallets and packaging made from host species.

Adults can fly short distances, so the beetles may disperse locally when searching for host plants.

Check newly imported host plants, timber products and wooden pallets and packaging for:

• insect frass and wood shavings
• larval tunnels (up to 15mm wide) containing whitish grubs (up to 60mm long)
• round to oval exit holes where the adults have emerged
• live beetles, larvae, pupae or eggs.

If you see signs of longhorn beetles that you think may have travelled to Australia, report it using 1 of these methods:

• Report online.
• Phone Biosecurity Queensland on 13 25 23.
• Phone the Exotic Plant Pest Hotline on 1800 084 881.

Use these resources to help protect your farm from plant pests and diseases:

• Protecting your farm
• Farm biosecurity
• Biosecurity plan for the plantation forests industry (PDF, 1.9MB).

Exotic longhorn beetles are biosecurity matter under the Biosecurity Act 2014 .

Under the Act, everyone in Queensland has a general biosecurity obligation to report biosecurity risks and take action to prevent or minimise them.