Eucalyptus Longhorn Borer Fact Sheet
Identification
Adults: Adults are primarily reddish to dark brown in colour, with beige or cream-coloured markings on the wings. Adult beetles can grow to 15-23mm in length, with females growing larger than the male counterparts. The beetle’s most distinctive feature, its long antennae, typically spans the length of its body.
The Longhorn Borer can be spotted during dusk when temperatures are above 15 degrees celsius, flying around hosts trees.
Eggs: Longhorn Borer eggs measure at around 2.5mm to 3mm, are shaped in an elongated oval, and are yellow in colour. They can be found under loose or detached bark, clumped together in an average of 40 eggs (but can range from 10-100 eggs).
Larvae: As larvae mature, they can grow up to 30-40mm in length by 10mm in diameter. They will develop a cylindrical body, typical for borer species. They are yellowish-white to cream in colour.
Longhorn Borer larvae are difficult to spot, as they exist inside branches and trunks greater than 5cm in diameter and remain there, hidden, until maturing and emerging as an adult beetle.
Figure 1. Longhorn Borer eggs
Figure 2. Damage caused to tree by a Longhorn Borer
Life Cycle
Egg: Eggs are typically laid under loose or detached bark in groups, and take 1-2 weeks to mature depending on the weather conditions at the time. When exactly the eggs are laid depends on the climate and environmental conditions, with egg laying occurring numerous times during summer in temperate climates or all year round in warmer climates.
Larvae: After hatching, larvae development can take from 60-180 days depending on climate and environmental conditions.
Pupae: Pupation may take up to 10 days, depending on the climate and environmental conditions
Adult Beetle: The adult beetle may be found throughout the summer season, mating, feeding and ovipositing. But in some climates it can be found all year round.
Figure 2 & 3. An adult Longhorn Borer
Symptoms and Damage
Symptoms
- Die-back in canopy
- Wilting leaves
- Dead branches
- Entire tree death
Signs
- Larvae tunnel entrances underneath bark.
- Frass on bark, at tunnel entrance.
Damage
- Tunnels being chewed out inside the stems and truck of wood.
- Galleries can cut of nutrient transportation system of the tree.
- Tunnels can impact the structural integrity of branches, leading to failure.
- Larvae can attract birds which strip bark and dig at the tree with their beak to access the grubs, causing damage to the tree in the process.
Host Species
| Liable | Resilient |
| Eucalyptus globulus | Eucalyptus trabutii |
| Eucalyptus grandis | Eucalyptus citriodora ‘Lemon Gum’ |
| Eucalyptus diversicolor | Eucalyptus dairympleana |
| Eucalyptus vimanilis | Eucalyptus camaldulensis |
| Eucalyptus platypus | Eucalyptus sideroxylon |
| Eucalyptus nitens | Eucalyptus cladocalyx |
| Eucalyptus saligna | Eucalyptus robusta |
Control
The best defence against Longhorn Beetle is good tree health. Attempt to reduce the stress and environmental factors impacting the tree, which can include laying mulch, providing irrigation during droughts, refraining from using herbicides, and improving the soil condition.
The handling of eucalyptus wood should be managed by stripping the bark of felled logs, so there is no suitable habitat for female beetles to lay eggs.
In the case where an infected tree has been removed, stripping the bark from felled trees will eliminate the potential habitat for new eggs. Additionally, splitting and drying the wood removes the soft fresh wood larvae feed on.
Beyond these measures, it must be noted that there exists significant natural predators that will impact the survivorship of larvae. Numerous parasitic wasps predate upon the beetle and larvae, ants also contribute to removing laid eggs from trees.
Bird species may hunt out the larvae, but this is likely to be a small impact on overall numbers.
Longhorn Borer damage images are the copyright of of Tasmanian Tree Care.
Longhorn Borer damage images are the copyright of of Tasmanian Tree Care.
Images courtesy of Brisbane Insects and Spiders and the European Institute Of Planted Forest.