Eucalyptus Longhorned Borer – The Garden Pest Extraordinaire

If you have eucalyptus plants in your garden, you need to know all about the eucalyptus longhorned borer, if you want to keep them safe.

Borers are known to be one of the most devastating types of hardwood pests, and rightly so. 

The eucalyptus longhorn borer larva girdles trees (discussed in detail later) and can potentially kill them.

The eucalyptus tree genus falls among the most popular urban forest trees. 

Unlike many other tree species, the risk of fires from dead leaves piling up in loads under trees is lower. 

This also makes eucalyptus longhorned borer infestation a common problem. Let’s find out more about these pests and how you can tackle them.

Eucalyptus Longhorned Borer
Eucalyptus Longhorn

What Is a Eucalyptus Longhorned Borer?

Eucalyptus longhorned borer refers to two closely related borer beetle species – Phoracantha semipunctata and Phoracantha recurva. 

The former originated in Australia and was eventually spotted in Southern California in 1980. 

The latter was discovered in 1995 in several Californian counties – San Bernardino, Los Angeles, Orange County, and Riverside.  

Adult eucalyptus longhorned borers feed on the pollen of eucalyptus trees and lay eggs in the bark of eucalyptus trees. 

Stressed and freshly cut trees are particularly at risk from these borers.

What Does It Look Like?

Growing to a size of about an inch with brown bodies, adult eucalyptus longhorned borers have segmented antennae. The legs and antennae are of a reddish-brown color.

Like all beetles, they feature a pair of elytra, or hard hind wings.

Yellow-brown in color, these elytra have a thick black band crossing both their posterior ends. Each wing also features two vaguely connected spots.

The larvae resemble white grubs and are often over an inch long. However, you’ll rarely see them as they remain hidden within the tree bark.

Eucalyptus Borer

What Damage Does It Cause?

Moving on, let’s check out what kind of damage Eucalyptus longhorned borers can cause. 

The discoloration and the wilting of eucalyptus leaves are among the first symptoms of an infestation. 

Eventually, the tree limbs will begin to die back too. As the larvae continue to feed on the tree, oval-shaped holes will start appearing in the bark.

The problem with P. semipunctata/recurva infestation is that the larvae destroy the cambial layer – the layer responsible for the transportation of water and nutrients in trees. 

If left unchecked, the infestation will spread throughout the circumference of the tree and may remove a strip of bark (known as girdling).

You may also notice a liquid oozing out of the trunks and limbs of infested trees. It’s a resin produced by the trees to resist a borer attack.

Different eucalyptus species display varying levels of resistance. It depends on the attributes of eucalyptus trees. 

For instance, a drought-resistant species will also be less vulnerable to borer infestations.

Longhorned borer attacks are particularly common during the hot summer months when the trees are stressed. 

When infesting healthy trees with plenty of moisture content, the larvae may suffer mortality in trees by drowning. 

Opening up a tree infested with these pests will also reveal large networks of tunnels bored by the larvae. These tunnels are usually filled with their excrement.

Lifecycle of the Eucalyptus Longhorned Borer

The lifespan of a eucalyptus longhorned borer may vary a lot, depending on the season. In summer or spring, three to four months are enough for them to complete their life cycle. 

The ones hatching in winter take longer, up to nine months. The four life cycle stages are as follows:

Larva of a Eucalyptus Borer

Egg: Female beetles of this species lay up to 300 eggs, distributing them into groups of 3 to 30. These eggs are typically laid in loose bark and take around a week or two to hatch.

Larva: Eucalyptus longhorned borer larvae may take anywhere from 70 to 180 days to develop, depending on the moisture content in the wood. 

The drier the eucalyptus wood, the slower would be their development process. 

These larvae start boring tunnels and mine inward, going through the bark to reach the cambium and sometimes the xylem.

Pupa: Once the larvae are done feeding and ready to pupate, they create pupal chambers in the wood. 

Plugging off the entrances with wood shavings and frass, they remain inside and pupate into adults.

Adult: The adult beetles chew their way out through the wood shaving and frass plugs I mentioned earlier. They eventually lay eggs again, and the cycle continues.

Depending on the egg-hatching timings, there might be two to three generations of eucalyptus longhorned borers per year.

How To Get Rid of Eucalyptus Longhorned Borer?

If you’re dealing with a eucalyptus longhorned borer infestation, here are a few remedies that you may try.

Cultural remedies

  • As water-stressed trees are more vulnerable to borer attacks, make sure to irrigate the eucalyptus trees well. Apply the water at a small distance from trees directly below the edge of the canopies. Don’t water too close to the tree – it would promote root disease.
  • If you’re keeping eucalyptus logs for use as firewood, try to dry them quickly or solarize them. Any amount of moisture may promote beetle generation.
  • Heavily-infested host trees might need to be cut down, burned, or chipped to prevent the spread of the pests.

Eucalyptus Borer

Biological remedies

  • Specialized parasites can get rid of an infestation by destroying the borer eggs. A. Longoi, an encyrtid egg parasitoid, is particularly effective.
  • If you’re going to try biological remedies, avoid applying any persistent and broad-spectrum insecticides on the bark.

Chemical remedies

  • Managing eucalyptus longhorned beetles requires systematic insecticides, i.e., insecticides that move through trees along with water and nutrients.
  • Chemical remedies might be especially necessary against P. recurva due to its resistance to biological remedies.

Apart from these, you can use tree care kits to keep your eucalyptus trees healthy, strong, and resistant to infestations.

Frequently Asked Questions

How do you treat borers in eucalyptus trees?

Borers in eucalyptus trees can cause significant damage to the tree, so treatment is essential.
Trees should be inspected for signs of borers, such as holes in the bark and sawdust on the ground.
Depending on how far along the infestation is, one may need to remove large chunks of bark to reach and exterminate the larvae.
After destroying the borers, prune affected branches and apply an insecticide or antifungal treatment.
Additionally, improving overall tree health by irrigating during times of drought and providing fertilizer during active growing periods may help prevent future infestation.

Can a tree survive borers?

Yes, a tree can survive borers depending on its condition. Borers are wood-boring insects that feed off of living tissue inside your trees.
If the tree is healthy and adequately managed, it has plenty of defenses against borer populations.
It is important to carefully inspect your tree for signs of infestation and to address any issues as soon as possible before they become more severe.
Proper pruning techniques and balanced fertilization can also help a tree avoid or overcome borer damage.
Proper cultural care, like preventive treatments in the early spring season, can also deter borer larvae from taking up residence in your trees.

What insecticide kills borers?

Borers can be difficult to kill as they live and feed in the inner bark of trees.
The most effective insecticide for exterminating borers is Dursban, which is a broad-spectrum organophosphate pesticide that eliminates both wood-boring insects and their larvae.
When using insecticides, it’s important to select a product with appropriate levels of toxicity based on the size of the borer being targeted.
These products should only be used according to label instructions by trained professionals to minimize risks to non-target organisms and human health.

What bug kills eucalyptus trees?

The eucalyptus longhorn beetle is a major pest in Australia, and it kills eucalyptus trees by boring tunnels into the trunk and hollowing out the inside.
Their larvae feed off of nutrients in the tree, eventually starving it of life.
This beetle can spread rapidly through many different regions, as the tree-to-tree transmission is common. As a result, infested trees can die very quickly, making them a serious threat to forests.
Control methods include pruning affected branches and using specialized insecticides.

Wrap Up

As we can see, the two borer variants in question can cause significant damage to eucalyptus trees and may even result in tree mortality. 

Protect your eucalyptus trees from drought stress to keep them safe and take the necessary steps to treat a borer infestation. 

Thanks for reading, and I hope you can control the borer infestation before it grows out of hand.

Authors

    by
  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

    View all posts
  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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12 thoughts on “Eucalyptus Longhorned Borer – The Garden Pest Extraordinaire”

  1. Oops… Phoracantha semipunctata would actually seem to be more fitting… The only difference that I can actually visibly see is at the top of the wings on P. semipunctata the dark region is more pronounced than with P. recurva. Sorry about the ranting once again, I just get vaguely irritated that Hawaii is constantly not included in bug identification guides for the U.S. Hawaii does have a site that will assist with identification of local flora and fauna (http://ask.bishopmuseum.org/), but I actually prefer your site. I wasn’t upset with your site, so I really hope you didn’t take it as such. Your site was actually how I identified the beetle to begin with (should have just come here in the first place… lesson learned). Sorry if there are any grammatical errors, or typos, it is getting rather late here, but I just wanted to clear all that up. Oh and could those ants be pharaoh ants instead? I looked up the Argentine ant, and an eighth of an inch is a bit too big for those ants (the beetle was rather small, maybe half of an inch or so). I will try my best to get better macros of them, but they move rather quickly.

    Reply
  2. I had a bug appear on the upper inner right arm that apparently tried to bore into me. I have searched and found on your site, what I believe to be, a Eucalyptus borer. I’m in Miami Florida and the county is attempting to kill off all the Eucalyptus trees. This bug left quit a wound but now, on the inner lower side of my right arm, I am getting an itchy rash directly below and in line with the wound. The bite happened 03/21/2012 and the rash just began about three days ago. You say the bugs are harmless but this one doesn’t seem to be and I’m wondering if there is actually an effect from such a bite/boring. Can you enlighten me? I still have the dead bug.

    Pete 02/26/2010

    Reply
    • We are not qualified to diagnose skin conditions. The bite and the rash might not even be related. We would suggest seeking professional medical advice if you are concerned.

      Reply
  3. we now have allot of these eucalyptus borers every time a night light is left on for a few minutes we get hundreds! Thanks to You Dwight Takemine and his brilliant notion of arranging the planting of twenty thousand acres of eucalyptus on the Hamakua coast of Hawaii.

    Reply
  4. Hi Mate, just doing a bit of research, one of these just bit my hand, fairly painful & burning sensation.
    This is exactly the one in the photo as shown.

    Is this bug dangerous, poisonous or harmful?

    Thanks MIke

    Reply
  5. Hi Mate, just doing a bit of research, one of these just bit my hand, fairly painful & burning sensation.
    This is exactly the one in the photo as shown.

    Is this bug dangerous, poisonous or harmful?

    Thanks MIke

    Reply
  6. I live in the Bay Area and have now found 2 of these in my house! I also thought initially that it was a cockroach but due to the markings decided it wasn’t too. Why are they in my house and how do you get rid of them?

    Reply
  7. Hi Amina,
    Hi what’s that bug Team,

    I have found the same bug at home. It came out of a hole that it made in my tv table. The table was brought from London about 5 years ago and the eggs were probably in it as I’ve never seen such a bug before. When it came out of one of the wholes, it was lethargic too. I don’t know why, maybe because of the first exposure to light. But anyways, I want to ask if there is anyway to stop them from spreading to the rest of the furniture or if there’s anyway I can kill them as they’re ruining the table with the holes they’re coming our from.

    The bug I saw looked exactly like this and the holes were about half a centimeter in diameter while the bug was about 2-3 cm tall.

    Looking forward to hearing from you.

    Kind Regards,

    Ahmed.

    Reply
    • Dear Ahmed,
      Often times wood boring beetles emerge many years after something is created from the felled tree that was the home to the larva. Any beetles that emerge will not infest your furniture.

      Reply

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