Borers are a type of destructive pest that cause damage to certain trees and woody shrubs, resulting in potentially devastating infestations. As adults, borers are winged insects (either moths or beetles) that utilize vulnerable timber in their breeding cycle. After mating, females lay their eggs on the bark of an unlucky plant host. Upon hatching, these borer larvae burrow beneath the bark in search of food—devouring the tree’s carbohydrate-rich cambial layer, which transports water and nutrients throughout the tree. Stripped of its conductive tissue, an infested tree can die within just a few weeks of initial contact.

Two prominent borer pests in the Brisbane area are the eucalyptus longhorned borer (Phoracantha semipunctata) and the Poinciana borer (Agrianome spinicollis). Both species of borer belong to the longhorn beetle family (Cerambycidae) and can wreak havoc on your landscape when left unchecked.

The eucalyptus longhorned borer is native to Australia but has become an invasive species in temperate and tropical regions around the globe, predominantly California. This borer affects, as the name suggests, eucalyptus trees. These beetles are large, approximately 22-28 mm long, and have relatively long antennae which span at least the length of the body. In color they are a deep, reddish brown with yellow patterning on the abdomen.

In late spring the adults emerge from the previous season’s infested timber and begin looking to mate. Volatile chemicals emanating from stressed eucalyptus trees actually attract the adult beetles and copulation takes place upon the bark, where the females then deposit their eggs. In less than a week, the larval P. semipunctata hatch, immediately burrowing deep beneath the surface of the host tree.

The larval eucalyptus longhorned borer is much smaller than its adult counterpart and is ivory in color, though as the larvae portion of the lifecycle takes place entirely inside the tree host they are rarely seen without interference.

The Poinciana borer is also native to Australia and affects a range of host trees, most notably the Poinciana, fig, and pecan. Adult A. spinicollis specimen can measure in at an impressive 60 mm long, much larger than their cousin, the eucalyptus borer, and are russet-brown in color, with lighter brown, transluscent wings covering the abdomen.

Early to mid-summer is when the first beetles of the season emerge; breeding takes place in the following weeks. The larvae, sometimes called “witchetty grubs,” look like portly, pearlescent worms and have been enjoyed as a delicacy by aborigines for countless generations.

Catching a borer infestation in the early stages can be tricky, but it can also mean the difference between life and death for your ornamental. The first step in borer prevention is identifying the most-susceptible species in your yard. Do you have any eucalypt varieties? Any Poincianas, figs, or pecans? Know which of your plants are the most at-risk for becoming hosts.

Next, examine the susceptible specimens for any sign of borers. Some tell-tale signs include the entry holes of the larvae on the trunk, discoloration and wilting of foliage, and thinning and die-back amongst the crown. In some extreme cases, the incessant gnawing of the larvae is actually audible to humans at a distance of several feet. When examining eucalyptus trees it is necessary to be especially thorough, as the female eucalyptus longhorned borer will in fact lay her eggs underneath the loose, exfoliating bark.

As the saying goes, the best defense is a good offense. Keeping your plants healthy is the key to ensuring that these destructive pests stay away from your yard in the first place, as stressed plants actually emit chemicals that are attractive to adult borers looking to reproduce. Fresh wounds are attractive entry points for egg-laying adult females, so take extra care to avoid any damage to your ornamentals when doing routine yard work like mowing or pruning.

Don’t let borers catch your ornamentals on a bad day! In addition, selecting the proper cultivar for your region and hardiness zone is essential—an ill-adapted cultivar will only become fussy and cause problems for you down the road, eventually becoming so stressed that it becomes the perfect target for a borer infestation. If you have any eucalyptus make sure that they are getting enough water, as underwatering is one of the most glaring issues in eucalyptus care outside of their native environment.

When and if your first line of defense, preventative health, fails, there are some alternative techniques that can come in handy. One such tactic utilizes wire to kill the larvae mechanically, by shoving the material down the telltale entry point holes in the bark. This method is most affective early on in the larval life cycle, before they have time to grow stronger.

A second borer-ridding tactic involves disrupting the reproductive process of the adult insects and so prevents the larvae from ever entering the host tree at all. In order to correctly execute this technique, pheromone lures must be placed out in correspondence with the adult borers emerging from the previously-infested trees. These new adults immediately set to work finding a suitable mate, relying on their finely tuned ability to detect the sex pheromones of the opposite sex. The unsuspecting beetles are thus attracted to the lure, captured, and subsequently killed, decreasing the number of borer specimen that are able to reproduce.

Many people turn to insecticides when trying to rid themselves of insect pests. Insecticides can be helpful in dealing with many insect species, but that is not the case with borers. Because the larvae burrow into the wood immediately after hatching, conventional insecticides are hardly effective, as the juvenile borers are protected beneath the surface of the bark, where any insecticide would be applied. In fact, the layers of wood provide such good protection that there are reported cases of borer larvae surviving even forest fires.

No matter if your ornamentals have been targeted by the eucalyptus borer or the less selective Poinciana borer, both species are capable of destroying your landscape trees in a matter of weeks. Educating yourself on these pests is an imperative first step in protecting your yard from becoming a breeding ground and participating in the cycle infestation.