Shothole Borer Beetle – an Ecological Tragedy Gogga of the Month Shot Hole Borer Beetle

Life is a Garden has some essential information to share this month. The shot hole borer beetle, known also as Euwallacea fornicates, is a huge threat to South African biodiversity and our gardens are certainly no exception. From the 80 species of trees under attack, 20 of these are reproductive hosts for this most gagga gogga, and with so many trees in SA and in private gardens, the threat is closer to home than we may think. Here’s some must-know info to help save our trees!

 

How the shot hole borer operates

This invasive bugger from Asia is black in colour and smaller than a sesame seed (about 2mm long). Shot hole beetles dig tunnels in the trunks and branches of host trees where they then lay their eggs. The female beetle carries a fungus (Fusarium euwallaceae), which she spreads through these tunnels, which then becomes food for both larvae and adults.

 

What happens to our trees

The fungus spread inside tunnels completely disrupts the flow of water and nutrients of trees. Simply put, infected trees begin to die from the inside as the larvae hatch, digging through what’s left of the tree, and spreading more deadly fungus that causes trees to basically die from malnutrition. These beetles move a kilometre per week, rapidly infesting and reproducing.

 

Identifying an infected tree

Look out for signs of possible infestations by inspecting the trunks and branches of your trees and those in the surrounding area. Symptoms may vary across tree species, but here are the tell-tale indicators to take note of:

  • Multiple round 1mm wide entry-holes, similar to paper punch holes.
  • Dark, wet staining, oozing, and thick gumming around suspicious holes.
  • Streaks of white powder, sugar volcanoes, or fine sawdust coming from trunk/branch holes.
  • Wilting trees and dead branches.

Let’s save our trees! Shothole Borer

Gardens are under attack by an enemy that we can barely see. Arm yourselves with this valuable information and be ready to go to war!

Over 200 tree species are under attack by a tiny, nasty little tree killing borer beetle with a mouthful for a name; polyphagus shot-hole borer beetle, (or PSHB). The beetle, which is only the size of a sesame seed, creates tunnels deep into the tree where it reproduces and infect the tree with a fungus which in turn becomes the beetles’ food source as it eats the fungus.  This fungus grows from the tunnels into the tree, harming it and can kill full grown untreated trees within a few seasons. The trees it infects include both indigenous and exotic species including some fruit trees such as avocados.

What to look out for:

Since the shot-hole borer is so small and often not seen, it is easier to look for signs of infestation. The symptoms vary from one tree species to the next:

  • Wilted leaves or shedding of leaves
  • Dead or dying branches
  • Tiny, pen-tip sized holes randomly spaced in the bark
  • The holes may have stained marks around them, or have white sugary powder, (known a sugar volcanos), or even gummy beads oozing out of the holes, or most likely “sawdust” on the tree and below it on the ground.

To view images of infested trees: PSHB.co.za/pshb-tree-identification/

To view the beetles: PSHB.co.za/pshb-beetle-identification

What can I do to protect my trees?                                                                                        

The good news is that not every tree will be suitable as a host for the beetle. Strong, healthy trees are less likely to be attacked and if infested, will withstand an attack better. You can boost the health of your trees by:

  • Mulching the tree’s root area
  • Water sufficiently
  • Add nutrients to your trees via fertilizers, composts and manures, (ask your local GCA Garden Centre for advice).