Fungus first for new dung beetle species

By  Ian Dewar 2 June 2023 3 min read

Between 2018 and 2023, we imported three new dung beetle species from Morocco, via our quarantine facility in France. Their job is to stop dung building up on the soil surface in southern Australia in spring. They come from a similar climate so should be a perfect match.

However, something happened that we didn't expect. The dung beetles became infected with the fungus Beauveria australis while in a rearing facility and outdoors in farm cages. It was the first time this deadly insect fungal infection has been found in dung beetles or in any member of the scarab beetle family.

The dung beetles would have encountered this Australasian fungus only upon their release in the wild. The infections could explain in part why some dung beetle species introduced to Australia have failed to survive. 

Beauveria is related to the infamous zombie ant fungus Cordyceps. It infects grasshoppers, ants, wasps and various kinds of beetles. Once the fungus reaches the insect’s body cavity, there is no chance of survival for the insect!

Poo believers: our dung beetle story

Since the 1960s our dung beetle program has released 44 African and European species of dung beetles to clean up livestock dung.

Australia's native dung beetle species evolved to clean up the small, dry, fibrous poo of native marsupials. The introduced dung beetles focus on cleaning up after livestock, which generally have larger and wetter dung. They bury the dung, which helps to recycle nutrients, aerate the soil, reduce runoff and reduce fly and parasite populations.

But only 23 of the species we've released have thrived in the field so far.

Certain fungi would be new pathogens to the introduced dung beetles. Exposure to these may have contributed to the failure of some of the dung beetles to establish here.

Dung beetles infected

Our entomologist Dr Valerie Caron and her team discovered the local fungus B. australis infecting dung beetles for the first time, along with the more common Beauveria bassiana. The latter is also known as the icing sugar fungus and is found around the world.

“The outbreak occurred in a rearing laboratory, in a population that had been raised for several generations post-quarantine,” Valerie said.

The fungus was already here and didn’t come from overseas as B. australis does not occur where the new beetles originate. The beetles are thoroughly cleaned and checked according to strict biosecurity procedures before being sent from overseas to our quarantine facility.

“Only eggs are released from the quarantine facility and all eggs are surface sterilised before being released. We then hatch the eggs in our rearing laboratory and raise the new dung beetles for field release,” Valerie said.

“In this case we managed the fungal outbreak successfully, so it didn’t spread any further to other populations in the rearing laboratory.”

The Beauveria fungi

Mycologist Dr Cecile Gueidan from the Australian National Herbarium said these fungi come from the same family as Cordyceps (Cordycipitaceae) and have the same nutrition mode – that is, they feed on insects (they are entomopathogenic).

“The spores attach to an insect’s body and germinate, and the fungal filaments then pierce the insect’s exoskeleton,” Cecile said.

“Once they reach the body cavity, the fungal filaments change form and spread out, producing toxins and enzymes to digest the insect from the inside.

“The fungal filaments then sprout out of the insect’s body and disperse to the soil or other insects.”

It’s thought that the virulence of the fungi is highly variable depending on the strain. In this case the fungi killed 23.5 per cent of the laboratory population.

The fungal infection most likely came from local soil and dung and posed no threat to humans.

These two fungi species have been previously reported in South-East Australia. B. Bassiana is found around the world, but B. Australis is only found in Australia and Asia.

Finding these local fungi infecting dung beetles offers an interesting insight into how imported dung beetles are impacted by the Australian environment. Further research is needed to investigate how widespread the Beauveria fungi are and how they affect wild populations of dung beetles.

The findings have been published in the Journal of Invertebrate Pathology.