Australia: Using fungi for beetle biocontrol in almond orchards

Agriculture Victoria research scientists are investigating the use of biopesticides such as entomopathogenic or insect-killing fungi to reduce populations of carpophilus beetles in almond orchards.

Carpophilus beetles can cause significant damage to Australian fruit and nut crops, as the beetles feed on crops and act as vectors for various plant diseases.

This pest can cost the Australian almond industry $20 million in revenue loss per year, and kernel losses of up to 10 per cent.

Agriculture Victoria Research PhD student Will Boston said it is difficult to target carpophilus beetles with conventional pesticides.

“Spraying orchards may not be that effective as this beetle species resides within nuts, additionally the beetles quickly spread to new season nuts by harbouring in residual nuts left after harvest,” Mr Boston said.

This research involved testing the effectiveness of seven strains of the fungus Beauveria bassiana against both adult and larval stages of two species of carpophilus beetles in laboratory conditions.

For the beetle species that favours almonds the mortality was 19 per cent when treated with the most effective fungus, compared with 52 per cent for the beetle species that favours stone fruits.

However, when used against larvae, the mortality for both beetle species was generally higher, with four fungal strains causing greater than 80 per cent mortality in the stone fruit beetles, while only one fungus was effective against the almond beetles with 73 per cent mortality.

“We found particular entomopathogenic strains can kill carpophilus beetles – particularly larvae – in the laboratory, and these findings show the fungi have potential to be developed as biopesticides and applied as part of an integrated pest management strategy."

More research is already underway, and as part of his PhD studies Will is examining whether adult beetles can be used as vectors to transmit the fungi to the larvae.

“We are developing an auto-dissemination strategy, which involves trapping the adult beetles, infecting them with fungal spores and releasing them; the hypothesis is when the beetles return to the nuts they will spread the pathogen to the eggs and develop larvae,” he said.

The research could potentially be effective against two different pest species that afflict almonds.

“The beetle is likely to be found in nuts together with another important pest, the carob moth, so there is potential for the pathogen to spread to the moth larvae as well.”

If successful, this research could provide growers with a targeted low-labour cost pest management solution that, unlike conventional pesticides, would have minimal impact on insects.

“Shifting public perceptions of chemical pesticides, increases in insect pesticide resistance and the rise in organic farming is driving the development of more environmentally sustainable pest management solutions,” Mr Boston said.

Exploring the use of entomopathogenic fungi as biopesticides forms part of the biological control component of the Almond Integrated Pest Management research project.

This research in biopesticide development – aligns with the Grow, Modernise and Protect themes of the Victorian Agriculture Strategy – which is supported by the Almond Board of Australia and Agriculture Victoria Research.

The research, Virulence screen of Beauveria bassiana isolates for Australian Carpophilus (Coleoptera: Nitidulidae) beetle biocontrol, was published in Agronomy.