A national research project is underway aiming to develop biopesticides containing insect-killing fungi for managing Queensland fruit fly in Australia. The project forms part of a national biocontrol project for fruit fly, which is led by Agriculture Victoria and co-funded by the Department of Agriculture, Water and the Environment.

The use of microbial-based biopesticides as alternatives to conventional pesticides has rapidly increased in the last decade. Many growers will be familiar with spinosad, an insecticidal compound based on toxins of the bacterium Saccharopolyspora spinosa.

Spinosad is already used in traps and protein bait sprays for fruit flies. Another example of a bacteria-based biopesticide is Dipel, which contains the toxins produced by Bacillus thuringienesis as its active ingredient.

As well as bacteria and their toxins, pathogenic fungi have also been commercially formulated for use against various insect pests worldwide.

“Beauveria and Metarhizium species are the fungal agents commonly used in insecticidal biopesticides,” said Agriculture Victoria project lead Dr Aimee McKinnon.

“These entomopathogenic [insect-killing] fungi can be applied as foliage sprays, as a soil drench, or in a bulk granular formulation, at relatively low cost. They don’t affect plants, and certain insect pathogenic fungi may even enhance plant and soil health through mycorrhizal-like associations.”

Entomopathogenic fungi as a new tool in fruit fly management

The current toolkit to manage Queensland fruit fly includes protein bait sprays, male annihilation technique (MAT), mass trapping, and sterile insect technique (SIT).

“None of these tools target the soil-dwelling life stages of the fly,” Dr McKinnon said. “This is where biopesticides may come to the fore, killing larvae after they emerge from rotting fruit to burrow into soil and pupate.”

Entomopathogenic fungi (EPF) occur naturally in soil throughout Australia. The spores of these microbes attach to the insect cuticle and germinate into the insect body, invading the blood and tissues, and eventually causing death.

Above. Queensland fruit fly pupae infected with Beauveria bassiana

While EPF were first identified for their insecticidal activity as far back as the 19th century, Dr McKinnon said it is only recently that research has looked at the possibly of using them in fruit fly management.

“In the past, biopesticides have often failed to perform well outside of a laboratory. But recent advances in formulation technologies have greatly improved the efficacy of biopesticide products.

“For example, a new fungal based product called Campaign has been registered in various countries in Africa, where it is being used against mealybugs, thrips and fruit flies. Campaign has received some attention recently, for its efficacy as a drench treatment to kill soil-dwelling stages of fruit flies.”

As some EPF work better than others, testing which species and strains cause highest mortality in Queensland fruit fly is currently underway at Agriculture Victoria.

“In our lab studies, we’ve observed from 92–100 per cent mortality of pupae from one fungal strain applied at a field-realistic dose, and only 50 per cent mortality from another strain – which really highlights the importance of testing these different strains,” Dr McKinnon said.

“We aim to move our studies to the field to see how the best strains perform in a real-world scenario.”

PhD student Madita Lauer, who is based at Agriculture Victoria’s Tatura SmartFarm is looking more closely at EPF that naturally inhabit fruit orchards. “I’m exploring what factors influence EPF that attack Queensland fruit fly in the Victorian climate and soil types,” Ms Lauer said. “By better understanding this, my research will help make more effective biopesticides that are suited to environments where fruit flies proliferate.”

Will biopesticides impact beneficial insects?

Worldwide, honeybees and other bee species have been rigorously tested for susceptibility to fungal biopesticides. While bees can potentially become infected, they typically must come in contact with a very high dose of fungal spores. Bees have evolved excellent defensive behaviours and mechanisms to avoid infection by these fungal pathogens, so biopesticides are typically compatible with pollinators.

The research project will test for compatibility of fungal biopesticides with other potential biocontrol agents of Queensland fruit fly, such as parasitoid wasps.

“Our research will hopefully provide local growers with more artillery in the war on Queensland fruit fly,” Dr McKinnon said. “We have a much better chance of suppressing fruit fly populations if we hit the flies from all angles—egg, larvae, pupae and adult.”

The project A national biocontrol strategy for Queensland fruit fly in Australia is funded by the Australian Government through the Department of Agriculture, Water and the Environment Strengthening Australia’s Fruit Fly System Research Program.