Hoverflies are already well known to be farmers’ friends, providing natural pest control and pollination services, but research from Sweden suggests that they could also deliver beneficial microbes to help curb crop disease.
Swedish University of Agricultural Sciences experts tested whether Eupeodes corollae, a common European hoverfly species, could serve as what is known as an entomovector — an insect used in farming systems to move biological control products to where they are most needed.
Pollinators, predators…now entomovectors?
This ‘flying doctors’ approach has been successfully proven to work with bees, in particular bumblebees which are hairy and able to transport larger loads of pollen and other materials. Hoverflies, up to now, have been associated with the ecosystem services of pollination, being vital to yields for many crops, as well as preying on pests such as aphids and thrips.
The scientists tested E. corollae’s even broader potential in a strawberry cropping system, loading the hoverfly with a strain of the yeast Metschnikowia fructicola in an attempt to tackle grey mould, caused by the fungus Botrytis cinerea. Grey mould gets in strawberry flowers and affects the quality and longevity of post-harvest fruit.
Lab bench to polytunnel
They first showed in the lab that M. fructicola was an effective biological control agent against the mould, which can be a big problem with several different crops. Then they showed that the hoverflies could transport viable yeast from one dish to another.
Proof of concept complete, the scientists then used a polytunnel experiment with strawberry plants to assess how effectively the flies moved the yeast onto flowers (they could do it well). Finally, in a precision greenhouse facility, they assessed how effectively the technique controlled B. cinerea sprayed onto strawberry plants, compared to:
- Plants sprayed with the pathogen and yeast
- Hoverflies not vectoring the yeast and plants sprayed with pathogen
- Plants sprayed with just the pathogen
- Plants sprayed with water
- Untreated plants
Disease reduction, fruit quality boost
They found that the hoverfly vectoring brought results. Strawberries treated with the yeast-shifting hoverflies had the lowest signs of disease, reducing infection by 50-70% after the fruit had been two weeks in cold storage. The treatment also improved fruit shape and quality, highlighting the value of the insects’ pollination role. Hoverflies without the yeast also had a positive impact, second only to the vectoring hoverflies for reducing signs of disease and fruit quality.
Implications for integrated management
Dubbing the hoverflies “flying agents,” the scientists advocated for a hoverfly role in integrated pest and pollinator management (IPPM), a growing trend in protected crops which brings managed pollinators together with strategies to reduce pest pressure.
“This strategy supports the use of beneficial insect and microorganism species simultaneously in agroecosystems,” they wrote in Journal of Pest Science. “Moreover, this approach offers a sustainable alternative to application of chemical fungicides.”
The treatment didn’t affect survival of the flies used in the study, but the researchers called for further work exploring whether it might affect their fitness in other ways, as well an examination of how the technique affects the microbiome of flowers.
While the approach was studied in strawberry crops, it could also be extended to other crop systems, they suggested, underlining another area where future studies could be directed.
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