Wood ants that actively combat plant diseases could be used in organic apple orchards

25 Nov 2024, 17:50 by Aarhus University

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Agar plates showing the results of A the live ant activity, B crushed ant extract, and C washed ant extract. For A, the left side of the agar plate shows the ant-free control compartment, while the right side shows the ant compartment, where three ants have been roaming for 24 h. For B, the two vertical filter papers were treated with crushed ant extract; they show growth of fungal and bacterial colonies from the extract. The two horizontal filter papers were treated with sterilized Milli-Q water and were overgrown with M. fructigena (the white, fluffy fungus growing circularly across the agar plates). For C, vertical filter papers were treated with washed ant extract, while overgrown horizontal filter papers were Milli-Q controls. The right side of C shows a zoomed-in picture of the inhibition zones around the filter papers and of the microbial growth on the paper. All replicates for each experiment can be found in the Supplementary information. Credit: Microbial Ecology (2024). DOI: 10.1007/s00248-024-02464-2

The small industrious wood ant can do more than just build high nests in spruce forests. A newly published article in the journal Microbial Ecology reveals that ants combat a range of plant diseases, including those affecting apples. At the same time, ants hunt pests like winter moth larvae, which can defoliate apple trees, to feed their larvae. This opens up entirely new perspectives for biological control of plant diseases.

In light of these new results, researchers have now initiated the "AntFarm" project, which aims to develop methods to cultivate wood ants for use in organic apple orchards.

Very clean communities

Ants live incredibly close together in very large communities. As in all other dense communities, there is a high risk of rapid spread of diseases. This is a problem that ants have developed effective measures against through long evolution.

"Ants are extremely clean," explains senior researcher Joachim Offenberg from the Department of Ecoscience, Aarhus University, who has studied ant communities for many years and is a co-author of the scientific article.

Ant communities have their own dung heaps, located away from the nest, and their own garbage collectors. Some species even have the ability to remove waste from the nest and dump it in streams. Moreover, ants are the only animals that have developed a gland on their bodies that secretes antibiotic substances. Researchers describe this as the ants' internal stable defense.

Interaction with bacteria

But ants have more tricks up their sleeves. Researchers have previously shown that wood ants reduce diseases like scab and apple rot in apple orchards. However, they were not entirely sure what was causing the positive effect.

"A possible answer lies in the bacteria and fungi that live on the ants' legs," says Ida Cecilie Jensen, a Ph.D. student at the Department of Ecoscience, Aarhus University, who led the investigations.

Through relatively simple experiments, researchers showed that they could prevent apple rot fungus from growing on agar plates if ants had walked on the plates. They also rinsed the ants with water and found that this "rinsing water" could combat the growth of apple rot fungus.

Researchers managed to isolate five species of microorganisms that live on the ants' legs. Two of them combat both apple rot and apple scab—diseases that have significant economic impact on apple production.

One of these microorganisms also combats two other important plant diseases: gray mold and fusarium head blight, which attack hundreds of different crops. The promising effects of ants against various diseases, as well as their impact on pests, make them promising candidates for biological control of diseases and pests.

Bacteria have a very short generation time, and the interaction with bacteria can be interpreted as the ants' external defense mechanism, which can quickly adapt to new conditions.

New perspectives with AntFarm

The world spends billions each year on chemical pesticides to combat plant diseases. However, these have a range of harmful effects and also impact human health.

"If we use ants and the microorganisms associated with them to combat pests and plant diseases, we ensure a much more sustainable and climate-friendly production," says Jensen, who also points out that organic fruit growers otherwise only have access to a few tools to combat diseases and pests.

Researchers have now initiated the AntFarm project to investigate whether it is possible to cultivate wood ants on a large scale for relocation in organic apple orchards.

"We expect that organic fruit growers will achieve higher and more stable yields with the help of ants, while also increasing biodiversity in the orchards," says Jensen.

Over the next two years, AntFarm will assess the economic feasibility of cultivating ants for biological control, and the researchers have high expectations regarding the antibiotic substances produced by the ants' microorganisms.

Around the world, researchers are currently investigating whether we can also use the antibiotic substances from ants and their microorganisms to combat diseases in humans, who are increasingly plagued by diseases that develop resistance to known antibiotics.

More information: Ida Cecilie Jensen et al, Fungus Fighters: Wood Ants (Formica polyctena) and Their Associated Microbes Inhibit Plant Pathogenic Fungi, Microbial Ecology (2024). DOI: 10.1007/s00248-024-02464-2

Provided by Aarhus University