Biological pest control: Fighting harmful soil organisms with nematodes and soil bacteria

Entomopathogenic nematodes (EPN) and bacteria (EPB) have a potential as biological control agents against, but their application is hampered by inefficient methods. We embedded the microorganisms in alginate beads, which facilitates the application concomitant with the sowing of the cultures.

  • Background (completed research project)

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    We previously found that populations of entomopathogenic nematodes (EPN) are extremely low in Swiss agricultural soils compared to natural habitats. In crop fields that suffer from soil insect pests, an augmentative approach can increase the numbers of these beneficial organisms. The greatest obstacles to an effective application are the high cost of
    current application methods and a limited shelf-life of the biological control agents.

  • Aim

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    The project intended to develop and improve a novel application method based on encapsulation of EPN and EPB in alginate beads by improving the formulation and by
    supplementing the beads with useful plant-derived substances, i) a quiescence factor which keeps the embedded microorganisms in good shape until they need to be set free in the soil, and ii) attractants and/or feeding stimulants to encourage the pest insects to feed on the beads. Furthermore the compatibility of EPN and EPB was ascertained. The optimized
    beads were tested for their efficacy against soil-dwelling pest insects: native fly maggots that are a problem in Swiss cabbage cultivation and invasive pest insects feeding on maize.

  • Results

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    With the developed formulation we were able to produce robust and easy to handle beads in which the biocontrol agents readily survived for more than a month, depending on
    abiotic conditions. EPN and EPB were found to be compatible. The beads provide poor control of root fly larvae, but trials against rootworm and weevil larvae are highly promising.

  • Importance for research

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    We made significant progress towards the goal to identify a quiescence factor that puts EPN in a state of dormancy. If we succeeded in identifying the reactivation principle, it would open ways to study its biological function (e.g. defence against plant parasitic nematodes).

  • Practical significance

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    We developed a product that can be used for the biological control of soil-dwelling pest insects. With some further optimization it can be effective against several important invasive pest insects and it offers a safe and environmentally harmless alternative to pesticides.

  • Original title

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    Alginate beads as vehicles for the application of entomopathogenic nematodes and bacteria against economically important soil-dwelling pests