Scientists at AgResearch are working on a new discovery that may lead to cheaper, and more easily produced, sustained-release bioinsecticides.

Conidia (spores), are the active ingredients in some bioinsecticides. They are generally produced in solid fermentation using large volumes of substrate, from which they then need to be recovered. This is labour-intensive, costly, and difficult to scale up. Conidia are also usually very sensitive to environmental and storage conditions.

Recently, researchers described resistant structures that are easy to produce, harvest, store and apply to the soil.

Called microsclerotia, they are small, compact structures of hardened fungal cells. Under the right conditions, they can persist in the environment and then regenerate to form infective conidia. They have been described for biocontrol agents such as Trichoderma harzianum, and Metarhizium spp. 

For the first time, AgResearch scientists have been able to form microsclerotia with two important bioinsecticial fungal species: Beauveria pseudobassiana and Beauveria brongniartii.

The scientists then studied the stability of microsclerotia produced by the New Zealand strain of B. pseudobassiana, which is being investigated as a potential biocontrol product for African black beetle and other soil-dwelling scarab pests.


This sporulated black beetle was infected with conidia produced by microsclerotia of the New Zealand strain AgR-F704 (Beauveria pseudobassiana).

 The microsclerotia, formulated as granules, survived better than conidia under low moisture and ambient temperature storage. They were also able to produce conidia after germination, as reported in their recent publication in Biocontrol Science and Technology (DOI:10.1080/09583157.2018.1514584)(external link)

This suggests it may be technically and economically feasible to use microsclerotia to produce sustained-release biopesticide granules.
The scientists are now working to scale up and optimise the fermentation process to improve yield and microsclerotia harvesting.

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