What entomopathogenic fungi are
Entomopathogenic fungi can infect and kill insects. Natural epizootics of these fungi have been known for a long time: in the 19th century entomologists already noted that mummified bees, flies and beetles covered in white or green "fuzz" were not mold but a parasitic fungus in the sporulation phase.
The two species best studied as biopesticides are Beauveria bassiana and Metarhizium anisopliae. Both infect insects through the cuticle, grow into the body, multiply in the hemolymph and kill the host within days.
What the studies showed
Stamets devotes a separate chapter of "Mycelium Running" and a series of later publications to entomopathogenic fungi. The main points:
- Host range. Metarhizium anisopliae attacks termites, bark beetles, locusts, ticks. Beauveria bassiana — a broad range of insects, including the Colorado potato beetle and forest pests.
- Selectivity. Unlike broad-spectrum chemical insecticides, a specific strain can be tuned to a particular host, reducing collateral damage to beneficial insects.
- Compatibility with IPM. Fungal preparations are used in integrated pest management (IPM) schemes alongside biological and agronomic methods.
Field trials
According to reviews in peer-reviewed journals, preparations based on Beauveria bassiana and Metarhizium anisopliae proved effective in field conditions for controlling:
- rice weevil (Sitophilus oryzae) in grain storage;
- Colorado potato beetle (Leptinotarsa decemlineata) in potato fields;
- termites in underground traps;
- Varroa destructor mites in hives — here the topic intersects with mycelium extracts for bees (see Mushrooms and bees).
Limitations and criticism
Stamets emphasizes several limitations often omitted in popular accounts:
- Dependence on conditions. Fungal spores are sensitive to ultraviolet light, humidity and temperature. Outdoors, a biopesticide needs repeated applications.
- Cost and storage. Live-spore preparations have a limited shelf life and need a cold chain in transport.
- Regulatory barriers. Biopesticide registration takes years in different countries; several Beauveria- and Metarhizium-based products are already registered, and the range keeps growing.
Our comment
We do not recommend experimenting with entomopathogenic fungi on your own: strains suitable for field use undergo separate selection and registration. Stamets repeatedly stresses that "wild" isolates from the forest are unsuitable as biopesticides — their effectiveness is hard to predict, and they may harbor other microorganisms.