The Beauveria bassiana is a useful entomopathogenic fungus for microbiological control. It can be considered a biological insecticide, thus not harmful to the environment and animal and plant species. When we talk about microbiological control, we mean a vegetable garden defense strategy that involves the exclusive use of microorganisms already present in nature. An example we have already seen is the Bacillus thuringiensis. The use of Beauveria bassiana is simple and effective. For this reason, it is used both by organic farms and those using conventional methods. With the necessary knowledge, this product can also be used by those who have an organic home garden.
Let’s get to know Beauveria bassiana, its mechanism of action, and the correct ways to use it.
What is Beauveria bassiana
Beauveria bassiana is a fungal species discovered by the botanist and naturalist Agostino Bassi (from whom the scientific name derives). In the first half of the 19th century, Bassi understood that this agent caused a severe disease in the silkworm (Bombyx mori). It was soon realized that the microorganism Beauveria bassiana could be used as a natural insecticide to defend crops against pests.
Mechanism of Action
Beauveria bassiana, an endophytic and entomopathogenic fungus, is used in many European countries as a tool for microbiological control. Let’s see how. The microorganism enters the insect following the spore germination. This occurs upon contact with the insects’ cuticle, under specific temperature conditions and high relative humidity. Subsequently, a thin hypha penetrates, developing from the appressorium. The latter is an anchoring organ through which the fungal germ tube adheres to the body of the unfortunate insect, which has only one way to survive: molting. Otherwise, the infection doesn’t stop, progressing to the underlying tissues, leading to the entry of hyphal fragments (or blastospores) into the lymphatic system. The proliferation of material from the fungus will be followed by the production of toxins causing the death of the parasite within 3-5 days, depending on the developmental stage, size, and number of distributed spores. However, the mechanism of action just described is not derived from the strains of Beauveria bassiana on the market. These strains do not produce toxins because the germ tube exerts a physio-mechanical action on the cuticle, piercing it and causing the insect’s death by dehydration. Moreover, the hyphae continue to proliferate by taking nutrients from the deceased body. This way, the infection continues to spread through new spores that move on to a new insect. After death, conidial efflorescences appear outside the body of each insect. It’s a kind of white foam contributing to further fungal dissemination.
Strains of Beauveria bassiana
Just like for Bacillus thuringiensis, there are different strains of Beauveria bassiana.
The main ones are:
- Jw-1, Atcc 74040, which is sold in liquid formulation (you can buy it here)
- Gha, which is sold in powder form (you can buy it here)
The use of these products is allowed in organic farming, and they can be purchased online without the license required for plant protection products. Both strains of Beauveria bassiana can be used on various crops and to combat numerous insect species.
Crops on which Beauveria bassiana is effective
Regarding crops, Beauveria bassiana is recommended on:
- Solanaceae (potato, tomato, eggplant, pepper)
- Cucurbitaceae (watermelon, melon, pumpkin, zucchini, cucumber)
- Leafy vegetables (lettuce, endive, radicchio, basil)
- Drupaceae (peach, plum, apricot, almond, cherry)
- Pomaceae (apple, pear, quince, medlar, strawberry tree)
- Vine and olive
- Citrus fruits (lemons, oranges, mandarins, clementines)
- Fig and prickly pear
- Flower crops
Insects Against Which Beauveria Bassiana is Effective
- Coleoptera like the Colorado potato beetle (Leptinotarsa decemlineata)
- Lepidoptera like the pine processionary (Thaumatopea pityocampa) or the codling moth (Cydia pomonella)
- Aleyrodidae like the whitefly (Bemisia Tabaci)
- Thrips like the Frankliniella occidentalis
- Some species of the superfamily aphids (Aphis fabae, Myzus persiceae, Aphis gossypii, Aphis spiraecola)
- Red spider mite (Tetranychus urticae)
Effectiveness is higher when acting on the insects’ young stages.
Beauveria bassiana can be distributed using normal spraying machines or with a simple backpack pump (like this one).
It should always be diluted with water, which enhances its ability to penetrate the insects’ cuticles. It’s recommended to prepare the mixture 3-4 hours before the biological treatment to encourage fungal spore germination.
Distribution is advisable during the early morning or at sunset when relative humidity is higher, and the adults are less mobile. It’s also important that the intervention occurs when the infestation level is low. In organic farming, it can be sprayed on crops along with copper and sulfur. These products do not significantly affect spore germination. For dosages and application methods, which vary depending on the crop and insect, refer to the product label.
Another consideration is that commercial products have a 0-day waiting period. That means there’s no need to wait even a day before harvesting vegetables because Beauveria bassiana is not toxic to plants, animals, or aquatic organisms.
Commercial products contain live spores, so it’s important to store Beauveria bassiana in a cool place away from light. The product remains stable if stored at 4-6 °C in the refrigerator.