Enhanced Oil-Based Formulation of a Native Beauveria bassiana Isolate: Optimisation of Carriers and Adjuvants for Improved Conidial Viability

In the world of agriculture, farmers have long relied on chemical sprays to stop insects from devouring their crops. However, a quieter, more natural approach has gained ground: using living fungi to fight pests. Among these microscopic allies, a fungus called Beauveria bassiana is a star performer. It naturally infects and kills a wide variety of harmful insects, offering a way to manage pests without the heavy environmental toll of synthetic chemicals. Yet, for this biological weapon to work in the real world, it faces a significant hurdle. The tiny spores that carry the infection are fragile. When exposed to drying air, harsh sunlight, or temperature swings, they often die before they can reach their target. To make these fungi useful for farmers, scientists must package them in a way that keeps them alive and ready to strike, a process known as formulation.

Researchers at Kerala Agricultural University set out to solve this packaging problem for a specific, native strain of the fungus. They knew that mixing the fungal spores with oil could help protect them from drying out and help them stick to insect bodies better than water-based mixtures. However, not all oils are created equal, and adding the wrong ingredients could kill the fungus instead of saving it. The team tested five different vegetable oils—palm, sesame, sunflower, rice bran, and coconut—to see which ones the fungus could tolerate. They also experimented with four different additives, including glycerol, a common thick and slippery liquid, to see if these substances could act as a shield for the spores during storage.

The first step was to see which oils would let the fungus grow and which would stop it dead in its tracks. The researchers placed the fungal spores on plates and introduced the different oils. The results were clear and immediate. Sunflower, rice bran, and coconut oils acted as barriers, preventing the fungus from growing at all. Sesame oil was better, allowing the fungus to survive, but palm oil proved to be the clear winner. It did not inhibit the fungus in any way, and when the team stored the spores in palm oil for fifteen days, the number of living spores remained significantly higher than in any other oil tested. This identified palm oil as the ideal carrier, the liquid vehicle that would hold the fungal army.

With the best oil selected, the team moved on to finding the perfect additive to mix into the palm oil. They tested various concentrations of glycerol, a substance that holds onto moisture, along with other common additives like emulsifiers and thickeners. The goal was to find a mixture that kept the spores alive for as long as possible. The results pointed to a specific recipe: palm oil mixed with three percent glycerol. This combination kept the highest number of spores alive after thirty days of storage. Other additives, such as a common emulsifier called Tween-80 and a plastic-like substance called PEG, actually reduced the number of living spores, performing no better than plain oil with no additives at all. The glycerol mixture, however, created a stable environment that protected the spores.

The final test was to see how long this new mixture could last on a shelf. The researchers stored their best formulation, the palm oil and glycerol mix, in glass bottles under normal room conditions and checked the number of living spores every month for a year. The mixture performed remarkably well. For the first five months, the number of living spores stayed high, well above the minimum level required for a product to be considered commercially useful. Even after four months, the count remained strong. However, by the sixth month, the number of living spores dropped below the acceptable standard, meaning the product would no longer be reliable for farmers. In contrast, a control group of spores stored in plain water died off much faster, losing viability within two months.

This study demonstrates that a simple combination of palm oil and a small amount of glycerol can significantly extend the life of these beneficial fungal spores. By finding the right oil and the right additive, the researchers created a formulation that keeps the fungus alive and ready for use for up to five months. This is a crucial step toward making biological pest control more practical and reliable for large-scale farming. While the product does not last forever, extending its shelf life from a few weeks to five months makes it a viable option for integrated pest management programs, offering a sustainable alternative to chemical pesticides that can be stored and shipped without losing their power.