Aug. 9, 2019
Author: Caroline Woelfle-Gupta (Research Scientist, Dow)
Bacillus thuringiensis (Bt) is one of the most commonly used microbial pesticides and currently represents the largest share of the biopesticides market. Bt is highly active against insects such as caterpillars, mosquito larvae, and blackflies that transfer river blindness in Africa. During the sporulation of Bt, crystal aggregates of proteins are produced, which along with its spores, are responsible for high insecticidal activity. However, Bt lacks long-term activity in the field due to low persistence of the crystal proteins on plant leaves due to rain and UV sensitivity of the spores.
Rain and sunlight are difficult conditions to control. How can a formulator improve a product’s resistance to these environmental factors and take full advantage of Bt benefits in the field?
Dow is currently developing materials to provide rainfastness and UV resistance to Bt. These materials have been shown to perform above benchmarks for both liquid and dry flowable Bt formulations available today.
These novel materials from Dow can enable 75 percent Cry protein retention for a liquid Bt formulation even after two hour exposure to simulated rain. In comparison, no Cry proteins remain on the surface of the mimic plant leaf when the control Bt formulation is exposed to simulated rain for the same duration of time (Figure 1). The materials are also spray-dryable and enable up to 58 percent Cry protein retention after exposure to simulated rain after spray-drying and re-dispersion of the dry product in water (Figure 2). Benchmark products tested are not spray-dryable and stick to the chamber of the spray-dryer during the process.
Dow’s materials deliver enhanced UV resistance as well. Bt spore viability retention is 95 percent after two hour exposure to simulated sunlight. No viable spores are obtained when the control formulation is exposed to the same conditions (Figure 3).
Figure 1. Percentage of protein retention after mimic plant leaf with dried on liquid Bt formulation is exposed to simulated rain at various durations in a lab.
Figure 2. Percentage of protein retention after spray-drying and re-dispersion of a liquid Bt formulation containing Dow’s rainfastness material.
Figure 3. Percentage of Bt viability retention after two hour exposure to simulated sunlight in a lab at an intensity equivalent to 6-7 times peak summer sunlight intensity.