Abstract: At present, the production technology of microbial pesticide technical materials in China has reached or even exceeded the level of developed countries, but there is a large gap in preparation technology, which is mainly reflected in the unreasonable dosage form structure, poor preparation quality, only a few pesticide additives, and the overall low level of dosage form processing technique. The market demand and application benefit of functional microbial products such as Bacillus thuringiensis (Bt) are closely related to the dosage form. This test was initiated to determine the best dosage form of the new biological nematicide NBIN-863. A high content Bt suspension (5.2―7.9 billion CFU/mL) was developed by selecting different additives, including preservative, dispersant and suspending agent. The dosage form was optimized by adding 0.4% preservative potassium sorbate, 1.0% dispersant magnesium aluminum silicate, and 4.0% suspending agent calcium lignosulfonate to the Bt fermentation broth, and by adjusting the pH value to 4.5 using hydrochloric acid, which produced the maximum number of spores 7.9×10⁹ CFU/mL before the thermal storage at 54 ℃. The dosage form showed the highest activity against Caenorhabditis elegans, with a LC₅₀ value of 2.83 mg/L, and field control efficiency on cucumber root knot nematode of 68.64%. Based on all the indexes, especially the half lethal concentration to Caenorhabditis elegans, the nematocidal NBIN-863 suspension (7.9 billion CFU/mL), with good fluidity and long shelf life, is of high potential for controlling crop root knot nematode disease.

Key words: Bacillus thuringiensis, bio-nematicide, high content suspension