Determination of Milbemectin Activity

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Milbemectin is a new type of broad-spectrum, non-cross-resistant microbial natural product pesticide with broad-spectrum activity, high efficiency, and low toxicity against agricultural and forestry pests, not easily polluting the environment, and not easy to produce resistance.

Milbemectin is a hexadecyl macrolide mixture, compared with ivermectin in the C-13 position less disaccharide group, so its activity in the inheritance of ivermectin stability and long-lasting at the same time, but also has a higher fat solubility than ivermectin. It is a golden yellow semi-transparent viscous substance at room temperature, easily soluble in hexane, benzene, acetone, ethanol, methanol, and chloroform, but almost insoluble in water, and the mixture of its A3 and A4 components has high acaricidal activity.

The mechanism of action of milbemectin is different from that of γ-aminobutyric acid agonist ivermectin, which can cause the opening of a glutamate-gated chloride channel (glutamate-gated chloride), thus increasing the inward flow of chloride ions and preventing the release of normal action potentials, leading to the death of insect paralysis.
Reagents, Materials, and Apparatus
Tetranychus cinnabarinus is selected as the test organism. 95% milbemectin (A3:A4=3:7) and 96% ivermectin are used as the agents and are configured in different mass concentrations. All other reagents are analytically pure.

Experimental equipment such as Potter spray tower, Olympus dissecting microscope, air compressor, pipette, brush, and punch are prepared.

Experimental Procedures
Determination of virulence of milbemectin against female adult of Tetranychus cinnabarinus.

Fava bean leaves of uniform growth are selected and leaf disks of 2 cm diameter are made using a hole punch.
The leaf discs are placed on skimmed cotton wool in the center of a plastic dish and three leaf discs are placed in each dish.
Female adult mites are inoculated onto the leaf disks with a small brush, 45 mites per leaf disk, and the appropriate amount of water is added.
The leaf discs are placed in an incubation room at (26±1) ℃ with a light intensity of 3000-4500 lx and a photoperiod of 14 hours.
The number of female adult mites is checked and recorded 2 h after inoculation to ensure that the number of mites on each leaf dish is not less than 30.
Spray treatments are carried out using a Potter spray tower at different mass concentrations of milbemectin and abamectin solutions.
The treated leaf disks are continued to be incubated for 24 hours and then examined microscopically and the number of dead and surviving mites is recorded.