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United States Department of Agriculture

Agricultural Research Service

Research Project: INTEGRATED PEST MANAGEMENT FOR MID-SOUTH AREA ROW CROPS

Location: Southern Insect Management Research Unit

Title: Photodegradation of emamectin benzoate and its influence on efficacy against the rice stem borer Chilo suppressalis

Authors
item Jun, Zhu -
item Yueping, He -
item Gao, Mingxing -
item Weijun, Zhou -
item Hu, Jun -
item Shen, Jinliang -
item ZHU, YU CHENG

Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 24, 2011
Publication Date: August 3, 2011
Citation: Jun, Z., Yueping, H., Gao, M., Weijun, Z., Hu, J., Shen, J., Zhu, Y. 2011. Photodegradation of emamectin benzoate and its influence on efficacy against the rice stem borer Chilo suppressalis. Crop Protection Journal. 30:1356-1362.

Interpretive Summary: Emamectin benzoate is a novel insecticide with characteristics of translaminar movement into plant leaf tissue. The compound was derived from the avermectin family, which has relatively shorter residual activity due to its vulnerability to UV light photodegradation. Because of variable photodegradation in the different ecosystems, this study was conducted to investigate the stability of emamectin benzoate under UV light, and then to evaluate its toxicity against the rice stem borer, after exposure to UV light for different time lengths. Results showed both initial insecticide (MAB1a) concentration and UV light treatment length (0-120 hours) had significant impact on photodegradation rate. The degradation rate increased as exposure duration increased, but relatively decreased as initial MAB1a concentration increased. The half-life of MAB1a at 1 mg per liter was less than 3 hours. In addition, the photodegradation of emamectin benzoate was also examined for its influence on the efficacy against the rice stem borer. The results of bioassay were consistent with that of chemical analysis. Initial concentration of emamectin benzoate and exposure duration to UV light had significant influence on the efficacy against the stem borer. As the exposure time increased, the efficacy of emamectin benzoate against the stem borer dropped. Compared with none-UV treatment, the efficacy reduction rate decreased as initial insecticide concentration increased from 1 to 1000 mg per liter. The results indicated that UV photodegradation had a significant effect on the efficacy of emamectin benzoate against the stem borer and the effect was concentration-dependant. This finding suggests that maintaining emamectin benzoate above certain concentration in formulation and the application solution may reduce photodegradation and increase efficacy against target pests.

Technical Abstract: Emamectin benzoate is a novel insecticide with characteristics of translaminar movement into plant leaf tissue. The compound was derived from the avermectin family and improved with thermal stability, greater water solubility, and a broader spectrum of insecticidal activity than avermectin. To determine photodegradation of emamectin benzoate, HPLC analysis was applied to determine the content of MAB1a, the major content in emamectin benzoate, after exposure to UV light for different time length. Results showed both MAB1a concentration and UV light treatment length (0-120 h) had significant impact on photodegradation rate. The degradation rate increased as exposure duration increased, but relatively decreased as initial MAB1a concentration increased. The half-life of MAB1a at 1 mg AI per liter was less than 3 h. In addition, the photodegradation of emamectin benzoate was also examined for its influence on the efficacy against the rice stem borer, Chilo (C.) suppressalis. The results of bioassay were consistent with that of HPLC analysis. Initial concentration of emamectin benzoate and exposure duration to UV light had significant influence on the efficacy against C. suppressalis. As the exposure time increased, the efficacy of emamectin benzoate against C. suppressalis dropped. Compared with none-UV treatment, the efficacy reduction rate decreased as initial MAB1a concentration increased from 1 to 1,000 mg AI per liter. The results indicated that UV photodegradation had a significant effect on the efficacy of emamectin benzoate against C. suppressalis and the effect was concentration-dependant. This finding suggests that maintaining emamectin benzoate above certain concentration in formulation and the application solution may reduce photodegradation and increase efficacy against target pests.

Last Modified: 9/10/2014
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