Joint Acaricidal Action Of Scopoletin And Bisdemethoxycurcumin And Preparation Of Its Suspension Concentrate

Phytophagous mites are serious agricultural pests that are difficult to control because of their reproductive efficiency and short generations in China. The "3R"(residue, resistance, and resurgence) of synthetic chemical acaricides makes this problem worse. Botanical acaricides and new aqueous formulations are protection tools used to control mites and retard residue, resistance, and resurgence. We isolated the botanical acaricidal substances scopoletin and bisdemethoxycurcumin (BDMC) from Artemisia annua and turmeric(Curcuma longa). The main action modes of scopoletin against Tetranychus cinnabarinus were contact killing, systemic killing, repellency, and oviposition inhibition. Scopoletin significantly inhibited the activities of acetylcholinesterase, monoamine oxidase, Na+-K+-ATPase, and Ca2+-Mg2+-ATPase. The main action modes of BDMC against T. cinnabarinus were contact killing, repellency, and oviposition inhibition. The acaricidal mechanism of these compounds may be the inhibition of superoxide dismutase, gultathione S-transferases, and catalase activities. The high melting point, high polarity, and slight water solubility of scopoletin and BDMC make them suitable for producing pesticide suspension concentrates. Scopoletin and BDMC have different action modes, mechanisms, and physical characteristics. In this study, we determined whether the joint action of scopoletin and BDMC leads to synergistic acaricidal activities, more action modes, low toxicities, and low residue contents. We hypothesized that these compounds can be effectively applied as environment-friendly botanical acaricides. Therefore, we used the optimal scopoletin-to-BDMC ratio and suspension concentrate. We also analyzed the performance and acaricidal activities of10%suspension concentrate (SC) scopoletin and BDMC. The main results are as follows:1. Screening for optimal scopoletin-to-BDMC ratio. The acaricidic activities of scopoletin and BDMC were evaluated using the methods of slide dipping and leaf-disc dipping. A higher scopoletin-to-BDMC ratio indicated synergism against female adults of T. cinnabarinus. The synergistic mass ratios of scopoletin to BDMC ranged from1:0.2to1:3.0. Using SPSS software, the relationship between corrected toxicity ratio (y) and scopoletin content in mixture (x) was fitted as follows:y=-1.206x2-1.301x+0.926(F=81.40, r=0.976). The optimal ratio of combined effect, the LC50after48h of treatment, and the co-toxicity coefficient were7:6,0.1899mg?mL-1, and129.0, respectively. These data indicate synergism with an efficiency of28.98%. Moreover, the optimal scopoletin-to-BDMC ratio indicated synergism against Panonychus citri. At24and48h after the treatment, the co-toxicity coefficients were141.3and198.6, respectively, suggesting synergism with efficiencies of41.33%and98.63%, respectively. The optimal scopoletin-to-BDMC ratio also demonstrated synergism against Petrobia harti. At24h after the treatment, the co-toxicity coefficient was125.4. The compounds showed independent actions at48h after the treatment.2. Evaluation of the action modes of optimal scopoletin-to-BDMC ratio. The contact activities of the optimal ratio against female adults, nymphs, larvae, and eggs of mites were significantly improved, with LC50values of0.1899,0.1783,0.0624, and1.5161mg-mL"1, respectively. Certain activities of systemic killing, repellency, and oviposition inhibition against T. cinnabarinus were also found. The LC50of the optimal ratio for systemic toxicity against female adults and nymphs of T. cinnabarinus were5.6228and6.5242mg-mL-1, respectively. At24h after the treatment, the repellency activity of1.0312mg-mL-1of the optimal ratio was higher, with the mortalities of female adults and nymphs adjusted to69.49%and72.50%, respectively. In addition, the oviposition inhibition rate was55.49%. Therefore, scopoletin and BDMC are botanical acaricides with a multi-mode mechanism of action. Furthermore, the contact activities of the optimal scopoletin-to-BDMC ratio against female adults, nymphs, larvae, and eggs of T. cinnabarinus were stronger, with certain activities of systemic, killing repellency, and oviposition inhibition.3. Evaluation of the lethal effects of optimal scopoletin-to-BDMC ratio. A time-dose-mortality model and a time-dose effect were established to determine the lethal effect of the synergistic activities of scopoletin and BDMC against mites. At8h after the treatment, the cumulative mortality was spanking exaltation, and the peak mortality of T. cinnabarinus was found at32h after the treatment with the optimal scopoletin-to-BDMC ratio. The median lethal times (LT50) of the optimal ratio were6.1and5.0h at concentrations of1.0and2.0mg-mL-1, respectively. Moreover, the optimal scopoletin-to-BDMC ratio showed synergism against P. citri at24and48h after the treatment, with LC50values of0.2848and0.0255mg-mL-1, respectively. The LT50values of the optimal ratio were15.3and10.0h at concentrations of1.0and2.0mg-mL-1, respectively. Furthermore, the LC50of the optimal ratio against P. harti at24h after the treatment was0.9031mg-mL-1, with LT50values of29.1and26.4h at concentrations of1.0and2.0mg-mL’1, respectively. In summary, the sensitivity of the three mites treated with the optimal ratio was in the order of P. citri>T. cinnabarinus>P. harti.4. Formulation of10%SC scopoletin and BDMC, and performance evaluation. The optimal scopoletin-to-BDMC ratio was used to prepare10%SC scopoletin and BDMC using the methods of flow point, triangle-coordinate figure, and so on. The optimal prescription is listed as follows (wt.%):5.4%scopoletin,4.6%BDMC,2.0%Morwet D-500,3.0%1602,0.1%xanthan gum,2.0%magnesium aluminum silicate,1.0%organic bentonite,2.0%ethylene glycol,0.5%n-octanol, and100%aqueous solution. The optimal grinding time of10%SC scopoletin and BDMC ranged from2.0h to2.5h. The quality control indexes of10%SC scopoletin and BDMC conformed to the basic requirements of SC under hot and cold storage. After heat and cold storage, the particle sizes were2.26and2.35μm, respectively. After dumping and washing less than8.0%and1.0%of the residual ratio, the suspension rates were87.96%and90.36%, respectively. The surface tension ranged from52.50mN-m-1to42.40mN-m-1when the concentration of10%SC scopoletin and BDMC ranged from10mg-L-1to250mg-L-1, with a critical micelle concentration of100mg-L-1. The contact angles were less than90°of10%SC scopoletin and BDMC solutions on citrus and cotton leaves. The order of the contact angle drops of citrus and cotton leaves was as follows:cotton abaxial leaf>cotton adaxial leaf>citrus abaxial leaf>citrus adaxial leaf. Moisten indicated that the solutions can be efficacious wetting citrus and cotton leaf, and the spreading wetting on citrus and cotton leaf was in the sequence of cotton abaxial leaf>cotton adaxial leaf>citrus abaxial leaf>citrus adaxial leaf. The maximum retention of10%SC scopoletin and BDMC was higher in the cotton leaf than in the citrus leaf. Therefore, the physical stabilities of10%SC scopoletin and BDMC were qualified. These compounds can effectively wet and adhere to plant leaves, making them worthy to be developed for further applications.5. Evaluation of the biological activities of10%SC scopoletin and BDMC. The LC50values of10%SC scopoletin and BDMC against female adults and nymphs of T. cinnabarinus were93.3and41.9mg-L-1, respectively. Control acricides spirodiclofen (24%SC) and propargite (73%EC) were used to treat female adults and nymphs of T. cinnabarinus. Their LC50values against female adults were48.1and152.1mg-L-1, respectively, whereas their LC50values against nymphs were11.3and79.3mg-L-1, respectively. These results indicate that the acaricidal activities of10%SC scopoletin and BDMC were greater than those of73%EC propargite but less than those of24%SC spirodiclofen. At concentrations of167,100, and292mg-L-1, the efficacies of10%SC scopoletin and BDMC,24%SC spirodiclofen, and73%EC propargite sprayed for3days against carmine spider mites in indoor potted cowpea seedlings were91.75%,93.67%, and92.66%, respectively. At concentrations of167,100, and292mg-L-1, the efficacies of10%SC scopoletin and BDMC,24%SC spirodiclofen, and73%EC propargite sprayed for3days against T. cinnabarinus in a cotton field were71.69%,81.14%, and71.53%, respectively. Their efficacies were not significant. At7and15d after spraying, the efficacies of10%SC scopoletin and BDMC against T. cinnabarinus were95.27%and94.82%, respectively. The results indicate that10%SC scopoletin and BDMC is an effective environment-friendly botanical acaricide with a multi-mode mechanism of action. At a concentration of167mg-L"1, this botanical acaricide can prevent and control indoor and cotton fields of carmine spider mite.