Synergistic Effects and Toxic Mechanism of Phosphine with Ethyl Formate against Citrus Mealybug (Planococcus citri)

Abstract

Methyl bromide (MB) has been used in a wide range of applications, but since it was determined to be an ozone-depleting compound, it has only been used for pre-shipment and quarantine purposes in trade. Phosphine (PH3) is currently the ideal fumigant as an MB alternative worldwide. However, the development of PH3 resistance in the target insect pest and longer PH3 fumigation treatment times raise questions about the continued use of PH3. This study attempted to shorten treatment time via combination treatment with ethyl formate (EF). Planococcus citri was used as the main quarantine pest in Korea, and the acute toxicity of EF, PH3, and EF + PH3 was determined at every developmental stage. EF treatment at 4 h showed LCT99 values of 45.85~65.43 mg∙h/L, and PH3 treatment at 20 h showed that of 0.13~0.83 mg∙h/L depending on the developmental stage. The efficacy of PH3 decreased after reducing the treatment time, but synergistic effects were observed at all stages of development of P. citri when both fumigants were used simultaneously for 4 h. After combined treatment, dihydrolipoyl dehydrogenase expression and the production of two phospholipids, PI(O-16:0) and PC(18:2), were significantly reduced in treated P. citri adults compared with the control. Therefore, combined treatments might be key to reducing the treatment time and resistance of PH3 in the field.

Toxicity of Ethyl Formate to Tribolium castaneum (Herbst) Exhibiting Different Levels of Phosphine Resistance and Its Influence on Metabolite Profiles

“…At the bottom of the desiccator, a small fan was placed to stir the fumigant and ensure even distribution. To assess the dose response to EF fumigation, ten concentrations ranging from 10 to 30 mg/L were tested over a 4 h exposure period [19].…”

“…Calibration and detection for EF and PH 3 were carried out based on previously established methods [19]. The concentration of EF was assessed utilizing a gas chromatograph (GC6890, Agilent Technology Co., Ltd., Santa Clara, CA, USA) equipped with a flame ionization detector (GC-FID) after separation in an HP-Innowax capillary column (30 m length × 0.25 mm i.d., film thickness of 0.25 µm; Agilent Technology Co., Ltd., Santa Clara, CA, USA).…”

“…Nitrogen (99.99%) was used as the carrier gas at a flow rate of 1.2 mL/min. The oven temperature was programmed to 100 • C for 2.5 min; the injection port temperature was set at 200 • C; and the detector temperature was maintained at 250 • C [19,20]. PH 3 concentrations were tested using a gas chromatograph and thermal conductivity detector (GC-TCD) following separation with a stainless steel column (3 m length × 3 mm i.d.)…”