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.
Highlights
When importing and exporting grains, fruits, vegetables, and plants in the trade between countries, fumigation agents are normally used against quarantine pests [1,2,3]
As a fumigated compound for the control of P. citri, ethyl formate (EF) and PH3 were treated as a single treatment or a combination treatment as Methyl bromide (MB) alternatives
With reference to the Lethal Concentration-Time (LCT) values resulting from the single treatment of EF and PH3, the treatment amount of PH3 was set to the level of 1 mg/L for the combination fumigation, and the LCT10, LCT25, and LCT50 values of EF were treated at the same time
Summary
When importing and exporting grains, fruits, vegetables, and plants in the trade between countries, fumigation agents are normally used against quarantine pests [1,2,3]. Based on previous studies of alternatives to MB, phosphine (PH3) is the most ideal fumigant in the world, but it has several drawbacks, including slow activity and increased insect resistance [8]. Studies on PH3-related resistance mechanisms, discovering the optimum concentration of PH3 for pest fumigation, and the development of combination fumigation methods with PH3 and EF have been widely conducted [11,12,13]. These various trials for solving the resistance problem are essential for prompt pest quarantine applications of PH3
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