Abstract: In order to examine the residual levels and dissipation dynamics of abamectin and β-cypermethrin (β-CP) in pitaya fruit, the fruit were sprayed with 5.2% abamectin-β-CP emulsifiable concentrate (EC) at a recommended dose of 46.8 g/hm2 at different times before harvest. The two insecticides were extracted from the fruit samples using acetone, purified and then concentrated prior to analysis. Abamectin was detected by reversed-phase high performance liquid chromatography while β-CP by gas chromatography. The limits of detection (LODs) were 0.002 and 0.02 ng/μL, and the limits of quantification (LOQs) 0.005 and 0.1 mg/kg for abamectin and β-CP, respectively. The spiked recoveries ranged from 93.8% to 97.2% for abamectin and from 94.0% to 99.2% for β-CP with relative standard deviations (RSDs) less than 9.4%. The dissipation dynamics of abamectin and β-CP sprayed on pitaya fruit was fitted to a first-order kinetic model, and their half-lives were 2.76–4.20 and 3.09–6.08 d, respectively. The final minimum residue values of abamectin and β-CP were < 0.005 and < 0.1 mg/kg, respectively, and the maximum residue values 0.009 and 0.13 mg/kg, respectively. The results showed that the abamectin-β-CP EC could be fast degraded and the pre-harvest interval (PHI) was 14 d, so that it could be recommended for safe pest management. The present study provides basic data and a useful guidance for the use and safety evaluation of abamectin and β-CP on tropical fruits.

Key words: abamectin, β-cypermethri, Hylocereus undatus, residue, dissipation dynamics