The impact of interruptions on cold treatment efficacy for the Mediterranean fruit fly (Diptera: Tephritidae)

Cold treatments are widely used for disinfestation of commodities in international trade and mostly require an uninterrupted duration of exposure to temperatures that do not exceed a specified threshold. The effect of temporary interruptions on cold treatment efficacy was tested on second instar larvae of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in Valencia oranges. In a first series of experiments using one room, a cold treatment of 6 d at a target pulp temperature of 0.9 °C was used. When applied continuously, this constituted the uninterrupted treatment. Interruptions to this treatment were simulated by removing fruit from the cold room until pulp temperatures reached either 3.1 °C or 5.1 °C and as soon as these were reached, fruit were brought back. The timing (first or second half), intensity (3.1 °C or 5.1 °C) and frequency (single or double) of interruptions were investigated in this series. In a second series of experiments using 2 cold rooms at a target pulp temperature of 0.9 °C, interruptions were induced by switching off cooling in one of the cold rooms until pulp temperature reached 5.1 °C. Once the latter was reached, cooling was switched on again. The total interruption time was at least 33 h with a minimum of 16 h for pulp temperatures to reach 5.1 °C and a minimum of 17 h for return to target temperature. In experiments conducted for either 6 or 14 d, there were no significant differences in larval mortality between interrupted and uninterrupted treatments. This study demonstrated that cold treatment efficacy was not compromised by temporary temperature interruptions.