ABSTRACT
A systems approach was developed as an alternative to a standalone quarantine disinfestation treatment for Thaumatotibia leucotreta in citrus fruit exported from South Africa. The systems approach consists of three measures: pre and postharvest controls and measurements, postpacking inspection, and postharvest exposure to low temperatures. Different cold treatment conditions with a range of efficacy levels can be used for this last measure. A series of trials reported here evaluated the efficacy of seven temperatures ranging from 0 to 5°C for durations from 14 d to 26 d. Mortality of the most cold-tolerant larval stages of T. leucotreta was determined. Temperatures of 0, 1, 2, and 3°C for 16, 19, 20, and 24 d respectively, induced 100% mortality of the tested populations. Probit 9 level treatment efficacy was achieved at 0 and 1°C for 16 and 19 d respectively. Mortalities higher than 90% were obtained with temperatures of 4, 4.5, and 5°C, after exposure for the longer durations. We demonstrated a significant difference in cold-induced insecticidal efficacy between 1, 2, 3, and 4°C. There was no significant difference in insecticidal efficacy between 4 and 4.5°C, but both of these temperatures were more efficacious than 5°C. The results of this study are valuable to support the use of cold treatment conditions with lower risk of fruit chilling injury in an effective systems approach, where the cold treatment efficacy can be augmented with other components of the systems approach.
Subject(s)
Citrus , Moths , Animals , Cold Temperature , Larva , TemperatureABSTRACT
The litchi moth, Cryptophlebia peltastica (Meyrick) (Lepidoptera: Tortricidae), is endemic to sub-Saharan Africa and certain Indian Ocean islands. It is an important pest of litchis and to a lesser extent macadamias. Litchis are exported to certain markets that consider C. peltastica as a phytosanitary pest. Consequently, an effective postharvest phytosanitary treatment is required. This study sought to develop a cold disinfestation treatment for this purpose. First, it was established that the fifth instar was the most cold-tolerant larval stage, as it was the only instar for which there was still some survival after 12 d at 1°C. It was then determined that cold treatment trials could be conducted in artificial diet, as there was no survival of fifth instar C. peltastica in litchis after only 9 d at 1°C, whereas it took 15 d at this temperature before no survival of fifth instar C. peltastica was recorded in artificial diet. Consequently, cold susceptibility of fifth instar C. peltastica and the most cold-tolerant larval stages (fourth and fifth instar) of false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), were compared in artificial diet. There was no survival of C. peltastica after 13 d at 1°C, whereas this was only so for T. leucotreta after 16 d. Consequently, it can be concluded that any cold treatment that has been proven effective against T. leucotreta would be as effective against C. peltastica. Finally, it was confirmed that the cold susceptibility of T. leucotreta in artificial diet did not overestimate the effect of cold on T. leucotreta larvae in litchis.
