Efficacy of Various Low Temperature and Exposure Time Combinations for Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) Larvae.

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.

Cold Tolerance of Immature Stages of Ceratitis capitata and Bactrocera dorsalis (Diptera: Tephritidae).

Bactrocera dorsalis (Hendel) is a new fruit fly pest of some fruit types in the north and north eastern areas of South Africa. In order to determine whether existing cold disinfestation treatment schedules for an indigenous fruit fly pest: Ceratitis capitata (Wiedemann) would be effective for B. dorsalis, cold tolerances of four immature stages of the two species were compared. Studies were done in an artificial carrot-based larval diet. The developmental rates of the immature stages of the two species in the carrot-based larval diet were first determined at a constant temperature of 26°C. The developmental times for eggs and three larval stages were found to be similar for the two species. Incubation times of both species after egg inoculation were determined to be 0, 3, 4, and 6 d for obtaining egg, first larval, second larval, and third larval stages respectively for the cold treatment. At a test temperature of -0.6°C, mortality rates of C. capitata eggs, first instars, second instars, and third instars were lower than those of B. dorsalis. These results demonstrate that the current cold treatment schedules for disinfestation of C. capitata can be used as equally or more efficacious treatments for B. dorsalis.

Are Yeast Autolysate Attractants for Ceratitis Species (Diptera: Tephritidae) in South Africa More Attractive and Palatable Than a Currently Used Protein Attractant?

Due to increasing usage of copper fungicides in citrus orchards shortly before the application of protein baits for fruit fly control and the risk of this combination causing fruit phytotoxicity, an investigation of attractants containing higher amounts of yeast autolysate rather than protein hydrolysate was conducted. A commercial yeast autolysate from Australia was less attractive than a South African product HymLure (with a mixture of autolysate and hydrolysate) to three Ceratitis species: Ceratitis capitata (Wiedemann), Ceratitis rosa s.s. Karsch, and Ceratitis cosyra (Walker). Other custom-formulated autolysates were also inferior to HymLure for these species. Consumption of autolysates during the first hour of feeding was similar to that of HymLure. The inferior attraction of these three species of fruit flies to autolysates, relative to one containing hydrolysate, did not warrant further investigation of autolysates for use in baits to control these quarantine pests.

The Cryptophlebia leucotreta granulovirus-10 years of commercial field use.

In the last 15 years, extensive work on the Cryptophlebia leucotreta granulovirus (CrleGV) has been conducted in South Africa, initially in the laboratory, but subsequently also in the field. This culminated in the registration of the first CrleGV-based biopesticide in 2004 (hence, the 10 years of commercial use in the field) and the second one three years later. Since 2000, more than 50 field trials have been conducted with CrleGV against the false codling moth, Thaumatotibia leucotreta, on citrus in South Africa. In a representative sample of 13 field trials reported over this period, efficacy (measured by reduction in larval infestation of fruit) ranged between 30% and 92%. Efficacy was shown to persist at a level of 70% for up to 17 weeks after application of CrleGV. This only occurred where the virus was applied in blocks rather than to single trees. The addition of molasses substantially and sometimes significantly enhanced efficacy. It was also established that CrleGV should not be applied at less than ~2 × 1013 OBs per ha in order to avoid compromised efficacy. As CrleGV-based products were shown to be at least as effective as chemical alternatives, persistent and compatible with natural enemies, their use is recommended within an integrated program for control of T. leucotreta on citrus and other crops.

Cold treatment of Ceratitis capitata (Diptera: Tephritidae) in oranges using a larval endpoint.

South Africa currently exports fresh citrus (Citrus spp.) fruit to Japan using an in-transit cold treatment protocol of 14 d or 12 d at temperatures <0 degrees C for treatment of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in 'Clementine' mandarins (Citrus reticulata Blanco) and other citrus types, respectively. To reduce the risk of chilling injury with this treatment, research was conducted with temperatures >0 degrees C. Earlier South African research had shown that young (6-d-old) larvae were slightly more tolerant of cold treatment and that there were no significant differences between cold tolerance of these larvae in different citrus types [oranges, Citrus sinensis (L.) Osbeck; grapefruits, Citrus paradisi Macfad.; lemons, Citrus limon (L.) Burm.f.; and mandarins). Due to their ready availability, 'Valencia' oranges were used in this study. When 62,492 larvae in total were treated in three replicates at a mean temperature of 1.5 degrees C for 16 d, there were three larval survivors. The trial was therefore repeated with oranges using a 16-d period at a mean temperature of 1.0 degrees C and a mean of 1.4 degrees C for the hourly maximum probe readings. Three replicates were again conducted and the resultant mean mortality in the control was 8.1% of 21,801 larvae, whereas the cold treatment mortality was 100% of 71,756 larvae. This treatment at a mean temperature of 1 degree C exceeded the Japanese confidence level requirement and also exceeded the Probit-9 mortality level, but not at a confidence level of 95%. These data support the establishment of a treatment protocol of 16 d at temperatures <1.4 degrees C, commencing once all fruit pulp probes reach a temperature of 1 degree C or lower.