Validation of the Phenology Model for the Codling Moth, Cydia pomonella (Lepidoptera: Tortricidae), in South African Pome Fruit Orchards

The codling moth, Cydia pomonella (Linnaeus) (Lepidoptera: Tortricidae), is a key pest of pome fruits in the Western Cape, South Africa. Up to 1993, the industry recommendation for commencement of the codling moth spray programme was at 75 % petal fall in order to avoid the negative impact of organophosphate sprays on bees during bloom. However, codling moth can emerge, mate and oviposit before and during full bloom in pome fruit orchards. Consequently, petal-fall does not necessarily correspond with the commencement of egg-laying or first egg hatch. The availability of insecticides with a softer environmental profile made it possible to apply sprays earlier than 75 % petal-fall. The development of phenology models provided a means of accurately predicting biological events such as the initiation of egg-laying and first egg hatch. Using lower and upper development thresholds of 10 °C and 32 °C, respectively, and hourly temperature recordings, phenology models were evaluated by comparing the number of degree-days (°D) accumulated using a selection of three biofixes, and date of first egg hatch. The number of °D accumulated from the selection of biofixes to first observed egg hatch varied from 130.7 to 179. The least variation in the number of °D between biofix and first egg hatch occurred when the second trap catch was used as the biofix. A biofix based on the first evening when the temperature reached or exceeded 17 °C at 18:00 after first trap catch also showed less variation than when the biofix was based on first trap catch. The mean number of °D at which 50 % of the moths of the first flight emerged was 166.6 °D, while the mean number of °D at which 50 % oviposition occurred was 290 °D following biofix. The number of °D between the second and third flight biofixes varied between 488.7 and 531.2 °D, with a mean of 508.1 °D. The results are of significance in improving the timing and reducing the number of insecticide sprays for codling moth control.