Field and laboratory studies on the effects of temperature on the development of the carrot fly (Psila rosae F.)

Summary The thermal requirements for the pre‐oviposition period, egg, larval, pupal and adult stages of the carrot fly were measured under field conditions and at a range of constant temperatures in the laboratory. In the laboratory, the pre‐oviposition period lasted from 4 days at 24 o C to 28 days at 9 o C. In general, female carrot flies laid about 20–40 eggs in each batch. Once the first eggs had been laid, subsequent batches were laid after an average of 3 days at 24 o C to 7 days at 11.5 o C. The numbers of days required for egg, larval and pupal development ranged from 5, 31 and 24 days respectively at 21.5 o C to 25, 145 and 84 days respectively at 9 o C. Under laboratory conditions, complete development from egg to adult required from 60 days at 21.5 o C to 254 days at 9 o C. Newly‐formed carrot fly pupae were exposed to temperatures of 22–30 o C for various 5–10 day periods during pupal development. Exposure to temperatures of 24 o C and 26 o C caused some, and exposure to 28 o C and 30 o C caused all, of the pupae to delay development. Pupae were sensitive to high temperatures only for approximately 4–10 days after pupation. Under field conditions between mid‐May and early September, full carrot fly development (egg‐adult) took 84–100 days. The numbers of day‐degrees required (base temperatures of 2 o C and 4 o C) for carrot fly development in the laboratory and in the field were similar for egg hatching but not for the pre‐oviposition period or for egg‐adult development. The thermal requirement for fly development in the field varied between inoculation dates, fewest day‐degrees being required when development was rapid.