AN IMPROVED REARING PROCEDURE FOR THE CARROT RUST FLY (DIPTERA: PSILIDAE) WITH OBSERVATIONS ON LIFE HISTORY AND CONDITIONS CONTROLLING DIAPAUSE INDUCTION AND TERMINATION

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Abstract
Carrot rust fly (CRF), Psila rosae (Fabricius) (Diptera: Psilidae), caged with 2-month-old carrot plants at 20 °C, 50–70% RH, and 16:8 L:D laid an average of 109 eggs per female. With ca. 50% survival from egg to pupae, the rearing procedure yielded a 25 × population increase per generation. The duration of the life cycle at 20 °C was ca. 65 days. Calculated threshold temperatures and degree days above those temperatures necessary for complete development were: eggs, 4.5 °C and 94 degree days (°D); larvae, 2.02 °C and 625 °D; and pupae, 1.47 °C and 374 °D. Larvae collected in the field in fall developed normally when incubated at 22 and 19 °C; ca. 40% of the pupae entered diapause at 16 °C, and 100% at 13 and 10 °C. Fall-collected larvae chilled at 1 °C for ca. 3 months developed normally at all temperatures including those which induced diapause in pupae from unchilled larvae. With laboratory-reared pupae, 100% diapause was induced with > 10 days exposure to 13 or 10 °C. Twenty weeks storage at 1 °C was sufficient to terminate diapause in > 95% of the pupae. The ability of both CRF larvae and pupae to survive cold temperature conditions suggests that 2 separate spring emergence peaks may occur, which could have important implications if the spring flight is to be predicted on the basis of °D accumulations.