Induction and development of winter larval diapause in a drosophilid fly, Chymomyza costata

Photoperiodic response during induction of larval hibernal diapause of Chym omyza costata was characterized and the course of diapause development was analyzed in the laboratory. C. costata becomes sensitive to photoperiodic s timuli during an unspecified stage of its early development (embryo, Ist la rval instar); the sensitivity gradually increases during the 2nd and early 3rd larval instars and reaches its maximum just before the moment when it a bruptly ceases at the age of 15-19 days after oviposition. Diapause intensi fies during a period of 2-3 weeks after induction and, later, is maintained without apparent development until death (between 150 and 250 days) under 18 degrees C and a short-day photoperiod (L10:D14, SD). Diapause may be ter minated in a horotelic process by exposure to a low temperature (2 degrees C) during which larvae subsequently (1) synchronize their post-diapause dev elopment (requires up to 14 days of chilling), (2) lose photoperiodic sensi tivity (2 months), and finally (3) terminate diapause (5 months). Alternati vely, diapause may be terminated in a tachytelic process by exposure to a h igh temperature (18 degrees C) and long-day photoperiod (L16:D8, LD) during which no synchronization occurs and pupariation takes place after a mean o f 25.2 days (with a broad range from 8 to more than 50 days). Larvae that a re transferred from LD to SD during their sensitive period switch their dev elopmental programming from pupariation to diapause. Proliferation of adult primordial structures (imaginal discs, neuroblasts) slows down within 1 da y after transfer. In contrast, whole body growth continues for at least 3 d ays before its rate slows down and matches the rate characteristic for SD c onditions. (C) 2000 Elsevier Science Ltd. All rights reserved.