[01] Shigeru Kikukawa, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [02] Ryou Hashizume, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [03] Yuka Inoue, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [04] Mina Miyabayashi, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [05] Natsuko Mori, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [06] Risa Sakata, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan. [07] Yuki Takigaura, Biological Institute, Faculty of Science, University of Toyama, Toyama, Japan.

Rhythms in physiological and behavioral activities of insects can be entrained by photoperiod and/or thermocycle (thermoperiod). The present study investigates the free-running eclosion rhythm of Plodia interpunctella Hübner (Lepidoptera: Pyralidae) by applying either a single light pulse or a thermocycle. To prevent larval diapause, all insects are maintained at 30°C and kept in constant darkness (DD) for 14 days after oviposition. Thereafter, the insects were maintained at 25°C DD. At day 27 after oviposition, the insects are subjected to a single light pulse (2-16 h). Average time from the light-off signal to the first peak of eclosion rhythm in DD is c. 17.5 h, indicating that the insects interpret the ‘light-off’ signal as a Zeitgeber to entrain the rhythm at 25°C, since the rhythm normally free-runs for a period of c. 23 h. A single light pulse in otherwise DD can entrain the adult eclosion rhythm in this species at 25°C. In contrast, the rhythm can be entrained by applying a thermocycle consisting of 30°C thermophase (12 h) and 20°C cryophase (12 h) regardless of background illumination (DD or constant illumination (LL)). The insects are exposed to the thermocycle in DD or LL from days 15 to 28 after oviposition and subsequently maintained at 25°C in DD or LL. The rhythm is observed to free-run for a period of c. 22 h. Thus, the adult eclosion rhythm in this species can be entrained by either a light pulse or a thermocycle. However, it is unclear whether the photoperiodic and thermoperiodic time-keeping mechanisms are controlled by the same physiological processes.

Adult Eclosion, Free-Running Rhythm, Plodia Interpunctella, Light Pulse, Thermoperiod

[01] Beck, S. D., 1980 Insect Photoperiodism, 2^nd edn. Academic Press, New York. [02] Saunders, D.S., 2002 Insect Clocks, 3^rd edn. Elsevier, The Netherlands. [03] Kikukawa, S., Hashizume, R., Honda, M., Inoue, Y., Maekawa, T., Sakata, R., Takahashi, N., Tanaka, K. & Uchida, Y., 2012 Effects of photoperiod and temperature on the rhythm and free-running of adult eclosion in the Indian meal moth Plodia interpunctella. Physiological Entomology, 37: 258-265. [04] Pittendrigh, C.S., 1954 On temperature independence in the clock system controlling emergence time in Drosophila. Proceedings of the National Academy of Sciences, U.S.A., 40: 1018-1029. [05] Pittendrigh, C.S., 1966 The circadian oscillation in Drosophila pseudoobscura pupae: a model for the photoperiodic clock. Zeitschrift für Pflanzenphysiologie, 54: 275-307. [06] Lankinen, P., 1993 North-south differences in circadian eclosion rhythm in European populations of Drosophila subobscura. Heredity, 71: 210-218. [07] Joshi, S., Hodgar, R., Kanojia, M., Chatale, B., Parihar, V. & Joshi, D.S., 2002 Mutations for activity level in Drosophila jambulina perturbed its pacemaker that controls circadian eclosion rhythm. Naturwissenschaften, 89: 67-70. [08] Khare, P.V., Barnabas, R.J., Kanojiya, M., Kulkarni, A.D. & Joshi, D.S., 2002 Temperature dependent eclosion rhythmicity in the high altitude Himalayan strains of Drosophila ananassae. Chronobiology international, 19: 1041-1052. [09] Scott, W.N., 1936 An experimental analysis of the factors governing the hour of emergence of adult insects from the pupae. Transactions of the Royal Entomological Society of London, 85: 303-329. [10] Zimmerman, W.F., Pittendrigh, C.S. & Pavlidis, T., 1968 Temperature compensation of the circadian oscillation in Drosophila pseudoobscura and its entrainment by temperature cycles. Journal of Insect Physiology, 14: 669-684. [11] Kikukawa, S., Hashizume, R., Honda, M., Inoue, Y., Maekawa, T., Sakata, R., Takahashi, N., Tanaka, K. & Uchida, Y., 2013 Adult eclosion rhythm of the Indian meal moth Plodia interpunctella: response to various thermocycles with different means and amplitudes. Physiological Entomology, 38: 253-259. [12] Watari, Y, & Tanaka, K., 2014 Effects of background light conditions on thermoperiodic eclosion rhythm of onion fly Delia antiqua. Entomological Science, 17: 191-197.