Physiology of diapause in pupae of Pieris brassicae L. (Lepidoptera: Pieridae)
¹Institute of Agricultural and Enviromental Sciences, Estonian Agricultural University, Kreutzwaldi 64, 51014 Tartu, Estonia; e-mail: firstname.lastname@example.org
²Institute of Physics University of Tartu, Riia 142, 51014 Tartu, Estonia
Respiration patterns, water loss and heart activity were investigated during the first three months of diapause in non-acclimated pupae of Pieris brassicae. To observe and record diverse events during pupal diapause, a complex apparatus was used: a micro-calorimeter, an electrolytic respirometer, a fibre-optical oxygen sensor, a flow-through respirometer (infrared gas analyzer), an infra-red actograph and a thermocouple cardiograph. Most of the pupae (about 80%) reared in 2004 were characterised as long-cycle individuals whose discontinuous gas exchange cycles (DGCs) were very regular and lasted 26 hours on average. The remainder of the pupae studied were short-cycle individuals displaying irregular DGCs lasting less than 2 hours. Standard metabolic rates (SMR) measured during the first month of diapause between long- and short-cycle pupae did no differ significantly, being about 0.018 ml O2 g-1 h-1. At the same time, water loss rate (WLR) in long- and short-cycle pupae differed significantly, being 1.07 and 1.61 mg g-1 day-1, respectively. During the first three months of diapause, the values of SMR and WLR did not change significally in the long-cycle pupae. In the short-cycle individuals, SMR and WLR thereupon increased gradually during the months, but the values of SMR never reached the levels characteristic of pharate adult development. The heartbeat reversal was characteristic for both the long- and short-cycle individuals but heart pauses in the first pupal group were regular, lasting 20–30 min, whereas in the second group the heart pauses were shorter and irregular.
From the results we concluded that the intensity of pupal diapause varied individually despite the apparently similar developmental conditions of the individuals, however, some hidden factors were obviously involved in diapause induction. The primary cause of the enhanced water loss in the short-cycle pupae was obviously the disturbing of the water conserving mechanisms due to the irregular gas exchange.