Dynamics of cold hardiness, supercooling and cryoprotectants in diapausing and non-diapausing pupae of the cabbage root fly, Delia radicum L.

Abstract

The cabbage root fly, Delia radicum L., overwinters as a phanerocephalic pupa (PCP) in a diapause state and its development may be temporarily stopped at the PCP stage even by high summer temperatures. Cold acclimation (5 days at 5 °C) of non-diapausing PCP resulted in an increased cold hardiness (survival of exposure to − 15 °C for 1 or 20 days) and was associated with an increase of trehalose content (from 6.6 to 10.0 μg/mg wet weight). Non-diapausing pupae in a high-temperature quiescence had a higher osmotic pressure of haemolymph (623 mOsm) and a higher glucose content (3.4 μg/mg) in comparison to normal non-diapausing pupae (550 mOsm, 1.4 μg/mg). Diapausing PCP at the start of diapause showed cold hardiness levels equal to non-diapausing PCP. Their cold hardiness rapidly increased during the first 10–30 days of diapause development attaining a maximum between days 30 and 50 followed by an obvious decrease. Osmotic pressure increased from about 550 mOsm at the start of diapause to 860 mOsm by day 80 and then dropped slowly. Trehalose increased from 4.7 to 11.2 μg/mg during the first 80 days and then declined too. Glucose showed transitional increase of concentration during the first 20 days of diapause development followed by an abrupt drop until about day 50 and repeated the increase toward the diapause termination. Myo-inositol level increased slowly during diapause development showing a plateau after 80 days. Supercooling capacity of the PCP stage was similar irrespective of the physiological state or age of the pupa.