Thermoperiodic acclimations enhance cold hardiness of the eggs of the migratory locust

Treatment of thermoperiods that simulate the patterns of natural occurrence is most efficient in enhancing cold hardiness. To examine the effects of different thermoperiods on cold hardiness of eggs in the migratory locust, Locusta migratoria (L.), the survival rates, cryoprotectant levels and three hsps expressions in mid-stage eggs (7-day-old) were measured after the eggs were subjected to three different thermoperiod regimes, : short (2 day), long (10 day), and nature-mimicking thermoperiodic acclimation. The thermoperiodic acclimations resulted in the highest egg survival rates in both the short and the long period acclimation groups in comparison with the groups treated with constant temperatures. The egg survival of nature-mimicking thermoperiod groups was significantly higher than those of constant temperature groups for the same acclimation duration. The survival rate of eggs under single daily thermoperiod was higher than that of multiple daily thermoperiods. The concentration of cryoprotectants (myo-inositol, trehalose, mannitol and sorbitol) and the expression levels of hsp20.5, hsp70, and hsp90 all increased in thermoperiodic acclimation eggs.