Egg Cold Hardiness of the Migratory Locust Locusta migratoria L.Under Different Photoperiod Conditions

Eggs laid by migratory locusts reared under conditions of long photoperiod (LP)(L∶D=14∶10) and short photoperiod (SP) (L∶D=10∶14) were collected.Supercooling points of some eggs were measured using a thermocouple method.The remained eggs were treated with a series of low temperatures (0,-5,-10,-15 and -20 ℃) in different periods of time (6 h,1,3,5 and 10 d),and then incubated at 28 ℃.The number of surviving eggs could be judged with that of incubated nymphs,and then the survival ratio of eggs in low temperature (SL) and low-lethal temperature causing death of 50% of the eggs (LT[50]) were calculated.No difference was found in the supercooling points between LP and SP groups;SL decreased with the decline of treated temperature and the increase of treated time and SL in SP group was higher than that in LP group at -5 and -10 ℃;LT[50] increased with increase of time in low temperature,and LT[50] of SP group was lower than that of LP group.The results suggest that the cold hardiness of locust eggs could be induced by a short photoperiod experienced by parents,that is,eggs produced in autumn would better overwinter.