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 (LT50) 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 ℃;LT50 increased with increase of time in low temperature,and LT50 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.