Apolygus lucorum has become one of the most pestiferous pests of cotton and fruits with widely applications of transgenic Bt cotton in China.Cold tolerance of its overwintering eggs was studied,and the content of biochemical substances was also determined,to evaluate its overwintering adaptability.The results showed that there were significant differences on cold survival ability of the overwintering eggs among months.Lt50 of the overwintering eggs was in order of January February December March April at the temperature of-10 ℃ or-20 ℃,and in order of January December March February April at the temperature of-30 ℃.The mortality of protected eggs in the April(4.32%,5.36%,5.42%,6.79% and 7.63%) was significantly lower than non-protected eggs in the April(46.06%,51.84%,54.59%,63.07% and 74.41%) when they were treated at the temperature of-20 ℃for 1,2,3,4 and 5 days.The cold tolerance to lower temperature of artificial diapause eggs was higher than the normal eggs,while lower than the diapause overwintering eggs.The cold acclimation increased the cold tolerance of overwintering eggs of A.lucorum.The mortality of overwintering eggs at the temperature of-20 ℃for 100 hours decreased significantly after the overwintering eggs was treated at 0 ℃ for 20 minutes,and the mortality was always about 37% at the temperature of-20 ℃for 100 hours after was treated at 0 ℃ for more than 40 minutes.The content of biochemical substances of overwintering eggs changed seasonally.The water content of overwintering eggs in winter was significantly higher than those after winter,and was highest in January(43.98%) and lowest in April(38.79%).The fat content of overwintering eggs decreased from 38.24% in December to 27.08% in April over the winter.The protein content and glycogen content all reduced at first,then increased.The protein content decreased from 78.77 μg/mg in December to 59.80 μg/mg in January,then increased gradually to 73.62 μg/mg in April.The glycogen content decreased from 39.60 μg/mg in December to 21.17 μg/mg in January,then increased gradually to 35.10 μg/mg in April.In conclusion,cold tolerance of overwintering eggs of A.lucorum changed seasonally.The overwintering eggs showed high tolerance to the low temperature in winter,and the protection of overwintering place improved its overwintering adaptability.