Studies On Cold Hardiness Of Dolycoris Baccarum(L.)(Hemiptera:Heteroptera:Pentatomidae) And Its Mechanisms

Dolycoris baccarum harms a variety of crops and widely distributed in China and other countries in the Palaearctic region.It enters diapause as an adult to overwinter,the overwintering adults are the main source of insects in the following year.Therefore,the study of cold hardiness and survival ability of the Dolycoris baccarum at low temperature is important for analyzing the reasons for its distribution in high latitudes,predicting population dynamics,forecasting the occurrence and integrated control.In order to analyze the overwintering cold hardiness of the Dolycoris baccarum,this paper investigated the supercooling point,low temperature survival ability and free water content of diapause and non-diapause adults of Dolycoris baccarum,the main results are as follows:1.Supercooling points of diapause and non-diapause adults of Dolycoris baccarumThe supercooling points of diapause and non-diapause adults of Dolycoris baccarum were determined by thermocouple method.The supercooling points of diapause were-13.07±0.44℃（♀）and-12.86±0.67℃（♂）,respectively,and those of non-diapause were-12.19±0.94℃（♀）and-12.32±0.66℃（♂）for non-diapause,respectively.The supercooling points of diapause adults were lower than that of non-diapause adults,indicating that the supercooling point of adults decreased after diapause（P>0.05）.2.Lethal temperature of diapause and non-diapause adults of Dolycoris baccarumThe mortality of diapause and non-diapause adults treated at-5℃、-10℃,-13℃,-15℃,-18℃for 1h was determined.At-5℃,both diapause and non-diapause adults survived with 0%mortality.At-10℃,the mortality of diapause and non-diapause were 8.93±4.49%（♀）and 7.20±3.73%（♂）,16.99±1.66%（♀）and 18.28±0.96%（♂）,respectively.At-13℃,the mortality of diapause and non-diapause were 24.09±2.15%（♀）and25.47±4.03%（♂）,35±2.55%（♀）and 38.33±2.89%（♂）,respectively.At-15℃,the mortality of diapause and non-diapause were 68.26±1.58%（♀）and 70.08±5.90%（♂）,83.42±3.78%（♀）and 80.24±3.09%（♂）,respectively.When the temperature is-18℃,both diapause and non-diapause mortality were 100%.The mortality of diapause adults was significantly lower than that of non-diapause adults under all low temperature treatments except for the-5℃and-18℃treatments,which showed that the low temperature survival ability was significantly improved after diapause.The half-lethal temperatures(Ltemp₅₀)of diapause adults were-13.44℃（♀）and-13.40℃（♂）,respectively,and that of non-diapause adults were-12.56℃（♀）and-12.53℃（♂）.The Ltemp₅₀of diapause adults were significantly lower than that of non-diapause adults,indicating a significant decrease in the Ltemp₅₀of adults after diapause.3.Lethal time of diapause and non-diapause adults of Dolycoris baccarumThe mortality of diapause and non-diapause adults was measured at-5℃for different treatment time.After treatment for 1-4 days,both diapause and non-diapause adults survived.After 5 days of treatment,the mortality of diapause and non-diapause were 15.56±2.94%（♀）and18.59±1.99%（♂）,respectively,26.87±3.85%（♀）and 28.87±0.89%（♂）,respectively.After 6 days of treatment,the mortality of diapause and non-diapause were 32.12±2.86%（♀）and 35.26±3.29%（♂）,respectively,50.00±2.22%（♀）and 53.10±4.22%（♂）,respectively.After 7 days of treatment,the mortality of diapause and non-diapause were 46.67±3.33%（♀）and 53.10±4.21%（♂）,respectively,69.37±1.41%（♀）and 69.24±4.67%（♂）,respectively.Within 4-7 days after low temperature treatment,the survival rates of diapause adults were significantly higher than those of non-diapause adults（P<0.05）,which indicated that the low temperature survival ability was significantly improved after diapause.After 8 days of treatment,both diapause and non-diapause mortality rates were 100%,with no survival.The half-lethal time(Ltime₅₀)of diapause adults were 6.41d（♀）and 6.19d（♂）,respectively,the half-lethal time(Ltime₅₀)of non-diapause adults were 5.62d（♀）and 5.56d℃（♂）,respectively,indicating that there was a significantly prolongation of the Ltime₅₀of adults after diapause.4.Pronotum width of diapause and non-diapause adults of Dolycoris baccarumThe individual sizes of diapause and non-diapause adults were compared by measuring the pronotum width（PW）of diapause and non-diapause adults of Dolycoris baccarum.The pronotum width of diapause adults were 9.05±0.05mm（♀）and 8.21±0.05mm（♂）,respectively,the pronotum width of non-diapause adults were 8.77±0.07mm（♀）and8.02±0.06mm（♂）,respectively.And the body size of diapause adults was significantly larger than that of non-diapause adults between the same sex（P<0.05）.5.Free water content of diapause and non-diapause adults of Dolycoris baccarumThe free water content of the diapause and non-diapause adults of Dolycoris baccarum was determined by freeze-drying method.The free water contents of diapause adults were 53.23±1.51%（♀）and 52.50±1.46%（♂）,respectively.The free water content of non-diapause adults were63.79±0.55%（♀）and 61.22±0.99%（♂）,respectively.The free water content of diapause adults was significantly lower than that of non-diapause adults（P<0.05）.The above results showed that the cold hardiness of diapause adults was significantly stronger than that of non-diapause adults.The overcooling point of diapause adults was lower than that of non-diapause adults,and the lethal temperature of diapause adults was significantly lower than that of non-diapause adults,and the lethal time of diapause adults was longer than that of non-diapause adults,indicating that the diapause state of Dolycoris baccarum strengthens the ability to resist low and improves the survival rate of low temperature.The body size of diapause adults was significantly larger than that of non-diapause adults,and the free water content of diapause adults was significantly lower than that of non-diapause adults,indicating that the management of water after diapause was changed and the ability to resist low temperature was enhanced.