Effects Of Low Temperature Acclimation On The Cold Tolerance Of Dolycoris Baccarum(l.)

In order to analyze the seasonal adaptation ability of Dolycoris baccarum(L.),the low temperature adaptation ability was measured after acclimation.1.Effects of low temperature acclimation on supercooling pointsThe diapause adults were acclimated at 15?,10?,5?and 2?for 2 days(d)and 7 days(d),respectively.the supercooling point(scp)of the diapause adults was determined.the results of the measurement,domestication 2 days of SCP-13.98±1.21?(?)and-13.52±1.81?(?),-14.92±1.62?(?)and-14.56±1.76?(?),-14.91±1.79?(?)and-14.86±1.05?(?),14.22±2.27?(?)and-14.64±1.58?(?):domesticated 7 days scp-13.95±1.78?(?)and 14.96±2.18?(?),-13.33±0.93?(?)and-13.31±2.80(?),15.63±0.78?(?)and-15.04±1.74?(?),-14.87±1.63?(?)and-15.38±0.95?(?)compared with those of non-domesticated diapause adults(13.07±0.44?)and-12.66±0.62?(?),the overcooling points were significantly lower after domestication.with the decrease of acclimation temperature and the extension of acclimation time,scp decreased(P<0.05).2.Effects of low temperature acclimation on lethal temperatureAfter acclimation at 15?,10?,5?,2?for 7 days,the mortality of diapause adults was observed at-5?,-10?,-13?,-15?,-18?,-20?for 1 hour.At-5?and-10?for 1h,no death occurred in adults without acclimation and at all temperatures.The mortality rate without domestication was 31.82±9.64%(?)and32.59±9.99%(?)after 1h exposure at-13?.the mortality rates of domestication at 15?,10?,5?and 2?were 37.50±19.47%(?)and56.67±17.00%(?),8.33±11.79%(?)and 0%(?),7.41±10.47%(?)and16.67±23.57%(?),62.70±9.91%(?)and 72.81±10.50%(?).The results showed that mortality was significantly reduced after domestication(P<0.05),and the mortality of 10 and 5?domestication was significantly lower than that of 15 and 2?domestication(P<0.05).The mortality rate without acclimation was 63.39±6.09%(?)and72.86±10.60%(?)after 1h exposure at-15?.the mortality rates of domestication at the four temperatures(15?,10?,5?and 2?)were63.33±12.47%(?)and 66.67±9.43%(?),33.33±9.43%(?)and 40±0%(?),54.17±25.19%(?)and 80.90±16.38%(?),83.01±2.34%(?)and100%(?).the results showed that at-15?exposure,the mortality rate of 10?domestication was significantly lower than that of no domestication and other temperature domestication(P<0.05).After 1h exposure at-18?,the mortality rate without acclimation was 100%.the mortality rates of domestication at the four temperatures(15?,10?,5?and 2?)were 0%(?)and 93.33±9.43%(?),87.78±8.75%(?)and 82.96±4.19%(?),93.33±9.43%(?)and 100%(?),100%(?,?),respectively.the results showed that at-18?,some adults were still alive after acclimation at 15?,10?and 5?,and the mortality rate of acclimation at 10?was significantly lower than that of non-acclimation and other temperature acclimation(P<0.05).At-20?for 1h,no acclimation or any temperature acclimation survived,and the mortality was 100%.Based on the above results,the semi-lethal temperature(Ltemp50)after no acclimation and four kinds of acclimation(15?,10?,5?and2?)was calculated.the were-13.33?(?)(y=-7.697x-52.576,R~2=0.9098)and-13.32?(?)(y=-7.990x-55.358,R~2=0.8889)and-13.48?(?)(y=-7.867x-56.078,R~2=0.8956)and-13.09?(?)(y=-7.6365x-50.314,R~2=0.9031),15.11?(?)(y=-7.2966 x 60.264,R~2=0.787)and 15.27?(?)(y=7.2463x-60.665,R~2=0.7678),-14.48?(?)(y=-7.6758x-61.139,R~2=0.8103)and-14.78?(?)(y=-8.138x-59.941,R~2=0.8158),-12.55?(?)(y=-7.981x-50.176,R~2=0.8734)and-11.66?(?)(y=-7.8056x-41.019,R~2=0.857).the results showed that the lethal temperature of acclimation at 10?and 5?decreased significantly,and the cold tolerance was improved.3.Effects of low temperature acclimation on lethal timeAfter 7 days of domestication at 15?,10?,5?and 2?,diapause adults were exposed to-5?and-10?for 1 day,3 days,5 days,7 days,9 days,11 days,15 days,20 days and 25 days,respectively.according to the mortality rate of different exposure days,the results of half-death time(Ltime50)were calculated.the semi-lethal time of domestication at 15?,10?,5?and 2?were 3.63d(?)(y=17.241x-12.596,R~2=0.9768)and6.50d(?)(y=17.623x-11.749,R~2=0.9706),3.38d(?)(y=16.501x-5.7129,R~2=0.9579)and 3.91d(?)(y=16.551x-14.854,R~2=0.953),3.70d(?)(y=16.457x-10.964,R~2=0.9866)and 3.76d(?)(y=17.712x-16.629,R~2=0.9824),4.04d(?)(y=17.844x-22.236,R~2=0.968)and 3.69d(?)(y=17.187x-13.411,R~2=0.9881),3.96d(?)(y=18.297x-3.2767,R~2=0.9423)and 3.28d(?)(y=17.771x-8.262,R~2=0.9467)without domestication.After acclimation,the semi-lethal time was prolonged(P<0.05),enhance the tolerance to low temperature,enhance cold resistance.4.Effects of low temperature acclimation on free water content in vivoThe freeze-drying technique was used to determine the content of free water in the diapestic adults of The lyophilized species after 7 days of domestication at 15?,10?,5?and 2?.The free water content of non-domesticated adults was 62.35±3.35%(?)and 60.42±2.20%(?).The domestication at different temperatures(15?,10?,5?and 2?)was 56.33±4.62%(?)and 56.03±1.90%(?),52.39±2.23%(?)and51.2±2.02%(?),48.32±4.95%(?)and 47.65±8.14%(?),45.66±8.20%(?)and 41.22±5.31%(?),indicating that the free water content in their body decreased significantly after low temperature acclimation(P<0.05).5.Effects of low temperature acclimation on glycogen content in vivoAfter acclimation at 15?,10?,5?and 2?for 7 days,the content of body glycogen was determined.After domestication at 15?,10?,5?and 2?,the glycogen content in body was 74.19±7.67 mg/g(?),63.10±5.91 mg/g(?),44.95±8.74 mg/g(?),18.14±4.55 mg/g(?),41.60±4.99 mg/g(?),46.42±4.60 mg/g(?),52.91±9.40 mg/g(?),55.45±6.32 mg/g(?).the results showed that low temperature acclimation significantly reduced glycogen content(P<0.05).The above results indicate that the survival rate of low temperature can be significantly improved by low temperature acclimation,which can significantly reduce the supercooling point,prolong the semi-lethal time and decrease the semi-lethal temperature.the effects of low temperature acclimation on the free water and glycogen contents in adults were significant.With the decrease of acclimation temperature,the free water and glycogen contents decreased significantly,indicating that low temperature acclimation promoted water management,induced glycogen metabolism,and enhanced the ability to resist low temperature.