| The terrain of Yan ’an is dominated by ravines.It is cold in winter and the planting area of facility vegetables is large in the area.They are important vegetable sources.Cruciferae vegetables such as Chinese cabbage and Shanghai Green have become the main planting species due to their rich species and short growth cycle,which plays an important role in the local economic development.Plutella xylostela,a diamondback moth,belongs to Lepidoptera:Plutellidae),which feeds on Cruciferae plants.Because of its strong resistance and non-diapause characteristics,it still survive and continue to damage in winter in vegetable greenhouses,which has seriously affected the yield and quality of vegetables in this family.In order to determine the overwintering ability of this insect in the local greenhouse,the 4th instar larvae,pupae and adults of Plutella xylostella were treated with direct low temperature(represented by CS)and post-adaptation low temperature(represented by CA)at 15℃ respectively according to the low temperature at night(8℃ and 4℃)in the local winter greenhouse.with the constant temperature of 26℃as the control,the survival and reproduction related parameters were recorded and calculated.the activities of catalase(CAT),peroxidase(POD)and superoxide dismutase(SOD)and detected the expression pattern of antioxidized enzyme genes three above,Px Cat,Px Pox,Px Sod,and two heat shock protein genes,Px Hsp83 and Px Hsp20.Therefore,the cold tolerance capacities would be estimated,and the cold tolerance mechanisms would be inferred.The main results were showed below:(1)Compared with diamondback moth reared at 26℃,the pupation rate of 4th instar larvae decreased significantly at low temperature,and the inhibition of CA treatment on pupation rate was deeper.The emergence rate was significantly inhibited by low temperature,and the emergence rate decreased more significantly after CA treatment,and the emergence rate of CA in pupal stage was the lowest(70% of the control group).The life span of adults treated with low temperature in pupal stage is longer than that of adults treated with low temperature in 4th instar larvae stage,and that of male adults is generally longer than that of female adults.In terms of reproduction,all low-temperature treatments reduced the proportion of oviposition adults,and the proportion of oviposition individuals under CA treatment was lower than that under CS treatment.Low temperature significantly reduced the number of eggs laid by females,especially in CA.After 96 hours of CA treatment at 8℃,the number of eggs laid by females was only 17.94 eggs/female,compared with 73.88 eggs/female in CS group.The oviposition period of female moths was significantly prolonged under low temperature.At 8℃,the oviposition period of adult treated with CA(2.048 d)was significantly shorter than that of the control group(4.419d),but slightly longer than that of the control group under CS(6.676 d).Under the same duration,the oviposition period of females treated with CS at 4℃ was significantly shortened.(2)The results of enzyme activity test showed that the CAT activity of 4th instar larvae had no obvious influence at this stage.After low temperature treatment at pupal stage and adult stage,the CAT activity of each treatment in CA group decreased significantly at the corresponding stage,but the CAT activity of each treatment in CS group did not change obviously.Pupa and adult are more sensitive to CAT than 4th instar larvae in low temperature environment,and the activity of CAT is inhibited by CA treatment.The POD activity of 4th instar larvae,pupal stage,male and female adults under different low temperature duration decreased significantly compared with the control group,while the POD activity increased after CS treatment for 4th instar at 8℃-24 h,8℃-96 h and female adults at 8℃-48 h,8℃-96 h.The SOD activity of 4℃-CA treatments in pupae,female and male adults decreased significantly,while that of all CS and CA treatments increased significantly in the 4th instar larvae stage.SOD activity of 4th instar larvae increased significantly at low temperature.(3)The results of real-time quantitative PCR showed that the expression of Px Cat in pupal stage which in 8℃-CA,4℃-CA,and male adults in 8℃-CA,4℃-CS and 4℃-CA,except for 8℃-CS-96 h in female adults.Compared with the control group,the expression of Px Cat in other treatment groups decreased significantly.After the 4th instar larvae were treated at low temperature,the relative expression of Px Cat did not change significantly,which was consistent with the change trend of CAT activity.The relative expression of Px Cat gene in pupae and adults increased significantly after adaptation when the low temperature stress lasted for 24 hours.The expression of Px Pox in male adults increased significantly,while that in pupal stage and female adults decreased significantly.It shows that Px Pox is related to the cold tolerance of male adults.The expression of Px Sod decreased significantly under CA treatment.Compared with the control,the expression of Px Hsp83 in 4th instar larvae and female adults at 4℃ decreased significantly,but the decrease degree of CA treatment was significantly less than that of CS treatment,while that of pupa and male adults at 8℃-CS was higher than that of control,but the expression of Px Hsp83 in this part of CA treatment was significantly lower than that of CS.Compared with the control group,the expressions of 8℃-CA,4℃-CS and 4℃-CA Px Hsp20 in pupae and female adults decreased significantly,while the expressions of 8℃-CS and 4℃-CS in4 th instar larvae increased significantly.In conclusion,short-term low-temperature stress has adverse effects on Plutella xylostella in different developmental stages.When the short-term low-temperature treatment temperature is 8℃ and 4℃,the adaptive temperature before low temperature can not improve the fitness of Plutella xylostella,but inhibits the scavenging of superoxide anion caused by low temperature by protective enzymes. |
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