Study On Tolerance Of Melon Fly, Bactrocera Cucuribitae Coquillett To Low Temperature And Its Hysiologigal And Biochemical Mechanisms

The melon fly, Bactrocera cucuribitae (Coquillett) is an important international and domestic quarantine pest which is classified to genus Baclrocera Macquar, family Tephritidae, order Diptera. To investigate the cold tolerance of B. cucuribitae, we test the biological and physiological responses. The variation of supercooling point (SCP), water content, lipid content, glycerin content and carbohydrates content at different developmental stages of B. cucuribitae, were measured respectively. And the survival rates of different low temperature to the B. cucuribitae for different exposure times, were reflected. Moreover, the effects of cold acclimation on survival in B. cucuribitae adults and responses of the SOD, CAT, ATP, LDH activity of adults underlying chill injury were also in investigated. The main results were summarized as follows.1. The SCP and freezing point at5day-old pupae were the lowest among all the developmental stages, which was-17.04℃and-14.51℃, and the highest SCP and freezing point were detected in1day-old larva, which was-11.82℃and-6.83℃. However, there was no significant difference of SCP between male and female adults in the same age.2. With the growth of the age, the water content reduced from79.64%at1day-old larvae to65.31%at5day-old pupae, which was the lowest among all the developmental stages. The water content of female adults were significantly higher than male in the same age. The fat content at5day-old larva was32.90%, which was the highest among all the developmental stages. The lowest fat content were found in1day-old male adults (15%) and14day-old male adults (15%). The glycerol content in the larval stage decreased from3.32%to1.12%, and it increased gradually during the pupal stage. The highest point was detected in14day-old female adults (5.90%). The total sugar content, trehalose content and glycogen content in1day-old larva all were the highest among all the developmental stages, which were7.51%,0.94%and1.93%, respectively. The carbohydrates content decreased gradually during the pupal stage, and they increased with the growth of age in the adult stage.3. As temperature was lowered or duration of exposure was prolonged, the survival rate of B. cucuribitae declined gradually. And the survival rate of B. cucuribitae different significantly among the developmental stages. The results showed that eggs could not survive at10℃,8℃or6℃over10days and4℃,2℃or0℃over4days. When exposed to10℃for5days, the survival rate of developmental stages of B. cucuribitae was higher than60%. When larvae, pupae and adults of B. cucuribitae under cold temperatures at8℃for5days, survival rate were higher than40%. When they at6℃for5days, survival rate was30%for larvae, pupae and adults. When they at4℃for2days, the survival rate of developmental stages of B. cucuribitae was higher than40%. When exposed to2℃for2days, the survival rate of developmental stages of B. cucuribitae was higher than20%. Almost of B. cucuribitae could not survive for15days under6℃and8days under4℃or2℃as well as4days under0℃. At2days exposure, the temperature needed to kill50%individuals (Ltempso) of B. cucuribitae were2.170℃for eggs,1.205～1.619℃for larvae,0.798～1.148℃for pupae and1.188℃-3.017℃for adults. And the time needed to kill50%individuals (Ltime50) of B. cucuribitae were3.030days for eggs,7.531～10.121days for larvae,7.335～9.429days for pupae and6.493~8.222days for adults at8℃. Therefore, the order in cold resistance of developmental stages of B. cucuribitae was presented as:eggs﹤adults﹤larvae﹤pupae.4. The adults increased their resistance to cold stress when they were acclimated at10℃. The survivals were improved from both72%for female and male (without cold acclimation) to91%for female and88%for male when adults were acclimated for1day. After induction3days or5days at10℃, the survival rates of adults decreased. The superoxide dismutase(SOD), catalase(CAT) and Na+, K+-ATPase(ATP) activities significantly increased after cold stress1days at10℃. However, SOD and Na+, K+-ATPase activities of the adults were inducted3days or5days no significant difference with those without cold acclimation. But CAT activities of female adults lower than those without cold acclimation, to the male, CAT activity were higher than those without cold acclimation. With duration of exposure was prolonged, the lactate dehydrogenase (LDH) activities of male increased, and significantly higher than male without cold acclimation, LDH activities of female had no significant difference with non-induced.