| Neoseiulus barkeri(Hughes)is an excellent biocontrol agent and widely distributed,and has been commercialized.Nowadays,with its rapid development rate,low natural mortality,high fecundity,strong dispersal ability and vast prey range,N.barkeri plays important roles in the biocontrol of thrips and spider mites.However,since the commercial available N.barkeri are usually under the most appropriate temperature at 25°C for long–term production,their biological control efficiency against thrips and spider mites often decrease due to its poor adaptability under field conditions.Therefore,a high temperature adapted strain(HTAS)of the predatory mite Neoseiulus barkeri Hughes was selected from its conventional strain(CS)via a long–term heat acclimation(maintained at 35°C)for multiple generations.Our previous studies have showed that HTAS had an enhanced tolerance to high temperature.However,the survival and reproduction of organism in nature are affected by many environmental factors.In recent years,the decrease in stratospheric ozone layer has led to the increased of ultraviolet–B radiation,which has direct deleterious effects on behavior,development and population of insects.Moreover,the environment of high temperature is usually associated with enhanced ultraviolet radiation.In this study,we compared the survival of female adults,the hatchability of eggs and predation response of these two strains,and focused on two physiological aspects:oxidative stress and antioxidant enzyme genes under UV-B radiation stress.Hereby,to insight into the difference of the two strains adaptation mechanisms for UV-B radiation stress,the main results are as follows:1.Effects of bio–ecology of N.barkeri under UV-B radiation stressThe exposure of female adults to UV-B irradiation of 25?w/cm~2,75?w/cm~2 and 150?w/cm~2 all led to an increase mortality of N.barkeri.At all UV-B irradiances and for all durations of treatment,females of CS were more UV-B tolerant than that of HTAS,with HTAS mortality generally twice more than for CS.Moreover,the percentage of egg hatching decreased with UV-B irradiance and,for a given UV-B irradiance,with the duration of exposure of female eggs.Eggs of CS were more tolerant to UV-B irradiation than those of HTAS.To explore wheather UV-B irradiation stress affects the predation functional response of female adults of N.barkeri preying on nymph of T.urticae,the predators were exposed to UV-B irradiation of 25?w/cm~2,75?w/cm~2 and 150?w/cm~2 for 1 h,2 h and 3 h.The results showed that the female adults of N.barkeri exhibited a type II functional response to nymph of T.urticae wheather exposed to UV-B irradiation or not.However,the functional response of the two strains were affected by UV-B irradiation stress.The number of the nymph of T.urticae consumed decreased by the duration of exposure and UV-B irradiance increased.At the same time,the attack rate(a)was reduced,and the handling time(T_h)was prolonged,respectively.At the irradiance of 25?w/cm~2,the functional response of two strains were less affected and the female adults of HTAS showed stronger predation ability that of CS.However,at the highest irradiance of 150?w/cm~2,the female adults of HTAS were more vulnerable and the predation ability was significantly decreased.2.Effects of antioxidant enzymes activities of N.barkeri under UV-B radiation stressLevels of SOD,POD and CAT activities were measured in female adults after exposure to UV-B irradiation with 75?w/cm~2 for 1 h,2 h and 3 h.In control,female adults of CS had significantly higher SOD,POD and CAT activities than those of HTAS.SOD,POD and CAT activities were found to be induced by exposure to UV-B irradiation for female adults of CS,whereas no significant difference in CAT activity was found for HTAS.When exposure to UV-B irradiation for 1 h,three enzymes activities of female adults of CS were up–regulated,but all decreased when exposure for 3 h.SOD and POD activities of female adults of HTAS can also be induced when exposure to UV-B irradiation for 1 h and declined over time.CAT activities of female adults of HTAS showed no significant difference compared with the control when exposure to UV-B irradiation.The redox balance of N.barkeri may be destroyed by long–time UV-B irradiation,which finally caused individual death with lipid peroxidation.3.Sequence and phylogenetic analysis of antioxidant enzyme genes of N.barkeriAccording to the transcriptome sequencing data of N.barkeri from our research group,five antioxidant enzyme genes have been identified and characterized and named NbSOD1(encoding a protein with 153 amino acids(aa),GenBank number KX505992),NbSOD2(185 aa,KX505993),NbSOD3(215 aa,KX505994),NbPHGPX1(208 aa,KX505995)and NbPHGPX2(199 aa,KX505996),respectively.The three SOD genes were identified to belong to CuZnSOD and mitochondrial MnSOD and two PHGPX genes belonged to phospholipid glutathione peroxidase.The results of multiple protein alignments showed that the five antioxidant enzyme genes had high similarity with Metaseiulus occidentalis with an identity of over 70%.4.The expression patterns of antioxidant enzyme genes of N.barkeri under UV-B radiation stressThe results of q–RTPCR at different stages of the N.barkeri life cycle showed that the two PHGPX genes were highly expressed in male adults which demonstrated that they might play a more crucial role in male adults stage.NbSOD1 and NbSOD2 showed the highest expression in female adults and the expression of NbSOD3 were the highest in larvae.SOD genes may be in the regulation of development of N.barkeri since the expression of SOD genes increased by the growth of N.barkeri.The highest expression at adult stages of almost all antioxidant enzyme genes showed the adults of N.barkeri were the major population to tolerate environmental stresses.The expression of five antioxidant enzyme genes and unigenes can be induced by UV-B irradiation.The expression levels of three SOD genes and CAT and CPX genes of CS can be significantly induced by UV-B irradiation,however the expression levels of these genes of HTAS remained constant over time.The transcription levels of these genes of CS increased immediately with the treatment for 1 h,but declined over time.These genes played vital roles of CS than HTAS against UV-B irradiation stress.The results indicated antioxidant enzyme genes provided broad–spectrum protection against oxidative damage induced by UV-B irradiation and two stains of N.barkeri exhibited different defense mechanism when suffering oxidative stress. |
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