Study On The Responses Of Indigenous Predatory Mites To Different Temperatures And Rapid Cold Hardening

Amblyseius andersoni Chant and Neoseiulus striatus Wu are two species of indigenous phytoseiid mites newly found in Inner Mongolia,which show better predation potential against the two-spotted spider mite,Tetranychus urticae Koch.Temperature is one of the most important abiotic factors influencing the predation and oviposition performance of phytoseiid mites.Especially in the northern part of China with a large diurnal temperature fluctuation,the sudden drop of temperature will bring stress on the survival of phytoseiid mites.Therefore,it is important to study the responses and molecular mechanism of phytoseiid mites to different temperatures and rapidly changing low temperatures for understanding the fitness of indigenous predatory mites to different temperatures and analyzing the effects of rapid cold hardening（RCH）and its cold resistance mechanism.In this thesis,the developmental and reproductive potential of A.andersoni and N.striatus to T.urticae were firstly evaluated at five constant temperatures（17,20,25,30 or 35℃）by establishing the life table of experimental population,in order to understand the predation responses of two phytoseiid species to prey under different temperatures.Neoseiulus striatus showed better performance in reproductive potential to T.urticae than A.andersoni.Then,N.striatus was chosen to be subjected to rapid cold hardening to evaluate its response to low-temperature stress.Further transcriptome sequencing was conducted on N.striatus before and after rapid cold hardening,and 10 differentially expressed genes were selected for verification.The main results are as follows:1.The development and reproduction of A.andersoni under five different temperaturesThe development,reproduction,longevity,and life table parameters of A.andersoni were significantly affected by the different temperatures.The duration of the egg,larva,protonymph,deutonymph and total immature stages were reduced when the temperature increased.The total oviposition of A.andersoni was highest at 25°C and lowest at 17°C,and the daily average oviposition increased as the temperature increased,but few eggs were laid at 17°C.The values of the intrinsic rate of increase（r_m,0.108-0.200）,net reproduction rate（R₀,18.71-36.47）and the mean generation time（t,14.68-29.73）significantly differed among the five temperatures.The highest net reproduction rate（36.47）and intrinsic rate of increase（0.200）were obtained at 25°C and 35°C,respectively.2.The development and reproduction of N.striatus under five different temperaturesSimilarly,the development,reproduction,longevity,and life table parameters of N.striatus were significantly affected by the different temperatures.The duration of the egg,larva,protonymph,deutonymph and total immature stages were reduced when the temperature increased.However,the total oviposition of N.striatus was highest at 35°C and lowest at 17°C,and there was no significant difference between 25°C and 35°C.The life table parameters of N.striatus were also significantly affected by temperatures.Our results indicated that the fecundity of N.striatus was higher at high temperatures.The net reproductive rate（R₀）and intrinsic growth rate（r_m）of N.striatus were higher than those of A.andersoni at five temperatures.Thus,both A.andersoni and N.striatus had a promising predation potential against two-spotted spider mites,with the reproductive potential of N.striatus better than that of A.andersoni.3.Rapid cold hardening response of the phytoseiid mite Neoseiulus striatusThe critical temperature for N.striatus was-15°C,at which its survival dropped below10%.An exposure to 5°C for 2 h was optimal for rapid cold hardening,efficiently increasing survival in N.striatus.Rapid cold hardening was found in all developmental stages of N.striatus,and there was no significant effect of exposure on the consumption of spider mites.Thus,the exposure to 5°C for 2 h can enhance the cold hardiness of N.striatus but not reduce its predation ability,which will be favorable to its field release application in areas with large diurnal temperature fluctuations.4.Transcriptome sequence and bioinformatic analysis of Neoseiulus striatusAfter four different treatments were performed in N.striatus female adults,namely control group（25℃）,cold shock（-15℃,2h）,RCH（5℃,2h）and RCH+cold shock（5℃,2h+-15℃,2h）,the results of transcriptome sequencing in N.striatus showed that 83.28 Gb clean data were obtained through the sequencing quality control,and further assembled into83,161 Unigenes.There were 36,951 Unigenes obtained further functionally annotated in the NR,Swiss-Prot,KEGG,COG,KOG,GO and Pfam databases.The homology analysis of the Unigenes annotated in NR database indicated that 61.69%of N.striatus Unigenes was similar to sequences from another phytoseiid species of Galendromus（Metaseialus）occidentalis.5.Selection and analysis of differentially expressed genes of Neoseiulus striatusThere were significant changes in gene expression at the transcriptional level of N.striatus among three treatments（Cold shock,RCH,RCH+Cold shock）.Compared with the control group,the number of differentially expressed genes（DEGs）after RCH was the highest（3975）,and the number of DEGs after RCH+Cold shock was the lowest（63）,which indicated N.striatus responds to changes in ambient temperature by differentially expressing（up/down）related genes when exposed to short-term freezing（Cold shock）,short-term low temperature（RCH）,and short-term low temperature+short-term freezing（RCH+Cold shock）.10 DEGs（Control VS RCH）were selected for verification by real-time quantitative PCR.The results showed that the expression trend of DEGs and transcriptome sequencing was consistent,which proved that the results of transcriptome sequencing were reliable.