| Delphastus catalinae(Horn)is an important predator of whiteflies.In recent years,researchers have done a lot of basic researches on the biology and ecology of this ladybird.However,the research on diapause of this beetle has not been reported so far.The study on the diapause can lay a foundation for future artificial propagation,and it also helps to understand the development mechanism and adaptation mechanism of this natural enemy insect.Under laboratory conditions,the effects of photoperiod and temperature on the diapause of D.Catalinae were preliminarily explored,and biological and physiological characteristics of diapause D.Catalinae were also studied.Illumina’s Hisq 2500 technology was used to perform transcriptome sequencing of non-diapause,diapause and diapause termination stages of D.Catalinae to understand the molecular mechanism.Sequencing of transcriptomes enriched the genome information of D.Catalinae as well.We got the following conclusion.1.Photoperiod and temperature have a decisive role in diapause D.Catalinae.The pre-oviposition period was used as the main criterion for judging adult diapause.Diapause was also determined by observing the development degree of the ovary.Diapause induction was influenced by temperature and photoperiod.At the same temperature,the diapause rate decreased with increasing daylight(L16: D8< L14: D10< L12: D12< L10:D14< L8: D16).However,at the high temperature(26°C and 31°C)conditions,the diapause rate of females of the above five photoperiods was 0%.Under the same photoperiod,the diapause rate decreased with increasing temperature(21°C< 16°C< 11°C).The critical daylight was10-12hr/d at low temperature(11℃).Diapause termination was determined by measuring the pre-oviposition period.At the same temperature,the pre-oviposition period of diapause induced females extended with increasing light duration(L14: D10< L8: D16).Under the same photoperiod,the pre-oviposition period of diapause induced females extended with increasing temperature(21°C< 16°C< 11°C).Therefore,low temperature(11℃)and short-day photoperiod(L8: D16)can maintain diapause.2.There are differences between the biological characteristics of diapause and non-diapause D.Catalinae.Short day and low temperature reduced the life history parameters of adults,the daily egg production of females for the first 40 days and had a negative impact on F1 generation.Diapause adults reared for 40 days at low temperature 11°C,short-day photoperiod L8: D16 or L10: D14.Compared with non-diapause adults(reared at high temperature 26°C and long-day photoperiod L14: D10),the life history parameters of diapause adults decreased significantly,that is,the life span of female and male were shortened,the oviposition period were decreased and the total fecundity of diapause female(egg/female)within 40 days was reduced.What’s more,for diapause D.Catalinae,the dynamic level of fecundity was not stable and the peak period of fecundity was later than those of non-diapause female.The egg production per day per female was also lower than non-diapause female.Finally,the hatching rate,pupation rate,adult acquisition rate and adult emergence rate in F1 generation of diapause female were decreased.However,different photoperiods had no significant effect on biological characteristics of diapause adults.The females could continue to lay eggs for a long time even under the diapause-induced short-day photoperiod(L8: D16 or L10: D14).There was no significant difference in the parameters of the above two photoperiods on F1 generation of diapause D.Catalinae.3.Changes in physiological characteristics of different developmental stages of D.Catalinae(non-diapause,diapause,and diapause termination)were determined.The study found that the diapause of D.Catalinae was a kind of glycogen accumulation.Trehalose and sorbitol were not the main protective agents in diapause adults.D.Catalinae relied on the total protein consumption to survieve at low temperature(11℃)and short-day photoperiod(L8: D16).In addition,it was also found that the activity of 5 enzymes related to glucose metabolism changed correspondingly,and the activity of 3 protective enzymes increased significantly in the diapause period.The changes of above various chemicals can protect the ladybird beetle from diapause.4.Using Illumina Hisq 2500 technology,transcriptome sequencing of D.Catalinae in three states were conducted(non-diapause,diapause and diapause termination).Differential expressed genes(DEGs)and their functions,classifications and pathways were preliminarily analyzed by bioinformatics methods.DEGs was determined by comparison,that is,between diapause and non-diapause,between diapause termination and diapause,and between non-diapause and diapause termination respectively.And then eight diapause-related genes were then verified using q PCR.By comparing the relative expression levels of eight genes in D.Catalinae at different diapause stages,the q PCR results were obtained to demonstrate the reliability of transcriptome sequencing. |
