Research On The Effects Of Temperature And Photoperiod On Diapause Regulation Of Baryscapus Dioryctriae

Korean pine,Pinus koraiensis,an evergreen tree species of the Pinaceae family,is under the national class II protected plants.It widely distributes in northeast China,which expedite its widespread use in ornamental plants landscape such as in parks,street planting and courtyards as well as for afforestation.In recent years,cone borers including Dioryctria pryeri Ragonot,D.abietella(Denis et Schiffermiiller)and Eupithecia abietaria debrunneata caused serious damage to the cones and branches of Korean pine,which is a thrilling challenge to our achievements of afforestation,ecological environment and forestry industry.Chemical control not only caused the problem of environmental safety,but weak control effect due to the concealed life circle of the pests in the pine cones or under bark.Thus,the effective measures to control the pine cone borers have always been on the way.Baryscapus dioryctriae Yang & Song: Hymenoptera: Eulophidae,,which is a new species found by our team of Jilin Provincial Academy of Forestry Sciences in Lushuihe Forestry Bureau published in Annals of the Entomological Society of America in 2017.Field test showed that the control effect could reach up to 70% by releasing B.dioryctriae,which demonstrated potential of the chalcid as an excellent natural enemy for biological control practice.Mass rearing of the parasitoids is the material base for biological control,so artificial breeding of B.dioryctriae is of great significance for urban forest as well as forestry industry.During the breeding and application,it is necessary to control the breeding cycle of B.dioryctriae by artificial intervention.In this way,plenty of natural enemy product may be accumulated for intensive field releasing in suitable season of pest control.The effects of temperature and photoperiod on diapause induction of B.dioryctriae were studied in the paper,meanwhile systematical research in physiological and biochemical changes of the treated larva were made.Then applied basic studies on the effect of diapause on the biological characteristics of the chalcid were carried out.The main findings are as follows:(1)The best diapause rate was 100% at 10℃ and L12:D12.With the decrease of temperature,the diapause rate of B.dioryctriae increased significantly,and the diapause rate of B.dioryctriae decreased significantly after 12 hours of light exposure.Temperature(F=1130.6,df=2,P<0.001)and photoperiod(F=70.486,df=2,P<0.001)had significant effects on the diapause rate,in which temperature is the dominant factor.The interaction of temperature and photoperiod also affected the diapause rate(F=16.7,df=4,P<0.001).Low temperature and short light are the major environmental factors for diapause of B.dioryctriae,their interaction may induce more individuals of the B.dioryctriae into diapause.(2)During diapause,the mature larvae of B.dioryctriae accumulated a lot of sorbitol,and its content increased significantly with the decrease of temperature,which indicated that sorbitol is mainly used as a low temperature protective substance to enhance its cold resistance.Content of the trehalose was at a low level during the whole diapause.Whereas content of the protein remained at a fairly high level during the diapause,which reached the highest at 14L: 10 D after12 hours of diapause.The content of amino acids in larvae was significantly affected by temperature,and the content of amino acids at 10 ℃ and 15 ℃ was significantly higher than that at 20 ℃.The activity of sorbitol dehydrogenase at 10 ℃ and 20 ℃ was significantly higher than that at 15 ℃,which increased significantly at the early stage of diapause with a trend of decreasing-increasing-decreasing.The trehalase activity in the wasps maintained at a high level and fluctuated gently.During diapause,the activity of glycogen phosphorylase tended to decrease-increase-decrease,and the activity of glycogen phosphorylase phosphorylase increased with temperature.The lipase activity at 20 ℃ was significantly higher than that at 10 ℃ and15 ℃.The activity of POD,SOD and CAT remained high level during the diapause,and continued to increase when the diapause prolonged.(3)In several treatments,some chalcids didn’t diapause but the emergence of B.dioryctriae delayed with the lower temperature and has significant difference with control.The sex ratio of the chalcids has significant difference with control but no significant difference between treatments.(4)Diapause period of 30 d,45d and 60 d has different influence on time of emergence,quantity of emerged adults,percentage of emergence and male-female ratio.Compared with control,quantity of emerged adults,percentage of emergence and male-female ratio decreased with longer diapause period.