Occurrence And Damage Mechanism Of Scolytus Schevyrewi Semenov In Apricot Orchard In Desert Oasis Area Of Xinjiang

The Xinjiang Uygur Autonomous Region is located on the northwestern edge of China.Because of its continental arid climate and extensive management of orchards,Scolytus schevyrewi is easy to outbreak.In this paper,the occurrence and damage mechanism of S.schevyrewi was studied systematically on the basis of the previous studies.It provided the basis for the integrated control system of S.schevyrewi.This research mainly includes the following four parts.(1)The occurence and spatial distribution of S.schevyrewi were studied in apricot orchards.The results showed that S.schevyrewi required 35-49 days to complete the life cycle and had three to four generations per year in Kashi area of Xinjiang.S.schevyrewi emerges from overwintering sites in early April,with a peak during mid to late April.The 1st,2nd and 3rd generation of adult reached to peak in early to mid June,mid to late July and early to mid September,respectively.The quantity of the initial entrance hole in different part of apricot tree from large to small in turn was main branch,lateral branch,bearing branch,trunk and the long fruitbranch.The spatial distribution type of S.schevyrewi was aggregative distribution,with individuals attracting each other,and the individual group was the basic component in its distribution.When the population density was below 1.68 individuals per plant,the environmental condition was the main cause of the aggregation.When the population density was more than 4.92 individuals per plant,the environmental factor and aggregation behavior of S.schevyrewi were the main cause.(2)During the emergence period of S.schevyrewi,the growth character of the vulnerable host tree was investigated in apricot orchard.The results showed that the damage degree of S.schevyrewi had significantly negative correlation with the mean length and diameter of the new shoot and the mean weight per hundred leaves.The apricot trees with the mean length of the new shoot less than 14.85 cm,the mean diameter less than 0.31 cm,the mean hundred leaf weight less than 52.40 g were easy to be infested by S.schevyrewi.The apricot trees with the mean length of the new shoot less than 7.05 cm,the mean diameter less than 0.26 cm,the mean hundred leaf weight less than 43.69 g were easy to be infested and die.Resin secretions of apricot trees damaged to different degrees presented normal distribution.Resin secretions of the vulnerable apricot trees under sporadic or continued damage were significantly greater than that of the healthy or vulnerable to infestation and dead apricot trees.(3)Volatiles from native apricot(Prunus aremeniaca L.cv.Saimaity)logs by headspace sampling,and identified by coupled gas chromatography-mass spectrometry(GC-MS)and coupled gas chromatography-electroantennographic detection(GC-EAD).The results showed that antennae of female responded to 17 volatile compounds(2-Methyl-3-pentanone,a-Pinene,Camphene,Hexanal,3-Carene,(R)-(+)-Limonene,(E)-2-Hexenal,Dodecene,Octanal,6-methyl-5-Hepten-2-one,1-Hexanol,Nonanal,N,N-Diethyl-formamide,cis-Linalol oxide,(+)-a-Longipinene,Decanal and Linalool)from apricot tree.Y-tube Assays and field trapping experiments showed that(-)-a-Pinene?(S)-(-)-limonene?(+)-3-Carene?Hexanal,Camphene,(+)-a-Pinene,a-Pinene,Dodecene attracted males and females,respectively.S.schevyrewi was repelled by Octanal.(4)The associated fungi and bacteria of S.schevyrewi were isolated and identified.The results showed that among the associated fungi,Yamadazyma mexicana was the dominant strain,Candida xinjiangensi and Wickerhamomyces ciferrii were the major strains,Cladosporium macrocarpum,Meyerozyma guilliermondii and Paecilomyces sp.were the minor strains.A new species of Candida was identified and named as Candida xinjiangensis sp.nov.Among the intestinal and surface bacteria,Enterobacter xiangfangensis,Pantoea agglomerans and Enterobacter cloacae were the dominant strain.Serratia marcescens was the major strains,Enterobacter aerogenes,Serratia nematodiphila,Acinetobacter rudis,Kluyvera cryocrescens,Lactococcus lactis subsp.,Bacillus firmus,Curtobacterium plantarum and Alcaligenes faecalis were the minor strains.The associated fungi and bacteria could be divided into four kinds.The first kind was plant-pathogen or conditioned pathogen,it mainly included Y.Mexicana,C.macrocarpum,E.cloacae,P.agglomerans and E.aerogenes.The second kind was the pathogen of plant and insect,it mainly included S.marcescens.The third kind was the antagonist of the plant-pathogen and the pathogen of insect,it mainly included M.guilliermondii,S.nematodiphila,B.firmus and A.faecalis.The fourth kind was neutral bacteria,it mainly included L.lactis subsp.