Occurrence Of Pine Wilt Disease In Chongqing And The Transmission Ability Of Bursaphelenchus Xylophilus By Monochamus Alternatus (Coleoptera: Cerambycidae)

Pine wilt disease is one of important quarantine disease and Monochamus alternatus is the primary vector of Bursaphelenchus xylophilus.After emergency of M.alternatus adults,the majority of B.xylophilus aggregates in trachea system in head and breast parts and few stings to exterior body parts of M.alternatus.When M.alternatus feeds pine trees for nutrition,B.xylophilus larvae slip into the trees.M.alternatus adults are inclined to lay eggs in those pine trees infested by B. xylophilus,and next year the adults of M.alternatus emerge from the infested trees with a large number of B.xylophilus,carry the latter into the un-infested trees when feeding,and thus result in the proliferation of the disease.Pine wilt disease has become the most dangerous and crucial quarantine pest species for forestry in Chongqing,and the study on spread and occurrence dynamics of the disease can provide the theoretical basis for scientific control of the disease.To understanding of the biological,ecological traits and transmission ability of M.alternatus in Chongqing will supply effective information and possess essential significance for the prevention of pine wilt disease spread and control of M.alternatus.After two years' investigation and analysis,the results were summarized as follows:1.Occurrence dynamics of pine wilt disease in ChengqingIn Chongqing,pine wilt disease was first discovered at the band of Fuling and Changshou and in 2003 the disease was reported in Jiangbei,Banan and Yubei Districts.Through the consistent eradication of infested pine trees,no infested trees have been found in Yubei District for the last three years and in Banan District for last two years.In 2004,Shapingba District and Zhongxian County were listed as newly infested area,and Yunyang County was also enrolled in 2006.By the end of year 2007,there have been seven districts and counties where pine wilt disease ever reported.2.Molecular detection or B.xylophilus in ChongqingThe morphology identification results,through the classification of dead Chinese red pine samples from Fulin,Wanzhou,Yunyang and Beibei with the morphological method in combination of the molecular marker characters,showed that the nematodes classified from Fulin possess the traits of B.xylophilus while those from other three districts were more suitable to be clustered into B. mucronatus.The PCR amplification of nematodes DNA with B.xylophilus and B.mucronatus specific primers verified the results above.3.Preliminary study on natural enemies and discerning pheromone ofM.alternatus femalesIt has been reported that discerning pheromone probably exists in M.alternatus females,and male adults receive these signals via the sensilla on antenna,maxillary palpus and labial palpus.No mating behavior occurred in the bioassay with purified pheromone by n-hexane and the reason might result in no effective purification of sex pheromone by n-hexane.According to the current investigation,microorganisms,predator and parasite natural enemies were the mainly natural enemies of M.alternatus.In forestry,Scleroderma guani acted as the dominant natural enemies and it can parasite in larvae and pupae of M.alternatus.4.Detection of B.xylophilus amount in M.alternatusTotally 101 M.alternatus adults emerged in laboratory were detected,B.xylophilus were found in 93.1%of adults and averagely there were 2181 B.xylophilus per M.alternatus.The highest number of B.xylophilus in M.alternatus was 32096.The majority of M.alternatus carried an amount of B.xylophilus ranging from 1000 to 9999 and there was no significant amount difference between females and males adults.The emergency stage of M.alternatus in laboratory could be divided into three stages,that is,pre-emergency period,emergency peak period and last emergency period.At pre-emergency period,the carrier amount of B.xylophilus expressed highest with an average of 4311 per M.alternatus and males carried a far larger amount than females.At last emergency period,there was an average carrier amount of 1675.At emergency peak period,M. alternatus carried least amount with an average of 778 B.xylophilus per adult but a higher carrier amount in females.5.Transmission dynamics of B.xylophilus by M.alternatus and effects of temperature on transmission abilityDuring feeding pine trees for nutrition,B.xylophilus larvae slip into the healthy trees.The quantity character study of B.xylophilus transmission by M.alternatus through culture in laboratory and statistics suggested that few B.xylophilus were detected in the first 5 days after M.alternatus' emergency,the amount of B.xylophilus increase greatly as time went on and the transmission number amounted to peak in the 20th day with an average of 700 per M.alternatus to healthy trees. Besides,the effects of temperature on transmission amount were studied.The study based on three temperatures(that is,22℃,28℃and 34℃)revealed that with the increase of temperatures there was a shorter longevity of M.alternatus adults with a shorter longevity in females and no uniform emergency progress.The tracing record of transmission amount to healthy trees showed that higher temperature,earlier transmission peak period.There was a lowest transmission rate of B.xylophilus in 34℃suggesting that there were inhibitory effects of high temperatures on the occurrence of B. xylophilus.