Entomopathogenic Fungi And Their Pathogenicity In Curculio Davidi Fairmaire

Curculio davidi Fairmaire(Coleoptera: Curculionidae)is known as the main pest to Castanea mollissima,which is also called chestnut weevil.The pest damage occurs every two years in the most areas of China,leading to the lost of edibleness and commodity value.So far,the common method to prevent or kill the pests is pesticide spraying in tree crown,but it can not be the efficient way to solve the larvae problem living inside of the fruit.Based on the long diapause time(about eight months)of the mature larvae,we studied some entomogenous fungus as biological control agent to control the C.davidi.Research contents1.The experimental orchard of chestnut was selected in Xiyang County,Shanxi Province for regular sampling.The occurrence,infestation,morphology and biology variations of C.davidi were studied with the help of laboratory anatomy.2.The amino acids components of the larval body of C.davidi were analyzed.3.The infection effects of three strains(TST05,FDB01,SYN01)were studied,including the infection symptoms,lethallty rates,extracellular enzyme activities(protease,chitinase and lipase)of the fungal strains,and the relativities between the extracellular enzyme activity and the strain virulence.4.The adhering,germination and invasion of Beauveria bassiana to the larval body were observed by using the scanning electron microscope.5.The strains of fungi were isolated from the larval cadavers of C.davidi which were naturally infected by pathogens.The morphological features of strains were identified with light and canning electron microscope.The DNA sequence characteristics were used series of molecular experiments.Base on these characteristics,the species and their status were confirmed.Research results1.The diseased fruit rate could reach to 40 percent in Xiyang County and the C.davidi had completely one generation once a year.The mature larvae took off the fruit and went into the soil at the end of September and the beginning of October,then accomplished the life cycle in May of next year.During this time,C.davidi could be controlled by entomopathogenic fungi.2.The C.davidi larvae contained 17 kinds of amino acids,including Glutamate and Phenylalanine,which could promote the growth of fungal hyphae and the formation of conidia,respectively.3.The C.davidi larvae began to show diseased symptoms,to die and to be coated with some white hyphaeon in the next three days,infected by three strains of B.bassiana(TST05,FDB01,and SYN01).SYN01 strain caused the highest corrected mortality and the fastest lethal velocity of the larvae,so that SYN01 strain could be considered as an effective entomopathogenic fungus to control C.davidi.4.There were significant linear correlations between Pr1 activity,chitinase activity of entomopathogenic fungi and strain virulence.It indicated the important roles of these two enzymes in the processes of fungus infection in C.davidi larvae,which could act as the virulence index to screen and evaluate the strain virulence.5.The conidia of entomopathogenic fungi were easier to adhere to the mouthparts,antenna,folds,furrows,spines and setae of body surface.And the fungus invaded integument by hyphae and germtube penetrating.6.Three strains of LXY01,LXY02,and LXY03 were isolated and purified from the naturally infected larvae.LXY01 and LXY02 were identified as B.bassiana and LXY03 as Fusarium proliferatum,which were provided useful sources for control of C.davidi.