Studies On Physiological Characteristics, Pathogenic Mechanism And Molecular Biology Of Aschersonia Aleyrodis

The sweetpotato whitefly, Bemisia (abaci causes damage to over 600 plant species in the world with economic losses of hundreds of million dollars annually. Insecticides historically served an important role in the control of the whitefly, but recent research showed the pest had a propensity to develop resistance to insecticides. Aschersonia, as an important member among entomopathogenic fungi, can advantageously infect their hosts by direct penetration of the body wall and successfully control whitefly populations.In order to suppress B. (abaci more effectively, a diverse assemblage of Aschersonia strains were collected throughout the world and isolated in China. Then high virulent isolates were selected from the pathogens using bioassay of B. (abaci. Infection behavior of A. aleyrodis on the sweetpotato whitefly was investigated with aid of the scanning electron microscopy and light microscopy. Effects of carbon sources, nitrogen sources, metal ions, vitamins and insecticides on spore germination, mycelial growth and conidial production of A. aleyrodis were revealed in viiro, displaying many scientific data for its further research. Some of important biologically active secondary metabolites were found by the assay of B. (abaci, Myzus persicae and Aedes albopiclus. Genetic analyses were carried out based on different molecular markers such as RAPD, RFLP and LSU rDNA, which could provide a new method to investigate Aschersonia molecular phylogenesis, to clarify ambiguous morphological species, and to distinguish the sibling species within the genus Aschersonia.Main results were expressed as following.Isolation and identification of A. aleyrodis from infected citrus whitefly in ChinaAn entomopathogenic fungal isolate Aa, was isolated from the infected citrus whitefly (Dialenrodes ciiri) collected in Fujian, China. The Homopteran-specific fungal pathogen Aa was highly virulent against Bemisia (abaci larvae, and other members of the family Aleyrodidae. Light and electron microscopic investigations of infected insects showed that gross pathology, morphology, and ultrastructure of the entomopathogen were similar to those described earlier for A. aleyrodis. Based on our morphological and pathogenic investigations we proposed to name this species Aschersonia aleyrodis Webber.Virulence of different Aschersonia isolates to sweetpotato whitefly, B. tabaciEntomogenous. fungi of the genus Aschersonia are pathogens of scale insects and whiteflies. They can be targeted as biocontrol agents of sweetpotato whitefly, Bemisia (abaci. Fifteen isolates of Aschersonia spp. were used to test for their ability to sporulate and germinate on PDA and to infect insect hosts. Four isolatessporulated poorly (less than 1x107 conidia/ml), 4 had high sporulation (more than 1x108 spores/ ml) and 11 were able to parasitize the whitefly species. Infection level was positively correlated (r=0.86) with germination on water agar. After a selection based on spore production and infection, virulence of 11 isolates was evaluated on second instar nymphs of the whitefly on cauliflower. Whitefly infection levels varied between 17.8% and 88%. Several isolates, among which identified species of A. aleyrodis originating from China, Japan and Java showed high spore production on semiartificial medium and high infection levels of the whitefly species tested. In addition, investigation of infection characteristic of the fungus revealed that first to third instar nymphs were most susceptible and the infection rate of second instar nymphs could reach 88%.Infection behaviour of A. aleyrodis on the sweetpotato whitefly B. tabaciInvestigation on infection characteristic of the fungus revealed that first to third instar nymphs were most susceptible and the infection rate of second instar nymphs could reach 98%. Infection rate increased with prolongation of treatment duration or increase in inoculation concentration of conidia. Infected whitefly nymphs usually died in the following stage after treatments. Scanning electron microscopy and light micros...