Screening Of High Pathogenicity Strains Of Ento Mopathogenic Fungi Against Bactrocera Dorsalis

Bactrocera dorsalis（Hendel）is classified as an important dangerous quarantine pest,because of its multiple hosts,and high destruction.It has caused serious economic losses to the production of vegetable and fruit in many countries and regions.A large number of works have been conducted to study the more safety and effective methods for controlling this pest in the past years.As an important biological control factor,entomopathogenic fungi has been successfully applied to control many species of agriculture and forestry pests and diseases.In this paper,six strains of entomopathogenic fungi:Isaria fumosorosea IFCF01,Metarhizium anisopliae Ma01,Metarhizium anisopliae Ma04,Metarhizium anisopliae Ma09,Beauveria bassiana Bb02,and Metarhizium anisopliae Bb04 were selected as candidates.Studies were carried out to evaluate the pathogenicity of these different entomopathogenic fungi strains against the pupae and adult of B.dorsalis under the laboratory conditions.And then,the entomopathogenic fungi strain with the highest pathogenicity was selected to determine its median lethal concentration and lethal time against the pupae and adult of B.dorsalis.In addition,the relationship between pathogenicity of this strain to the B.dorsalis pupae and the moisture contents of soil was evaluated under the laboratory conditions.The main results are as follo ws:1.Screening of high pathogenicity strains of entomopathogenic fungi against B.dorsalis.The pathogenicity of six entomopathogenic fungi strains against B.dorsalis pupa was determined under the laboratory conditions.Results indicated that there was difference in the pathogenicity among the tested entomopathogenic fungi strains.The corrected cumulative mortality rates of B.dorsalis pupae on the 6^{t h} day after exposure to IFCF01,Ma01,Ma04,Ma09,Bb02,and Bb04 were 4.44±1.11%,4.44±1.11%,12.22±4.84%,7.78±1.11%,5.55±2.22%,and 6.67±1.93%,respectively.After exposure to entomopathogenic fungi,the surviving fruit flies could emerge successfully,but the survival and fecundity of emerged adults were lower than those of controls which wer e not treatment with entomopathogenic fungi.The mortality rate of B.dorsalis adults gradually increased from the 2^nd day which after adult emergence,when exposing to entomopathogenic fungi during their pupal stage.And the corrected cumulative mortality rates of B.dorsalis adults were 34.5±1 to 70.87±1.44%on the 8^{t h} day post-adult emergence.After exposure to entomopathogenic fungi during the pupal stage of B.dorsalis,the median lethal time(LT₅₀)of IFCF01,Ma01,Ma04,Ma09,Bb02,and Bb04 against adult flies were 10.2 d,8.48 d,4.5 d,9.19 d,10.78 d,and 10.94 d,respectively;thus,compare with the other 5 entomopathogenic fungi strains,Ma04 exhibited a higher pathogenicity against B.dorsalis adults.In addition,after exposure to entomopathoge nic fungi during pupal stage,the mean fecundity of emerged B.dorsalis adults was significantly decreased,compare with those of the control adults;furthermore,after treatment with Ma04,the emerged B.dorsalis adults produced lowest eggs（50.83eggs/female）.Therefore,Ma04 was considered to be the optimal candidate for controlling B.dorsalis.2.Pathogenicity determination of Ma04 against B.dorsalis pupae and adults.The corrected mortality rate of B.dorsalis pupae and adults gradually increased as the spore suspensions concentration of Ma04 increased.After exposure to Ma04 spore suspensions at 1×10¹⁰ spore/ml during pupal stage,the highest corrected cumulative mortality rate of pupae on the 6^{t h} day which after treatment was 36.67±1.93%,and the highest corrected cumulative mortality rate of adult on the 8^{t h} day which post-adult emergence was 94.92±1.93%;however,when directly spraying adults with spore suspensions of Ma04 at 1×10¹⁰ spore/ml,the highest corrected cumulative mortality rate of adult on the 8^th day was 97.78±1.21%.The results of pathogenicity determination indicated that the median lethal concentration(LC₅₀)of Ma04 against B.dorsalis pupae and adults were 2.53×10¹⁰ and 2.50×10⁷ spore/ml,respectively;the median lethal time(LT₅₀)of Ma04 against B.dorsalis pupae and adults gradually decreased as the spore suspensions concentration increased.After exposure to spore suspensions of Ma04 at 1×10⁸,1×10⁹,and 1×10¹⁰ spore/ml,the LT₅₀ of pupae were 11.29 d,9.51 d,and 6.93 d,respectively;and the LT₅₀ of adults were 6.57 d,4.99 d,and 3.54 d,respectively.Therefore,compared with B.dorsalis pupae,the death speed of adults were more quick,once they were exposure to Ma04.3.The intereaction of different moisture content of soil and different spore suspensions concentration of Ma04 to the pupa of B.dorsalisIt showed that the concentration of spore suspensions and moisture content of soil had influence on the mortality of B.dorsalis caused by infection of Ma04.The cumulative mortality of different pupae was different under different soil water content.When the relative water content of soil was 40%,60%,80%and 100%,the cumulative mortality of pupae increased gradually with the increase of soil water content.Under the same soil water content,the higher the concentration of spore suspension,the higher the cumulative mortality of pupae.