Pathogenicity Of Beauveria Bassiana To Tetranychus Urticae Koch (Acari:Tetranychidae) And The Sublethal Effect On Phytoseiulus Persimilis (Acari:Phytoseiidae)

Tetranychus urtice Koch is a worldwide pest mite.With the extensive use of traditional pesticides,the resistance of T.urtice is increasing.Therefore,the use of biological control methods to control T.urtice has developed rapidly.Beauveria bassiana is an important broad-spectrum entomopathogenic fungus with high pathogenicity to T.urtice.In addition,the predatory natural Phytoseiulus persimilis,as a dedicated natural enemy of T.urtice,is also commonly used in the control of T.urtice.And the combined application of B.bassiana and P.persimilis can more effectively control T.urticae.Due to the broad-spectrum insecticidal activity of B.bassiana,it also has a potential pathogenic risk to predatory mites.For example,when B.bassiana and predacious mites are used together,B.bassiana may indirectly affect predacious mites by infecting T.urticae.Based on this hypothesis,this study detected the pathogenicity of B.bassiana at different concentrations on T.urticae,and observed the infection process of T.urticae by B.bassiana with scanning electron microscope.The effect of T.urticae infected by B.bassiana on the development and fecundity and the sublethal effect of B.bassiana on the P.persimilis were determined;the secondary metabolites of B.bassiana spores from three successive generations after rejuvenation were determined,and the differences of metabolites of B.bassiana from successive generations were analyzed.The results are as follows:1.The pathogenicity of B.bassiana to T.urticaeThe mortality of T.urticae was increased with the B.bassiana concentration increasing,when T.urticae was infected by B.bassiana in different concentrations,The highest corrected death rate was 83.8%under the concentration of 1×10⁸/mL,the LT₅₀0 was 50 d,the LC₅₀0 was 1.37×10⁶/mL.The infection process of B.bassiana to T.urticae was observed by scanning electron microscopy.It was found that B.bassiana could complete spore attachment,form bud tube,produce infection structure,penetrate the epidermis and successfully invade the insect body within 60 h.2.The sublethal effect of B.bassiana on P.persimilisAfter being sprayed with B.bassiana for 16 h,24 h,36 h and 48 h,T.urticae was fed to the P.persimilis.The mortality,development period and oviposition of P.persimilis were analyzed.The mortality rate of the P.persimilis in different treatments was less than 2.0%.In the F0 generation,compared with the control,the egg,deutonymph and preoviposition and the whole generation durations of P.persimilis were prolonged in 48 h treatment;the deutonymph and preoviposition durations of P.persimilis were prolonged in 36 h treatment;preoviposition durations of P.persimilis were prolonged in 24 h treatment;the other treatments were unchanged.In the F1generation,compared with the control,there was no significant difference in the developmental duration of each stage and the generation durations of P.persimilis among treatments.In the F0 generation,compared with the control,the egg number per female of P.persimilis was lower in 36 h and 48 h treatments,In the F1generation,the egg number per female of P.persimilis was not different among treatments.3.Secondary metabolites analysis of B.bassiana spore powderThe secondary metabolites of B.bassiana spore powder in successive generations were detected by LC-MS.There were 49 secondary metabolites in F0generation;28 secondary metabolites in F1 generation;68 secondary metabolites in F2 generation.And the same 18 secondary metabolites of B.bassiana spore powder were found in F0,F1 and F2 generations.At the same time,beauverine was detected in the spore powder for each successive generations.The results showed that the secondary metabolites of B.bassiana spore powder in different generations were different,but there are few same secondary metabolites in the three generations.This study evaluated the pathogenicity of B.bassiana to T.urtica and its sublethal effect on P.persimilis.The results indicated that B.bassiana showed high pathogenicity to T.urtica,but had little sublethal effect on P.persimilis.Therefore,it is feasible to combine B.bassiana with P.persimilis to control T.urtica.The secondary metabolites of B.bassiana spore powder was determined.It was found that the secondary metabolites of B.bassiana spore powder was different in different generations,but all generations of B.bassiana spore powder contained beauverine.All in all,the results provide theoretical basis for the combining B.bassiana with P.persimilis to control T.urtica.