Effects Of Short-term High Temperature Stress On The Biological Characteristics Of Beauveria Bassiana And Neoseiulus Barkeri (Hughes)(acari: Phytoseiidae)

Neoseiulus barkeri is a local predator that has been commercialized in China due to its advantages of rapid fertility and strong diffusion ability,and plays a key role in modern agricultural green prevention and control.Beauveria bassiana is an important species in the application and research of Entomogenous fungi.It is a relatively common parasitic fungus that can act on a variety of pests with good control effects.The application of biological control methods can not only delay the increase of pest resistance,but also is sustainable and environmentally friendlly.In recent years,the development and utilization of biological control technologies has attracted more and more attention.At the same time,global warming and frequent extreme weather also affect the control effect of Beauveria bassiana and Neoseiulus barkeri on pests in field applications.This study explored the effects of high temperature on the joint prevention and control of fungi and mites on the basis of screening for Beauveria bassiana that has significantly lethal effect on the target pest mite and the study of the effect of Beauveria bassiana on Neoseiulus barker.i meMeanwhile the pathogenicity of Beauveria bassiana under short-term high temperature stress and the effect on the predation efficiency of experimental populations of Neoseiulus barkeri were studiedin order to clarify the constrained effect of short-term high temperature events on the joint prevention and control of Beauveria bassiana and Neoseiulus barkeri.The main research contents are as follows:1 Screening of a strain of Beauveria bassiana and its pathogenic effect on Eoteranchus kankitus and Neoseiulus barkeriThe pathogenic effects of 5 strains of Beauveria bassiana strains on adulth female of Eotetranychus kankitus were determined.During the screening process,all strains showed certain pathogenicity to Eotetranychus kankitus,and the treatment concentration was 1×10⁷ spores·m L^-1,the corrected mortality rate was 56.21-82.91%,and the time-mortality linear fitting was performed under this concentration treatment to obtain that its median lethal time(LT₅₀)is 4.41-7.42 d.The corrected mortality rate of Bb025 against spider mites was significantly higher than that of other strains,so Bb025 was identified as a superior strain with potential control effect on Eoteranchus kankitus.The pathogenicity of Bb025 to Eoteranchus kankitus was further determined,and the LC₅₀0 value was 3.481×10⁵ spores·mL^-1.The infection of Beauveria bassiana Bb025 against Neoseiulus barkeri showed that the mortality rate reached 25.3%and the LT₅₀0 was 16.1 d when the spore suspension concentration was 1×10⁹ spores·mL^-11 in9 days.The selectivity test of Neoseiulus barkeri and Eoteranchus kankitus on Beauveria bassiana treated citrus leaves were carried out through the disc leaf dipped method.It was found that the leaves of 0-120 min after treatment showed significant avoidance behavior.It is indicated that Beauveria bassiana does affect the habit of mites.Scanning electron microscopy was used to record the infection process of Beauveria bassiana against Neoseiulus barkeri.On the 5th day after treatment,hyphae were observed attached to the surface of the mite body.The corresponding DNA fragment of Bb025 was extracted from the body of Neoseiulus barkeri by nested PCR technology.2 The effect of temperature on the growth and infection of Beauveria bassianaThe effects of six different temperature treatments on the growth of Beauveria bassiana were studied..At 25?,Bb025 had the best growth state,and the colony diameter and average growth rate reached the maximum.When the test temperature was higher than 28?,the colony diameter of Beauveria bassiana decreased while the treatment temperature increased.When the temperature reached 35?,Beauveria bassiana stopped growing.The results of short-term warming treatment exclusively onBeauveria bassiana indicate that short-term high temperature stress can affect the growth viability of Beauveria bassiana,which further leads to a decrease in pathogenicity.The results showed that the heating treatment for 2 hours is of no significant effect on the infection effect during the short-time heating treatment,and with the prolongation of the temperature-increasing treatment time,the infectivity of Beauveria bassiana to Neoseiulus barkeri and Eoteranchus kankitus also decreased.The number and the viability of spores carried in short-term high temperature treatment were studied.The results showed that the number of spores carried by Neoseiulus barkeri was not affected by temperature stress.As the treatment temperature prolonged,the vitality of the spores decreased.Meanwhile the germination rate of Beauveria bassiana spores carried by Neoseiulus barkeri gradually decreased with the prolongation of temperature stress treatment time,and the germination rate was only71.67%at 35?for 6 h.3 Effects of Beauveria bassiana on the biological characteristics of Neoseiulus barkeri under short-term high temperature stressShort-term high temperature events were simulated in the laboratory?treated at35?for 4 h,treated at 25?without stress as the control group?,and thereproductive characteristics ofthe newly hatched female Neoseiulus barkeri was evaluated.The results showed that the female adult Neoseiulus barkeri infected by Beauveria bassiana after the treatment of a short-term high temperature stress,and the pre-oviposition period significantly increased,and the total egg production significantly decreased,and the average life span of female mites decreased.In order to clarify whether the potential co-control ability of Beauveria bassiana and Neoseiulus barkeri to the Eoteranchus kankitus was affected by short-term high temperature events,the female Neoseiulus barkeri was pre-treated with high temperature stress tostudy its predation functional response.Under the short-term high temperature event,compared with the control group,the Neoseiulus barkeri showed a decreasing trend in its predation to Eoteranchus kankitus,the instantaneous attack coefficient decreased,and the treatment time decreased.It is conclude that short-term high temperature events may cause a certain negative impact on the appetite of Neoseiulus barkeri,and anorexia is indicated in the short term.