Optimization Of Wettable Powder Formulation Of Beauveria Bassiana Bb324

Beauveria bassiana is a common entomopathogenic fungus with broad-spectrum insecticidal properties that is widely used in biological pest control.In order to develop and apply this fungus in production,the wettable powder formulation of B.bassiana Bb324was screened using the response surface method.The efficacy of the wettable powders against Gryllotalpa orientalis was evaluated through indoor toxicity and potting tests.The main results of this study are as follows:1.Selection of the most suitable medium:The Bb324 strain was inoculated on six common fungal media,and the SDAY medium was found to have the best spore production rate of 1.68×10⁸spores/cm².The Bb324 spore powder obtained was tested for quality,with a water content of 6.6%,a spore content of 1.31×10¹¹spores/g,and a live spore rate of 80.16%.2.Screening of auxiliaries:Six carriers were selected to determine their wetting time,suspension rate,colony growth rate,spore production,and spore germination rate.Kaolin was determined to be the best carrier,and Nonylphenol ethoxylate（NP-10）was determined to be the best wetting agent.Sodium methylene bisnaphthalene sulfonate（NNO）was identified as the best dispersant.Beet powder was determined to be the best UV protectant.3.Response surface optimization of additives:The Plackett-Burman experimental design and response surface method were used to optimize the formulation of B.bassiana Bb324 wettable powder.The results showed that Kaolin,Beet powder,and Polyethylene glycol were the main factors affecting the spore germination rate,while the other four factors had less influence on the spore germination rate of the powder.Under natural conditions,the maximum viable spore rate of the wettable powder was achieved when the formulation was 60.75%Kaolin,7.27%Beet powder,4.29%Polyethylene glycol,5.59%NP-10,5.59%NNO,2.80%Sodium carboxymethyl cellulose,3.73%Polyvinyl alcohol and 10%spore powder,which was consistent with the predicted model germination rate of 97.31%.The shelf life of the optimized wettable powder was 91.12%after 6 months of storage at 4°C.4.Laboratory toxicity test:The laboratory toxicity of the optimized Bb324 wettable powder to G.orientalis was determined.The results showed that the cumulative corrected mortality rate of Bb324 WP 50x dilution was 91.67%and the LT₅₀was 2.82 d.In the screening test of biological agents,the lethal effect of 0.3%Azadirachtin EC on G.orientalis was found to be better than 6.0%Rotenone ME.0.5%Matrine AS and 6.0%Spinetoram SE.The compatibility test between the strains and Azadirachtin was carried out and the results showed that low concentrations of Azadirachtin had less effect on B.bassiana Bb324,with spore germination inhibition of 11.86%,mycelial growth inhibition of 1.94%and spore production inhibition of 10.11%for a 4000x solution of Azadirachtin.Subsequently,the virulence of the 50-fold dilution of the fungicide and the 4000-fold Azadirachtin mixture was measured against G.orientalis and the optimum volume ratio was found to be 7:3.The cumulative corrected mortality rate of G.orientalis after 4 d of treatment was 96.65%.5.Pot trials:To evaluate the control effect of mixed agents against G.orientalis in the east with the reference indexes of physiological characters and correction control efficiency of tobacco plants.The results showed that 28 d after application,there was no significant difference in physiological indexes between the insect-free control group and the insect-mixed treatment group.The control effect can reach 79.30%,and the corrected control effect is 63.17%when wettable powder is used alone.