Study On The Synergism And Wettable Powder Of Beauveria Bassiana To Bemisia Tabaci

Bemisia tabaci（Gennadius）is one of the most important pests in the field of agriculture and forestry.Therefore,using Beauveria bassiana to control Bemisia tabaci has gradually become the research focus of biological control,but its development is limited by its long incubation period and its vulnerability to environmental factors.This problem can be effectively solved by the combination of bacteria and drugs or the preparation of Beauveria bassiana.The main results are as follows:1.Indoor toxicity test of Beauveria bassiana against Bemisia tabaci:spray method was used to determine Beauveria bassiana Bb13 strain LC₅₀to 2.197×10⁵spores/ml,which is highly toxic to Bemisia tabaci and can be formulated as a compounding agent.2.Biocompatibility test of chemical insecticides with Beauveria bassiana:under the three concentration gradients of lethal concentration,sublethal concentration and sublethal concentration,the effects of 11 insecticides on spore germination,colony growth and sporulation of Beauveria bassiana were measured,including 25%thiamethoxam water dispersing agent,50%butylurea suspension agent,10%acaronitrile suspension agent and Beauveria bassiana The growth inhibition of the strain is small,and it has good biocompatibility,so it can be mixed with Beauveria bassiana.3.Screening of combined toxicity and synergistic combination:LC₅₀of 25%thiamethoxam water dispersible granule was 12.26mg/l for Bemisia tabaci.The co-toxicity coefficient of the mixture of Beauveria bassiana Bb13 and 25%thiamethoxam was more than 100 in each volume ratio,which indicated that the mixture of Beauveria bassiana Bb13 and 25%thiamethoxam had different synergistic effect on the biological control of Bemisia tabaci in each volume ratio,the highest co-toxicity coefficient was 198.10.Therefore,the compound of 25%thiamethoxam water dispersible granule and Beauveria bassiana Bb13 has a better synergistic effect on the biological control of Bemisia tabaci.4.Calculation of the theoretical optimal mixture mode:calculate the mass fraction K of Beauveria bassiana in the mixture,and then get the anti sine conversion value x through the formula.Finally,fit the anti sine conversion value x with the co-toxicity co-efficienty of the mixture,and we can see that the theoretical optimal concentration of Beauveria bassiana Bb13 with 2.197×10⁵spores/ml and 25%thiamethoxam water dispersible granule with 12.26mg/l are obtained The ratio was1:0.8353 by volume,and the highest co-toxicity coefficient was 198.10.5.The control effect of the theoretical optimal mixture on Bemisia tabaci in Greenhouse:the single agent of Beauveria bassiana Bb13,25%thiamethoxam water dispersible granule and the compound agent with the theoretical optimal ratio have higher control effect on Bemisia tabaci,and the toxicity of the compound agent is obviously higher than that of the single agent.The control effect order of three groups of treatments on Bemisia tabaci was as follows:theoretical optimal proportion compound>LC₅₀dose 25%thiamethoxam water dispersible granule>LC₅₀dose single B 13 of Beauveria bassiana.Therefore,it can be considered that the compound of the theoretical optimal compound mode has synergistic effect on the control of Bemisia tabaci.6.Selection of wettable powder formula and determination of its quality index:the spore powder of Beauveria bassiana strain Bb13 was harvested by liquid-solid two-phase fermentation,with spore content of 1.11×10¹¹spores/g,germination rate of 96.25%and water content of 1.55%.The formula of wettable powder was developed by using the spore powder.Based on the selection of carrier,wetting agent,dispersant and UV protectant,and the calculation of the proportion of insecticide according to the theoretical optimal compounding mode,the formula of the wettable powder of Beauveria bassiana was determined as follows:25%spore powder,5%wetting agent,BX,5%sodium lignosulfonate,0.3%xanthan gum,11.6%thiazosin,53.1%expansion of carrier Moistening soil.According to the national standard,the quality index of wettable powder was determined:the spore content of wettable powder was 2.75×10¹⁰spores/g,the live spore rate was 93.58%,the wetting time was86.4s,the suspension rate was 90.21%,the fineness was 96.32%（200 target sieve）,the water content was 1.76%,and the p H was 6.7.Meet the requirements of national standards.7.Indoor toxicity test of wettable powder:the LC50 of wettable powder to Bemisia tabaci was 1.02×10⁵spores/ml,and the LT₅₀of 10⁸spores/ml was 2.81d,which was good for the lethality and quick response of Bemisia tabaci infection.