| Hyphantria cunea is a worldwide quarantine pest.Due to the environmental pollution caused by traditional chemical control,the highly efficient,sustainable and pollution-free control strategies of Hyphantria cunea have become the focus of current research.However,the use of a single biocide for biological control has exposed the disadvantages of slower larvae infection and mortality in the control process.During the period of severe white moth disaster,Bacillus thuringiensis is an important bio-insecticide.It has the advantages of low toxicity,pollution-free,and environmental friendliness.It has achieved certain results in the control of the Hyphantria cunea.However,the use of a single bio-pesticide for biological control of Hyphantria cucurbitae has the disadvantages of low mortality rate and slow death rate of Hyphantria cuneae larvae during the prevention and control process.It is unable to efficiently and quickly kill Hyphantria cucurbitae.Studies have shown that the rational use of biological pesticides is one of the effective ways to solve the problem of instability and increased virulence of a single biocide.Therefore,the adoption of the mixed use of Bacillus thuringiensis and other biological insecticides is increasingly favored by researchers,which is also in line with the development requirements of future pesticides.In this paper,the toxicity of a strain of Bacillus thuringiensis strain CF1262,which is highly toxic to Hyphantria cunea,was first determined.The compatibility test between Bacillus thuringiensis and other biological pesticides was conducted to screen out biopesticides with good compatibility with Bacillus thuringiensis.The Bacillus thuringiensis and the selected biological pesticides were mixed at different concentrations to test the indoor combined virulence,and a combination of synergistic effects was selected by calculating the coefficient of co-toxicity.After that the mathematical model was used to calculate the most Excellent compounding mode.Finally,determine the control effect of the optimal compounding mode on the Hyphantria cunea.The main findings are as follows:1.Determination of high virulent strains:The virulence of Bacillus thuringiensis strain CF1262 against Hyphantria cuneae was determined by leaf dipping method.In this method,the LC50 of Hyphantria cunea is 1.887×10~5 cells/ml,and the LT50 is 3.68d.The results are as follows,the mortality rate of moth and the quick effect of the moth have been increased.Therefore,Bacillus thuringiensis CF1262 strain has high virulence to the Hyphantria cunea and can be further used for the preparation of compound formulations.2.Determination of the compatibility of Bacillus thuringiensis with other biological pesticides:Under the high,medium and low concentration gradients,the inhibition of colony growth of the three biological pesticides tested against Bacillus thuringiensis strain CF1262 was different.Among them,matrine had a significant influence on the colony growth of Bacillus thuringiensis under conventional concentration dilution.After 48 hours culture,the growth diameter of colonies under conventional lethal concentration was 4.83mm,and the growth diameter of colonies in the control group was 10.29mm,and the inhibition rate reached 53.04.%,while avermectin and diflubenzuron III had little effect on the colony growth of Bacillus thuringiensis,showing good compatibility and further compounding with Bacillus thuringiensis.3.Preliminary screening of combined virulence and synergistic combinations:The LC50 of1.8%avermectin cream single oil to the white moth is 7.1276 mg/L,LC50 of the single agent of1.3%marine water is 72.948 mg/L.The co-toxicity coefficient of the mixture of Bacillus thuringiensis CF1262 and 25%diflubenzuron III suspending agent in each volume ratio is higher than 100.It can be seen that the mixture of Bacillus thuringiensis and diflubenzuron have different degrees of synergistic effect on the biological control of Hyphantria cuneae in all volume ratios,with the highest co-toxicity coefficient being 165.67.Bacillus thuringiensis CF1262 and avermectin also showed perfect synergy.4.Calculation of theoretical optimal compounding mode:Calculate the mass fraction(K)of Bacillus thuringiensis strain CF1262 in the compounding agent,and then obtain the arcsine conversion value(X)by the formula,and finally convert the arcsine sine(X)Coincidence coefficient(Y)of the compound with the compounding agent was found after fitting:the theoretical optimum of 1.887×10~5 cells/ml Bacillus thuringiensis strain CF1262 and concentration of 72.948 mg/L 25%diflubenzuron III suspension.The ratio is 1.8753:1 by volume.5.The control effect of the theoretical optimal compound on the white moth:a single dose of Bacillus thuringiensis CF1262 strain,a single dose of 25%diflubenzuron III,and a compounding agent with the theoretical optimum ratio under LC50 concentration All the white moths showed high control effect,and the virulence of the compounding agent was obviously better than that of the single agent.The most top control effect of the three treatments on the white moth was 56.71%,54.69%,and 81.39%respectively,within 8 days after application.The order of the control effects against the American moth was:theoretical optimal mix ratio>Bacillus thuringiensis A single dose of CF1262 strain>25%diflubenzuron III suspensions in a single dose.Therefore,it can be further concluded that the theoretically optimal compounding agent has a synergistic effect on the control of Hyphantria cuniculus. |
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