A Study On The Virulence And Application Of Metarhizium Anisopliae And Beauveria Bassiana Strains Against Larvae Of Bemisia Tabaci

Bemisia tabaci is an important worldwide pests. For a long time, Bemisia tabaci dependent on the chemical control, and the drug resistance is very prominent.Therefore, the research and development on effective and economic sustainable alternative technology against Bemisia tabaciis imminent.In this paper,3strains Metarhizium anisopliae and6strains of Beauveria bassiana were selected from the laboratory strain repository, and had conducted a series of comparative experiments like the vegetative growth of the strains, the initial time of sporulation, spore production rate and germination properties in terms of biological characteristics.And conducting virulence determination tests on whiteflies3-4instar nymphy by leaf dipping, using time-dose-mortality model for simulating the experimental data analysis, reveal the test insect mortality rat e and spore dose trends over time, in order to screen out the high virulent strains against Bemisia tabaci larvae. In the meantime, carrying out researchs about the compatibility between the highly pathogenic strains and commonly-used chemical pesticides and its insecticidal effect with the chemical pesticides which mixed with the highly pathogenic strains, it provides theoretical support for developing production of fungal agent for control of Bemisia tabaci. The main results are as follows:1. Screening the high virulence fungi strains of Bemisia tabaciSelect three strains of Metarhizium anisopliae and six strains of Beauveria bassiana and determinate their biological characteristics of vegetative growth, time of sporulation initial, sporulation and spore germination rate.The results showed:the biological characteristics is significant different between the different strains. In three strains of Metarhizium anisopliae,the Mf62strain has the largest colony diameter trained ten days, the sporulation initial relatively short period of time, sporulation and spore germination rate in24h, they are6.97cm,130h,7.06×108spores·cm-2and97%; In six strains of Beauveria bassiana, Bb781, Bb84and Bb52colonies vegetative growth, the initial time of sporulation, sporulation and germination rate are better, the best is Bb781strains, they are9.0cm,115h,10.17×108spores·cm-2and99.9%.Overall visible,the biological characteristics of Beauveria bassiana Bb781strain is best.In three strains of Metarhizium anisopliae, the strongest pathogenicity is Mf62strain, ten days cumulative mortality is45.33%; While Mf21and Ma98strain pathogenicity are poorer, cumulative mortality rate are only12.33%and12.33%, but the death time of three strains of Beauveria bassiana is longer more than10d, so three strains of B. bassiana strains to Bemisia tabaci larvae don’t have good control effect. In six strains of Beauveria bassiana strains, the strongest pathogenicity is Bb781strains, the half death time is shorter, only5.75d, and the ten days cumulative mortality was83.67%, and the Bb84strains is less than Bb781,the half death time and cumulative mortality rates were6.91d and77%. The worst strains is Bb22, only30%of the total mortality. Research shows that different strains have significant difference of Bemisia tabaci larvae in pathogenicity, Bb781and Bb84strains on Bemisia tabaci larvae were higher pathogenicity.On the basis of filtering out Bb781and Bb84strains,determined the virulence of two strains from low to high concentration gradient spore suspension on Bemisia tabaci larvae. The results showed:the cumulative corrected mortality of Bemisia tabaci larvae gradually increased with the increase of the concentration of spores. The mortality rates of Bemisia tabaci larvae processed by Bb781on various levels are higher than Bb84, two groups deal with the highest mortality rates were91.11%and85.56%, respectively. Inoculated with two strains of cumulative mortality of nymphs difference was not significant, but inoculation with Bb781strains1×108spore suspension on the third day the accumulated mortality rates of Bemisia tabaci larvae vaccination Bb84strain had reached3times than Bb84strains1×108spore suspension,the lethal speed of Bb781strains is faster than Bb84, which lag a great help to solve the efficiency of anti-fungal agents, so select Beauveria bassiana Bb781strains for further analysis.Using the time-dose-mortality model simulation analysis, the model passed the Hosmer-Lemeshow fit test for heterogeneity, indicating a good model,and estimated the lethal dose and lethal time of Beauveria bassiana strain Bb781on Bemisia tabaci larvae by the model.After the seven inoculation day, the LT50value of1.60×105spores·mm-2, LT90value of3.59×107spores·mm-2. Beauveria bassiana the Bb781spore suspension on Bemisia tabaci larvae lethal time with the number of dose related for the test agents LT50values decrease with the increase in the number of doses of the number of doses from6.0to8.0, the LT50reduced by the4.3d to2.9d. Visible the Beauveria bassiana Bb781strains with a strong virulence on Bemisia tabaci larvae,in the biological control of Bemisia tabaci has broad application prospects.2.The the compatibility of Beauveria bassiana Bb781strains with the commonly used chemical pesticides For ball spore Bb781strains of beauveria bassiana in nutrition growth, spore production rate and spore germination inhibitory rate of evaluation indexes, determinate six kinds of commonly used chemical pesticides in the lethal concentration, concentration of sub lethal concentration, time and death under the compatibility with the ball spore Bb781beauveria bassiana strains. Results show that with the increasing of concentration of chemical pesticide, the inhibition rate of strain is also rising. Abamectin strongest inhibition of spore strains during times of sub lethal concentration nutrition growth, germination rate and spore production quantity the inhibition rate of71%,71.88%and67.92%respectively; Imidacloprid, organism amidine and insect mite acrylic with ball spore Bb781Beauveria bassiana spores has good compatibility, the inhibition is the weakest of imidacloprid, in times of sub lethal concentration when the strain growth inhibitory rate was7.04%, the amount of spore production of inhibition rate is only8.18%, germination rate, the inhibition rate of only1.74%, the best compatibility with spores.3.Toxicity of Beauveria bassiana strain Bb781mixed with chemical insecticides on Bemisia tabaci larvaeThis study the virulence of Beauveria bassiana strain Bb781spore suspension mixed with the low concentrations of chemical pesticides with better compatibility on Bemisia tabaci larvae. The results showed that:used alone Beauveria bassiana strain Bb781spore suspension seven days cumulative mortality rate was76.67%,Beauveria bassiana strain Bb781spore suspension mix with imidacloprid, acetamiprid and Chlorfenapyr, seven days cumulative mortality rate reached91.11%,87.78%,84.44%, respectively. Visible bacterial agents mixture than single application of Beauveria bassiana strain Bb781spore suspension significantly increased virulence, but also shortens the incubation period,2d cumulative mortality rate began to rise significantly. Three mixtures LT50less than Beauveria bassiana strain Bb781spore suspension, especially imidacloprid mixture, the LT50of only2.9d. Therefore, the application of Beauveria bassiana strain Bb781spore suspension mixed with imidacloprid poisoning on Bemisia tabaci larvae is the best.