Pathogenicity Of Beauveria Bassiana On Toxoptera Aurantii And Synergism Methods

Toxopter aaurantii(Boyer)is one of the main pests on tea trees in China.As a sucking pest,it has a strong reproductive ability and a fast growth rate,and it will bring harm to the tea producing area in China in different degrees every year.This study screened out the strains of B.bassiana with high pathogenicity to T.aurantii,further studies the biological characteristics,and uses it by compounding with botanical insecticides and spore pre-germination treatment to explore the virulence and synergistic pathway of B.bassiana against T.aurantii.The main research results are as below:1.Using the Potter spray tower,the strains with the best pathogenicity to the T.aurantii are selected from nine strains of B.bassiana.The results show that the pathogenicity of Bb2032 strain to T.aurantii is relatively strong.The cumulative corrected mortality rates for adults and nymphs 8d are 100%and 96.23%respectively.By treating the adults and nymphs with five concentration gradients of Bb2032,the LC50 of the 8th day is 2.102×104 spores/ml and 5.813×105 respectively.The results of TMD model analysis show that the peak of death for adult aphids was on the 5th day,and the peak of death for nymphs was on the 6th.2.The growth of mycelium of Bb2032 strain cultured on five mediums for 12 days and the sporulation of 10d,and the spore germination rate at different temperatures are examined.The results show that the hypha of Bb2032 strain on SMAY grows the fastest,the difference is not obvious on PPDA,PDA,SDAY,and the slowest on SDA;Bb2032 is successfully cultured on PDA,the traits remain in the best condition,and the PPDA,SDAY and SDA are in relatively worse condition.The best medium for sporulation is PDA,which reaches 2.36×107/cm2 for 10 days.The sporulation order on the five mediums is PDA>SMAY>PPDA>SDAY>SDA.The optimal growth temperature of Bb2032 strain is 22-28℃.The spore germination rate is higher in this temperature range.The optimal germination temperature is 25℃.At 35℃,the spores begin to germination.The main germination time of spores was concentrated in the first 12h of culture.Under laboratory conditions,Bb2032 strain can be cultured at 25℃ on PDA medium.3.The compatibility and toxicity synergism of three common botanical pesticides with Bb2032 strain were determined.The results showed that the inhibition rate of Bb2032 spore germination of veratridine was stable and compatible better with Bb2032.Among the three botanical pesticides,roteno Compatibility and toxicity synergism of botanical pesticides with Bb2032 strain.The results showed that the inhibition rate of Bb2032 spore germination of veratridine was stable and compatible better with Bb2032.Among the three botanical pesticides,rotenone had the strongest virulence to T.aurantii,and veratrine is significantly more toxic to nymphs than to adults.In terms of toxicity and synergistic effect,the T.aurantii toxicity of the mixture was higher than that of the single botanical pesticide,and the the sub-lethal concentration of rotenone(×10)and Bb2032 strain has the best mixed effect.The corrected accumulative mortality of adults and nymphs on the 8th day are 100%and 95.25%respectively,and LT50 is 3.331d and 4.146d respectively.4.The synergistic effect of spore pre-germination treatment on the control of aphids by Bb2032 strain.The spore suspension is pre-germinated by shaking culture.The proportion of sporeling in the spore suspension increases with the increase of shaking time.After the pre-emergence spore suspension is inoculated with T.aurantii,the mortality of adult aphids does not change significantly.The death rate of nymph aphids increases with the prolonged germination time,and the optimal time for pre-germination is the 8th hour.The spore germination rate of Bb2032 strain was counted by adding 1%and 0.1%of six kinds of sugars(glucose,fructose,maltose,sucrose,trehalose,lactose),seven kinds of amino acids(methionine,glycine,lysine,valine,leucine,isoleucine,histidine)and two kinds of insect powder(Greater wax moth(Galleria mellonella L.),Yellow mealworm(Tenebrio molitor L.))to the spore suspension for 24 hours.Compare the virulence of Bb2032 to T.aurantiiwith pre-germination at 0h,4h,6h and 8h,and compare the pathogenicity to T.aurantiiwith Bb2032 spore suspension pre-germination for 4h,8h and 12h after adding different nutrients.The results showed that the addition of several substances basically promoted the spore germination of Bb2032,and the concentration of 1%is better than 0.1%.The addition of trehalose,maltose,glucose and sucrose in sugar significantly reduced the proportion of single buds in Bb2032 spore germination;Among the nutrients in each group,glucose,methionine and yellow mealworm powder were better in the germination promoting effect of Bb2032 spores.0.1%yellow mealworm powder,1%glucose,and 1%methionine are used as pre-germination nutrients.After the three groups of spore suspensions are inoculated with T.aurantii,the addition of 0.1%yellow mealworm powder reduces the pathogenic effect of Bb2032 on adult aphids.The other groups all have a synergistic effect on the pathogenicity of Bb2032 on T.aurantii,and the synergistic effect is 1%methionine=1%glucose>0.1%Tenebrio molitor.