Effect Of Beauveria Bassiana And Azadirachtin On Experimental Population Of Trialeurodes Vaporariorum Westwood

As one kind of global agricultural pest,Trialeurodes vaporariorum Westwood can only relies on chemical pesticides to control its occurrence and harms in recent days' production with the features of wide distribution,huge quantity of hosts.Due to the extensive use of chemicals and its ecological strategy of short-time growth period and large amount of production,its resistance to drugs is increasing sharply.The application of biological control measures can not only delay the growth of insect resistance,but also has the effectiveness of environmental friendly and control sustainably.Therefore,it gets more attention of developing biological control measures.So,this paper does the research of different strains of Beauveria bassiana and azadirachtin to T.vaporariorum on the aspect of pathogenicity and virulence effect by using different ratio of mixed test,evaluation of both its development and blending effect of reproduction and survival,and by using scanning electron microscopy to observe the infection process.The main research contents are as follows.1.The screening of strains of Beauveria bassiana and its effect on the survival and development of Trialeurodes vaporariorumThis experiment tested the pathogenic effect of eight strains of B.bassiana to the experimental population of third instar nymphs of T.vaporariorum;during the preliminary screening process,all strains showed pathogenicity.When the spore suspension concentration reached to 1 × 107 conidia/mL,the corrected mortality rate was about 27% ~ 70.6%,and the rate of ringworm was between 27% ~ 67.5%,at the same time,in the linear fitting experiment of time and rate of death under the above concentration,the measured time ranged from 4.9 ~ 7.9 days,the strain of Bb252 has better performance.So,it can initial confirmed that Bb252 is the excellent strain for against T.vaporariorum and the value of LC50 is 3.99 × 106 conidia/mL.Study on the potential control effect of B.bassiana Bb252 on T.vaporariorum showed that after the different Bb252 spore suspension treatment of 1 × 104,1 × 105,1 × 106,1 × 107,and 1 × 108conidia/mL,it has a significant effect on the feeding and oviposition behavior of T.vaporariorum,while under the concentration of 1 × 108 conidia/mL,the effect on its feeding deterrent rate,food refusal rate,oviposition deterrent rate is significant,already reached to 78.8%,80.9% and 78.8% respectively.Under the different concentration,with the increasing concentration,the growth period of T.vaporariorum decreased gradually;under the concentration of 1 × 108 conidia/mL,the growth period is about 20.73 ± 0.30 days,which is significantly shorter than the control group of 23.48 ± 0.23 days.By using the survival analysis method of Kaplan-Meier,the results show that survival cumulative percentage of T.vaporariorum reached to the lowest value of 0.482 in the day of 22 under the concentration of 1 × 108 conidia/mL.2.The effects of azadirachtin on the survival and development of Trialeurodes vaporariorum WestwoodThis experiment tested the pathogenic effect of different concentration of azadirachtin on three instar nymphs of T.vaporariorum and results showed that the value of LC50 is 5.76 mg/L.In the analysis of deterrent effect,growth period influence and life cycle functions,under the five concentration treatment of azadirachtin of 500 mg/L,50 mg/L,5 mg/L,1 mg/L and 0.5 mg/L,its food refusal rate is 17.81% ~ 60.11%,oviposition deterrent rate is 14.58% ~ 69.64%,and the works of deterrent effect is more obvious with the increase of concentration.In addition,it not only can reduce feeding of the group of T.vaporariorum,but also extend the growth period after eating the leaves through treatment by azadirachtin;when the concentration reached 50 mg/L,its growth period extended to 24.95 ± 0.83 days and the survival accumulate percentage reached to the lowest value of 0.432 in the day of 25 d.Therefore,in addition to directly cause the death of T.vaporariorum,azadirachtin also has a potential effect of aversion,food refusal and disturbs normal development.3.The effect analysis of the blending of Beauveria bassiana and azadirachtin on Trialeurodes vaporariorum westwoodThe compatibility experiments between B.bassiana and azadirachtin were carried out.By using different concentration of azadirachtin to formulate toxic containing medium and then inoculate fungus of B.bassiana;when the concentration reached to 500 mg/L,the inhibition rate is 65.3%,when the concentration is lower than 50 mg/L,the inhibition rate is lower than 30%,which shows the great compatibility.In the concrete mixing process,blending proportions between azadirachtin and Beauveria bassiana in the concentration of LC50 are 9?1,4?1,1?1,1?4,and 1?9,while the proportion of 1?1 and 1?4 showed a synergistic effect,and the highest value is 294.23 under the proportion of 1?4.Finally,this experiment using the scanning electron microscopy to observe spore germination and infection process between single agent and the optimal mixture agent,the results showed that the spore of B.bassiana is more likely to attach on the indentation and folds of the hosts and easily to fall off at the back of the veneer.The influence of two forms drugs on spore germination is not significant,and both of them can be germinate within 48 h;only in the late growth stage of hyphae and formed the nets structure to surround the host(about in the time of 96 to 120 h),the nets structure of mixed hyphae was smaller than that of the single agent.