| Bemisia tabaci is one of the most important agricultural pests around the world because of its high reproductive capacity,wide host range and transmission of a large number of plant viruses,causing serious damage to crops.Up to now,management of B.tabaci mainly depends on chemical pesticide,but the abuse of chemical pesticide has led to resistance of B.tabaci to various pesticides.Biological control not only prevents pests developing resistance,but also greatly reduce the amount of chemicals agents used,is an important strategy for sustainable and green agriculture.Entomopathogenic fungi is one of the important biological control measures to control B.tabaci.However,entomopathogenic fungi have some disadvantages in pest controlling,such as slow infection process and unstable control efficiency.Therefore,finding biological control material with high compatibility with chemical pesticide is the key to rapid and sustainable control of pests.In this paper,neonicotinoids,plant-based pesticides,microbial pesticides and other different types of chemical pesticide were selected.This study screened out chemical pesticide showing good compatibility with Beauveria bassiana,and then combined B.bassiana with low dose chemical pesticide,evaluated synergistic control effects of chemical pesticide and B.bassiana on B.tabaci,identify the potential for combined application,to provide reference for sustainable green control of B.tabaci.The main results are as follows:1.Effect of ten chemical pesticide on biological characteristics of B.bassianaTen representative pesticides were selected from several types of chemical pesticide,such as neonicotinoids,plant-based pesticides,microbial pesticides.The inhibition of mycelial growth,spore germination and sporulation of B.bassiana by chemical pesticide were determined to screen out,chemical pesticide with better compatibility with B.bassiana strain no.252(Bb252).The results showed that pymetrozine inhibited mycelial growth of B.bassiana Bb252 by-0.87%,-2.73% and-0.79% under field recommended concentration,field recommended concentration diluted 5 times,field recommended concentration diluted 10 times.The inhibition rates on spore germination were 43.31%,32.41% and 5.24%,and the inhibition rates of sporulation were 57.50%,49.75% and32.50%,respectively,demonstrating that it was compatible with Bb252 very well.In addition,the compatibility of spinetoram with Bb252 was only second to pymetrozine.It’s inhibition rates to Bb252 mycelial growth were 4.81%,7.12% and 5.78%,to spore germination were 18.42%,16.21% and 9.73%,and to sporulation were 92.33%,63.92%and 46.18%,respectively.2.Effects of pymetrozine and spinetoram on physiology,biochemistry and pathogenicity of B.bassianaIn this study,the effects of pymetrozine and spinetoram on the activities of chitinase and extracellular protease in B.bassiana were determined.The results showed that the chitinase activities of B.bassiana were 110.06,109.72 and 113.06 U/m L,respectively,at the recommended field concentration,the recommended field concentration diluted by 5times and 10 times.The chitinase activity of B.bassiana was significantly decreased by the other two concentrations except when the recommended field concentration was diluted by 10 times.Different from chitinase,the extracellular protease activity of B.bassiana was 7.87,7.63 and 9.34 μg/min.m L,respectively.All these three concentrations affected the extracellular protease activity of B.bassiana.The chitinase activity of spinetoyam against B.bassiana was 108.10,112.72 and 114.27 U/m L,respectively.Only the recommended concentration in the field significantly reduced the chitinase activity.The extracellular protease activity was 21.63,22.06 and 21.20 μg/min.m L,The three tested concentrations did not affect the activity of extracellular protease.Secondly,the influence of two agents on the virulence of B.bassiana was determined.The results showed that after the treatment of B.bassiana with pymetrozine and spinetoyam,there was no significant difference in the mortality of B.bassiana to B.tabaci eggs,first instar nymphs,second instar nymphs and third instar nymphs compared with the control.Finally,the effects of B.bassiana on feeding and oviposition selection of B.tabaci were determined.The results showed that treatment with pymetrozine and spinetoyam did not affect the repellent effect of B.bassiana to B.tabaci.3.Toxicity of spinetoyam combined with B.bassiana against B.tabaciSpinetoyam,which did not demonstrate significant negative effects on the physiology,biochemistry and pathogenicity of B.bassiana,was further studied to evaluate their combined effects on pest.The toxicity of B.bassiana and low-dose spinetoram used in different sequences on B.tabaci were compared to find out the most effective way for combined applications.When the pests were exposed to spinetoram for24 h,48 h,72 h followed by B.bassiana,the survival curves of B.tabaci were all within the confidence interval of the predicted curves,showing no obvious synergistic effect;when B.tabaci were firstly exposed to B.bassiana for 24 h,48 h,72 h followed by spinetoram exposure,the survival curve of B.tabaci was lower than predicted value only when the interval of the two treatments was 72 h,showing a significant synergistic effect.In addition,the death rate of B.tabaci was determined at 9:1,4:1,1:1,1:4 and 1:9ratios of spinetoram and B.bassiana,the results showed that when the ratio of spinetoram and B.bassiana was 9:1,4:1 and 1:4,the cotoxicity coefficients were 159.08,153.12 and258.45,all higher than 120,showing a certain synergistic effect.Cotoxicity coefficient was highest when the ratio of them was 1:4,which was supposed to be the recommended ratio of spinetoram and B.bassiana.In conclusion,the spinetoram with the least influence on biological characteristics of B.bassiana was screened from different types of chemical pesticide in this dissertation.The optimal mode of combined application of spinetoram and B.bassiana was determined by combing application sequence,time interval,and mixing ratio.This study provided a theoretical basis and technical support for the green and sustainable control of B.tabaci. |
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