Toxicological And Biochemical Basis Of Synergism Between The Entomopathogenic Fungus Beauveria Bassiana And The Insecticide Matrine Against Spodoptera Litura

The Spodoptera litura is an important agricultural insect which causes serious damage to different crops.At present,it management is mainly dependent on chemical control which has resulted in development of insecticide resistance.Beauveria bassiana is an important entomopathogenic fungus,which is well known for its effectiveness against different insect pests.In this study,S.litura was challenged with different combinations of B.bassiana and matrine(botanical insecticide)to investigate their compatibility.Our results revealed a synergistic relationship between matrine and B.bassiana on mortality and enzyme activities of S.litura.The main results of the study are as follow:The effects of different concentrations of matrine(0.05,0.125,0.25,0.5 and 1.0mg/mL)on the conidial germination,mycelial growth rate of different B.bassiana strains(SB006,SB010,SB015)were determined.The results showed that matrine and B.bassiana were compatible at concentrations of 0.05,0.125,0.25,0.5 and 1.0 mg/mL.The strains SB006,SB010,and SB015 are well compatible and can be reconstituted in the paper.Virulence of matrine and B.bassiana alone or in combinations against 2~ndd instar larvae of S.litura was determined by artificial diet dipping method.The increased mortality of S.litura following matrine and B.bassiana joint application suggests a strong synergistic effect between both agents.The effects of different B.bassiana,matrine and their mixtures on the individual feeding and food utilization efficiency of S.litura were determined by artificial diet dipping method.The results showed that average individual food intake of S.litura in the control group was significantly higher than the treatment groups,indicating that the feed intake of S.litura decreased significantly.The average individual growth rate of S.litura in the control group was significantly higher than that of the treatment groups,indicating that the S.litura larvae after intake of B.bassiana and matrine The growth rate was significantly reduced.It was known that B.bassiana and matrine have certain toxicity to S.litura.The pupation rate and adult emergence rate of S.litura in each treatment group were significantly lower than those in the control group,demonstrating a strong synergistic effect between both agents.When B.bassiana combination matrine against S.litura 7 days,the activities of 5enzymes(acetylcholinesterase,peroxidase,catalase,superoxidedismutase,glutathione-S-transferase)was monitored in the fat body and hemolymph.After treatment,each enzyme activity in S.litura changed significantly.The activity of five enzymes in each treatment group was significantly lower than that in the control group on the 7~thh day,which may be related to the inhibition of enzyme activity by the joint action of B.bassiana and matrine.The glutathione-S-transferase activities decreased from 3 d to 7 d.Trends,and when treated for 3 days,the enzyme activities in the fat bodies of S.litura treated with the insecticide and mixtures were significantly higher than those of the control,so it was illustrated that the glutathione-S-transferase in fat bodies had detoxification effects on B.bassiana.Acetylcholinesterase showed a decreasing trend from 3 d to 7 d,and each treatment at different time was significantly lower than that of the control group,indicating that acetylcholinesterase activity in fat body and hemolymph may be inhibited.