Toxicological And Physiological Effects Of Bacillus Thuringiensis HA And HD On Phyllotreta Striolata(Fabricius)Adults

Bacillus thuringiensis is an effective and eco-friendly biological control measure to substitute the chemical control of insect pests.In this study,we investigated the toxicities of two strains of Bacillus thuringiensis(Bt-HA and Bt-HD)against Phylloetreta striolata adults,to further explore the mode of action of Bacillus thuringiensis and improve its insecticidal activity.The main research results are as follow:1.The two strains of B.thuringiensis had very different features.Under the scanning electron microscope,the strains of Bt-HA and Bt-HD formed rhombic and rectangular crystal proteins,respectively.The SDS-PAGE analysis indicated that Bt-HA mainly produced 65 kDa protein and Bt-HD produced 77 kDa protein.The cultured shapes of the strains of Bt-HA and Bt-HD were also different.Similarly,the growth curve of the Bt-HA strain had a higher growth rate than Bt-HD.Moreover,the plasmid profile indicated that the strains of Bt-HA and Bt-HD had only one band.2.Bioassay of the two strains against P.striolata adults for 14 days indicated that Bt-HD had a higher insecticidal activity.The LC50 values of the strains of Bt-HA and Bt-HD were 4.01×108 and 8.23×107 CFU/ml,respectively.Survival analysis indicated that Bt-HA and Bt-HD had a significant impact on the longevity of P.striolata adults compared to the control individulas.3.The Bt-HA and Bt-HD strains decreased the food consumption of P.striolata adults.For the same strain of Bt,the concentration had a negative correlation with the food consumption,i.e.the increased Bt stimulated antifeedant activity and decreased the food consumption of P.striolata adults.For the same concentration,the strain of Bt-HD had a better inhibitory action on the food consumption of the P.striolata adults.Bt-HA and Bt-HD also affected the activity of the GST enzyme of P.striolata.4.Histopathological analysis of P.striolata adults revealed that the microvillus in the midguts had been destroyed four days post-treatment with Bt-HD strain and the basement membrane of P.striolata adults'midguts had been destroyed when treated for 14 days.In Bt-HA treatment,the microvillus of P.striolata adult's midguts had been destroyed when treated for 14 days.In control treatment,no obvious morphological changes of P.striolata adults were observed.In conclusion,this study illustrated both the strains of Bt-HA and Bt-HD had insecticidal activity against P.striolata adults that significantly affected the food consumptionand destroyed the microvillis of the midguts.Bt-HD also destroyed the basement membrane.P.striolata adults increased the activity of GST enzyme to defend itself against Bt infection.The mechanism of the strains of Bt-HA and Bt-HD towards P.striolata adults should be further investigated.