Screening Of Highly Pathogenic Beauveria Bassiana And Anti-oxidative Reaction To Plutella Xylostella

The Plutella xylostella is a world pest with a strong adaptability a strong adaptability and can spread far and wid.The occurrence algebra of the P.xylostella has an obvious difference between the north and south of China.With the overuse of pesticide,the resistance of the field population has developed rapidly.Beauveria bassiana is an entomopathogenic fungus that has been studied and applied most widely than any other species.It has the advantages of wide insecticidal range,strong pathogenicity,simple application and no pollution.It provides a new direction for the green prevention and control and pesticide reduction of the P.xylostella.This paper carried out the investigation of the occurrence of P.xylostella in Tongnan Chongqing National Modern Agricultural Science and Technology Park,monitored the field population resistance,screened the highly pathogenic B.bassiana strains,analyzed the toxicity and compatibility of B.bassiana with the insecticides,scanning electron microscope was used to observe the infection process of B.bassiana to the body wall of P.xylostella,and measured the antioxidation reaction level in the body of P.xylostella after infected by B.bassiana,providing theoretical and technical guidance for the prevention and control of the P.xylostella using entomopathogenic fungi.The main results were as follows:1 Investigation on the occurrence of Plutella xylostella in the field of TongnanThe occurrence of P.xylostella was investigated using five point sampling method in Tongnan Chongqing National Modern Agricultural Science and Technology Park from October 2016 to March 2017.Cabbage was planted in October 11th,and the larvae of P.xylostella was 40/100 in October 25th.The adult trapping amount of P.xylostella was 40 per week.The larvae and adult entered the overwintering period in January 10th and December 20.After overwintering,the larvae and adult activities began to appear on March 7th,the number of larvae reached 20/100 plants,and the adult trapped was 2 per week.The occurrence of larvae and adults of P.xylostella decreased with the decrease of temperature,and increased with the increase of temperature.In winter,survey found that larvae were surviving on 24 January and February 7 with the daily average temperature is 7°C.The number of pupae in the overwintering form of P.xylostella is significantly more than that of 4 instar larvae.In the January,the number of overwintering pupae of P.xylostella reached20/100 plants,and the four instar larvae were 8/100 plants.2 Screening of the highly pathogenic Beauveria bassiana and mixing with chemical insecticides against the Plutella xylostellaThe pathogenicity of 9 different strains of B.bassiana aginst the P.xylostella was determined by the immersion method.The results showed that the infection rate of Bb0601,Bb0604,Bb07,Bb014,Bb252 and Bb0603 strains aginst P.xylostella were higher.Their lethal concentration was9.74×10⁶/ml,1.11×10⁷/ml,1.44×10⁷/ml,1.74×10⁷/ml,1.50×10⁷/ml and 12.28×10⁷ml.Among them,the best was Bb0601 its accumulative corrected mortality was 85.19%in the 6th day.Toxicities of 5 insecticides to diamond back moth,the LC₅₀ of Abamectin,Chlorantraniliprole,Tebufenozide,Betacypermethrin,Emamectinbenzoate were 250.52 mg/L,7.52 mg/L,35.18 mg/L,335.30 mg/L and 8.72 mg/L.In Tongnan area,the resistance index of P.xylostella to Abamectin,Cypermethrin,Emamectin Benzoate and Chlorantraniliprole were 12562,94.45,91.35,32.7,no resistance to Tebufenozide.Compatibility test between B.bassiana（Bb0601）and 5 insecticides declare that the spore germination rate in these insecticides from low to high were Betacypermethrin（27.02%）,Emamectinbenzoate（43.86%）,Abamectin（46.21%）and Chlorantraniliprole（61.21%）,Tebufenozide（77.38%）.The result indicated that inhibiting effect of Chlorantraniliprole and Tebufenozide were lowest.Toxicity of mixing of Chlorantraniliprole and B.bassiana（Bb0601）,Tebufenozide and B.bassiana（Bb0601）were 22.60 mg/L and 5.20mg/L.Compared with the two insecticides,the LC₅₀0 decreased by 35.76%and 30.85%respectively.That the spores could attach,germinate and penetrate on the body wall was observed by scanning electron microscopy after using the mixture of B.bassiana and insecticides.The results showed that the germination and growth of the spores were involved in the early lethal effect of the mixture aginst P.xylostella.3 Antioxidant response of Plutella xylostella infected by Beauveria bassianaThe antioxidant level of P.xylostella 3 instar larvae after being infected by B.bassiana（Bb0601）with concentration was 4.2×10⁶/ml,and control group replaced with distilled water.The results showed that the activity of CAT,SOD and POD of P.xylostella increased in varying degrees within 16h,indicating that the three enzymes were involved in the antioxidant activity in the early stage of the infection.The activity level of SOD was higher than that of control group all the time,indicating that the enzyme played an important role in the resistance of P.xylostella to B.bassiana.The activity level of POD was lower than that of the control group all the time.The activity of CAT decreased rapidly and lower than that of the control group after being infected for 24 hours.It indicates that the activity of POD and CAT was inhibited,probably because of the decrease in the level of the synthetic protein of P.xylostella infected by B.bassiana,maybe it was related to the decline of the synthetic protein level and break of its physiological balance of P.xylostella infected by B.bassiana.