| The moth Orvasca subnotata Walker (Lepidopetra:Lymantriidae) is a severe defoliator of Dalbergia odorifera T. Chen found in man-made forests, its biological characteristics and the determination of its larval instars are the important basis for the pest forecast and control in the forest. Through the study of Orvasca subnotata toxicity by use of the microbial pesticide, the purpose is to provide theoretical reference for microbial control of D. odorifera plantation. The purpose of our use of microbial agents is to reduce the use of chemical pesticides.(1) Biological characteristics of O. subnotata.The morphological characteristics, the habit of each developmental stage and the life history of O. subnotata were investigated though regular field sampling. Through regular forest sampling and morphological characterization, three indicators of larval instar features including the head capsule width, prothoracic verrucae width and body length were recorded and analyzed. Give the result as follows:We described the biological characteristics of O. subnotata with an emphasis on its developmental features. Our results showed that as the larvae grow, the prothorax gradually darkens, and the abdominal back line and poison gland color gradually deepen. Statistical analysis of the body measurements showed that both the head capsule width and prothoracic verruca width could be used as indicators of developmental stages with head capsule width being superior to prothoracic verruca width, and the prothoracic verruca width and head capsule width were significantly correlated (y=0.994x-0.114,R=0.999). The body length distribution fits the Dyar’s law. However, due to the overlap distribution among developmental stages, body length is not a reliable indicator of larval instar determination. We draw up the fitted curve, the object are number of larval instars and measured variables. The result showed that the compound and growth and exponential models (R>0.999,P<0.001) have the best fitting results, followed by the quadratic curve (R≥0.991. P≤0.001) and the cubic curve (R≥0.999, P≤0.005).(2) O. subnotata’s Virulence of stomach is determined by using of helicoverpa armigera nuclear polyhedrosis virus.O. subnotatca’s Virulence of stomach is determined by using of helicoverpa armigera nuclear polyhedrosis virus, it is antithesis of chemical pesticide that lambda cyhalothrin and abamectin and deltamethrin. Leaf be uesd for processing by a leaf dipping method, treated leaf be used for feeding 2 instar larvae. We made use of the method of uniform design to find the optimal model, the maximum numerical number of cotoxicity coefficient and the best mixing ratio by stepwise regression analysis. The results are as follows:Median lethal concentration (LC50) of helicoverpa armigera nuclear polyhedrosis virus is 1137.35 PIB/ul, the intercept of the regression equation is-1.2380. Median lethal concentration (LC50) of lambda cyhalothrin is 8.93mg/L, the intercept of the regression equation is 3.3002. Median lethal concentration (LC50) of deltamethrin is 16.99mg/L, the intercept of the regression equation is 1.7254. Median lethal concentration (LC50) of abamectin is 2.12mg/L, the intercept of the regression equation is 2.8138. It will be seen from this that Heliothis armigera nuclear polyhedrosis virus’s virulence is lower than group of chemical pesticide antithesis to O. subnotata, O. subnotata sensitivity to Heliothis armigera nuclear polyhedrosis virus is lower than that of group of chemical pesticide antithesis. The maximum numerical number of cotoxicity coefficient of the combination of heliothis armigera nuclear polyhedrosis virus and abamectin is 97.39 and the combination of heliothis armigera nuclear polyhedrosis virus and lambda cyhalothrin is 177.46 and the combination of heliothis armigera nuclear polyhedrosis virus and deltamethrin is 126.03 by test of co-toxicity. Therefore, the combination of heliothis armigera nuclear polyhedrosis virus and lambda cyhalothrin is the best synergistic combination. Their maximum cotoxicity coefficient is 177.46 and the optimal concentration of the mixed ratio is 106:3. When the control effect test in Dalbergia odorifera grove, we used 900 ml/ha of Heliothis armigera nuclear polyhedrosis virus and 150 ml/ha of Heliothis armigera nuclear polyhedrosis virus and lambda cyhalothrin mixed agent can effectively prevent O. subnotata.(3) O. subnotata’s virulence of stomach is determined by using of Bacillus thuringiensis.The same method be used, our result is Median lethal concentration (LC50) of B.thuringiensis is 26.93 IU/ul, the intercept of the regression equation is -1.5149. Therefore, B.thuringiensis’s virulence is lower than group of chemical pesticide antithesis to O. subnotata, O. subnotata sensitivity to B.thuringiensis is lower than that of the chemical control group. The maximum numerical number of cotoxicity coefficient of the combination of B.thuringiensis and abamectin is 81.06 and the combination of B.thuringiensis and lambda cyhalothrin is 190.44 and the combination of B.thuringiensis and deltamethrin is 94.56 by test of co-toxicity. The combination of B.thuringiensis and lambda cyhalothrin is the best synergistic combination. Their maximum cotoxicity coefficient is 190.44 and the optimal concentration of the mixed ratio is 4:3. When the control effect test in Dalbergia odorifera grove, we used 1950 ml/ha of B.thuringiensis and 675 ml/ha of Bacillus thuringiensis and lambda cyhalothrin mixed agent can effectively prevent O. subnotata.(4) Detection and statistics of Bacillus thuringiensis in soil and Field control proposal.We used the method of sodium acetate antibiotics to isolate B. thuringiensis in soil. The results show that The result showed that the number of colonies of B.thuringiensis of isolated in soil of D.odorifera forest of spraying 1950 ml/ha and 1500 ml/ha of B.thuringiensis is 38.9 and 14.7; the number of colonies of B.thuringiensis of isolated in soil of D.odorifera forest of spraying 675 ml/ha and 525 ml/ha of B.thuringiensis and lambda cyhalothrin mix is 0.7 and 0.1;soil ofD. odorifera forest of spraying cyhalothrin and water have not isolate any colonie. So that, there is Bacillus thuringiensis in the absence of the original soil. In a certain concentration range, the concentration of our spraying B.thuringiensis is high. Bacillus thuringiensis base in soil is bigger. The existing research shows that B.thuringiensis and Heliothis armigera nuclear polyhedrosis virus is sensitive to high temperature and ultraviolet radiation. Therefore, we can alternate spraying 1950 ml/ha Heliothis armigera nuclear polyhedrosis virus and 900 ml/ha of Bacillus thuringiensis in 10-11 months. In 3-9 months, we can turn the application of 150 ml/ha of Helicoverpa armigera nuclear polyhedrovirus and cyhalothrin mixed agent and 675 ml/ha of Bacillus thuringiensis and cyhalothrin mixed agent. We can choose to apply pesticide in the morning or in the evening. |
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