| The Asian corn borer?ACB?Ostrinia furnacalis?Guenée?,the major corn pest in China,were widely distributed and cause damage to corns throughout their growing season.The ACB is serious in Chongqing because the corn are mainly sown in spring,which is also the favorable season for a wide variety of weeds in the field.The great diversity of host plants including weeds and corn enhanced the growth and reproduction of corn borer.In Chongqing the corn are mainly planted individual peasants,who are lack of guidance on pesticide application.The production of corn would be reduced and the damage would be heavier in the next year without pesticide application.The overuse of pesticide would lead to environmental pollution and health hazard owing to the pesticide residues.Therefore,screening high-efficiency pesticide and adjuvants against ACB,which can reduce pesticide application,is crucial for improving corn production and minimizing environmental hazard.Additionally,to provide timely and accurate guidance for pesticide application,the control threshold of ACB should be established,which are necessary for the integrated pest management of ACB.In this dissertation,the laboratory toxicity tests were conducted to assay the efficiency of pesticide and adjuvants by leaf immersion with corn leaf and the second instars of ACB.Based on data of the past few years and the result from field survey by pheromone traps in 2019,the population dynamics of ACB was determined.The damage of ABC to corn were checked in the second peak of the ABC population by releasing ABC in the field.The control threshold was estimated according to the damages to the stem and production of corn.The results are as follows:firstly,through the pilot study five pesticides were confirmed to be effective with the tested six levels of concentrations.Compared with control,the LC50 of Chlorfenapyr,Emamectin benzoate,Chlorantraniliprole,Indoxacarb,Chlorfenapyr,Emamectin,Chlorantraniliprole is 0.023?0.019–0.029?mg/mL,0.023?0.017–0.033?mg/mL,0.050?0.034–0.072?mg/mL,0.107?0.075–0.149?mg/mL(95%0.097?0.457–1.799?mg/mL,0.223?0.129–0.523?mg/mL,0.790?0.034–0.072?mg/mL,1.272?0.751–2.778?mg/mL,respectively.Among the four pesticides,Chlorfenapyr and Emamectin benzoate showed much higher efficiency.Secondly,the performance of Chlorfenapyr and Emamectin benzoate with two concentrations respectively were determined with silicone?the main component is polytrichlorosilane?and orange essential oil as adjuvants,which were diluted 1000 times with pure water.The pure water and the adjuvants diluted 1000 times were set up as control.The results showed that at higher pesticide concentrations,the efficiency of Chlorfenapyr were improved by 18.33%and20.00%with silicone and orange essential oil,while 20.00%and 21.66%for Emamectin benzoate.However,at lower pesticide concentrations,the efficiency was not as good as at higher concentrations.Overall,the laboratory experiments showed that Emamectin benzoate with orange essential oil were the most efficient.Lastly,the pheromone traps of Asian corn borer conducted in 2019 to decide the releasing date based on the previous data.It was known from the pheromone traps that the ABC can be observed from middle April to early September.And the peak of the population was late April to middle May,late June to middle July.According to previous data,the ABC were released on 28th June,and investigation were conducted 25th July.The results demonstrated that the number and depth of wormholes caused by ABC increased with their releasing density,leading to decrease in corn production.Notably,the releasing density showed significant linear relationship with the number of wormholes and 100-seed weight.Considering the price of corn and the cost of pest control,the control threshold was 9.2 egg cluster per 100plants when the pest density and loss of production were fitted in the model. |
PDF Full Text Request