Extraction And Isolation Of Destruxins And The Toxicity Of Mixed Pesticides To Aphis Ciricola

Aphis citricola is one of the main pests of apple trees.Shanxi province is one of the main apple production areas in China,the damage of Aphis citricola has caused huge economic costs in our province every year.At present,the main way for Aphis citricola control is chemical pesticides.Dued to the unreasonable use of chemical pesticides,Aphis citricola has developed resistance to many pesticides,and the quality of fruit is declining year by year.That also causes environmental pollution.So it is necessary to look for environmentally-friendly control methods.Destruxin is a biological insecticide that has a broad-spectrum insecticidal effect against insects,it is secreted by the entomopathogenic fungi-Metarhizium anisopliae.Destruxin has the characteristics of high efficiency,low toxicity,environmental friendliness,not easy resistance,and safety to humans and animals.But the costs of extraction are too high,it is difficult to promote the application in a large area.In this study,the best compounding ratio of destruxin and routine chemical pesticides was screened for reduce the use of chemical pesticides.In this paper,we determined the toxicity of destruxin,chemical pesticides and their mixture on Aphis citricola,then the mixed pesticides were developed.The main results are as follows:1?Firstly,we isolated and purified the strain of Metarhizium anisopliae from the grubs?scarab larvae?.Through fermentation,organic toxins were extracted by liquid phase extraction,then toxins were separated by half-mass spectrometry high performance liquid chromatography.The results showed that four toxin mixtures?destruxin A?B?D?E?were extracted from the fermentation broth.The purity of destruxin A by the chromatographic separation was 91%,and the output of the destruxin A was 0.07 g/mL fermentation broth.2?The leaf dipping method was used to determine the toxicity of destruxin and pesticides on Aphis citricola.The results showed that the median lethal concentrations(LC₅₀)of destruxin,beta-cypermethrin,avermectin,imidacloprid,acetamiprid,and nitenpyram were 0.016 mg/L,0.221 mg/L,0.221 mg/L,2.242 mg/L,and 8.247 mg/L and 9.793 mg/L.By comparison,the toxicity of destruxin on Aphis citricola is the highest.3?To determine the toxicity of the mixed pesticides on Aphis citricola,destruxin and pesticides were mixed in different proportions.The bioassay results showed that the toxicity of mixture of destruxin and avermectin on Aphis citricola was the best combination in the five mixed modes,and the LC₅₀ after the combination of destruxin and avermectin was 0.148 mg/L.When the destruxin and avermectin were mixed in a ratio of 9:1,the co-toxicity coefficient was 176.36 and the toxicity was the best.According to the experimental results and economic costs,the ratio of 4:6 was used to develop pesticide mixture.With the emergence of insecticide-resistant,the application of pesticide mixture is becoming more and more widespread.In this study,we first reported the use of destruxins and pesticides mixture for controlling Aphis citricola,the results of this study have great significance for reducing pesticide residues,improving the quality of fruits and vegetables,and protecting the ecological environment.At the same time,it also provided the basis for green pest control,and protected the sustainable development of agriculture in our country.