Development and application of plant pesticide neem

1 The development of Azadirachta indica, a plant pesticide, has been fighting against pests and diseases since people engaged in agricultural production As early as 3000 years ago, it had been used to control borers and locusts; around 300 B.C., it began to use agricultural technology and mineral chemicals to control pests; more than 1600 years ago, it began to use insects to control pests; in the sixth century, it also had an understanding of the selection of insect resistant varieties, rotation and seed treatment methods Using plants to kill insects, our ancestors have accumulated rich experience in thousands of years of labor practice Until the 1940s, plant pesticides and inorganic pesticides were still powerful weapons to control pests Subsequently, a large number of organic synthetic agents came out, which were widely used because of their advantages such as good control effect, quick effect, simple use method, less limited by seasons and suitable for large-scale use The invention and use of pesticides has undoubtedly greatly improved agricultural productivity, which is called a revolution in agricultural production China is a large agricultural country, with an average of 180-187 million Hm2 of diseases and insect pests per year, and an area of 153 million Hm2 of pesticide application, saving 20-30 billion kg of national grain loss For example, organochlorine pesticides once played an important role in China's agricultural production, with the output accounting for about 50% of China's total pesticides Until the 1960s, it was found that some organochlorine pesticides, such as DDT and BHC, had enrichment and residue accumulation in the environment and organisms, and if the high toxicity and three carcinogenic (carcinogenic, teratogenic and mutagenic) effects of dry organochlorine pesticides, people realized that long-term The use of chemical pesticides has brought a series of new problems The first is that pests and pathogenic bacteria constantly produce resistance; the second is that chemical pesticides, while eliminating pests and diseases, also kill natural enemies in a large amount, destroying the ecological balance, causing the main pests to become rampant again, and the secondary pests to rise to the main pests; the third is that they pollute the ecological environment and agricultural products, such as the atmosphere, water, soil, and so on, resulting in "public hazards"; the fourth is that due to the increased resistance of pests, pesticides The times of application increased, the dosage increased, and the cost of control increased These problems have caused serious social problems and environmental problems, and have been widely concerned by all countries in the world In order to find alternatives to chemical insecticides, pesticide scientists began to work hard to develop new pesticides with high efficiency, low toxicity and low residue, striving for the new goal of super efficiency, no residue and no pollution In this transformation, human beings hope to seek natural substances to inhibit harmful organisms in nature, while pollution-free botanical pesticides attract the interest of these scholars and experts In 1996, many countries made a commitment at the World Conference on environment and development: "at the beginning of the 21st century, botanical pesticides should account for 60% of the total global pesticide use." This is enough to show that plant-based pesticides will be the development trend of pesticide production in the future, which has a huge social demand and a very broad market prospect Plants are the natural treasure house of bioactive compounds More than 97 species of plants have been screened out from 2000 species of plants The extracts of pests fed on them have the functions of antifeeding, repelling, hindering growth and development, avoiding spawning, sterility, contact killing and stomach toxicity The development of a new round of botanical pesticides started in the 1970s, the focus of which is no longer to find toxic substances that can touch or stomach poison pests from plants, but to find substances that have specific effects on pests, such as antifeeding, hindering growth and development, inhibiting pupa development, eclosion and sterility, including interfering with female sex pheromone The secondary compounds that secrete, interfere with mating, repel oviposition and affect the development of ovary can not only effectively inhibit harmful organisms, but also be safe to higher animals, harmless to beneficial insects and natural enemies, and pollution-free to the environment, which is in line with the goal of modern pesticide development Therefore, the botanical pesticides produced by these specific secondary substances are a kind of "environment compatible pesticides" There are many kinds of botanical pesticides, such as tobacco, neem, pyrethrum, Celastrus, marigold, ginkgo and so on According to the survey, neem is the most promising plant among about 1600 insecticidal plants in the world Azadirachta indica, as the most potential insecticidal plant recognized in the world, has been paid more attention by the whole world because of its wide application, remarkable insecticidal effect, high content of bioactive substances and easy extraction Neem belongs to neem family, native to India and Myanmar The tree is tall, with dense branches and leaves, white flowers, sweet fragrance, yellow fruit, about 2cm long, sweet pulp, 1 seed in the core, 3-5-year-old is the initial fruit stage, 10-year-old is the full fruit stage, each plant can produce 20-50kg of fruit, and the fruit stage is more than 200 years Generally, it grows in the tropics and subtropics with an altitude of about 700m and is suitable for growing in acid soil Neem is distributed in India, Pakistan, Thailand, Myanmar and other arid areas abroad In the 1920s, it was introduced to Africa and other places as a tree species for desertification control in arid areas In the 1960s, German scientists found that it had insecticidal function, so Azadirachta indica became one of the most important insecticidal plants in the world At present, the research on neem is mainly focused on the test of insect control effect of neem extract, propagation and cultivation technology, development, production and utilization of plant pesticides and medical and health products The production of neem products (mainly neem pesticides) is still in the initial stage The United States has the fastest growing Azadirachtin production and the largest number of products, followed by Germany, India and Australia Neem has no natural distribution in China In 1986, Professor Zhao Shanhuan was introduced to China from Togo, Africa for the first time, and the trial was successful in Wanning County, Hainan Province In 1995, researcher Lai Yongqi, Institute of Entomology, Chinese Academy of forestry, introduced neem seeds from India and tested them in Yuanjiang and Yuanmou in the dry hot valley By 1999, neem had blossomed and fruited, and the seeds had normal viability The results showed that Azadirachta indica has been introduced successfully in the dry hot valley of China By the end of 1999, the planting area of neem in Yuxi, Chuxiong and Honghe of Yunnan Province was 233.33hm2 Neem has been listed as one of the key development projects of plant resources in Yunnan Province In terms of product processing, Yunnan, Guangdong and other places have started to build neem pesticide production plants 2 The effective components and properties of Azadirachta Azadirachta all over the body In India, neem is a famous "rural medicine", which has a history of nearly one thousand years It is found that neem contains more than 60 kinds of medicinal components Azadirachtin is the main component of azadirachtin, which is distributed in seeds, bark, leaves and other parts of azadirachtin Neem seed is the best raw material to prepare pollution-free plant pesticide and prevent chemical pesticide pollution Azadirachtin is mainly triterpenoids, which is similar to steroids and steroids Azadirachtin has a high specific inhibitory effect on Orthoptera, Lepidoptera, Coleoptera and other pests, and it is safe for higher animals Therefore, Azadirachtin is recognized as the most successful botanical pesticide with modern significance, which is the most suitable for the integrated management of crops and pest management Using 3% Azadirachtin to dilute 1000-3000 fold solution can be used to control many important pests on vegetables, such as greenhouse whitefly, Plutella xylostella, aphid, Tetranychus mite, etc Neem extracts not only have inhibitory effects on pests and mites, but also on plant pathogens and nematodes Neem preparations (trilogy and triac 90EC) are used to control leaf spot, downy mildew, powdery mildew and other diseases of fruit trees and crops 3 Insecticidal Mechanism of neem extract the active components of neem extract are similar to many hormones in insects in structure and composition When the pests ingest the active components of Azadirachta indica, the hormone balance in their bodies is destroyed, the endocrine system is dysfunctional, metabolism, growth and development are maladjusted, the functions of brain and body parts are disordered, resulting in the loss of reproductive function, unable to reproduce, and finally the number of insect population decreases For example, azadirachtin, salannin and nimbin, the active ingredients of azadirachtin, have the basic structure of triterpenoids, which is similar to the structure of some hormone hormones in insects When these active ingredients enter into insects, the production and release of many hormone substances necessary for the growth and development of insects are inhibited As a substitute, these "simulated hormones" are involved The metabolism of insects has been seriously damaged 4 The main way of the insecticidal action of neem is that there are many active components and different structures of neem extract The insecticidal action of neem extract on different kinds of pests is also different under different conditions Scientists at the China Rice Research Institute believe that there are mainly several following: 1., insect pests are repellent and repellent to plants For example, the rice plants with 3% neem oil spray have reduced the number of adults on brown planthopper, and showed obvious smell avoidance effect 2 To prevent or reduce the oviposition of female, neem oil, neem leaves and seed nucleus extracts have repellent effect on the oviposition of some Lepidoptera, Diptera and Coleoptera insects, such as cotton bollworm, Lucilia sericata and Douxiang 3 The results showed that the mouthparts of the larvae of Pieris rapae were sensitive to azadirachtin, and the mechanism was that Azadirachtin continuously activated the anorexic neurons of the cone sensilla of the lower jaw plug, and also inhibited the signal emission of the neurons that caused the appetite When the larvae were treated with Azadirachta derivatives of different concentrations, the molting delay, incomplete molting (deformity) and death were observed If Azadirachtin (0.75mg/kg body weight) was injected into the nymphs of the first and second instars of Periplaneta americana, the molting deformity of nymphs could be seen Higher concentration can make nymphs all dead The results also showed that neem extract could inhibit and destroy the growth and development of adults, nymphs, eggs and pupae For example, Azadirachtin has the effect of juvenile hormone or ecdysone on some Hemiptera insects Azadirachtin is introduced into the fourth instar nymph of bloodsucking stink bug through blood feed, and ecdysone and juvenile hormone are introduced in the same way It can be seen that Azadirachtin can counteract the effect of azadirachtin The study of its mechanism shows that Azadirachtin first affects the central nervous system and its endocrine system of insects, interferes with some transmission media regulating the synthesis and release of ecdysone, interferes with the production of brain neuropeptides, and thus inhibits the growth and development of insects 4 To reduce the oviposition ability of adult insects and to sterile the eggs of rice plants treated with 6% neem oil, the oviposition quantity of white backed Planthopper and two black tailed leafhopper decreased greatly, and the eggs produced could not hatch The toxicity of azadirachtin to interfere with oviposition showed that when Azadirachtin was injected into the female of tropical locust 2-10 days after eclosion, the production of egg sac was inhibited This is mainly because Azadirachtin prevents the production of juvenile hormone, thus preventing the synthesis of yolk protein and egg formation in fat body It may also be through hormone control, interfering with the result of yolk protein At the end of oogenesis, the concentration of ecdysone in the ovaries of the treated females was much lower than that of the control, which was the result of the disturbance of neuroendocrine system Therefore, Azadirachtin