Namely, the abbreviation of Bacillus thuringiensis, Bt insecticide is the use of Bt insecticidal bacteria, a microbial preparation produced by culture. This insecticidal bacterium produces spores and forms a protein toxin during growth and development. It is observed under a microscope that it is usually an irregular rhombohedral crystal called parasporal crystal. When pests erode the parasporal crystals and spores, the parasporal crystals dissolve in the alkaline environment of the pest's intestine, releasing toxins that have a strong toxicity effect on lepidopteran larvae. This toxin numbs the midgut of the larvae and presents with symptoms of poisoning, loss of appetite, failure to respond to contact stimuli, anorexia, vomiting, diarrhea, slowing of movement, atrophy or curling. Generally no harm is caused to crops. After a period of disease, the gut wall is damaged, toxins enter the blood, causing sepsis, and the spores multiply rapidly in the digestive tract, accelerating the death of pests. The dead larvae are soft and black. Therefore, pests can only eat Bt bacteria in the stomach, and then go through a pathogenesis, they can die, about 48 hours before they can achieve the purpose of killing pests, not as fast as chemical pesticides, but the pests after infection, on the spit Scalding, no eating, no longer harm the crop. Therefore, do not be impatient when using Bt insecticides to kill insects. Bt pesticides have many advantages over chemical pesticides. They are non-toxic to humans and animals and safe to use. The protein toxins of Bt bacteria do not work in the gastrointestinal tract of humans and domestic animals and poultry. Second, it is selective and does not harm natural enemies. Bt bacteria only specifically infect certain types of insects and protect natural enemies. Third, it does not pollute the environment and does not affect the activities of soil microorganisms. It is a clean pesticide. Fourth, the continuous use of insect pests will form an epidemic area, resulting in the widespread spread of pest pathogens, to achieve the purpose of natural control of population density. Fifth, there is no residue, and the products produced can be eaten safely. At the same time, the color and flavor of vegetables and fruits are not changed. sixth. Not easy to produce drug resistance, this is only relatively speaking. The struggle between humans and harmful insects is extremely difficult and complex. Drug resistance has recently been reported, but it is not as fast as chemical pesticides. Production and application of Bt insecticides The production methods of Bt insecticides mainly include liquid deep fermentation and semi-solid fermentation. The successful two-step production method researched by the Institute of Biology, Hebei Academy of Sciences is an effective, simple and practical Bt pesticide production technology that has been improved, improved, and created on the basis of semi-solid fermentation methods. Its production process is simple. The scale is very variable, especially suitable for promotion in rural SMEs, can significantly reduce the production costs of pesticides, and played a positive role in the development of microbial pesticides. In particular, control effects on leafy vegetable pests such as cabbage caterpillars and diamondback moth are very significant. The prevention and control of cotton bollworm and pine caterpillar is also widely promoted. Application of Bt insecticides Note In the field application, to ensure the quality of pesticides, to meet the Bt bacteria rapid growth temperature conditions, the higher the temperature, the stronger the virulence. To avoid strong sunlight, because ultraviolet rays will cause damage to Bt bacteria, it is best to apply after 4 pm. In addition, attention must be paid to the living habits and sensitivities of the target pests, the host crops and environmental conditions, and the use of synergists. For example, the prevention and control of borer pests should be in the hatching period of eggs, spraying 2 times -3 times, especially for aphids, control effect is good. Once the locust infested into the stem, the control effect was poor. To prevent and treat corn borer, it is necessary to strictly control the use of drugs at the end of the corn heart leaf stage in order to receive good results. Prevention and treatment of cotton bollworm, should be controlled in the 2 days to 3 days after the peak of ovulation application, the effect is significant. The masses have the prevention and treatment experience of "preventing insects from seeing insects and fighting eggs and not fighting insects." In this way, when the larvae hatch, they kill the insecticide by biting the eggshell and quickly die of poisoning. The residual period of B2 insecticide can generally reach 7 days to 10 days. If rainfall occurs after application, the rain will wash away the liquid and it should be re-sprayed. Application methods can be spray, dusting, irrigation, jet spraying and so on. Either way, be sure to apply the pesticide evenly to ensure that pests have a chance to eat before they can play a poisonous role. The addition of traces of chemical insecticides to Bt insecticides or their combination with other microbial insecticides can have a synergistic effect and can significantly increase pest mortality. At present, biopesticides formulated with Bt insecticides and other biological agents have a broader insecticidal spectrum and are welcomed by the general public.
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