Research Progress on fumigation technology of stor

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Since the 1980s, people's awareness of environmental protection and requirements for food hygiene have been continuously improved. Many old fumigant varieties have been eliminated successively for one reason or another, and new widely accepted varieties are difficult to develop, which has continuously reduced the varieties of fumigants available in the world. The only remaining varieties that have been widely used for a long time are phosphine and bromomethane. However, methyl bromide is also listed as a controlled substance that destroys the atmospheric ozone layer by the Montreal Protocol of the United Nations Environment Programme in 1992; In 1997, the Ninth Conference of States parties to the protocol also decided that developing countries should completely stop using it by 2015. In this way, only phosphine is widely recognized to continue to be used. Moreover, some scientists believe that the fumigant widely replacing methyl bromide in the future will not only include an 8-bit successive approximation converter, but also phosphine. However, phosphine is also facing the growing resistance of stored grain pests to it. Especially in tropical and subtropical areas, some of their resistance levels have reached the level of ineffective treatment by conventional fumigation methods. Nevertheless, scientists still generally believe that fumigants are the most cost-effective and important means to eliminate stored grain pests. Human beings cannot live without this weapon. In the face of this grim reality, many internationally renowned experts are committed to the development of new fumigants and the more reasonable and effective use of phosphine fumigation. The computer display is used to show the whole process of the experiment. Australia, Germany, Canada, the United States, Britain and other countries are in a leading position in this regard

it can be said that there has been progress in the development of new varieties, but the effect is not great. The new varieties that can fumigate grain and have obtained domestic patents include carbon oxysulfide (Australia), acetonitrile (Australia) and methylphosphine (UK); Sulfuryl fluoride can be used to kill insects in empty warehouse. In addition, some old fumigants, such as carbon disulfide and ethylene oxide, were also re evaluated; As a result, due to the reasons of application safety and residual toxicity, it is still allowed to be used only under specific conditions. In a word, these newly developed and re evaluated varieties can not replace phosphine and bromomethane because of their own shortcomings, or due to problems such as residual toxicity and cost. It is expected that the future development prospects are also limited

the development of phosphine application technology can be said to be mainly derived from three basic research achievements, namely (1) the toxic effect of phosphine on insects is different from other fumigants. It takes a long time to be effective, and time is the main factor to exert its efficacy; (2) Some main stored grain pests will produce anesthetic reaction to higher phosphine concentration, and the pests may survive, resulting in failure of fumigation; (3) Phosphine will not burn and explode at a certain low concentration and low wind speed, so it can be used for circulating fumigation. The development of new dosage forms, new packaging, new application methods and equipment of phosphine in recent years, as well as new measurement and control instruments and equipment, are the specific application and development of these basic research results

for example, new dosage forms such as compressed phosphine in steel cylinder, mixed compression agent of phosphine and carbon dioxide, aluminum phosphide slow-release packaging and so on have been developed; In terms of application methods, we have developed low concentration flow fumigation, re circulation fumigation of gaseous dosage form outside the warehouse, closed loop re circulation of aluminum phosphide on grain surface, and multi bin series circulation fumigation. Automatic or semi-automatic phosphine concentration detector and safety alarm instrument have also been developed in Australia, Britain, the United States, Canada and other countries; The United States and Australia have also developed equipment that can automatically detect and control the concentration according to the set indicators (concentration and time)

as for the fumigation concentration of phosphine, many experts have proved through laboratory and field experiments that the concentration as low as ml/m3 can completely kill the insect stages of common stored grain pests as long as it is stable for enough time. In order to prevent the anesthetic phenomenon of pests in fumigation, the concentration cannot be increased blindly. Some experts in the United States have proposed that the upper limit of phosphine fumigation concentration should be 150ml/m3. However, the British research report points out that if phosphine fumigation is used to control mites, the effective phosphine concentration should be almost 10 times that of common pests; It is pointed out that phosphine fumigation is generally not suitable when the temperature is lower than 15 ℃; If necessary, increase the concentration or extend the time. As for the duration of fumigation, it is agreed that it should be determined by comprehensive analysis of various factors such as insect species, insect population density, resistance level, temperature and humidity, as well as the time limit of fumigation requirements. Generally, it should be 14 ~ 28 days, and the shortest should not be less than 7 days

as for the reasons and Countermeasures for the increasingly prominent problem of Phosphine Resistance, from the 1980s to now, after repeated investigation, well-known international experts pointed out that most of the occurrence and malignant development of resistance are not due to insufficient dosage, but due to the leakage of a large amount of phosphine gas under the condition of poor air tightness, resulting in the sharing of surviving pests (including all development stages) after each fumigation. The mode is caused by the movement. Especially in developing countries, improving the air tightness of fumigation places is not only a key basic work, but also an urgent and long-term task

facing the severe situation of stored grain fumigation technology, scientists have repeatedly stressed that fumigation is an effective method to destroy pests in closed places, but we should also fully understand the shortcomings of fumigation technology. For example, it has no protective effect on the infection of pests after treatment, phosphine can not completely destroy pests in 24 hours or 3-5 days like methyl bromide; Moreover, it has been proposed abroad that attention should be paid to the environmental pollution caused by the emission of fumigants (including carbon dioxide) after treatment. Therefore, fumigation technology can only be regarded as an important means in the comprehensive management of pests, and should be used or not used as little as possible. Only on the basis of doing a good job in cleaning and hygiene, improving and controlling the storage environmental conditions, and organically combining with other methods such as protective agents and pheromones according to local conditions, can the best effect be achieved. (end)


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