How to determine the efficacy of pesticides ? The relevant experts of China Pesticide Network have summarized: through indoor virulence determination and inter-forest efficacy test.
Indoor virulence determination Indoor virulence determination is mainly to determine the toxicity, virulence of a drug or to compare the virulence of several drugs. The results of the laboratory test, in addition to being used as a basis for the preliminary screening of the agent, can also provide a reference for the inter-forest test. Sometimes problems found in the forest must be taken back indoors for more detailed experimental research.
In-house tests should pay attention to: 1 The test organisms should be cultivated from the same environment, or collected from the same environment in the forest, the more consistent in physiology and development. 2 The test agent must be pure (crude oil or raw powder), at least with the exact active ingredient content. 3 Test under controlled conditions and apply uniformity. 4 The test generally requires 3-5 repetitions for each treatment, and each treatment requires 50-100 insects (the fungus spores are generally about 100 in the microscope 10×10 field of view, and each slide must be moved to check the slides. 3 times). 5 Various tests must be established. The controls provided were: completely untreated (under natural conditions), a so-called "blank" control; a formulation containing no active ingredient or a clear water control, a control treated with a standard agent.
In determining the virulence of a drug, a series of doses (or concentrations) are generally used to determine the percentage of death for multiple groups of organisms, and then the dose-mortality virulence curve is plotted at different doses and corresponding mortality rates. A line parallel to the abscissa is drawn from the mortality rate of 50% on the ordinate to intersect the curve. The dose (or concentration) there is LD50 (or LC50). However, since this curve is S-shaped, it is not easy to accurately obtain the value of LD50 or LC50, and it is not easy to compare with other curves by using the S-shaped curve. Therefore, it is necessary to change this S-shaped curve into a straight line. The common statistical method is to use the logarithm of the dose. The mortality rate is expressed by the probability value, and the S-shaped curve can be changed to a straight line. Often referred to as "dose log-proportional value straight line." Mortality check rate (see Schedule 2 probability and death percentage conversion table). From the slope of this line, the degree of sensitivity of the test organism to the drug is also known, that is, the greater the slope, the smaller the difference between the test organisms; the smaller the slope, the greater the difference. In the indoor virulence test, in the non-medicated control group, a small number of naturally-dead individuals often appear. If the natural mortality rate is below 5%, the mortality of the treatment group is generally corrected by subtracting the natural mortality rate. mortality rate. When the natural mortality rate reaches 5%~20~, the direct subtraction method cannot be used. The corrected mortality rate of the treatment group should be calculated according to the following formula. If the natural mortality rate exceeds 20%, the test organisms should not be used. The test or test should be repeated.
Inter-forest efficacy test The inter-forest test mainly measures or compares the efficacy of the agent under inter-forest conditions, and the results are closer to the actual situation. For the 1973 World Health Organization (WHO) Executive Committee, a classification method for distinguishing the harmfulness of pesticides was formulated. And adopted at the 28th World Health Conference in 1975 (Table 1). The toxicity classification of pesticides is mainly based on acute oral and transdermal toxicity in rats, which has become a standard method for determining toxicity classification in toxicology.
Table 1 Classification criteria for pesticide hazards recommended by the World Health Organization
Level
LD50 rat (mg/kg body weight)
Oral percutaneous solid liquid solid liquid
Ia extreme harm
(Extremely hazardous)
5 or <5 20 or <20 10 or <10 40 or <40
Ib high hazard
(Highly hazardous)
5-50 20-200 10-100 40-400
II moderate hazard
(Moderately hazardous)
50-500 200-2000 100-1000 400-4000
III mild hazard
(Slightly hazardous)
>500 >200 >1000 >4000
Note: “Solid†and “liquid†in the table refer to the physical state of the graded products and preparations.
Hazard in a classification refers to an acute hazard to health, that is, a hazard of one or more exposures in a relatively short period of time. This hazard is something that anyone who comes into contact with pesticides may have accidentally encountered.
According to the classification criteria for acute toxicity of pesticides formulated in China, the toxicity of pesticides is classified into highly toxic, highly toxic, moderately toxic and low toxicity (Table 2).
Table 2 China's pesticide acute toxicity grading standards
Level oral LD50
(mg/kg)
Percutaneous LD50
(mg/kg) 4 hours Inhalation LC50
(mg/m3) 2 hours highly toxic <5 <20 <20
High toxicity 5-50 20-200 20-200
Moderate toxicity 50-500 200-2000 200-2000
Low toxicity >500 >2000 >2000
Note: The LD50 in the table refers to the rat.
It can also be seen from the toxicity classification that high oral toxicity does not mean that the transdermal toxicity is necessarily high for the same pesticide. Toxicity classification is divided into three different ways for pesticides to enter the human body.
The above describes the types of pesticide poisoning and the classification of pesticides. The toxic effect of pesticides depends on the toxicity of the pesticide itself, as well as its dosage form and method of use. For example, carbofuran is a highly toxic pesticide, but the use of 3% carbofuran granules greatly reduces its harm. Another example is avermectin, which is also a highly toxic pesticide. However, due to the low content of the preparations processed by it, the oral and transdermal toxicity of the preparations are in the low toxicity range.
In general, the most toxic pesticide class for humans and animals is insecticides because of their ability to produce acute oral toxicity. Organophosphorus pesticides (such as parathion, ethyl azinphos, fusophosphorus and fast-acting phosphorus) are highly toxic and have a low LD50 value. The carbamate pesticides with the same action mode as organophosphorus have great toxicity changes. For example, aldicarb is highly toxic, but the toxicity of carbaryl and carbaryl is relatively low. Organochlorine insecticides (such as dieldrin and DDT) are very stable chemicals that can accumulate in the body or the environment and increase the risk of chronic toxicity (this is why they are banned). one). Pyrethroid insecticides such as fenvalerate and permethrin are less toxic or moderately toxic to humans or mammals but may be highly toxic to bees and fish. The LD50 of cypermethrin is 150 mg/kg, which is one of the most toxic pesticides in pyrethroid pesticides.
Herbicides are much less toxic than pesticides, but some herbicides such as organic arsenic (deophenol) and paraquat can also be toxic if not handled with care. In addition to mercury and cadmium compounds, fungicides are relatively toxic to mammals.
Production control provides a reliable basis.
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