A method for determining the toxicity of systemic insecticides to sweet potato ant weevil larvae

Abstract

The invention discloses a method for determining the toxicity of a systemic insecticide to sweet potato ant weevils larvae, which comprises the steps of collecting eggs with potato tubers, allowing the eggs to develop into larvae, placing the potato tubers with the larvae in wet sand containing a test agent for cultivation, and counting the number of live insects as the number of insects after the agent treatment; at the same time, correspondingly using potato tubers for egg collection and larval cultivation, and placing the potato tubers in wet sand containing water for cultivation as the initial number of insects before the agent treatment; calculating the toxicity regression equation and LC 50 The present invention provides an effective method for determining the toxicity of systemic insecticides to sweet potato ant weevils larvae that are located inside sweet potatoes and cannot be artificially raised in vitro, and the toxicity determination results can be used as a basis for insecticide screening; secondly, the correlation coefficient between the concentration of the agent and the relative mortality rate in the method of the present invention is above 0.96, and the determination result is highly reliable; the insecticide screened by the method of the present invention can significantly reduce the population size of the sweet potato ant weevils and reduce the damage caused by the sweet potato ant weevils.

Description

Technical Field

[0001] The invention belongs to the field of pesticides, and in particular relates to a method for determining the toxicity of a systemic insecticide to sweet potato ant weevil larvae. Background Art

[0002] The sweet potato weevil (Cylas formicarius, also known as the sweet potato weevil) is an oligophagous pest that mainly harms sweet potatoes. The damaged tubers have a foul odor and bitter taste and cannot be eaten or used as feed, causing the quality of the sweet potatoes to deteriorate. The sweet potato weevil is seriously occurring in the southern potato-producing areas of my country, mainly distributed in Fujian, Guangdong, Guangxi, Hainan and Taiwan. In recent years, it has spread to the potato-producing areas in the middle and lower reaches of the Yangtze River, and the situation has been getting worse year by year.

[0003] During the entire development period of the sweet potato ant weevil, only the adult insects emerge from the tubers after they emerge from their pupae and lay eggs in the feeding holes on the surface of the sweet potato. They can also feed on the main stem and other parts of the plant, while the eggs, larvae, pupae and other insect stages all feed and cause damage inside the sweet potato tubers. Based on the living habits of the adults that feed and lay eggs on the surface of the tubers after they emerge from their pupae, the current prevention and control of the sweet potato ant weevil focuses on preventing and controlling the adults. Therefore, for the toxicity determination and field control experiments of sweet potato ant weevils, the number of adult insects and the damage index of potato tubers are used as evaluation objects (such as Tara P. Smith et al. Journal of Economic Entomology. 2006, 99(6): 2024-2029; Chen Furu et al. Journal of Jiangxi Agricultural University, 2002, 24(4): 445-447; Lin Wendao. Fujian Agricultural Science and Technology, 2009, (5): 54-55; Wang Rongyan et al. Pesticides, 2015, 54(10): 777-780), while there are few evaluations on the effects of sweet potato ant weevils larvae. Patent CN105284876A discloses that sweet potato slices are immersed in a chemical and then inoculated with adult sweet potato ant weevils, the stomach toxicity of the chemical to the adult sweet potato ant weevils is measured, the lethal median concentration value and co-toxicity coefficient to the adult sweet potato ant weevils are calculated, and the toxicity thereof can be more accurately evaluated; whereas, when potato tubers carrying larvae or eggs of the sweet potato ant weevils are immersed in the chemical solution, only the hazard level of the potato tubers can be investigated, the hazard index of the potato tubers and the control effect can be calculated, but the toxicity level of the systemic insecticide to the larvae and eggs of the sweet potato ant weevils cannot be measured. Therefore, this method cannot correctly evaluate the toxicity level of the systemic insecticide to the larvae and eggs of the sweet potato ant weevils, nor can it provide a basis for screening corresponding insecticides.

[0004] According to the ministerial standard (NY / T1154.4-2006, Guidelines for Indoor Bioassay Tests of Pesticides, Insecticide Part 4: Continuous Leaf Dipping Method for Systemic Activity Test. Beijing: China Agriculture Press, 2006. Bai Tingting et al., Shandong Agricultural Science. 2019, 51(4):128-131), for the bioassay of systemic pesticides, the method of dipping rooted plants in the pesticide solution and inoculating leaves with insects is adopted. This method is suitable for the toxicity determination of insects that can survive and cause harm outside the plant body and can accurately determine the initial number of insects. However, this method is not suitable for the bioassay of sweet potato ant weevils larvae. Because the entire growth period of the sweet potato ant weevils, except for the adult stage, is completed in the tubers. The insect body cannot survive outside the tubers, and it is not possible to cut the tubers to know the initial number of insects and then conduct the pesticide treatment determination.

[0005] Acetamiprid (common name in English: Acetamiprid, its chemical name is N-(N-cyano-ethylimino)-N-methyl-2-chloropyridine-5-methylamine, chemical formula is C 10 H 11 ClN4) belongs to the neonicotinoid insecticide. Acetamiprid is widely used in the control of aphids, planthoppers and some lepidopteran pests in rice, especially vegetables, fruit trees and tea. It is also used for the control of coleopteran pests such as longhorn beetles and thysanopteran pests such as thrips (Zhou Yu et al., Plant Protection, 2006, 32(3): 16-20).

[0006] Imidacloprid (common name in English: Imidacloprid, its chemical name is: 1-(6-chloro-3-pyridylmethyl)-N-nitroimidazole-2-imide, chemical formula is: C9H 10 ClN5O2) belongs to the neonicotinoid insecticide, which has the characteristics of broad spectrum, high efficiency, low toxicity, low residue, and pests are not easy to develop resistance. It has multiple effects such as contact killing, stomach poisoning and systemic absorption. It is mainly used to control piercing-sucking mouthparts pests such as aphids, leafhoppers, planthoppers, thrips, etc. It also has a certain control effect on some coleoptera, diptera and lepidoptera pests. It is also often used to control sanitary pests and lawn pests (Yuan Wanling, master's degree thesis of the Chinese Academy of Agricultural Sciences, 2020).

[0007] After searching, no reports were found on methods for determining the toxicity of systemic insecticides to sweet potato ant weevil larvae. No reports were found on using acetamiprid and imidacloprid to control sweet potato ant weevil larvae. Summary of the invention

[0008] The present invention aims to provide a method for determining the toxicity of a systemic insecticide to sweet potato ant weevil larvae. The method can objectively and accurately evaluate the toxicity level of the systemic insecticide to the sweet potato ant weevil larvae, thereby providing a scientific basis for screening systemic insecticides for controlling the sweet potato ant weevil larvae.

[0009] Another object of the present invention is to provide the use of acetamiprid in preventing and controlling sweet potato ant weevil larvae.

[0010] The third object of the present invention is to provide an application of imidacloprid in preventing and controlling the larvae of sweet potato ant weevils.

[0011] To achieve the above object, the technical solution of the present invention is as follows:

[0012] The present invention provides a method for determining the toxicity of a systemic insecticide to sweet potato ant weevil larvae, comprising the following steps:

[0013] (1) Rooting culture of sweet potato tubers: Take sweet potato tubers of 175-225 g in size and bury 3-5 cm of the rooting part vertically in wet sand, and then carry out rooting culture in an incubator at 25°C and L16:D8;

[0014] (2) Egg collection: When the root of the tuber in step (1) grows to 1-10 cm and the bud grows to 0.2-1.0 cm, the tuber is taken out and the rooting part of the tuber is wrapped with plastic wrap, and then placed in a box with 20 healthy female adults of sweet potato ant weevils after mating, and fed for 24 hours to allow them to lay eggs on the tuber; then the tuber with eggs is taken out, the plastic wrap is removed, and the rooting part is buried in wet sand; and the tuber is cultured at 28° C. and L16:D8 for 5-6 days to allow the eggs in the tuber to develop and hatch into first-instar larvae;

[0015] (3) Preparation of test reagents: dilute the test reagents in a gradient manner to obtain different concentrations of solution; weigh 50-100 g of dry sand, add 10-20 mL of solution, and mix well; then put the mixed sand into a plastic cup;

[0016] (4) Chemical treatment and determination: Place the tubers obtained in step (2) into the plastic cups of step (3), with one tuber placed in each plastic cup, and place the rooting part of the tuber vertically downward into the sand in the plastic cup; culture at 28°C and L16:D8 for 7 days in a moisturizing environment; repeat the treatment of each concentration of chemical solution 3 times; dissect the tubers and check the number of live insects, which is used as the number of insects after chemical treatment;

[0017] (5) Counting the initial insect number: a single potato tuber rooted in step (1) is placed in a breeding box of 20 female adults of sweet potato ant weevils after egg collection in step (2) for egg collection for 24 hours; the potato tuber is taken out, and then replaced with another potato tuber for egg collection again for 24 hours; eggs are collected three times in total, as three repetitions, and the potato tubers corresponding to the egg collection treatment in step (2) are marked; the rooting part of the egg-collecting potato tuber is placed in wet sand with water, and moisturized and cultured at 28°C and L16:D8 for 12 days, and the potato tuber is dissected to check the number of live insects, which is the initial insect number before the drug treatment;

[0018] (6) Toxicity calculation:

[0019] Relative mortality rate (%) = (initial number of insects before treatment with the drug - number of insects after treatment with the drug) / initial number of insects before treatment with the drug × 100;

[0020] The drug concentration and relative mortality (%) were calculated using DPS7.0 software to calculate the toxicity regression equation, LC 50 Values ​​and 95% confidence limits.

[0021] The specifications of the plastic cup described in step (3) of the above method are 6-8 cm in diameter, 4-6 cm in bottom diameter, and 8-10 cm in height.

[0022] The specifications of the plastic cup are preferably 7 cm in diameter, 5 cm in bottom diameter and 9 cm in height.

[0023] The size of the potato chunks in step (5) of the above method is 175 to 225 grams.

[0024] The size of the potato chunks in step (1) or (5) of the above method is preferably 185 to 210 grams.

[0025] The present invention also provides the use of acetamiprid in preventing and controlling sweet potato ant weevil larvae.

[0026] The present invention also provides the use of imidacloprid in preventing and controlling the larvae of sweet potato ant weevils.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The larvae of sweet potato ants are usually located inside sweet potato tubers and cannot be artificially raised in vitro, so it is difficult to determine the toxicity of insecticides to the larvae of sweet potato ants, and it is also difficult to screen insecticides that can be used to control the larvae of sweet potato ants; while the method of the present invention solves the problem of determining the toxicity of systemic insecticides to sweet potato ants, and also solves the problem of screening systemic insecticides with high toxicity to sweet potato ants. (2) The correlation coefficient between the concentration of the systemic insecticide of the present invention and the average relative mortality rate is above 0.96, indicating that the results of the determination of the toxicity of the systemic agent to the larvae of sweet potato ants in tubers by the method of the present invention are highly reliable and reproducible. (3) The method of the present invention feeds the tubers for 24 hours to the female insects used for egg collection, and collects eggs three times continuously, which is repeated three times and cultured under the same conditions to keep the moisture. While checking the number of insects in the tubers treated with the agent, the number of insects is checked as the initial number of insects in the tubers corresponding to the toxicity determination of the female insects collecting eggs, and the data has good reproducibility. For the toxicity determination of borer pests that cannot be artificially isolated and raised in vitro, the mortality rate can be calculated more accurately. (4) The systemic insecticide screened by the method of the present invention can kill sweet potato ants in the early developmental stage, that is, the young larval stage, and can significantly reduce the population of sweet potato ants and reduce the damage caused by sweet potato ants. DETAILED DESCRIPTION

[0028] The present invention is further described below by specific examples, but does not constitute any limitation on the protection scope of the present invention. Unless otherwise specified, the methods described in the following examples are all conventional methods, and the agents are all conventional chemical reagents.

[0029] Example 1 Toxicity test of acetamiprid against sweet potato ant weevil larvae

[0030] Proceed as follows:

[0031] (1) Rooting culture of potato tubers: Take 190-210 g Longshu No. 9 potato tubers (cultivated by the Longyan Agricultural Science Institute of Fujian Province and available for purchase on the market) and bury them vertically in wet sand with 3-5 cm of the rooting part, and then carry out rooting culture in an incubator at 25°C and L16:D8.

[0032] (2) Egg collection: When the root of the tuber in step (1) grows to 5-8 cm and the bud grows to 0.5-0.8 cm, the tuber is taken out, the rooting part of the tuber is wrapped with plastic wrap, and the single tuber is placed in a box with 20 healthy female adult sweet potato ant beetles after mating, and fed for 24 hours to allow them to lay eggs on the tuber; then the tuber with eggs is taken out, the plastic wrap is removed, and the rooting part is buried in wet sand to allow the rooting part to absorb water; and the tuber is moisturized and cultured in an incubator at 28° C. and L16:D8 for 5 days to allow the eggs in the tuber to develop and hatch into first-instar larvae.

[0033] (3) Preparation of test agents: 99% acetamiprid original drug (produced by Hebei Derui Chemical Co., Ltd.) was prepared into a 10 g / L stock solution with acetone, and then the stock solution was gradiently diluted with 0.1% Tween 80 to obtain drug solutions with concentrations of 8 mg / L, 4 mg / L, 2 mg / L, 1 mg / L, and 0.5 mg / L, respectively; 100 g of dry sand was weighed, and 20 mL of the diluted drug solution was placed into the dry sand and mixed; the mixed wet sand was then placed into a plastic cup.

[0034] (4) Chemical treatment and determination: Place 3 to 5 cm of the rooting part of the potato tuber in step (2) vertically into the plastic cup (specifications: 7 cm diameter × 5 cm bottom diameter × 9 cm height) in step (3), place one potato tuber in one plastic cup, and place its rooting part vertically downward into the sand in the plastic cup; culture in a moisturizing incubator at 28°C, L16:D8 for 7 days, with the humidity of the sand maintained at 20%; repeat 3 times for each chemical concentration; dissect the potato tubers and check the number of live insects, which is used as the number of insects after chemical treatment.

[0035] (5) Statistics of the initial number of insects: Root Longshu No. 9 with a size of 190 to 210 grams according to the method described in step (1), then place the rooted single tuber into the breeding box of 20 female adults of sweet potato ants after egg collection in step (2) for egg collection for 24 hours, and then take out the tuber; then replace the tuber and collect eggs again for 24 hours; collect eggs for a total of 3 times, as 3 repetitions, and mark the tuber corresponding to the egg collection treatment in step (2). Put the rooted part of the egg-collecting tuber into wet sand and culture it in an incubator at 28°C and L16:D8 for 12 days; cut open the tuber to check the number of live insects, which is used as a control for the tuber treated with the drug corresponding to the egg collection of the female adults, that is, the initial number of insects before the drug treatment.

[0036] (6) Toxicity calculation

[0037] Relative mortality rate (%) = (initial number of insects before treatment with the drug - number of insects after treatment with the drug) / initial number of insects before treatment with the drug × 100.

[0038] LC of acetamiprid against sweet potato anthill 50 The correlation coefficient and toxicity regression equation were analyzed and calculated using DPS7.0 software.

[0039] The average number of eggs collected three times in step (5) was taken as the initial worm number (see Table 1), the number of live worms after 7 days of treatment was taken as the worm number after treatment (see Table 2), and the relative mortality rate was calculated (see Table 2).

[0040] Comparing the number of larvae in the 12 treatments from the initial insect count results (see Table 1), the maximum was 61.33 and the minimum was 31.33, with a large difference. If the initial insect count is not performed, but the insect count in the tubers treated with acetamiprid is used as the insect count for the drug treatment, and the insect count in the tubers not treated with the drug is used as the blank control insect count to calculate the corrected mortality rate, the result will be that the toxicity cannot be calculated due to the large difference in insect counts between the treatments.

[0041] As can be seen from Table 2, with the increase of acetamiprid concentration, the mortality rate of sweet potato ant weevil larvae also increased. This shows that there is an obvious positive correlation between the concentration of acetamiprid and the mortality rate of ant weevil larvae. When the concentration of acetamiprid is 8 mg / L, the relative mortality rate of sweet potato ant weevil larvae can reach more than 91%, indicating that acetamiprid has a good preventive effect on sweet potato ant weevil larvae.

[0042] The concentration of acetamiprid and the average relative mortality rate of sweet potato ant weevil larvae were subjected to correlation analysis. The results (see Table 3) showed that the correlation coefficient r value of acetamiprid was 0.9605. The linear relationship between the concentration of acetamiprid and the mortality rate of ant weevil larvae in the equation was good, indicating that the method of determining the toxicity of acetamiprid to ant weevil larvae using this method can objectively reflect the toxicity level of acetamiprid to sweet potato ant weevil larvae, and can be used to screen systemic insecticides for sweet potato ant weevil larvae pests that cannot survive outside the potato tubers.

[0043] It can also be seen from Table 3 that its LC 50 It is 1.1772 mg / L, indicating that acetamiprid has a good toxic effect on the larvae of sweet potato ant weevils and has high toxicity, that is, acetamiprid can be used to prevent and control the larvae of sweet potato ant weevils.

[0044] Table 1 Initial number of sweet potato ant weevil larvae when testing the toxicity of acetamiprid (heads)

[0045] Serial number Repeat I Repeat II Repeat III Average Standard Deviation 1 34 40 35 36.33 3.21 2 40 39 41 40.00 1.00 3 33 40 36 36.33 3.51 4 54 61 63 59.33 4.73 5 47 56 54 52.33 4.73 6 32 32 30 31.33 1.15 7 42 48 51 47.00 4.58 8 62 65 55 60.67 5.13 9 43 48 50 47.00 3.61 10 44 50 40 44.67 5.03 11 44 48 42 44.67 3.06 12 37 44 38 39.67 3.79 13 66 55 63 61.33 5.69 14 62 65 55 60.67 5.13 15 47 56 54 52.33 4.73

[0046] Table 2 Original data of acetamiprid toxicity test against sweet potato ant weevil

[0047]

[0048]

[0049] Table 3 The results of toxicity test of acetamiprid against sweet potato ant weevil larvae

[0050] Pharmacy Regression equation <![CDATA[LC 50 (mg / L)]]> Correlation coefficient (r) 95% Confidence Interval Acetamiprid y=4.8919+1.5263x 1.1772 0.9605 0.8170-1.6962

[0051] Example 2 Toxicity test of imidacloprid against sweet potato ant weevil larvae

[0052] Proceed as follows:

[0053] (1) Rooting culture of potato tubers: Take a 190-210 g Longshu No. 9 potato tuber and bury it vertically in wet sand with 3-5 cm of the rooting part, and then carry out rooting culture in an incubator at 25°C and L16:D8.

[0054] (2) Egg collection: When the root of the potato tuber in step (1) grows to 5-8 cm and the bud grows to 0.5-0.8 cm, the potato tuber is taken out, the rooting part of the potato tuber is wrapped with plastic wrap, and then the single potato tuber is placed in a box with 20 healthy and uniform female adult ant beetles after mating, and fed for 24 hours to allow them to lay eggs on the potato tuber; then the potato tuber with eggs is taken out, the plastic wrap is removed, and the rooting part is buried in wet sand to allow the rooting part to absorb water, and the tuber is cultured in an incubator at 28°C and L16:D8 for 5 days to allow the eggs in the tuber to develop and hatch into first-instar larvae.

[0055] (3) Preparation of the drug: 98% imidacloprid technical drug (produced by Hailier Pharmaceutical Group Co., Ltd.) was prepared into a 10 g / L mother solution with acetone, and then the imidacloprid mother solution was gradiently diluted with 0.1% Tween 80 to 16 mg / L, 8 mg / L, 4 mg / L, and 2 mg / L concentrations. 100 g of dry sand was weighed, and 20 mL of the drug solution was added to the sand and mixed; then the mixed sand was placed in a plastic cup.

[0056] (4) Chemical treatment and determination: Place 3 to 5 cm of the rooting part of the potato tuber in step (2) vertically into the plastic cup (specifications: 7 cm diameter × 5 cm bottom diameter × 9 cm height) in step (3), with one potato tuber placed in one cup, and its rooting part placed vertically downward in the sand in the plastic cup. Incubate in a 28°C, L16:D8 incubator for 7 days with moisture retention, and keep the humidity of the sand at 20%. Repeat 3 times for each chemical concentration. Cut open the potato tuber and check the number of live insects, which is used as the number of insects after chemical treatment.

[0057] (5) Statistics of the initial number of insects: According to the method described in step (1), a 190-200 g Longshu No. 9 tuber was rooted, and then the rooted tuber was placed in the breeding box of 20 female ant-like insects after egg collection in step (2). After 24 hours of egg collection, the tuber was taken out, and then the tuber was replaced and egg collection was performed again for 24 hours; a total of 3 egg collections were performed as 3 repetitions, and the tubers corresponding to the egg collection treatment in step (2) were marked. The rooted part of the egg collection tuber was placed in wet sand and cultured in an incubator at 28°C, L16:D8 for 12 days. The tuber was dissected to check the number of live insects, which was used as a control for the tuber treated with the drug corresponding to the female adult egg collection, that is, the initial number of insects before the drug treatment.

[0058] (6) Toxicity calculation

[0059] Relative mortality rate (%) = (initial number of insects before treatment with the drug - number of insects after treatment with the drug) / initial number of insects before treatment with the drug × 100.

[0060] LC of Imidacloprid against Myrmecophaga 50 The correlation coefficient and toxicity regression equation were analyzed and calculated using DPS7.0 software.

[0061] The average number of eggs collected three times in step (5) was taken as the initial worm number (see Table 4), the number of live worms after 7 days of treatment with the agent was taken as the worm number after treatment with the agent (see Table 5), and the relative mortality rate was calculated (see Table 5).

[0062] Comparing the number of larvae in the 12 treatments from the initial insect count results (see Table 4), the maximum was 43.33 and the minimum was 21.67, with a large difference. If the initial insect count is not performed, but the insect count in the tubers treated with imidacloprid is used as the insect count for the drug treatment, and the insect count in the tubers not treated with the drug is used as the blank control insect count to calculate the corrected mortality rate, the result will be that the toxicity cannot be calculated due to the large difference in insect counts between the treatments.

[0063] As can be seen from Table 5, with the increase of imidacloprid concentration, the mortality rate of sweet potato ant weevil larvae also increased. This shows that there is an obvious positive correlation between the imidacloprid concentration and the mortality rate of ant weevil larvae. When the imidacloprid concentration is 16 mg / L, the relative mortality rate of sweet potato ant weevil larvae can reach 94-100%, indicating that imidacloprid has a good insecticidal effect on sweet potato ant weevil larvae.

[0064] The concentration of imidacloprid and the average relative mortality rate of ant-like weevils were subjected to correlation analysis. The results (see Table 6) showed that the correlation coefficient r value of imidacloprid was 0.9788, and the linear relationship between the concentration of imidacloprid and the mortality rate of ant-like weevils in the equation was good. This indicates that the toxicity of imidacloprid to ant-like weevils measured by this method can objectively reflect the toxicity level of imidacloprid to sweet potato ant-like weevils, and the method of the present invention can be used for the screening of systemic insecticides for sweet potato ant-like weevils and similar pests.

[0065] It can also be seen from Table 6 that its LC 50 The concentration of imidacloprid was 2.8309 mg / L, indicating that imidacloprid has strong toxicity to the larvae of sweet potato ant weevils. Imidacloprid can be used to control the larvae of sweet potato ant weevils.

[0066] Table 4 Initial number of sweet potato ant weevil larvae when determining the toxicity of imidacloprid (heads)

[0067] Serial number Repeat I Repeat II Repeat III Average Standard Deviation 1 37 41 35 37.67 3.06 2 34 37 35 35.33 1.53 3 33 36 38 35.67 2.52 4 25 31 32 29.33 3.79 5 32 27 30 29.67 2.52 6 21 20 24 21.67 2.08 7 47 40 43 43.33 3.51 8 38 40 45 41.00 3.61 9 39 36 40 38.33 2.08 10 31 30 26 29.00 2.65 11 38 35 33 35.33 2.52 12 32 27 30 29.67 2.52

[0068] Table 5 Original data and calculation results of the toxicity test of imidacloprid to sweet potato ants

[0069]

[0070]

[0071] Table 6 Toxicity test results of imidacloprid against sweet potato ant weevil larvae

[0072] Pharmacy Related equations <![CDATA[LC 50 (mg / L)]]> Correlation coefficient (r) 95% Confidence Interval Imidacloprid y=4.0222+2.1637x 2.8309 0.9788 2.0939-3.8272

[0073] Example 3: A potted comparative test of the efficacy of acetamiprid and imidacloprid against sweet potato ant weevil larvae was conducted as follows:

[0074] The tubers of sweet potato Longshu No. 9 were placed in a feeding box with 20 mated female adults of sweet potato ant weevils for one day, then taken out, and the sweet potato ant weevils eggs were grown into first-instar larvae, and the tubers were placed in a culture box (culture box specifications: 50 cm long × 50 cm wide × 25 cm high), with 9 tubers in each culture box. The form of field seedling cultivation was simulated, and the tubers were covered with soil. 20% acetamiprid soluble concentrate (Hebei Weiyuan Biochemical Co., Ltd.) and 20% imidacloprid soluble concentrate (Qingdao Haina Biotechnology Co., Ltd.) were diluted with water respectively, and the dosage of 100 grams, 75 grams, and 50 grams of effective ingredients per mu were converted into the dosage of the culture box area, and evenly poured in the culture box to make the soil moisture in the box 20-30%. Each culture box was treated with one agent, and each treatment was repeated 3 times, and no drug application was used as a blank control. After 15 days, the damage classification of the tubers was investigated, and the damage index and control effect were calculated.

[0075] The grading standard for sweet potato tubers damaged by ant weevils is as follows: Grade 0, no damage; Grade 1, slight damage by ant weevils, only the potato skin is damaged, and the volume of damaged sweet potato tubers accounts for 1-5% of the total tubers; Grade 3, the volume of damaged sweet potato tubers accounts for 6-10% of the total tubers; Grade 5, the volume of damaged sweet potato tubers accounts for 11-20% of the total tubers; Grade 7, the volume of damaged sweet potato tubers accounts for 21-50% of the total tubers; Grade 9, severe damage by ant weevils, the tubers are inedible, and the volume of damaged sweet potato tubers accounts for more than 51% of the total tubers.

[0076] The calculation formulas for the damage rate, hazard index and control effect are as follows:

[0077]

[0078]

[0079]

[0080] As can be seen from Table 7, the effective ingredient content of 20% acetamiprid soluble solution is 100g / 667M 2 The control effect was the best, reaching 93.51%; 20% imidacloprid soluble solution was applied with an active ingredient of 100g / 667M 2 The control effect of acetamiprid was second, reaching 82.73%. This shows that acetamiprid and imidacloprid have high control effects on the larvae of sweet potato ant weevils, and the control effect of acetamiprid on the larvae of sweet potato ant weevils is significantly higher than that of imidacloprid.

[0081] Table 7 Potted test of acetamiprid and imidacloprid for controlling sweet potato ant weevil larvae

[0082]

[0083] From the results of Examples 1, 2 and 3 above, it can be seen that the LC of acetamiprid was 0.04477mol / L after indoor toxicity test on sweet potato ant weevil larvae. 50 The LC value of imidacloprid is 1.1772 mg / L. 50 It is 2.8309 mg / L; and by comparing and analyzing with the results of the potted test, it is shown that the results obtained by the toxicity determination method of the systemic agent according to the present invention can accurately evaluate the toxicity level of the systemic agent to the larvae of the sweet potato ant weevil, solving the problem of screening systemic insecticides for controlling the larvae of the sweet potato ant weevil.

Claims

1. A method for determining the toxicity of a systemic insecticide to sweet potato ant larvae, characterized in that: The steps include: (1) Rooting culture of sweet potato tubers: Take sweet potato tubers weighing 175-225 g and bury 3-5 cm of the rooting part vertically in wet sand, and then carry out rooting culture in an incubator at 25°C and L16:D8; (2) Egg collection: When the root of the tuber in step (1) grows to 1-10 cm and the bud grows to 0.2-1.0 cm, take out the tuber, wrap the rooting part of the tuber with plastic wrap, and then put it into a box with 20 healthy female adults of sweet potato ant weevils after mating, feed them for 24 hours, so that they lay eggs on the tuber; then take out the tuber with eggs, remove the plastic wrap, and bury the rooting part in wet sand; culture at 28°C and L16:D8 for 5-6 days to allow the eggs in the tuber to develop and hatch into first-instar larvae; (3) Preparation of test reagents: dilute the test reagents in a gradient manner to obtain different concentrations of solution; weigh 50-100 g of dry sand, add 10-20 mL of solution, and mix well; then put the mixed sand into a plastic cup; (4) Chemical treatment and determination: Place the tubers obtained in step (2) into the plastic cups of step (3), with one tuber placed in each plastic cup, and place the rooting part of the tuber vertically downward into the sand in the plastic cup; culture at 28°C and L16:D8 for 7 days in a moisturizing environment; repeat the treatment three times for each concentration of chemical solution; dissect the tubers and check the number of live insects, which is used as the number of insects after chemical treatment; (5) Counting the initial insect count: Place a single tuber rooted in step (1) into a breeding box of 20 adult sweet potato ant weevils after egg collection in step (2) for 24 hours; remove the tuber, then replace the tuber and collect eggs again for 24 hours; collect eggs for a total of 3 times, as 3 repetitions, and mark the tuber corresponding to the egg collection treatment in step (2); place the rooting part of the egg-collecting tuber into wet sand with water, and culture it at 28°C and L16:D8 for 12 days, then cut open the tuber and check the number of live insects, which is the initial insect count before the drug treatment; (6) Toxicity calculation: Relative mortality rate (%) = (initial insect number before treatment - insect number after treatment) / initial insect number before treatment × 100; The drug concentration and relative mortality (%) were calculated using DPS7.0 software to calculate the toxicity regression equation, LC 50 Values ​​and 95% confidence limits.

2. The method according to claim 1, characterized in that The specifications of the plastic cup in step (3) are: a diameter of 6 to 8 cm, a bottom diameter of 4 to 6 cm, and a height of 8 to 10 cm.

3. The method according to claim 2, characterized in that The specifications of the plastic cup are: a diameter of 7 cm, a bottom diameter of 5 cm, and a height of 9 cm.

4. The method according to claim 1, characterized in that The size of the potato chunks in step (5) is 175 to 225 grams.

5. The method according to claim 1 or 4, characterized in that: The size of the potato chunks in step (1) or (5) is 185 to 210 grams.

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