Method for constructing and maintaining nilaparvata lugens harmful experimental population

Abstract

The invention discloses a method for constructing and maintaining a nilaparvata lugens harmful experimental population, and belongs to the technical field of agricultural biology. According to the method, a directional feeding system based on host selection pressure is established, corresponding obligate identification varieties are selected as hosts according to different pest-causing types, and the specific pest-causing characteristics of the hosts are maintained by utilizing the host selection pressure; meanwhile, a regular monitoring system is established, and harmful drift of the population is found and corrected in time through a quality monitoring mechanism that purity spot check is performed every 5 generations and comprehensive evaluation is performed every 20 generations. Through the steps, the standard experimental population with clear damage type and stable heredity of the brown planthopper is constructed and maintained, the problems of inaccurate damage type identification and difficult population purity maintenance in the prior art are solved, and the method is suitable for screening of insect-resistant rice varieties, damage type monitoring and related basic research.

Description

Technical Field

[0001] This invention relates to the field of agricultural biotechnology, specifically to a method for constructing and maintaining a harmful experimental population of brown planthopper. Background Technology

[0002] The brown planthopper (Nilaparvata lugens Stål), belonging to the family Plantipodidae in the order Hemiptera, is one of the most devastating pests of rice production in Asia. Adults and nymphs congregate at the base of rice plants, sucking sap and causing the plants to wilt and die. In severe cases, it can cause "planthopper burn," leading to large-scale yield reduction or even total crop failure. For a long time, planting insect-resistant varieties has been considered the most economical and effective measure to control brown planthopper damage.

[0003] However, brown planthopper populations exhibit significant virulence type differentiation. Different virulence types of brown planthoppers can adapt to rice varieties containing different insect-resistant genes, leading to the potential loss of resistance in insect-resistant varieties after several years of widespread planting due to changes in the virulence type of the brown planthopper. Studies have shown that field brown planthopper populations are typically composed of a mixture of multiple virulence types, with complex genetic backgrounds and unstable virulence characteristics. Directly using mixed field populations for screening insect-resistant varieties or evaluating resistance genes often results in poor reproducibility and low reliability of experimental results due to unclear population genetic backgrounds and impure virulence types, making it difficult to accurately guide insect-resistant breeding and production layout.

[0004] Therefore, transforming field populations of brown planthoppers with complex genetic backgrounds into standard experimental populations with clearly defined pathogenicity and stable genetic characteristics plays an important foundational supporting role in monitoring the pathogenicity of brown planthoppers, breeding insect-resistant rice varieties, deploying resistance genes, and predicting and forecasting pests.

[0005] While there are scattered studies on the isolation or seedling identification of brown planthoppers using single female lines, these methods are generally fragmented and lack systematic integration. Specifically, a complete standardized technical system has not yet been established for key aspects such as how to efficiently identify the virulence type after isolation of single female lines, how to verify the identification results, and how to maintain the virulence characteristics of the target population in the long term without drift. In particular, during long-term subculture, the lack of targeted maintenance of host selection pressure and regular quality monitoring can easily lead to virulence drift or a decrease in genetic purity in the population, thereby losing the reliability of the standard experimental population.

[0006] Therefore, we propose a method for constructing and maintaining a harmful experimental population of brown planthoppers to alleviate or solve the above problems.

[0007] The information disclosed above in this background section is only for enhancing the understanding of the background section of this invention, and therefore may include prior art that is not known to those skilled in the art. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a method for constructing and maintaining a brown planthopper causative experimental population. This method solves the problems in the existing technology, which lacks a systematic technical framework covering the entire chain from field mixed populations to standard experimental populations, leading to inaccurate causative identification, unclear genetic background, and easy drift of causative characteristics during long-term successive rearing.

[0009] To achieve the above objectives, the present invention provides a method for constructing and maintaining a harmful experimental population of brown planthoppers, comprising the following steps:

[0010] During the peak migration period of brown planthoppers, egg-bearing long-winged female adults were collected and isolated and reared in insect rearing cages. The non-resistant rice variety TN1 was used as the host. The number of adult offspring in each cage was counted. Single female lines with a reproductive capacity of less than 30 offspring were eliminated, and high-vitality single female lines were retained and propagated. Young nymphs were collected as test insect sources.

[0011] The test insect sources were inoculated into a group of rice identification varieties containing multiple insect-resistant genes. When the mortality rate of the susceptible control TN1 reached more than 95%, the damage level of each variety was investigated. Based on the preset brown planthopper damage type response pattern, the damage type of each single female line was preliminarily determined.

[0012] Newly emerged long-winged female adults obtained from the development of the test insect source were used as test insects. Parafilm bags were used to attach one insect to the base of the rice stem of at least three core identification varieties. The amount of honeydew secreted by each test insect on each variety within 24 hours was collected and weighed. According to the preset honeydew amount judgment standard, the causative type of each insect was determined.

[0013] The population identification results are compared with the single-head verification results. If the proportion of the target causative type individuals in a single female line reaches 95% or more in the honeydew amount measurement, then the causative type is identified as the causative type of the population and the insect source is retained; otherwise, it is eliminated.

[0014] For the standard populations obtained through comprehensive screening, a targeted rearing system based on host selection pressure should be established, and the virulence stability should be monitored regularly to ensure the stability of the population's genetic characteristics.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] This invention establishes for the first time a complete technical system encompassing field insect source collection, single-female line isolation, dual-method identification, comprehensive judgment, and long-term maintenance, covering all aspects of the isolation and maintenance of the brown planthopper's pathogenicity phenotype. It employs a group identification and individual verification strategy, using a standard seedling-stage group screening method for preliminary determination of pathogenicity at the population level, followed by individual verification of pathogenicity at the single-individual level using honeydew content measurement, and finally combining the results of both methods for final judgment. This improves the accuracy and reliability of pathogenicity determination, ensuring that the purity of the pathogenicity phenotype in the final screened standard population reaches over 95%, with a clear genetic background and well-defined pathogenic characteristics.

[0017] This invention establishes a targeted rearing system and a regular monitoring system based on host selection pressure. By selecting specific identification varieties as hosts for different causative types, host selection pressure is used to maintain their specific causative characteristics. Furthermore, a quality monitoring mechanism involving purity checks every 5 generations and comprehensive evaluations every 20 generations promptly detects and corrects causative drift in the population. This solves the technical problem of causative drift during long-term rearing, ensuring the genetic stability of the standard population over dozens of generations.

[0018] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the method for constructing and maintaining a harmful experimental population of brown planthopper according to the present invention.

[0020] Figure 2 This is a flowchart illustrating the manufacturing process of the Parafilm pouch of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be noted that the drawings are schematic and not illustrated to scale. For clarity and convenience, the relative sizes and proportions of the parts shown in the drawings have been exaggerated or reduced in size. Any size is only illustrative and not limiting.

[0022] Example 1: Construction and Maintenance of Experimental Populations of Brown Planthoppers

[0023] I. Insect source collection and pretreatment for single female line isolation

[0024] During the peak migration period of brown planthoppers, 100 egg-bearing, long-winged female adults were collected from the field and brought back to the glass mesh house for later use.

[0025] Collected female adults were isolated individually in numbered 60-mesh mesh rearing cages (35 cm × 35 cm × 70 cm), using the non-resistant rice variety TN1 as the oviposition host. After the nymphs hatched, they were continued to be reared into adults. The number of adults in each cage was counted: cages with fewer than 30 adults were numbered, indicating low reproductive capacity or insufficient vigor of the single female line, and were culled; cages with 30 or more adults were retained and transferred to new TN1 rice seedlings for another generation of rearing. After the eggs hatched, the 1st and 2nd instar nymphs were collected as test insects for subsequent pathogen identification tests.

[0026] II. Identification of Brown Planthopper Lethality Types Using Standard Seedling Stage Group Screening Method

[0027] Nine rice varieties with representative insect-resistant genes were selected as identification hosts, specifically including:

[0028] No known insect-resistant genes: Taichung Native 1 (TN1); containing Bph1 gene: IR26, Mudgo; containing bph2 gene: ASD7, IR36, IR42; containing Bph3 gene: Rathu Heenati; containing bph4 gene: Babawee; containing bph2+Bph3 gene: Ptb33.

[0029] Seeds of the nine varieties were soaked and germinated until sprouts reached 0.2–0.3 cm in length. Using a randomized block design, seeds of each variety were evenly sown in enamel seedling trays (35 cm × 50 cm × 5 cm) filled with seedling substrate, one row per tray, with 25 seeds per row. After sowing, the trays were placed in a cement pool within a seedling greenhouse, and watered with a sprinkler in the morning and evening to maintain moisture. When the seedlings reached the 3-leaf stage, dead and weak seedlings were removed, leaving approximately 20 healthy, uniformly growing seedlings per row. The rows were then covered with a 60-mesh, light-transmitting, insect-proof net, ready for insect inoculation.

[0030] Inoculation was performed by placing 8 first- to second-instar nymphs per seedling. The experiment was conducted in triplicate, with each replicate using one tray for variety identification and correspondingly numbered. After inoculation, the seedling trays were placed in a cement pool, maintaining a water depth of 5–7 cm to ensure adequate moisture for seedling growth and prevent nymph escape.

[0031] When the seedling mortality rate of the infected control TN1 reached over 95%, a damage level survey was conducted on each plant according to the standards established by the International Rice Research Institute (IRRI, 1988). The damage grading standards are as follows:

[0032] Level 1: Unharmed or only the tip of the first leaf turns slightly yellow; Level 3: Partial yellowing of the first and second leaves; Level 5: Yellowing of the first to third leaves or stunting of the plant; Level 7: The plant begins to wither; Level 9: The plant dies.

[0033] Based on the survey results, the weighted average damage level of each variety was calculated. The resistance evaluation criteria were as follows: damage level 1.0–1.9 was highly resistant (HR), 2.0–3.9 was resistant (R), 4.0–5.9 was moderately resistant (MR), 6.0–7.9 was moderately susceptible (MS), and 8.0–9.0 was highly susceptible (HS).

[0034] Based on the response patterns of different causative types of brown planthopper to rice varieties listed in Table 1, the causative type of each numbered mono-female brown planthopper line was preliminarily determined.

[0035] Table 1. Response patterns of different causative types of brown planthopper to rice identification varieties.

[0036]

[0037] III. Verification of the causative type of brown planthopper using honeydew volume individual measurement method

[0038] The obtained 1st and 2nd instar nymphs were further reared until they developed into newly emerged long-winged female adults, which were then used as test insect sources for honeydew measurement.

[0039] Three core identification varieties, TN1, IR26, and IR42, were used as the identification hosts for honeydew content determination. Seeds were soaked and germinated until the sprouts reached 0.2–0.3 cm in length, then sown separately in seedling substrate. Once the seedlings reached the 3-leaf stage, they were transplanted into seedling pots filled with seedling substrate and placed in a cement tank within a netted greenhouse for routine fertilization and watering. Healthy plants aged 45–60 days, with uniform height, were selected for testing.

[0040] Cut the Parafilm film into small rectangular pieces measuring 3.3 cm x 6.5 cm, and fold them as follows: First, fold the small rectangular pieces in half, as shown in the attached diagram. Figure 2 As shown in Figure A; next, fold one edge back and press it firmly to form a seal, as shown in the attached figure. Figure 2 As shown in B; then, fold the top 2 / 3 of the section in half and press it down, as shown in the attached diagram. Figure 2 As shown in C; then fold the lower half of one side of the fold line inwards, as shown in the attached figure. Figure 2 As shown in D. Before inoculating the insects, open the inner cavity of the small bag to provide sufficient space for the adult brown planthoppers to move around, as shown in the attached diagram. Figure 2 As shown in E, this is to produce small Parafilm bags.

[0041] Individual measurements of honeydew volume were conducted under controlled environmental conditions. The experiment was carried out in an artificial climate chamber, with the indoor temperature controlled at 26-28℃ and the relative humidity maintained at 75%-85%. LED plant grow lights (light intensity 2000-3000 lx) were installed above the rice seedlings, providing 12 hours of light per day (7:00-19:00).

[0042] Two inoculation sequences were set up: IR26, TN1, IR42 and IR42, TN1, IR26, to eliminate potential differences in the physiological state of the test insects due to the inoculation sequence. 100 insects were inoculated in each sequence. Newly emerged, winged female adults were placed individually into a Parafilm bag, which was then fixed to the base of the rice stem of a 45-60 day old rice variety, 5 cm above the water surface. One bag was inoculated per stem, with one insect per bag, and each bag was individually numbered to accurately trace the honeydew levels of the same insect on different varieties.

[0043] Twenty-four hours after inoculation, each small bag was carefully removed, and the weight of the honeydew inside was measured using a 0.01% electronic analytical balance. Before weighing, the outer wall of the bag was blotted dry with filter paper. After recording the data, the test insects were transferred to new Parafilm bags and fixed onto a second rice variety. The bags were weighed again after 24 hours, and then transferred to a third variety. The final weighing was completed after 24 hours. If any suspected non-honeydew secretions were encountered, a filter paper pre-soaked in a 0.5% ninhydrin solution was used for testing. Those that did not change color were considered non-honeydew secretions, and their weight was deducted from the results.

[0044] Based on the honeydew content of each insect on the three different species, and referring to the evaluation criteria in Table 2, the causative type of each individual was determined. According to preliminary experiments and literature reports (Paguia et al., 1980), a honeydew content ≥5.0 mg / 24h can be used as the threshold for judging whether the brown planthopper can cause damage to the different species. For individuals with a honeydew content ≥5.0 mg on IR26 or IR42, the honeydew content on TN1 can be relaxed to ≥2.0 mg; if the honeydew content on TN1 is less than 2.0 mg, the data of that insect is discarded.

[0045] Table 2. Criteria for evaluating the individual virulence of brown planthoppers

[0046]

[0047] *If the honeydew amount on IR26 or IR42 is ≥5.0mg, the honeydew excretion amount on TN1 can be relaxed to 2.0mg. Test insects with a honeydew amount lower than this index should be discarded.

[0048] IV. Comprehensive Determination of the Damage Type of Brown Planthopper

[0049] Based on the population identification results of the standard seedling screening method and the single-head verification results of the honeydew-based individual measurement method, the final determination and screening of the causative type of each numbered brown planthopper single female line was conducted. The determination criteria are as follows: If 95% or more of the individuals of a certain number of brown planthoppers exhibit a causative type consistent with the causative type determined by the standard seedling identification method in the honeydew-based individual measurement, then the causative type is identified as the causative type of that brown planthopper population, and the source of insects with that number is retained and enters the subgeneration propagation process; if the results of the two methods are inconsistent, or the proportion of individuals consistent with the causative type is less than 95%, then the single female line of brown planthoppers with that number is culled.

[0050] Through the above dual screening, it is ensured that each brown planthopper population that is ultimately retained is a standard experimental population with a clear genetic background and highly homozygous virulence.

[0051] V. Maintaining the virulence of the population

[0052] Based on the differences in adaptability of different pathogenic brown planthopper strains to rice varieties, corresponding identification varieties were selected as obligate hosts for targeted rearing, utilizing host selection pressure to maintain their specific pathogenic characteristics. The specific operation is as follows:

[0053] Type of population: Use 45-60 day old susceptible species TN1 for rearing and egg laying, and then propagate through successive generations;

[0054] Type of population: Use 45-60 day old Mudgo breed containing the Bph1 gene for rearing and egg laying, and propagate by generation;

[0055] Type of population: Use 45-60 day old ASD7 breed containing the bph2 gene for rearing and egg laying, and then propagate the next generation;

[0056] Bengal type population: Use IR36 breed containing the bph2 gene, aged 45–60 days, for rearing and egg laying, and then propagate by generation.

[0057] All populations were raised in artificial climate chambers or intelligent glass greenhouses, with the following environmental parameters set:

[0058] Temperature is controlled at 26-28℃; relative humidity is maintained at 75%-85%; four rows of 18W red and white LED plant supplement lights (spectrum covering 660 nm red light and 450 nm blue light) are installed above each mesh insect rearing cage, with the light tubes about 30-50 cm away from the top of the rice plant, light intensity of 2000-3000 lx, and daily light duration of 12 hours (7:00-19:00).

[0059] Once each population reaches adulthood, select 100-150 healthy, egg-bearing female adults and transfer them to fresh TN1 rice seedlings (45-60 days old, 8-10 seedlings per pot) to continue egg-laying and generation. Replace the seedlings with fresh rice seedlings for each generation to ensure the population remains in good nutritional and growth condition. Maintain three parallel rearing cages for the population to prevent accidental losses.

[0060] After every 20 generations, samples were randomly selected from the population and subjected to bioassay of virulence using the standard seedling group screening method. This comprehensively assessed whether the population’s response pattern to the nine identifying varieties had changed and monitored whether its virulence characteristics had drifted.

[0061] Five generations later, the genetic purity of the population was checked by individual honeydew measurement. 30-50 newly emerged female adults were randomly measured in each population, and the proportion of individuals with the target causative type was counted to monitor the changes in the purity of the causative type in the population.

[0062] During the monitoring and verification of pathogenicity stability, if a significant deviation in the pathogenicity characteristics of a population is found or its purity does not meet the requirements, corresponding measures will be taken according to the specific circumstances, as follows:

[0063] For populations where the purity has decreased but the main causative type still dominates, as detected by the honeydew identification method, and the proportion of individuals with the target causative type is less than 95% but more than 70%, a single-head purification method can be used for purification and rejuvenation.

[0064] The specific procedures are as follows: Randomly select over 200 newly emerged female adults from the population to be purified. Identify the virulence type of each individual using the honeydew content assay. Select individuals that meet the criteria for the target virulence type. Transfer the selected homozygous individuals to the corresponding identification varieties for propagation to establish a new core population. After the new population is established, it needs to be monitored continuously for three generations. Only when the purity is confirmed to have recovered to over 95% can it be used as a normal test population.

[0065] Populations that have been confirmed by standard seedling group screening to have completely transformed into non-target types, or whose honeydew identification method shows that the proportion of individuals with the target harmful type is less than 70% and is difficult to restore through purification, should be culled entirely. During culling, the insect source must be subjected to high-temperature inactivation treatment, and the insect rearing cages and equipment used must be thoroughly disinfected to prevent contamination of other populations. The harmful population can be re-collected from the field during the peak migration period of brown planthoppers the following year, and then re-isolated and identified using the above method to reconstruct a standard population.

[0066] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0067] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing and maintaining a harmful experimental population of brown planthoppers, characterized in that, Includes the following steps: S1. During the peak migration period of brown planthoppers, egg-bearing long-winged female adults were collected in the field. After single-female separation and reproductive capacity screening, 1st and 2nd instar nymphs were collected as test insect sources. S2. The standard seedling stage group screening method was used to preliminarily determine the virulence of the test insect sources, and the honeydew content was measured individually to verify the results. S3. Based on the population identification results of the combined standard seedling group screening method and the single-head verification results of the honeydew quantity individual measurement method, the virulence type of each numbered brown planthopper single female line was finally determined and screened. S4. For the standard population of brown planthoppers obtained through comprehensive evaluation and screening, establish a pesticidal maintenance system that includes standardized feeding, environmental control, subspecies operation and quality monitoring.

2. The method for constructing and maintaining a harmful experimental population of brown planthopper according to claim 1, characterized in that, The specific steps of S1 are as follows: The collected female adult insects were isolated in numbered 60-mesh mesh insect rearing cages, and the rice variety TN1 without insect-resistant genes was used as the oviposition host. After the nymphs hatch, continue to raise them to adulthood. The number of adults in each cage is counted: cages with fewer than 30 adults are culled, while cages with 30 or more adults are retained. The retained numbers were transferred to new TN1 rice seedlings for another generation of rearing. After the eggs hatched, the 1st and 2nd instar nymphs were collected as test insects for subsequent virulence identification tests.

3. The method for constructing and maintaining a harmful experimental population of brown planthopper according to claim 1, characterized in that, In step S2, the standard seedling group screening method includes: Nine rice varieties were selected as identification hosts, including: TN1 without insect-resistant genes; IR26 and Mudgo containing the Bph1 gene; ASD7, IR36, and IR42 containing the bph2 gene; Rathu Heenati containing the Bph3 gene; Babawee containing the bph4 gene; and Ptb33 containing both the bph2 and Bph3 genes. Nine varieties were sown in seedling trays, with 25 seeds sown in each row. When the seedlings grew to the 3-leaf stage, about 20 healthy seedlings with uniform growth were retained in each row. Inoculate each seedling with 8 first- or second-instar nymphs, and repeat the process 3 times. When the mortality rate of the TN1 control plant reaches over 95%, the damage level is investigated for each plant, and the weighted average damage level of each variety is calculated. Based on the pre-defined response patterns of different causative types of brown planthoppers to rice varieties, the causative type of each numbered mono-female brown planthopper line was preliminarily determined. The causative types include type I, type II, type III, and Bengal type.

4. The method for constructing and maintaining a harmful experimental population of brown planthopper according to claim 3, characterized in that, In step S2, the individual method for determining honeydew volume includes: Three core identification varieties, TN1, IR26 and IR42, were used as identification hosts for honeydew quantity determination. The test insects were raised to newly emerged long-winged female adults and used as test insects. Cut Parafilm into small bags, then place a newly emerged long-winged female adult into the Parafilm bag, and then fix the bag to the base of the rice stem for variety identification at 45-60 days old. Two inoculation sequences were set up: IR26, TN1, IR42 and IR42, TN1, IR26. 100 larvae were inoculated in each sequence. The honeydew weight in the bag was measured every 24 hours to obtain the amount of honeydew for each test larva on the three varieties. Based on the amount of honeydew on the three identification varieties for each test insect, and referring to the preset individual causative type evaluation criteria, the causative type of each individual was determined. Among them, for individuals with a honeydew amount ≥5.0mg on IR26 or IR42, the honeydew amount on TN1 can be relaxed to ≥2.0mg, and test insects with a honeydew amount lower than this index were removed.

5. The method for constructing and maintaining a harmful experimental population of brown planthopper according to claim 4, characterized in that, The specific criteria for comprehensive determination of the hazard type are as follows: Based on the population identification results of the combined standard seedling group screening method and the single-head verification results of the honeydew quantity individual measurement method, the virulence type of each numbered brown planthopper single female line was finally determined and screened. When 95% or more of the individuals of a certain number of brown planthoppers exhibit a causative typology consistent with the causative typology determined by the standard seedling stage identification in the honeydew-drenching individual test, the causative typology is identified as the causative typology of that brown planthopper population, and the numbered insect source is retained and enters the subgeneration propagation process. If the results of the two methods are inconsistent, or if the proportion of individuals with the same causative type is less than 95%, then the entire colony of the single female brown planthopper with that number will be culled.

6. The method for constructing and maintaining a harmful experimental population of brown planthopper according to claim 1, characterized in that, In S4, the specific operation of standardized feeding is as follows: Type I population: Use 45-60 day old susceptible species TN1 for rearing and egg laying, and then propagate through successive generations; Type II population: Use 45-60 day old Mudgo breeds containing the Bph1 gene for rearing and egg laying, and propagate through generations; Type III population: Use 45-60 day old ASD7 breed containing the bph2 gene for rearing and egg laying, and then propagate the next generation; Bengal type population: Use IR36, a breed containing the bph2 gene, aged 45-60 days, for rearing and egg laying, and then propagate the next generation.

7. The method for constructing and maintaining a harmful experimental population of brown planthopper according to claim 1, characterized in that, During the maintenance of the population's lethality, quality monitoring includes: After every 20 generations, samples were randomly selected from the population and bioassays of lethality were performed using the standard seedling group screening method to comprehensively assess whether the population’s response pattern to the nine differential varieties had changed. Five generations later, the genetic purity of the population was checked by individual honeydew measurement. 30-50 newly emerged female adults were randomly measured in each population, and the proportion of the target virulent individuals was counted.

8. The method for constructing and maintaining a harmful experimental population of brown planthopper according to claim 7, characterized in that, Following the quality monitoring, the handling of substandard populations includes: For populations where purity has decreased but the dominant causative type still prevails, a single-head purification method is used for purification and rejuvenation. More than 200 newly emerged female adults are randomly selected from the population to be purified, and their causative type is identified one by one using the honeydew amount individual determination method. Individuals that meet the criteria for the target causative type are selected and transferred to the corresponding identification varieties for propagation to establish a new core population. After the new population is established, it is continuously monitored for three generations. Only when the purity is confirmed to have recovered to more than 95% can it be used as a normal test population. Populations that have been confirmed by standard seedling group screening method to have completely transformed into non-target types, or whose honeydew identification method shows that the proportion of target harmful individuals is less than 70% and is difficult to restore through purification, are culled as a whole. The insect source is then subjected to high-temperature inactivation treatment, and the insect rearing cages and equipment used are thoroughly disinfected. During the peak migration period of brown planthoppers the following year, egg-bearing adult females are collected again from the field, re-separated and identified, and the standard population is rebuilt.

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