Multi-layered core-shell granules for controlling underground pests, their preparation and application methods

Abstract

This invention discloses a multi-layered core-shell granular agent for controlling underground pests, along with its preparation and application methods. Belonging to the field of pest control technology, the granular agent comprises, from the inside out: a core layer containing a chemical insecticide and a slow-release carrier; a middle layer containing entomopathogenic nematodes and a calcium alginate gel protectant; and an outer shell layer containing an attractant and a disintegrant. The calcium alginate gel protectant physically isolates the entomopathogenic nematodes from the core chemical insecticide, preventing nematode damage. The disintegrant disintegrates upon contact with moisture, releasing the attractant to draw underground pests to ingest the granular agent. This invention also discloses the preparation method of the granular agent and its application in combination with functional bio-organic fertilizers, drip irrigation for nematode supplementation, and intercropping with repellent plants. This invention achieves the synergistic coexistence of chemical and biological control within the same granular agent, providing a progressive control effect of attraction-infection-killing with a long-lasting effect.

Description

Technical Field

[0001] This invention belongs to the field of pest control technology, specifically relating to multi-layered core-shell structured granules for controlling underground pests and their preparation and application methods. Background Technology

[0002] Underground pests refer to insects that spend most of their life cycle in the soil, damaging the underground parts of plants (such as roots, stems, tubers, and rhizomes) or near-surface parts. These pests mainly include grubs, wireworms, cutworms, mole crickets, and root maggots. These pests are characterized by their strong concealment, long period of damage, and difficulty in control, often causing missing seedlings, reduced yields, or even crop failure, posing a significant obstacle to agricultural production.

[0003] Currently, the control of underground pests mainly relies on three approaches: chemical pesticides, biological control, and physical control. Chemical control primarily uses insecticides such as organophosphates, neonicotinoids, and benzoylurea, typically applied as granules, seed dressings, or root drenching, offering advantages such as rapid effectiveness and ease of use. However, the long-term and excessive use of chemical pesticides has led to increasingly prominent problems such as increased pesticide resistance in pests, soil ecological damage, and excessive pesticide residues. Biological control utilizes natural enemies such as entomopathogenic nematodes, Metarhizium anisopliae, and Beauveria bassiana to kill underground pests. It is environmentally friendly and does not induce pesticide resistance, but in field applications, it suffers from drawbacks such as short-lasting effects of bioactive ingredients, susceptibility to soil environmental factors (temperature, humidity, ultraviolet radiation), and poor compatibility with chemical pesticides, making it difficult to achieve ideal control effects on its own.

[0004] In recent years, the strategy of combining chemical and biological control has attracted attention. Existing technologies have attempted to combine chemical pesticides with biological agents such as entomopathogenic nematodes through separate application or simple mixtures. However, in this approach, the direct contact between chemical pesticides and nematodes easily leads to nematode death or decreased activity, failing to achieve true synergistic effects. Some studies have also encapsulated nematodes in calcium alginate gels to improve their environmental tolerance; however, these gel capsules are all single-layer structures, containing only nematodes and attractants, without any chemical pesticide components, thus failing to solve the compatibility issues in synergistic chemical-biological control. Furthermore, existing technologies have developed multi-layered core-shell structured pesticide granules, but their multi-layered design is merely a functional layering of different chemical pesticides or fertilizers, without addressing the protection and release of biological control components. Summary of the Invention

[0005] To address the above problems, this invention provides a multi-layered core-shell structured granule for controlling underground pests, as well as its preparation and application methods.

[0006] A multi-layered core-shell structured granule for controlling underground pests, the granule comprising, from the inside out: The core contains chemical pesticides and slow-release carriers; The intermediate layer, which wraps around the outer surface of the core, contains entomopathogenic nematodes and calcium alginate gel protectant; The outer shell, which wraps around the outer surface of the middle layer, contains an attractant and a disintegrant; wherein, the calcium alginate gel protectant physically isolates the entomopathogenic nematode from the chemical insecticide in the core, so as to prevent the chemical insecticide from directly contacting and killing the entomopathogenic nematode; the disintegrant gradually disintegrates upon contact with soil moisture, releasing the attractant to attract underground pests to feed on the granules.

[0007] Preferably, the chemical insecticide is a compound of brofenoxam and flufenoxam, with a mass ratio of brofenoxam to flufenoxam of 1:21 to 1:54; the slow-release carrier is silica.

[0008] Preferably, the entomopathogenic nematode is selected from at least one of *Strombus schoenleinii*, *Strombus schoenleinii*, or *Heterobacter spp.*; the attractant contains a dried extract of Vitex negundo seeds, which inhibits cytochrome P450 enzymes in underground pests, thereby enhancing the insecticidal activity of chemical insecticides.

[0009] Preferably, the core has a particle size of 1-2 mm, the intermediate layer has a thickness of 0.2-0.5 mm, and the outer shell has a thickness of 0.1-0.3 mm; the disintegrant is selected from one or more of urea, ammonium sulfate, and phosphate.

[0010] A method for preparing a multi-layered core-shell structured granule for controlling underground pests includes the following steps: (1) The chemical insecticide is mixed with the slow-release carrier and then extruded and granulated to obtain the core; (2) Mix the insect pathogen nematode suspension with sodium alginate solution, spray it evenly on the core surface, and then immerse it in calcium chloride solution for cross-linking and curing to form an intermediate layer; (3) Mix the attractant with the disintegrant and the binder, coat the outer surface of the intermediate layer by rolling coating, and dry to obtain the product.

[0011] Preferably, in step (2), the sodium alginate solution is preheated to 50°C to dissolve and then cooled to below 25°C before being mixed with the entomopathogenic nematode suspension; the cross-linking and curing are carried out in a 0.2-0.8 mol / L calcium chloride solution for 10-30 minutes.

[0012] A method for using a multi-layered core-shell granular agent for controlling underground pests includes the following steps: (1) When sowing or transplanting crops, the multi-layer core-shell structure granules described in any one of claims 1 to 4 are mixed with functional bio-organic fertilizer and then applied in furrows or holes at a rate of 5 to 8 kg / mu. (2) After application, cover with soil and water thoroughly, and maintain soil moisture content at 15-25% for 7-10 days; (3) During the crop growth period, apply insect pathogenic nematode suspension every 30 to 40 days by drip irrigation at a concentration of 500 to 800 IJS / mL and a dosage of 100 million nematodes / mu. (4) Intercropping repellent plants between crop rows.

[0013] Preferably, the functional bio-organic fertilizer is prepared by the following method: well-rotted organic fertilizer, potassium humate, and diatomaceous earth are mixed in a weight ratio of 10:2:1, and Metarhizium anisopliae spore powder and Bacillus subtilis are inoculated, the moisture content is adjusted to 35-45%, and the mixture is aged at 25-30℃ for 5-7 days; the effective viable count of Metarhizium anisopliae spore powder is ≥5 billion / g, and the effective viable count of Bacillus subtilis is ≥10 billion / g.

[0014] Preferably, the entomopathogenic nematodes in the entomopathogenic nematode suspension are the same species as those in the granules; the repellent plant is chives or marigold.

[0015] The above-mentioned technologies are applied in the control of underground pests such as grubs, wireworms, cutworms, and mole crickets.

[0016] The advantages of this invention compared to the prior art are as follows: 1. The invention employs a three-layer core-shell structure: the core is a chemical insecticide (a combination of bromonitrile and flufenoxuron), the middle layer is an insect-pathogenic nematode encapsulated in calcium alginate gel, and the outer shell contains attractants and disintegrants. The calcium alginate gel layer physically isolates the nematode from the core chemical pesticide, preventing direct contact and damage to the nematode, thus solving the technical problem in existing technologies where chemical pesticides and biological enemies cannot coexist stably in the same formulation.

[0017] 2. The disintegrant in the outer shell gradually disintegrates upon contact with soil moisture, releasing plant-derived attractants (β-caryophyllene, α-pinene, dried extract of Vitex negundo seeds, etc.), attracting underground pests to the vicinity of the granules. When pests feed on or come into contact with the granules, they first come into contact with and carry the entomopathogenic nematodes from the middle layer. The nematodes invade the pest's body, multiply, and cause septicemia. After further feeding on the core, they ingest chemical pesticides, achieving a triple attack of "attraction-infection-killing." This progressive mode significantly improves the insecticidal efficiency per unit of insecticide, and because the pests actively feed on it, it avoids pesticide loss caused by passive application. Detailed Implementation

[0018] To make the objectives, technical solutions, and beneficial effects of the present invention clearer, the preferred embodiments of the present invention will be described in detail below to facilitate understanding by those skilled in the art.

[0019] Example 1: Preparation of multilayer core-shell structured granules 1.1 Kernel Preparation Weigh out 0.28 g of chlorfenapyr technical (98% by mass), 8.92 g of flufenoxuron technical (97% by mass), and 18 g of silica. Mix them evenly and granulate using a small rotary extruder (1.5 mm aperture). Dry the extruded granules with hot air at 50°C until the moisture content is ≤2%. Sieve the granules (1.0 mm and 2.0 mm screens) and collect the kernel particles with a particle size of 1.0–2.0 mm, yielding approximately 27 g of kernels. The average particle size is 1.6 mm, and the bulk density is 0.75 g / cm³.

[0020] 1.2 Preparation of the intermediate layer (1) Preparation of sodium alginate solution: Add 20g of sodium alginate to 1L of sterile water, heat to 50℃ and stir until completely dissolved, then cool to below 25℃ for later use.

[0021] (2) Preparation of entomopathogenic nematode suspension: Take the infecting stage nematodes of the small leafroller *Strombi squarrosa* (IJs), and prepare a suspension with sterile water to a concentration of 2×10⁻⁶. 4 Use a suspension of IJs / mL after microscopic examination shows a nematode survival rate >95%.

[0022] (3) Mixing: Mix the nematode suspension with the cooled sodium alginate solution at a volume ratio of 1:4, and stir slowly (50 rpm, 5 minutes) to make it uniform. The temperature of the mixture should be controlled at 20-25℃.

[0023] (4) Coating: The core particles prepared in step 1.1 are placed in a fluidized bed coating machine, preheated to 30°C, and the fluidizing air volume is adjusted (0.5-0.8 m³ / min) to suspend the particles. The nematode-sodium alginate mixture obtained in step (3) is atomized and sprayed onto the core surface through a dual-fluid nozzle at a rate of 0.5 mL / min for 60 minutes. The fluidization temperature is maintained at 25-30°C during the spraying process.

[0024] (5) Crosslinking and curing: The particles coated with calcium alginate pregel were quickly immersed in a 0.5 mol / L calcium chloride solution (liquid-to-solid volume ratio 5:1) and crosslinked and cured for 15 minutes. During the curing process, the particles were slowly stirred at 50 rpm to ensure that the surface of the particles was in uniform contact with calcium ions.

[0025] (6) Washing and Drying: The solidified granules were rinsed twice with sterile water (each time the amount of sterile water was 3 times the volume of the granules) to remove excess calcium ions and uncrosslinked sodium alginate. Then, they were dried in a 25℃ forced-air drying oven for 30 minutes to obtain intermediate-layer coated granules. The thickness of the intermediate layer was measured to be 0.3±0.05 mm, and the number of nematodes embedded in each gram of granules was (1.2±0.1)×10⁻⁶. 5 IJs.

[0026] 1.3 Preparation of the outer shell layer (1) Preparation of attractant: Take 50g of β-caryophyllene, 30g of α-pinene, 80g of dried extract of Vitex negundo seeds and 40g of castor bean leaf volatile oil, and mix them evenly.

[0027] Preparation method of dried-roasted Vitex negundo seed extract: After removing impurities from mature Vitex negundo seeds, roast them at 120℃ for 15 minutes (until the surface is slightly charred and fragrant), cool, and then pulverize through a 40-mesh sieve. Add 10 times the volume of 95% ethanol and reflux for 2 hours, then filter. Repeat the extraction once with the residue. Combine the filtrates and concentrate under reduced pressure (50℃, -0.09MPa) until no ethanol remains, yielding a brown paste, which is the dried-roasted Vitex negundo seed extract.

[0028] Preparation method of castor leaf volatile oil: Take 1 kg of fresh castor leaves, chop them, add 6 L of water, steam distill for 4 hours, collect the distillate, extract with diethyl ether, dry with anhydrous sodium sulfate and evaporate the diethyl ether to obtain a pale yellow oily liquid.

[0029] (2) Preparation of disintegrant: Take 100g of urea and 50g of ammonium sulfate, mix them evenly, and crush them through a 100-mesh sieve.

[0030] (3) Preparation of outer shell slurry: Mix the attractant, disintegrant and sodium carboxymethyl cellulose (binder) 20g, add water to make a slurry with a solid content of 30%, and shear at high speed (8000rpm, 10 minutes) to make it evenly dispersed.

[0031] (4) Coating: The intermediate layer coated particles obtained in step 1.2 are placed in a fluidized bed coating machine, preheated to 35°C, and the outer shell slurry is sprayed by bottom spraying at a rate of 0.8 mL / min for 40 minutes. The fluidization temperature is maintained at 35-40°C during the spraying process.

[0032] (5) Drying: After coating, dry with hot air at 40℃ until the moisture content of the particles is ≤3%, sieve (0.8mm and 2.5mm screens), and collect particles with a particle size of 0.8 to 2.5mm, which is a multi-layered core-shell structured granule.

[0033] The obtained granules were tested and found to have a particle size distribution of 1.2–2.2 mm, a bulk density of 0.68 g / cm³, and a shell layer thickness of approximately 0.2 mm. Disintegration test: 1 g of granules was placed in 50 mL of water at 25°C and gently shaken; the disintegration time was ≤5 minutes.

[0034] Example 2: Survival rate test of entomopathogenic nematodes in granules 2.1 Test Methods The granules prepared in Example 1 were sealed in aluminum foil bags and stored under different temperature conditions: 4°C (refrigeration), 25°C (room temperature, protected from light), and 35°C (accelerated test). 100g of granules were stored in each group, and samples were taken at 0, 15, 30, 60, 90, and 120 days to detect nematode survival rates.

[0035] A separate control group was established: a suspension of the same batch of entomopathogenic nematodes (concentration 2×10⁻⁶). 4 The nematode survival rate was detected by directly mixing IJs / mL with the core chemical pesticide (brofenoxam + flufenoxam, mass ratio 1:31.8) without gel embedding or layering, and storing them at 25℃ for the same time.

[0036] Detection method: Take 5 granules (or 1 mL of control suspension), soak them in 10 mL of sterile water for 10 minutes, gently shake to release the nematodes, and collect the nematode suspension. Take 10 μL of the sample solution on a glass slide, observe and count the surviving nematodes under a microscope (100×) (survival is defined as the body exhibiting a "J" shape or serpentine wriggling). Each treatment is repeated 3 times, with a minimum of 200 nematodes counted each time.

[0037] 2.2 Test Results The results showed that the calcium alginate gel in the granules of this invention had a good protective effect on nematodes. After 120 days, the survival rate of nematodes remained above 70%, while the survival rate of unprotected nematodes directly mixed with chemical pesticides dropped to 31.4% after 30 days, and almost all of them died after 120 days.

[0038] Example 3: Verification of the enzyme inhibition and synergistic effects of dried and roasted Vitex trifolia seed extract 3.1 Preparation of extract from dried and roasted Vitex negundo seeds The dry-roasted extract of Vitex negundo seeds (VbE) was prepared according to the method in Example 1.3 (1).

[0039] 3.2 In vitro enzyme activity assay Test insects: 3rd instar larvae of the green scarab beetle, collected from pesticide-free soil at the experimental base, and used after being raised indoors for 1 week.

[0040] Enzyme preparation: Five larvae were dissected, and their midguts were collected and placed in pre-cooled (4℃) 0.1 mol / L phosphate buffer (pH 7.4, containing 1 mmol / L EDTA and 1 mmol / L DTT). The mixture was homogenized on ice (10% w / v). The homogenate was centrifuged at 10,000×g for 20 minutes at 4℃, and the supernatant was used as the P450 enzyme source. Protein concentration was determined using the Bradford method.

[0041] Enzyme activity assay: 7-ethoxycoumarin (7-EC) was used as the substrate, and deethylation activity was detected by fluorescence assay. The reaction system (200 μL) contained: 0.1 mol / L phosphate buffer (pH 7.4), 0.2 mg enzyme protein, 50 μmol / L 7-EC, and 1 mmol / L NADPH. The following treatment groups were set up, with each group repeated three times: Control group: No inhibitors were added; instead, an equal volume of buffer solution was used. Bromnifenac group: Bromnifenac was added (final concentration 0.5 mg / L); VbE group: Added VbE (final concentration 100 mg / L); Bromnipotentiol + VbE group: Bromnipotentiol (0.5 mg / L) and VbE (100 mg / L) were added simultaneously.

[0042] Pre-incubate the enzyme solution with the inhibitor (or buffer) at 30°C for 30 minutes, then add the substrate and NADPH to initiate the reaction, incubate at 30°C for 30 minutes, and terminate the reaction by adding 200 μL of methanol. After centrifugation, collect the supernatant and measure the fluorescence intensity using a fluorescence microplate reader (excitation wavelength 390 nm, emission wavelength 460 nm). Plot a standard curve using 7-hydroxycoumarin as a standard. Inhibition rate (%) = (control group activity - treatment group activity) / control group activity × 100%.

[0043] result: VbE alone can significantly inhibit P450 enzyme activity (inhibition rate 45.4%), and when used in combination with bromonitrile, the inhibition rate is further increased to 61.8%, indicating that the two have a synergistic inhibitory effect.

[0044] 3.3 Toxicity determination (co-toxicity coefficient) The tested insects were the same as in 3.2.

[0045] The sand-powder mixing method was adopted. Fine sand (passed through a 60-mesh sieve) was mixed with the reagent in a certain proportion to prepare five concentration gradients: Bromnifenac single agent: 3.2, 6.4, 12.8, 25.6, 51.2 mg / L; Bromnipotentiol + Vitamin B1E combination group: Vitamin B1E was fixed at 100 mg / L, and the concentration of bromnipotentiol was the same as above.

[0046] For each concentration, treat 20 third-instar larvae of white grubs, place them in a 500mL beaker, add 200g of medicated sand, mix gently, and cover. Repeat 3 times. Use a blank control without medicated sand. Incubate at 25℃ in the dark for 72 hours, maintaining a sand moisture content of 15% during this period. After 72 hours, check for mortality (larvae that do not move when gently touched with tweezers are considered dead).

[0047] LC was calculated using Probit regression in SPSS software. 50 The co-toxicity coefficient (CTC) was calculated using Sun Yunpei's method: CTC = [Measured LC of the mixture] 50 Theoretical values ​​(i.e., LC50 of each single agent) 50 (Weighted average) / Measured LC of the mixture 50 [Actual value] × 100. CTC ≥ 120 indicates a synergistic effect.

[0048] result: Vitamin B1 itself has very low toxicity (LC) 50 >500 mg / L), but when combined with brofenoxam, the LC50 of brofenoxam is significantly lower. 50 The concentration decreased from 12.6 mg / L to 5.8 mg / L, with a co-toxicity coefficient (CTC) of 217.2 > 120, indicating a significant synergistic effect.

[0049] Example 4: Comparison of the attraction effects of composite attractants 4.1 Preparation of attractant substances Single attractant substances: β-caryophyllene (commercially available, purity ≥98%), α-pinene (commercially available, purity ≥98%), dried extract of Vitex negundo seeds (method of Example 1.3), and castor bean leaf volatile oil (method of Example 1.3).

[0050] The compound formulation of this invention is: β-caryophyllene:α-pinene:VbE:castor leaf oil = 5:3:8:4 (mass ratio), mixed evenly.

[0051] 4.2 Lure device and test method The trap method was used. A plastic basin (25cm in diameter and 10cm deep) was used as the trap, with the basin walls coated with talcum powder to prevent pests from escaping. A 5cm diameter filter paper was placed in the center of the basin, with a drop of attractant (total 20mg dissolved in 1mL of acetone, allowed to evaporate naturally before placement) added to the filter paper. The rim of the basin was level with the ground, and a plastic cover was placed on top of the basin using a wire frame (to protect against rain). The soil around the trap was kept moist.

[0052] Test insects: 3rd instar larvae of the green scarab beetle (grub), collected from the field and starved indoors for 12 hours before use.

[0053] Untreated cornfields were selected and divided into experimental plots (4 m² per treatment). No other traps were placed within a 3 m radius of each trap. Each treatment had 5 traps replicated, with a trap spacing of ≥10 m. 100 grubs were released 20 cm from the center of the trap (evenly distributed around the perimeter). Larvae that fell into the traps were collected and counted after 24 hours. Distilled water was used as a blank control (10 μL of distilled water was dropped onto filter paper), and acetone was used as a solvent control.

[0054] Attraction rate (%) = (Number of insects falling into the trap / Total number of insects released) × 100%.

[0055] 4.3 Results Different letters in the same column indicate significant differences (P<0.05, Duncan's new multiple range method).

[0056] The results showed that the composite attractant formulation of the present invention achieved a 24-hour attraction rate of up to 52.7% for grubs, which was significantly better than any single attractant (P<0.05) and higher than the sum of the attraction rates of each single substance, demonstrating a synergistic effect.

[0057] Example 5: Field control effect trial 5.1 Experimental Design The soil type was loam, pH=7.2, and organic matter content was 1.8%. The experimental crop was spring maize. The dominant underground pests were grubs (larvae of the green scarab beetle, natural density 2.3 individuals / m²) and wireworms (wireworms, natural density 1.1 individuals / m²).

[0058] The experiment included the following treatments: Each treatment area was 100 m², repeated 4 times in a randomized block design. A 1 m wide isolation strip was set between each treatment.

[0059] Preparation of functional bio-organic fertilizer: Mix well-rotted cow manure organic fertilizer, potassium humate, and diatomaceous earth in a weight ratio of 10:2:1, inoculate with Metarhizium anisopliae spore powder (effective viable count 5 billion / g) and Bacillus subtilis (effective viable count 10 billion / g), adjust the moisture content to 40%, and age at 28℃ for 6 days.

[0060] 5.2 Application Method T1 processing: Three days before sowing, mix the granules with functional bio-organic fertilizer and spread them evenly in the sowing furrow (15cm deep), cover with 5cm of soil, and then water thoroughly (40m³ per acre), maintaining the soil moisture content at 20-25% for 7 days.

[0061] Seven days after sowing (seedling stage), apply a suspension of Stellaria dichotoma (concentration 800 IJs / mL, dosage 100 million nematodes / acre) through the drip irrigation system.

[0062] During the jointing stage (30 days after sowing), apply another 100 million nematode suspensions of the same concentration per acre through the drip irrigation system.

[0063] Intercrop chives between corn rows at a ratio of 2:1 (2 rows of corn intercropped with 1 row of chives).

[0064] T2 treatment: Apply granules at the same dosage as T1 in furrows, without applying organic fertilizer, supplementing with nematodes, or intercropping chives.

[0065] T3 treatment: No granules are applied; only nematode suspension is drip-irrigated during the seedling and jointing stages (same concentration and dosage as T1); chives are not intercropped.

[0066] T4 treatment: No insect control treatment is performed.

[0067] 5.3 Survey Methodology (1) Control efficacy survey: Five points were randomly selected from each treatment at 30 days (seedling stage), 60 days (jointing stage), 90 days (tasseling stage), and 120 days (before harvest) after application. At each point, 0.25 m² of soil was dug to a depth of 20 cm, and the number of live insects (including grubs and wireworms) was counted. Control efficacy (%) = (number of live insects in the blank control - number of live insects in the treatment) / number of live insects in the blank control × 100%.

[0068] (2) Detection of nematode survival rate in granules: granules were randomly collected from the T1 treatment plot at 0d, 30d, 60d, 90d and 120d after application (5 granules were collected each time), and the nematode survival rate was detected according to the method in Example 2.

[0069] (3) Corn yield: Each treatment was threshed and the yield was calculated separately at harvest, and converted into the yield per mu (moisture content 14%).

[0070] 5.4 Test Results Table 1. Control efficacy of each treatment against underground pests (%) Different lowercase letters in the same column indicate significant differences (P<0.05, Duncan's new multiple range test). The average number of live worms in the blank control group was 9.3 worms / m² at 30 days and 12.5 worms / m² at 120 days.

[0071] Table 2. Nematode survival rate in granules (%, granules recovered from soil in T1 treatment) Table 3. Corn yield (kg / mu) 5.5 Results Analysis As shown in Table 1, the control efficacy of treatment T1 in this invention was significantly higher than that of T2 and T3 at 30d, 60d, 90d, and 120d (P<0.05). In particular, after 90d, the control efficacy of the chemical control T2 had decreased to 42.5%, while T1 remained at 81.3%; at 120d, the control efficacy of T1 was 76.8%, approximately 2.5 times that of T2 (31.2%). The control efficacy of T1 was superior to the sum of the control efficacies of T2 and T3 (31.2% + 41.7% = 72.9%), exhibiting a super-additive effect.

[0072] Table 2 shows that the survival rate of nematodes in the granules in the soil was still 51.8% after 120 days, indicating that calcium alginate gel has a good protective effect on nematodes.

[0073] In terms of yield, T1 increased production by 30.1% compared to the blank and by 16.1% compared to the chemical control alone, demonstrating significant economic benefits.

[0074] Example 6: Application Case in Peanut Fields 6.1 Experimental Overview Soil: Sandy loam, pH=6.8. Peanut variety: Yuhua 23. Dominant underground pests: White grubs (Dark-gilled scarab beetles), wireworms (Fine-breasted wireworms).

[0075] The experiment included two treatments: ① The treatment of this invention (using the method of Example 5 T1, 8 kg / mu of granules + 100 kg / mu of functional organic fertilizer + 2 applications of drip irrigation to supplement nematodes + intercropping with leeks); ② Conventional chemical control (5 kg / mu of 5% phoxim granules mixed with soil and applied in furrows, and 100 mL / mu of 48% chlorpyrifos emulsifiable concentrate sprayed at the seedling and pod-setting stages). Each treatment covered an area of ​​5 mu, with a 2 mu blank control.

[0076] 6.2 Results Compared with conventional chemical control, the treatment of this invention reduces the amount of chemical pesticides used by about 82%, increases the control efficacy by 25.3 percentage points, increases the yield by 18.0%, and reduces the rate of infested fruit by 6.6 percentage points.

[0077] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A multi-layered core-shell structured granular agent for controlling underground pests, characterized in that, The granules, from the inside out, comprise: The core contains chemical pesticides and slow-release carriers; The intermediate layer, which wraps around the outer surface of the core, contains entomopathogenic nematodes and calcium alginate gel protectant; The outer shell, which wraps around the outer surface of the middle layer, contains an attractant and a disintegrant; wherein, the calcium alginate gel protectant physically isolates the entomopathogenic nematode from the chemical insecticide in the core, so as to prevent the chemical insecticide from directly contacting and killing the entomopathogenic nematode; the disintegrant gradually disintegrates upon contact with soil moisture, releasing the attractant to attract underground pests to feed on the granules.

2. The multi-layered core-shell structured granular agent for controlling underground pests according to claim 1, characterized in that, The chemical insecticide is a compound of brofenoxam and flufenoxam, with a mass ratio of brofenoxam to flufenoxam of 1:21 to 1:54; the slow-release carrier is silica.

3. The multi-layered core-shell structured granular agent for controlling underground pests according to claim 1, characterized in that, The entomopathogenic nematode is selected from at least one of the following: *Strombus schoenleinii*, *Strombus schoenleinii*, or *Heterobacter spp.*; the attractant contains a dried extract of Vitex negundo seeds, which inhibits cytochrome P450 enzymes in underground pests, thereby enhancing the insecticidal activity of chemical insecticides.

4. A multi-layered core-shell structured granular agent for controlling underground pests according to claim 1, characterized in that, The core has a particle size of 1-2 mm, the intermediate layer has a thickness of 0.2-0.5 mm, and the outer shell has a thickness of 0.1-0.3 mm; the disintegrant is selected from one or more of urea, ammonium sulfate, and phosphate.

5. A method for preparing a multi-layered core-shell structured granule for controlling underground pests as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) The chemical insecticide is mixed with the slow-release carrier and then extruded and granulated to obtain the core; (2) Mix the insect pathogen nematode suspension with sodium alginate solution, spray it evenly on the core surface, and then immerse it in calcium chloride solution for cross-linking and curing to form an intermediate layer; (3) Mix the attractant with the disintegrant and the binder, coat the outer surface of the intermediate layer by rolling coating, and dry to obtain the product.

6. A method for preparing a multi-layered core-shell structured granule for controlling underground pests according to claim 5, characterized in that, In step (2), the sodium alginate solution is preheated to 50°C to dissolve and then cooled to below 25°C before being mixed with the entomopathogenic nematode suspension; the cross-linking and curing are carried out in a 0.2-0.8 mol / L calcium chloride solution for 10-30 minutes.

7. A method for using a multi-layered core-shell structured granule for controlling underground pests, characterized in that, Includes the following steps: (1) When sowing or transplanting crops, the multi-layer core-shell structure granules described in any one of claims 1 to 4 are mixed with functional bio-organic fertilizer and then applied in furrows or holes at a rate of 5 to 8 kg / mu. (2) After application, cover with soil and water thoroughly, and maintain soil moisture content at 15-25% for 7-10 days; (3) During the crop growth period, apply insect pathogenic nematode suspension every 30 to 40 days by drip irrigation at a concentration of 500 to 800 IJS / mL and a dosage of 100 million nematodes / mu. (4) Intercropping repellent plants between crop rows.

8. The method of using a multi-layered core-shell structured granule agent for controlling underground pests according to claim 7, characterized in that, The functional bio-organic fertilizer is prepared by the following method: well-rotted organic fertilizer, potassium humate, and diatomaceous earth are mixed in a weight ratio of 10:2:1, and Metarhizium anisopliae spore powder and Bacillus subtilis are inoculated. The moisture content is adjusted to 35-45%, and the mixture is aged at 25-30℃ for 5-7 days. The effective viable count of Metarhizium anisopliae spore powder is ≥5 billion / g, and the effective viable count of Bacillus subtilis is ≥10 billion / g.

9. The method of using a multi-layered core-shell structured granule agent for controlling underground pests according to claim 7, characterized in that, The entomopathogenic nematodes in the entomopathogenic nematode suspension are the same species as those in the granules; the repellent plant is chives or marigold.

10. The application of a multi-layered core-shell structured granule for controlling underground pests according to any one of claims 1 to 4, or the preparation method of a multi-layered core-shell structured granule according to any one of claims 7 to 9, in controlling underground pests such as grubs, wireworms, cutworms, and mole crickets.

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