Introduction

The preservation of paper-based cultural relics is critically challenged by biodeterioration, with insect pests representing a significant threat. Pests cause direct physical damage by feeding on cellulose, adhesives, and other organic components, leading to surface erosion, holes, and structural weakening. Moreover, their metabolic byproducts, including organic acids and enzymes, can accelerate paper degradation and staining, compromising both esthetic and informational integrity. The diversity of archival pests is well-documented; for instance, over 50 species have been recorded in China alone, belonging to 6 orders and 19 families1,2,3. The damage caused by pests to paper-based cultural relics is multifaceted. Beetles such as the house beetle and the wheat beetle feed on cultural relics, causing the surface to be uneven and full of holes, and even completely destroying their appearance and structure. Woodworm insects, such as wood moths, dig holes inside cultural relics to reproduce, causing them to lose their supporting force and become prone to breakage and deformation. These direct damages not only affect the appearance and integrity of the cultural relics but also their normal display and preservation. The metabolic products of insects contain organic matter and enzymes that accumulate on cultural relics and react with the materials, leading to color changes, damage to the fiber structure, and accelerating the aging and decay of cultural relics. In addition, pests also indirectly affect the historical and cultural value and readability of cultural relics. Some precious documents, ancient books, paintings, etc. cannot be read or displayed normally due to pests, which affects people’s understanding and research of history and culture. Therefore, doing a good job in preventing insects and mold on paper cultural relics plays a very important role and has significant meaning for their preservation and display4,5,6.

The methods for eliminating pests on paper cultural relics include physical pest control, chemical pest control, irradiation pest control, and biological pest control. Biological pest control is a method that utilizes the inherent characteristics of organisms to eliminate pests. Biological pest control methods can be carried out by using insects, microorganisms, or hormones. This method is mostly used for the control of agricultural pests, but its application in the control of archival pests is still at the stage of theoretical discussion7,8. Radiation pest control is a physical pest control method that utilizes the physical, chemical, and biological effects produced by the interaction between ionizing radiation released by specialized equipment and pests, leading to the infertility or death of paper pests9. At present, there are many types of radiation that can be used to kill paper-based pests, such as microwave irradiation, X-ray radiation, and cobalt source irradiation pest control. However, due to the high operational difficulty of radiation pest control and the need for professional institutions to provide technical and equipment support, it cannot be promoted10,11.

Physical pest control refers to the process of altering the temperature, humidity, and oxygen content in the environment where paper-based cultural relics are located, thereby disrupting the physiological functions of pests on paper-based cultural relics, causing them to become infertile or die, and thus achieving the purpose of pest control and sterilization. The commonly used physical pest control methods at present mainly include vacuum nitrogen filling pest control and low-temperature freezing pest control. Among them, the vacuum nitrogen filling pest control method involves placing paper cultural relics in the cavity of vacuum nitrogen filling equipment (placement time >72 h), creating severe oxygen-deficient conditions through vacuuming, which disrupts the metabolic function of oxygen-consuming pests, thereby achieving the purpose of pest control and sterilization. This method is an environmentally friendly and safe way to kill insects and sterilize. It not only does not cause any harmful effects on paper cultural relics, but also poses no threat to the operators. Since the suitable temperature range for most pests that harm paper cultural relics is 15 to 40 degrees Celsius, when the temperature exceeds this range, it not only affects the growth and development of the pests, but in severe cases, it may even lead to their death. The low-temperature freezing pest control method takes advantage of this characteristic of pests. Paper cultural relics are placed in special cold storage or freezing equipment. A method of killing pests on paper cultural relics by using low-temperature freezing. The specific temperature setting should be determined based on the suitable temperature range for the type of pest12,13,14,15.

According to the differences in the application of insecticides and the methods of using them, chemical insecticidal methods can be divided into the application method and the fumigation method. The placement method refers to the regular and quantitative placement of anti-mold and anti-moth agents, anti-mold and insecticidal tablets, camphor essence, mothballs, and natural aromatic anti-mold and insecticidal drugs in the paper cultural relic storage room, so as to achieve the purpose of preventing mold and insect infestation16,17. This method is relatively simple to operate and has a relatively low cost, and has been widely adopted by museums, archives, libraries, etc. However, the insecticidal effect of this method is always limited and requires regular application. Moreover, among these insecticides, except for the natural aromatic anti-mold and repellent insecticides, the others all have more or less significant adverse effects on the human body. Therefore, when using them, it should be noted that staff should try to avoid staying in an environment where these drugs have been administered for a long time. Fumigation is a method that, under closed conditions, uses the vapors of volatile chemical agents such as ethylene oxide, methyl bromide, sodium fluoride, aluminum phosphide, and ozone to pass through the respiratory system of pests, causing them to be poisoned and die. It is particularly suitable for killing paper pests that are stored in paper-based cultural relic storage rooms and inhabit hidden places such as crevices and binding lines. The re-steaming method has the characteristics of quick effect and thorough results. However, this method not only has strong toxicity to those who master chemical drugs or are responsible for handling paper-based cultural relics, but also the chemicals remaining on the carriers of paper-based cultural relics pose danger and harm to the paper-based cultural relics themselves, as well as the personnel who search for and utilize the archives18,19,20.

Current pest management strategies for cultural heritage include physical, chemical, and biological methods. Physical methods, such as modified atmospheres (e.g., anoxia or hypoxia) and low-temperature freezing, are considered artifact-safe but can be time-consuming and logistically demanding6,21,22. Chemical methods, like fumigation or the use of volatile repellents, offer rapid results but raise significant safety concerns for both personnel and the artifacts themselves due to potential toxic residues16,18. Biological control, while promising for agriculture, remains largely theoretical for the enclosed spaces of archives and museums7. The limitations of existing approaches underscore the need for novel, safe, and effective strategies that combine immediate efficacy with long-term preventive action.

The application of Na2B8O13·4H2O in modern agriculture has attracted widespread attention, especially in pest control and the development of antibacterial agents23. Its mode of action is considered multi-faceted, potentially interfering with enzymatic activity, nutrient absorption, and cuticle integrity in insects24. While borates are known for their low mammalian toxicity and environmental persistence, their application in paper-based cultural heritage conservation is nascent. Our previous work has shown its efficacy as a fungistatic agent in archival containers. However, the potential for combining this chemical treatment with physical methods like vacuum to create a synergistic pest control strategy, and its secondary benefit as a buffer against paper acidification, remains unexplored.

In this study, we introduce Na₂B₈O₁₃·4H₂O into the preventive conservation of paper-based cultural relics. We first compared its insecticidal efficacy against that of other inorganic materials on key pests (L. serricorne, T. castaneum, O. surinamensis). We then investigated the synergistic effects of combining Na₂B₈O₁₃·4H₂O with different vacuum protocols (continuous vs. intermittent) to optimize treatment. To understand the underlying mechanism, we employed transcriptomic analysis to identify pathways affected in L. serricorne larvae. Finally, we evaluated the material’s potential to mitigate paper acidification by incorporating it into protective packaging and assessing its buffering capacity under simulated acidic conditions. This integrated approach aims to provide a safer, more efficient, and artifact-compatible strategy for the long-term preservation of paper-based heritage(Fig. 1).

Fig. 1: Schematic diagram of the insect prevention effect of Na2B8O13·4H2O on paper-based cultural relics.
Fig. 1: Schematic diagram of the insect prevention effect of Na2B8O13·4H2O on paper-based cultural relics.The alternative text for this image may have been generated using AI.
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A Schematic diagram of the killing effect of Na2B8O13·4H2O mixed with gas on the insect damage of paper-based cultural relics. B Scenario where Na2B8O13·4H2O penetrates the paper to form an archival box, thereby protecting the paper inside from insect damage.

Methods

Materials

Sodium octaborate tetrahydrate (Na₂B₈O₁₃·4H₂O, ≥98% purity), Titanium dioxide (TiO₂, ≥99%), Zinc oxide (ZnO, ≥99%), and Silver powder (Ag, ≥99.9%) were purchased from Sigma-Aldrich. Red lead (Pb₃O₄, ≥98%) was also obtained from Sigma-Aldrich and used solely as a toxic reference control in laboratory bioassays, not as a material intended for heritage application. Whole wheat flour and yeast were sourced locally for insect rearing.

Pest isolation and identification

Pest samples were collected from infested paper-based cultural relics in the archives of Shaanxi Normal University. Adult insects were isolated and cultured for 48 h. Species identification was performed using a stereomicroscope (Olympus SZX16, magnification 10x–40x) and an optical microscope (Olympus BX53, magnification 100x–400x), based on morphological characteristics.

Insect cultivation

Lasioderma serricorne, Tribolium castaneum, and Oryzaephilus surinamensis were isolated from the pest damage suffered by the paper cultural relics in the archives of Shaanxi Normal University. Colonies were maintained in a mixture of whole wheat flour and 5% yeast at 28 ± 1 °C and 70 ± 5% relative humidity. Third-instar larvae of L. serricorne were used for transcriptomic analysis and for experiments requiring larvae. Mixed-age adult populations were used for other bioassays.

Preparation of Na₂B₈O₁₃·4H₂O-treated paper

Archive boxes and paper samples were prepared by immersing commercial Xuan paper (Jingxuan, 30 g/m²) in a 10% (w/v) aqueous solution of Na₂B₈O₁₃·4H₂O for 30 min. The paper was then air-dried at room temperature for 48 h. The resulting loading of Na₂B₈O₁₃·4H₂O on the paper was determined by weight difference to be approximately 12–15 g/m².

Insect observation

The insects separated from the paper-based cultural relics in the collection were observed under a microscope(Olympus, HS40) for the conditions of adult insects, larvae and eggs.

The insecticidal effect of inorganic materials combined with vacuum

Put the collected larvae/pupae/adults into non-woven bags, and at the same time place 50 g of flour and 50 g of inorganic materials(TiO2, Ag, ZnO, Na2B8O13·4H2O, Pb3O4), After thorough mixing, cultivate in a vacuum environment (0.09 Mpa), and observe the growth status of tobacco shells every day.

All bioassays were conducted in a custom-built vacuum chamber (volume 20 L). To compare the insecticidal effects of inorganic materials on insects under different vacuum conditions, consistent with the above experiment, we collected 20 tobacco beetles respectively and placed them in 100 grams of inorganic materials (TiO2, Ag, ZnO, Na2B8O13·4H2O, Pb3O4) at a 1:1 ratio, adjusting the vacuum environments to 0.01 Mpa and 0.05 Mpa respectively. Observe the survival status of insects at different time points.

To compare the effect of vacuum pressure, the experiment was repeated at two vacuum levels: 0.01 MPa and 0.05 MPa. For the intermittent vacuum (cyclical) treatment, the chamber was evacuated to 0.05 MPa and held for 2 h, then backfilled with air to atmospheric pressure for 1 h. This cycle was repeated for a total of 24 h. A control group was maintained under ambient atmospheric conditions.

The protective effect of Na2B8O13·4H2O penetrating into the archive box on paper-based cultural relics

Based on the insecticidal effect of inorganic materials on pests and whether introducing inorganic materials into the packaging materials of paper-based cultural relics can provide insect-proof protection for paper-based cultural relics, we chose to penetrate the common insect repellent, Na2B8O13·4H2O, into the paper to make archive boxes and evaluate the insect-proof effect of the archive boxes on paper-based cultural relics. First, we judged the insect repellent effect of the file box on pests. We laid a layer of filter paper at the bottom of the petri dish. Then, we cut the file box into a semi-circle and placed it in the petri dish. We selected 20 tobacco beetles and Oryzaephilus surinamensis Linne respectively and placed them evenly on the plate. Observe the numbers of the two kinds of insects in each area at different time points.

$${\rm{Avoidance\; rate}}( \% )=\left[(C-T)/(C+T)\right]\times 100 \%$$
(1)

C: Check the number of insects on the filter paper

T: The number of insects in the treatment group

At the same time, to verify the pest control effect, we compared filter paper, ordinary file boxes and Na2B8O13·4H2O permeated paper file boxes with pests after contact, and observed the pest control effect at different time points.

Transcriptomic analysis

Third-instar L. serricorne larvae (20 per replicate) were exposed to a combined treatment of Na₂B₈O₁₃·4H₂O (mixed with feed at a 1:1 ratio) and intermittent vacuum (0.05 MPa, 2 h on/1 h off) for a total of 2 h. After treatment, larvae were immediately flash-frozen in liquid nitrogen. Control larvae were maintained under ambient conditions. Total RNA was extracted from three biological replicates per group. Transcriptome sequencing was performed by Meiji Biological Medicine Co., Ltd. (Shanghai, China) on an Illumina platform. Differential expression analysis was conducted using DESeq2, with genes considered differentially expressed if |log2(fold change)| ≥ 1 and adjusted p-value < 0.05. GO and KEGG pathway enrichment analyses were performed on the Majorbio cloud platform.

Acidification protection assay

The protective effect of Na₂B₈O₁₃·4H₂O-treated archive boxes was evaluated by measuring the pH of Xuan paper samples stored within. A 10% acetic acid solution (200 mL) was placed in a sealed environmental chamber (3 m³) to simulate an acidic environment. Xuan paper samples were placed inside either a standard untreated archive box or a box constructed from Na₂B₈O₁₃·4H₂O-treated paper. The pH of the paper was measured at 0, 3, 7, and 13 days using a flat-surface pH electrode (Mettler Toledo, InLab Surface) following the standard method (TAPPI T 529 om-21). Three replicates were measured for each condition at each time point.

Statistical analysis

Statistical analysis was performed using GraphPad Prism 8.0. Data are expressed as mean ± standard deviation (SD). The significance of the results was evaluated by one-way analysis of variance. A P value < 0.05 was considered statistically significant, while a P value > 0.05 indicated no statistical significance (ns).

Ethics approval and consent to participate

This article does not contain any data based on experiments in humans or animals.

Results and Discussion

Isolation and identification of pests

We systematically separated and morphologically identified pest samples from the paper artifacts in the archives of Shaanxi Normal University (Fig. 2). We observed that the adult insect possesses a slender oval body with a moderately elevated dorsal surface, covered in medium-density short soft hairs, and exhibits a semi-reclined posture. The body color is reddish-brown (Fig. 3). The larval stage is characterized by a distinct scale-like morphology, with a generally pale yellow coloration. The oocytes are predominantly regular in shape, appearing mostly oval or oblong. Based on the observation of adult insects, we determined that the main species of pests were Tribolium castaneum, Oryzaephilus surinamensis Linne, and Lasioderma serricorne. Tribolium castaneum is an omnivorous insect that feeds on paper, starch adhesives, binding fabrics, and even dried specimens of animals and plants23. Oryzaephilus surinamensis Linne likes to eat broken and damaged grains and their products. It poses a greater threat to the damaged, aged, and debris parts of cultural relics24. The larvae of Lasioderma serricorne cause extremely serious damage, and the adults basically do not feed. I like to eat cellulose, starch, and rubber compounds. This is a typical disease where larvae burrow into the interiors of paper and book covers to feed, resulting in internal cavities and leaving only tiny circular, feathered voids on the surface. Lasioderma serricorne is highly concealed. By the time it is discovered, it has often caused irreversible damage and is the number one destructive pest in libraries and archives25.

Fig. 2: Books affected by pests.
Fig. 2: Books affected by pests.The alternative text for this image may have been generated using AI.
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On the left are the actual conditions of two ancient Chinese books that have been damaged by pests; on the right are enlarged images of the damaged areas caused by the pests.

Fig. 3: A schematic diagram of different forms of pests.
Fig. 3: A schematic diagram of different forms of pests.The alternative text for this image may have been generated using AI.
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The pictures respectively show the schematic diagrams of adult, larva and egg. The first row is Tribolium castaneum, the second row is Oryzaephilus surinamensis Linne, and the third row is Lasioderma serricorne.

Synergistic insecticidal effect of Na₂B₈O₁₃·4H₂O and vacuum

Vacuum nitrogen filling treatment is widely used in the pest control experiments of paper cultural relics. Various inorganic materials, such as Na2B8O13·4H2O are also widely used in various sterilization treatments. Then, we consider whether the combination of inorganic materials and vacuum treatment can be added to the pest control of paper cultural relics. Therefore, we compared the pest control effects of multiple inorganic materials combined with other inorganic materials. In our previous research, we found that Na2B8O13·4H2O can effectively inhibit the occurrence of microorganisms. Table 1 shows that when various inorganic materials are combined with vacuum, they all exhibit significant insecticidal effects, and the results are significantly better than those of the blank control group. Na2B8O13·4H2O shows the fastest and strongest lethal ability, achieving a 100% pest killing rate on the fourth day of the experiment, which is the highest insecticidal efficiency among all materials. ZnO and Ag also demonstrated excellent final effects, achieving a 100% mortality rate on the fifth day. While all tested materials showed improved efficacy over the control (vacuum alone), Na₂B₈O₁₃·4H₂O demonstrated the fastest and most complete activity, achieving 100% mortality of a mixed-insect population by day 4. ZnO and Ag achieved 100% mortality by day 5. The effect of vacuum pressure on efficacy was assessed (Table 2). At a lower vacuum (0.01 MPa), the control group mortality was only 50% by day 7. In contrast, the Na₂B₈O₁₃·4H₂O group reached 100% mortality by day 7, while the Pb₃O₄ group showed a rapid initial knock-down effect (75% mortality by day 5). At the higher vacuum (0.05 MPa), control mortality increased to 90% by day 7.

Table 1 The killing effect of inorganic materials on microorganisms under vacuum combined treatment conditions
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Table 2 Microbial killing effects of inorganic materials under combined treatment conditions of different pressures and vacuums
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To explore the killing effect of inorganic materials and vacuum pressure on tobacco cardamom, we compared the inhibitory effects of inorganic materials on tobacco cardamom under different vacuum pressures (Table 2). Under the condition of low vacuum (0.01 MPa), the mortality rate of the control group only reached 50% on the seventh day, with a slow insecticidal speed and incomplete effect. The effect of Na2B8O13·4H2O and vacuum results is the most prominent. The mortality rate starts from the first day, reaches 80% by the sixth day, and is 100% killed by the seventh day. The initial effect of Pb3O4 combined with a vacuum is the strongest. The mortality rate reached 75% on the fifth day, significantly higher than that of all other groups during the same period. Demonstrate a powerful and rapid knockdown ability. 100% killed on the 7th day. The ZnO effect is stable and reliable. The mortality rate reached 80% on the 6th day, and 100% was killed on the 7th day. The overall performance was lower than the above two, but far better than that of the control group. Under high vacuum (0.05 MPa), the mortality rate of the control group reached 90% on the seventh day. This indicates that merely increasing the vacuum from 0.01 MPa to 0.05 MPa can significantly raise the natural mortality rate (death due to hypoxia) from 50% to 90%. Vacuum degree is the key to pest control. Inorganic materials mainly exert effects on pests through chemical toxicity, metabolic interference and drying, but this process is slow and does not kill microorganisms too quickly. In a vacuum environment, a low-oxygen environment is mainly created, which leads to the suffocation of pests. The killing of pests in this process is rapid. The application method (continuous vs. intermittent vacuum) was compared. As shown in Table 3, while continuous vacuum combined with Na₂B₈O₁₃·4H₂O achieved 100% mortality by day 2, the intermittent vacuum (cyclical) treatment accelerated this process, achieving 100% mortality for all four tested pest species within 24 h. This effect was consistent across both vacuum pressures (0.01 and 0.05 MPa) for the intermittent protocol.

Table 3 The killing effect of inorganic materials on microorganisms under the combined treatment conditions of different pressures and vacuum
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To compare whether the introduction of inorganic materials would deal with pests in different vacuum environments, we chose continuous vacuum and intermittent vacuum (cyclic type) to compare the insecticidal efficiency in different environments. Table 3 results show that in a continuous vacuum environment, within two days, Tribolium castaneum, Oryzaephilus surinamensis Linne, Lasioderma serricorne, and the control group of the four insects, Trogoderma variabile, maintained a 100% survival rate. The circulating vacuum was maintained for 2 h under vacuum and 1 h under normal pressure, and the cycle was repeated. In a cyclic intermittent vacuum environment, 100% of four types of pests can be killed within one day. Intermittent vacuum circulation can cause drastic pressure changes in a short period of time, leading to boiling of the body fluids of pests, tearing of stomata and tissue damage. Each time the dry air is backfilled, it will accelerate the evaporation of water in the pests’ bodies26. Under different pressures of circulating vacuum, no obvious differences were observed, and all insects could be killed within one day.

The archive box is the smallest unit of paper-based cultural relic packaging. Then, can the introduction of inorganic materials enhance the insect-proof effect of the archive box? We designed an attraction and avoidance experiment, as shown in Fig. 4A. We placed the control group and the detection group on both sides of the petri dish division, respectively, and observed the pests staying there at different times. As shown in Fig. 4B, Oryzaephilus surinamensis Linne was found on both the common archival protection paper and the paper permeated with Na2B8O13·4H2O. It can be seen that compared with the filter paper in the control group, insects were evenly surviving on both the common paper and the filter paper. Almost all the pests in the Na2B8O13·4H2O group are on the surface of the filter paper. Fig. 4C quantitative data results show that Na2B8O13·4H2O has a strong and sustained repellent effect on Oryzaephilus surinamensis Linne. During the 24-hour observation period, the pest repellent rate of the Na2B8O13·4H2O treatment group was significantly higher than that of the control group. It is proved that this inorganic material can effectively prevent the Oryzaephilus surinamensis Linne pest from approaching the protected area. In the Na2B8O13·4H2O treatment group, pests showed a strong avoidance behavior at the beginning and almost completely avoided entering or staying in the treatment area. It is speculated that Na2B8O13·4H2O may affect the olfactory perception or central nervous system of Oryzaephilus surinamensis Linne by releasing some interfering chemical signals, thereby triggering its inherent avoidance instinct. However, the control group showed a repellent rate below 0, and a negative repellent rate occurred. This indicates that ordinary archive protection paper has no repellent effect on pests and may even attract insects to gnaw on it. As shown in Fig. 4D, Lasioderma serricorne found that insects were evenly distributed on both the ordinary archive protection paper and the Na2B8O13·4H2O permeated paper. It can be seen that in the control group, insects were evenly distributed on both the ordinary paper and the filter paper, while in the Na2B8O13·4H2O group, almost all pests were on the surface of the filter paper. Fig. 4E quantifiable data results. The same effect was also demonstrated in Lasioderma serricorne. Throughout the entire 24 h, the treatment group had a repellent effect on insects. The repellent effect was the strongest at 2–4 h, and the repellent rate reached 100%. Over time, the repellent rate of insects showed a sustained ability. The approach and avoidance rates of the control group still showed 0 and negative numbers. The results suggest that after Na2B8O13·4H2O penetrates into the paper, it has a relatively good repellent effect and can effectively repel pests. Figure E shows the distribution of ordinary file boxes and insects permeated with Na2B8O13·4H2O on their surfaces. It can be seen that insects are evenly distributed in the ordinary file boxes, while no insects are found in the file boxes permeated with Na2B8O13·4H2O on the paper. All the insects are hidden in the feed below.

Fig. 4: The repellent effect of Na2B8O13·4H2O on insects after penetrating into paper.
Fig. 4: The repellent effect of Na2B8O13·4H2O on insects after penetrating into paper.The alternative text for this image may have been generated using AI.
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A Schematic diagram of the insect approach and avoidance model; B Results of the approach and avoidance experiment of Oryzaephilus surinamensis Linne; C Quantification of the approach and avoidance experiment results of Oryzaephilus surinamensis Linne; D Results of the Lasioderma serricorne approach and avoidance experiment; E Quantification of the results of the Lasioderma serricorne approach avoidance experiment; F Pest attraction and avoidance of different paper-based cultural relics protection papers.

We conducted a detailed experiment on the repellency rate of pests, as shown in Table 4. After the control group was exposed for 2 hours and 4 hours, negative repellency rates (−40%, −70%) were displayed, indicating that Oryzaephilus surinamensis Linne was more inclined to remain in the ordinary paper area. That is, ordinary paper has no repelling effect on it. In fact, it may even attract pests due to its starch and fiber material. In the early stage of the experiment, we evenly distributed pests on ordinary paper and the paper after Na2B8O13·4H2O penetration. Some data points were 0% or lower positive values (10%, 15%), indicating that insects had no obvious preference for ordinary paper during the experimental stage. In the paper treatment group after Na2B8O13·4H2O penetration, the chemotactic rate remained consistently high positive, and the results were stable. At all time points and in all experimental repetitions, the chemotactic rate was always positive and concentrated in the high range of 20%–80%. The chemotactic rate reached 20%–70% at 2 h and 40%–70% at 4 h. The approach and avoidance rate reached 60% to 80% within 6 h, and remained stable at 70% within 24 h. The experimental results suggest that treating Na2B8O13·4H2O onto paper can endow the carrier with powerful and sustained pest repellent properties, and it can be widely used as insect-proof lining paper for paper cultural relics or as file folders.

Table 4 Attractant and repellent rates of Oryzaephilus surinamensis Linne with common paper and Na2B8O13·4H2O after penetration
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The repellency of Na₂B₈O₁₃·4H₂O-treated paper was evaluated. For O. surinamensis, the avoidance rate was high across all time points, reaching 80–100% within 6 h (Fig. 4, Table 4). In contrast, untreated paper showed no repellent effect, even displaying slight attractiveness at later time points. A similar, even stronger repellent effect was observed for L. serricorne, with avoidance rates reaching 100% within 2 h of exposure (Fig. 4, Table 5). The contact toxicity of the treated paper was also assessed. Mortality of L. serricorne was significantly higher on treated paper compared to controls after both 12 h (p < 0.01) and 24 h (p < 0.01), reaching 15–20% by 24 hours (Fig. 5).

Fig. 5: Contact insecticidal effect of ordinary paper and Na2B8O13·4H2O on insects after penetration.
Fig. 5: Contact insecticidal effect of ordinary paper and Na2B8O13·4H2O on insects after penetration.The alternative text for this image may have been generated using AI.
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A Diagram of the effect of Na2B8O13·4H2O penetrating paper on the attraction and avoidance of tobacco armor; Quantification of the effect of Na2B8O13·4H2O on the uptake and avoidance of tobacco A for 12 hours (B) and 24 hours (C).

Table 5 The attractant and repellent rates of Lasioderma serricorne with ordinary paper and Na2B8O13·4H2O after penetration
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Table 5 shows the repellent rates of Lasioderma serricorne and the paper after penetration with ordinary paper and Na2B8O13·4H2O. In the ordinary paper group, the repellent rates of insects at 2 h and 4 h were 0%, indicating that in the early stage of the experiment, Lasioderma serricorne had no definite preference between the treatment group area and the control group area, and the paper itself had no attractive effect. In the long-term effects of 6 hours and 24 hours, the approach and avoidance rates became significantly negative (−60%, −40%). This indicates that with the extension of exposure time, Lasioderma serricorne tends to gather in the area of common paper, that is, common paper has a slight attraction effect on Lasioderma serricorne. This might be because of the uniform insect distribution in the early stage of the experiment, and this environment has no obvious repellent effect on insects. The odors released by components such as cellulose or starch in paper accumulate over time to form an attractive source, suggesting that ordinary paper cannot repel Lasioderma serricorne and may increase the risk of pest accumulation in long-term contact. It is completely unsuitable as an insect barrier for paper-based cultural relics. In the repeated experiments of the Na2B8O13·4H2O penetration paper treatment group at all time points (2 h, 4 h, 6 h, 24 h), the chemotactic rate was always positive (80–100%). The chemotactic rate reached 80–100% at 2 hours, and it reached 100% in multiple repetitions at 6 hours and 24 hours. That is, all Lasioderma serricorne completely avoided the processing area, suggesting that the processed paper had a good chemotaxis effect on Lasioderma serricorne, and the chemotaxis effect took effect quickly (2 hours), had high strength, and could be maintained for a long time, demonstrating good chemotaxis performance. This provides experimental data for the development of new types of cultural relic protection materials, such as insect-proof lining paper, letter covers, and pads.

We evaluated the contact insecticidal effect of paper with Na2B8O13·4H2O on tobacco armor, as shown in Fig. 5A. We took blank filter paper as the control group, and compared the contact insecticidal rates of ordinary archive packaging paper and paper with Na2B8O13·4H2O on tobacco armor in the ordinary group. After the corresponding paper was laid on the corresponding dishes, We evenly placed the insects on the corresponding papers and observed the survival of the pests on the papers for 12 h and 24 h. As shown in Fig. 5B, the mortality rates in Control and Normal were extremely low, with the bar chart height approaching the 0% limit. This indicates that in the natural state, the mortality rate of Lasioderma serricorne within 12 hours in Control and Normal was very low, while the mortality rate significantly increased (10–15%) in the treatment group. The bar chart was significantly higher than that of the control group, and the difference was significant compared with the control group (p < 0.01). The results suggest that Na2B8O13·4H2O exerts a significant toxic effect in the early stage of exposure. Within 24 h, the mortality rate of the control group did not increase significantly (Fig. 5C), while the exposure rate of the treatment group was 15–20%, which was significantly different from that of the control group (p < 0.01). The results suggest that after Na2B8O13·4H2O is introduced into paper, it can effectively repel and continuously kill insects, creating an ideal physical-chemical dual barrier for the preservation of paper-based cultural relics.

Transcriptomic analysis of L. serricorne Larvae

To understand the molecular mechanism of the combined treatment, RNA-seq was performed on L. serricorne larvae. A total of 87 differentially expressed genes (DEGs) were identified between the treated and control groups, with 54 up-regulated and 33 down-regulated (Fig. 6A, B). GO enrichment analysis showed that DEGs were significantly enriched in processes related to chitin-based cuticle development, carbohydrate transport, and serine hydrolase activity (Fig. 6C). KEGG pathway enrichment analysis revealed that the treatment affected multiple pathways, including those involved in amino acid metabolism (e.g., valine, leucine, and isoleucine degradation), insect hormone biosynthesis, and fatty acid metabolism (Fig. 6D, E).

Fig. 6: Analysis of differentially expressed genes between the Control group and the Na2B8O13·4H2O treatment group.
Fig. 6: Analysis of differentially expressed genes between the Control group and the Na2B8O13·4H2O treatment group.The alternative text for this image may have been generated using AI.
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A Bar chart of differential metabolism of tobacco nail larvae; B Cluster analysis of tobacco nail larvae. Red indicates a higher expression level in the sample, while blue indicates a lower expression level. C Functional annotation analysis of the GO database for tobacco nail larvae; D Functional annotation analysis of KEGG database for tobacco nail larvae; E Functional enrichment analysis of KEGG database for tobacco nail larvae.

The adults of Lasioderma serricorne hardly feed and only need a small amount of water. Their main task is mating and reproduction. The larva is the only stage in its entire life history that actively and massively feeds. They will directly bore into paper, archives, books, tobacco, Chinese medicinal materials, etc., causing direct physical damage (wormholes, tunnels). Larvae like to burp into objects to feed. Their activities are concealed and hard to detect in time27,28,29,30. They are often only discovered after serious damage has been caused. At the same time, the larva is the stage that is most resistant to environmental stress and pesticides. Therefore, the larvae of our tobacco nail were subjected to transcriptome analysis after being treated with Na2B8O13·4H2O in a vacuum environment. Differential table analysis was conducted using DESeq2. Genes that met the condition of P adjust<0.05 & log2FC ≥ 1 were considered as differentially expressed genes. As shown in Fig. 6A, 87 differentially expressed genes (54 up-regulated genes) were screened out between the Control group and the Na2B8O13·4H2O group in tobacco conch larvae. Down-regulating gene 33. Heat map cluster analysis was conducted on all differentially expressed genes. The results showed that the three samples of tobacco beetle adults and larvae in the Control group and the three samples in the Na2B8O13·4H2O treatment group were significantly separated, indicating good repeatability within the experimental group and large differences between groups. The experimental data are stable and reliable and can be used for further analysis (Fig. 6B). Functional annotation and enrichment analysis of differentially expressed genes in tobacco nail larvae between the Na2B8O13·4H2O treatment and the control group were conducted using the GO database and the KEGG database. GO functional annotation analysis revealed that the differentially expressed genes in larvae were significantly involved in the three major categories of biological processes, cellular components, and molecular functions. In the finer secondary classification as shown in Fig. 6C, the biological processes of differentially expressed genes in larvae include chitin-based cuticle development (10) and Carbohydrate transport (3). The cellular components include Chitin-based extracellular matrix (9) and Cytosol (10), and the molecular functions include structural components of chitin-based larval cuticle (9). Sugar transmembrane transporter activity (3), Serine hydrolase activity (4), Serine-type endopeptidase activity (4). The epidermis of insect larvae is mainly composed of chitin and protein, which is a key structure for protecting the body, preventing water loss, and physical damage. Na2B8O13·4H2O treatment may have inhibited the expression of the chitin synthase gene or activated the expression of the chitin (chitin degradation) gene, resulting in the larvae being unable to form or maintain a tough epidermis normally. This will make the larvae vulnerable, prone to water loss, more susceptible to physical damage and pathogen invasion, and eventually lead to death31,32. In biological processes, sugars are the main source of energy for insects. The enrichment of this pathway indicates that the treatment severely interferes with the energy substance transport system within the larva. Affecting carbohydrate transport may lead to insufficient energy supply between cells or tissues, influencing all energy-consuming physiological processes such as growth and development, exercise, and detoxification, and triggering a comprehensive energy crisis. The main components of the damaged cells are abnormalities in the extracellular matrix and cytoplasm. It is indicated that the treatment will affect the most fundamental and core metabolic environment within the cells of tobacco nail larvae. A large amount of basal metabolism that occurs in the cytoplasm (such as glycolysis and protein synthesis) may be disrupted33,34. Serine hydrolase is a large family of enzymes, including many important digestive enzymes (such as trypsin, chymotrypsin), lipases, and neurolipases. Na2B8O13·4H2O may inhibit the digestive enzyme activity of larvae, preventing them from effectively digesting food to obtain nutrients. More notably, it may interfere with the function of acetylcholinesterase, an important enzyme in the nervous system (also a serine hydrolase), but this requires further verification. Extensive inhibition of enzyme activity can lead to the collapse of the metabolic network. Comprehensive analysis shows that Na2B8O13·4H2O destroys the physical barrier (epidermis) that the larvae rely on for survival, interferes with the sugar transport system of the larvae, interferes with the activity of digestive enzymes at the site, cuts off the energy and nutrient supply of the larvae, and causes them to fail from the inside. At the same time, it causes disorders in the basal metabolism of larvae, involving oxidative stress and imbalance of protein homeostasis.

KEGG annotations show Global and overview maps, Carbohydrate metabolism, Amino acid metabolism, Lipid metabolism, Energy metabolism (Fig. 6D). The category “Global and overview maps” contains an overview map of all core metabolisms. Its high enrichment is the strongest signal, directly demonstrating that the processing has triggered extensive reprogramming or dysregulation of the entire metabolic network. Corresponding to the “sugar transport” in GO analysis, it directly affects the fundamental source of energy. Amino acid metabolism is at the core of protein synthesis, decomposition, and energy supply. Lipid metabolism affects cell membrane structure, energy storage, and hormone precursor synthesis. The influence of Transcription means that cells cannot correctly respond to internal and external signals to synthesize essential RNA. Folding, sorting, and degradation mainly refer to the post-translational processing and degradation of proteins. Its disorder can lead to the accumulation of incorrect proteins and dysfunction of organelles (such as endoplasmic reticulum stress). Signal transduction, Signaling molecules, and interactions involve abnormal cell signal transduction and cell communication. Metabolism of cofactors and vitamins, Metabolism of terpenoids and polyketides, Transport and catabolism. Aging prompts the handling of specific metabolic and stress responses that affect cells.

KEGG pathway enrichment analysis revealed that Na₂B₈O₁₃·4H₂O treatment comprehensively disrupted the core metabolic network of tobacco nail larvae, with the effects concentrated on key life processes such as energy metabolism, amino acid metabolism, lipid synthesis, and hormone synthesis (Fig. 6E). Valine, leucine and isoleucine degradation, Glycine, serine and threonine metabolism, Propanoate metabolism beta-Alanine metabolism. These are the key amino acid catabolism pathways. Branched-chain amino acids (valine, bright, isbright) and serine, etc. are precursors for insects to generate energy through gluconeogenesis or to be converted into other important substances. The enrichment of these pathways (typically indicating that the expression of related genes is significantly upregulated or downregulated) suggests that the treatment forces the larvae to break down their own proteins (amino acids) in large quantities to obtain energy, which is a “self-rescue” response in a state of hunger or stress. This directly confirms the conclusion of the “energy transport” disorder in the GO analysis, indicating that the larvae are in a severe state of negative energy balance and protein consumption. Insect hormone biosynthesis, Terpenoid backbone biosynthesis indicates that the key pathways for the growth, development and metamorphosis of larvae are blocked, mainly including juvenile hormones and molting hormones, which precisely regulate the growth, development, molting and metamorphosis of larvae. Terpene skeletons are essential precursors for the synthesis of these hormones35,36. The effects of the Fatty acid elongation, Fatty acid degradation, and Steroid biosynthesis pathways suggest that the lipid homeostasis of the treated larvae is disrupted, affecting the synthesis of new cell membranes, cell membrane fluidity and function, and interfering with energy storage. Obstruction of Folate biosynthesis can seriously affect cell division and tissue growth, which is fatal during the rapidly developing larval stage. The influence of Metabolic pathways suggests that the effect of Na₂B₈O₁₃·4H₂O is not local but rather triggers a global, networked metabolic disorder. By integrating all the pathways, the toxic mechanism of Na₂B₈O₁₃·4H₂O can be analyzed by affecting the cell membrane and signal transduction, including signal disorder leading to hormone synthesis and hindering chitin synthesis, thereby initiating the cell death program. This involves a series of systemic poisoning triggered by multiple targets.

Protection against acidification

The pH of Xuan paper stored in a standard archive box decreased steadily over 13 days when exposed to an acidic atmosphere, reaching pH 6.0 by the end of the experiment. In contrast, paper stored in the Na₂B₈O₁₃·4H₂O-treated archive box maintained a stable pH, significantly higher than the control at all time points (p < 0.01), demonstrating a strong buffering effect (Fig. 7A). The occurrence of pests will accelerate the acidification and physical damage of paper, and acidification in turn promotes the occurrence of pests. At room temperature, Xuan paper was placed in a regular file box and a file box treated with Na₂B₈O₁₃·4H₂O, as shown in Fig. 7A. In the control group, the pH value of the paper in the regular file box showed a significant and continuous downward trend over time (0–13 days). On the 13th day, the pH value may have dropped to a relatively low level (pH 6.0), and the paper is in a clearly acidified state, with an extremely high risk of long-term storage. In the Na₂B₈O₁₃·4H₂O treatment group file box, the pH value showed an extremely stable trend over time. The curve was almost parallel to the time axis and was always significantly higher than that of the control group in the same period. This indicates that the file box processing group effectively blocked or neutralized the external acidic gas. Na₂B₈O₁₃·4H₂O, as a weakly basic substance, its borate ions may actively react with the acidic gas that penetrates in, “fixing” it and preventing it from coming into contact with and acidifying the paper. This directly verifies its theoretical function as an “acidic gas neutralizer”.

Fig. 7: Protection of paper in an acidic environment after Na₂B₈O₁₃·4H₂O treatment.
Fig. 7: Protection of paper in an acidic environment after Na₂B₈O₁₃·4H₂O treatment.The alternative text for this image may have been generated using AI.
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A The influence of two types of archive packaging materials on the pH value of the paper inside the packaging; B The protective effect of the two types of archive packaging materials on the interior of the paper after superimposition.

This study presents a comprehensive evaluation of Na₂B₈O₁₃·4H₂O as a multi-functional material for the preservation of paper-based cultural heritage. Our results demonstrate that Na₂B₈O₁₃·4H₂O is a highly effective insecticidal agent, and its combination with intermittent vacuum treatment provides a synergistic, rapid, and artifact-safe method for pest eradication. Furthermore, its ability to be incorporated into paper-based packaging to confer both repellent properties and acid-buffering capacity positions it as a promising component of integrated preventive conservation strategies. The superior insecticidal activity of Na₂B₈O₁₃·4H₂O compared to other inorganic materials is consistent with previous reports on its efficacy against a range of pests37,38. Our data suggest that its effectiveness is enhanced by vacuum, likely through a combination of modes of action. The transcriptomic analysis provides insight into this mechanism, revealing that treatment with Na₂B₈O₁₃·4H₂O under vacuum disrupts several critical biological pathways in L. serricorne larvae. The enrichment of genes involved in chitin-based cuticle development suggests that the material interferes with the synthesis or integrity of the exoskeleton, a known target of some borates39. Concurrent disruption of carbohydrate transport and amino acid metabolism indicates a systemic energy crisis, while the downregulation of pathways related to insect hormone biosynthesis (e.g., juvenile hormone and ecdysone) likely interferes with normal development and molting. This multi-targeted mode of action is a significant advantage, as it may reduce the likelihood of pests developing resistance. The observed synergistic effect of intermittent vacuum is noteworthy. While continuous vacuum alone induces death via hypoxia, the cyclical pressure changes likely impose additional physical stress. Rapid decompression and recompression can cause physical damage to insects, including the rupture of tracheal systems and the boiling of hemolymph at low pressures13. The combination of this physical stress with the metabolic and structural disruption caused by Na₂B₈O₁₃·4H₂O resulted in the rapid 100% mortality observed within 24 hours. This offers a practical advantage, as it is significantly faster than many conventional treatments that can take several days or weeks. A key finding of this study is the dual functionality of the Na₂B₈O₁₃·4H₂O-treated paper. The material not only acts as a potent repellent, effectively creating a barrier that pests avoid, but also exhibits contact toxicity. The near-complete avoidance of the treated paper by both O. surinamensis and L. serricorne demonstrates its potential as an insect-proof lining for shelves, boxes, or folders. This active repellent effect is a significant improvement over inert barrier materials. Furthermore, the treated paper’s capacity to maintain a stable pH in an acidic environment is an unexpected but highly valuable property. This buffering effect is likely due to the alkaline nature of the borate salt, which can neutralize penetrating acidic gases (e.g., acetic acid from off-gassing of materials or pollutants)14. This finding is particularly important as acidification is a primary mechanism of cellulose degradation, and the byproducts of pest activity can themselves be acidic, accelerating the deterioration process. Therefore, the material offers a dual protective function: actively repelling pests and passively mitigating acidification. While the results are promising, several limitations should be acknowledged. First, the long-term effects of Na₂B₈O₁₃·4H₂O on the mechanical and optical properties of the paper substrate were not assessed. Although borates are generally considered compatible with cellulose, a systematic evaluation of potential yellowing, embrittlement, or changes in tensile strength after extended aging is necessary. Second, the safety of borates for human health is a consideration, as they are classified as reproductive toxins. While the material is intended to be incorporated into passive packaging, its application must be managed with appropriate handling protocols. Third, the scalability of the proposed treatment is a practical consideration. While the vacuum treatment is effective for individual objects or small collections, implementing it on a large scale would require specialized infrastructure. Future work should focus on long-term stability studies, toxicity risk assessments for both handlers and the artifacts, and the development of practical protocols for the integration of Na₂B₈O₁₃·4H₂O-treated materials into existing storage systems.

This study demonstrates that Na₂B₈O₁₃·4H₂O is a promising multi-functional material for the conservation of paper-based cultural heritage. Its combination with intermittent vacuum treatment provides a rapid and synergistic method for pest eradication. When incorporated into paper-based packaging, Na₂B₈O₁₃·4H₂O effectively repels key insect pests and provides a significant buffering capacity against acidification. Transcriptomic analysis reveals a multi-targeted mode of action, disrupting chitin synthesis, energy metabolism, and hormonal regulation in pest larvae. This integrated approach, combining chemical and physical pest management with preventive environmental control, offers a novel and comprehensive strategy for safeguarding paper-based collections.