Modulation inducer for silkworm spinning movement and preventive agent for viral diseases

Abstract

To provide an inexpensive agent and sericulture technique, even when metabolism of silkworms is forcibly reduced by storing them in a low-temperature environment for a long period of time (e.g., at 5°C for 3 days), effectively preventing onset of viral disease in silkworms, and capable of changing the thickness of acquired cocoons by modulating the metabolism of the silkworms and changing a spinning speed.SOLUTION: A sericulture technique includes feeding silkworms with powder of rice chaff or stems (rice straw) containing naturally-derived amorphous silica whose amorphization is advanced by reducing two characteristic peaks of naturally-derived silica at diffraction angles of 9° and 35° obtained by X-ray diffraction measurement, to a trace level by physical pulverization, causing them to digest and absorb the naturally-derived silica, and enhancing resistance of the silkworms to viral diseases.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the discovery of an agent that is effective in preventing the onset of viral diseases when mixed with mulberry leaves or artificial feed and fed to silkworms raised in the sericulture industry.The present invention also relates to the discovery of an agent that induces changes in silk-spinning behavior of silkworms and enables them to produce silk of different thicknesses when mixed with mulberry leaves or artificial feed and fed to silkworms. [Background technology]

[0002] Until now, viral diseases in silkworms have been prevented by disinfecting silkworm rooms, but this does not completely remove the viruses attached to the eggs. As a result, silkworms live in coexistence with the viruses, and there has been a problem in that they develop viral diseases when exposed to environmental stress, particularly when placed in a low-temperature environment for a long period of time (for example, when 5th-instar raised silkworms were exposed to a low-temperature environment of 5°C for 24 hours, they died of nuclear polyhedrosis (Non-Patent Document 1)). When a viral disease occurs, there is no option but to incinerate all the silkworms being bred, and so there has been a demand for the development of an inexpensive agent to prevent viral diseases. On the other hand, in order to improve the feel and texture of silk products, there has been a demand for finer cocoon thread. In this case, the only option is to improve the breeding of silkworms, which requires a lot of labor, time, and money. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Fujiyoshi Matsubara, The world's first factory-wide year-round sericulture using an artificial feed and aseptic rearing method, Vicom Co., Ltd., 2012, 116 pages. [Non-Patent Document 2] Hamamura, Y., Feeding mechanism of silkworm and artificial diet. Chemistry and Biology, Vol. 1, No. 7, pp. 364-370, 1963. [Non-Patent Document 3] O. Tsutsui, R. Sakamoto, M. Obayashi, S. Yamakawa, T. Handa, D. Nishio-Hamane, I. Matsuda, Light and SEM observation of opal phytoliths in the mulberry leaf. Flora, vol. 218, pp. 44-50 (2016). [Non-Patent Document 4] Shinichiro Asano, Masashi Iwanaga, Insect Factory, Silkworm Experiments, Edited by the Japanese Society of Sericulture, NTS Co., Ltd., 2019, 295 pages. Summary of the Invention [Problem to be solved by the invention]

[0004] To develop an inexpensive agent that is effective in preventing viral diseases in silkworms even when the silkworms are forcibly stored in a low-temperature environment for a long period of time, thereby slowing down their metabolism. To develop an inexpensive agent that can change the silkworms' metabolism, change their spinning speed, and change the thickness of the resulting cocoon thread. [Means for solving the problem]

[0005] Although silica has no nutritional value, it has been reported that silkworms continuously consume cellulose coated with silica gel (SiO2·nH2O) (Non-Patent Document 2). Meanwhile, an analysis of mulberry leaves, which are the staple food of silkworms, has reported the accumulation of phytoliths (amorphous silica) (Non-Patent Document 3). Based on these findings, it was thought that amorphous silica may have some effect on silkworms. Silkworms have traditionally been raised by feeding them mulberry leaves, but the mulberry leaves supplied as food are not disinfected because this would kill the silkworms, and the silkworms grow by eating mulberry leaves that may be contaminated with viruses. However, the onset of viral diseases in silkworms has been significantly suppressed. Thinking that this might be related to the plant opal in mulberry leaves, the researchers focused on rice husks and stalks as an inexpensive and safe source of silica. They physically crushed the silica contained in them to make it completely amorphous, and then mixed it into silkworm feed and had the silkworms eat it. They found that even when the silkworms' metabolism was forcibly slowed down by storing them in a low-temperature environment for a long period of time (5°C, 72 hours) or by suffocating them in water at room temperature for two hours, the silkworms hardly developed viral diseases. This showed that natural silica that has been completely amorphous through physical crushing is effective in preventing the onset of viral diseases, leading to the present invention. On the other hand, it was found that when natural silica contained in rice husks and stalks is heat-treated at 400°C to 600°C, the natural silica is thermally denatured and the X-ray crystal diffraction peak of natural silica disappears. It was thought that the absorption of thermally amorphized silica might induce changes in the metabolism of silkworms, so rice husks and stalks containing natural silica that had been heat-treated at 400°C to 600°C were crushed into edible pieces and mixed with silkworm feed for raising the silkworms. When the resulting cocoons were examined, it was found that it was possible to produce cocoon threads of different thicknesses from the same variety of silkworm, which led to the present invention. Effect of the Invention

[0006] By preventing the onset of viral diseases in the sericulture industry, it is expected that the efficiency of cocoon production will improve. Even if the silkworms are of conventional varieties, the thickness of the obtained cocoon thread can be changed by feeding the heat-treated silica of the present invention to the silkworms without breeding them. Furthermore, by using this cocoon thread, it is possible to improve the texture and feel of silk fiber products, and the development of the textile industry that handles silk is expected. On the other hand, insects such as silkworms are the most evolved higher eukaryotes among invertebrates, and have many metabolic systems similar to those of humans. Therefore, using silkworms as insect factories, porcine circovirus disease vaccines (Germany: Boehringer Ingelheim), interferon for dogs and cats (Toray), tick desensitization therapy drugs for dogs (Nippon Zenyaku Kogyo), human papillomavirus vaccines (UK: GlaxoSmithKline), prostate cancer immunotherapy drugs (US: Dendreon), and influenza vaccines (US: Protein Science) are being developed and sold (Non-Patent Document 4). The knowledge gained in the present invention regarding the metabolic changes of silkworms caused by amorphous natural silica is expected to be a step towards the development of new therapeutic drugs in the fields of veterinary medicine and medicine in the future. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing the disappearance of peaks derived from natural SiO2 by physical crushing treatment of rice husk (Example 1). [Diagram 2] FIG. 1 shows the disappearance of the peak derived from natural SiO2 by physical crushing treatment of rice straw (Example 2). [Diagram 3] FIG. 1 shows the disappearance of peaks derived from natural SiO2 by heat treatment of rice husk at 500°C (Example 3). [Figure 4] This is a diagram showing the change in the lengthwise fineness of the cocoon filaments from the outside to the inside of a cocoon obtained from a silkworm that was fed an artificial diet containing powder of rice husks heat-treated at 500°C (Example 3). [Diagram 5] This is a diagram showing the change in the lengthwise fineness of the cocoon filaments from the outside to the inside of a cocoon obtained from a silkworm that was fed mulberry leaves that had been directly sprinkled with powder of rice husks that had been heat-treated at 500°C. (Example 4). [Figure 6] This is a diagram showing the change in the lengthwise fineness of the cocoon filaments from the outside to the inside of a cocoon obtained by feeding only mulberry leaves to mature silkworms from the 4th to 5th instars (Comparative Example 2). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0008] When rice husks were physically crushed and the diffraction intensity curve was measured by wide-angle X-ray diffraction, the peak derived from SiO2 before crushing disappeared as shown in Figure 1, and rice husk powder containing amorphous fine powder silica was obtained. The rice husk powder was mixed into artificial feed (product name: Kuwanohana for 1st instar) at 10% by weight, and 15 5th instar larvae (variety name: Gunma 200) were fed the mixture to produce mature silkworms. The mature silkworms were then stored in an incubator at 5°C for 3 days to reduce their strength and induce viral diseases, and 14 of the 15 silkworms survived and formed cocoons. The survival rate was 14 / 15 = 93.3%. EXAMPLES

[0009] When rice straw was physically crushed and the diffraction intensity curve was measured by wide-angle X-ray diffraction, the peak derived from SiO2 before crushing disappeared as shown in Figure 2, and rice straw powder containing amorphous fine powder silica was obtained. The rice straw powder was mixed with artificial feed (product name: Kuwanohana for 1st instar) at 5% by weight, and 50 5th instar larvae (variety name: Gunma 200) were fed the feed to produce mature silkworms. The mature silkworms were then stored in an incubator at 5°C for 3 days to reduce their strength and induce viral diseases, and 49 of the 50 silkworms survived and formed cocoons. The survival rate was 49 / 50 = 98.0%. Comparative Example 1

[0010] Twenty-five 5th instar larvae (variety: Gunma 200) were fed only artificial feed (product name: Kuwana no Hana for 1st instar) to produce mature silkworms. The mature silkworms were then stored in a 5°C incubator for 3 days to weaken them and induce viral diseases, but all of the silkworms died and no survival was confirmed, and no cocoons were obtained. Example 3

[0011] When rice husks are heat-treated at 500°C, the two characteristic peaks at diffraction angles of 9° and 35°, which are derived from natural silica, disappear due to thermal denaturation, while the diffraction peak at a diffraction angle of around 3° increases significantly, as shown in Figure 3. The rice husks containing the heat-denatured silica were physically crushed as needed and mixed with 10% by weight of commercially available artificial feed for silkworms (product name: Kuwanohana for 2nd instars), which was then fed to 5th instar larvae (variety name: Gunma 200) to mature silkworms and produce cocoons. The cocoons were boiled as usual, and the change in the lengthwise fineness of the cocoon threads from the outer layer to the inner layer was measured, resulting in the change in fineness shown in Figure 4. It was possible to produce cocoons in which the fineness of the cocoon threads significantly decreased from the outer layer to the inner layer. Example 4

[0012] Rice husks containing silica, which had been thermally denatured by heat treatment at 500°C and had the two characteristic peaks at diffraction angles of 9 degrees and 35 degrees specific to natural silica disappear, while the diffraction peak at a diffraction angle of around 3 degrees had increased dramatically, were physically crushed as appropriate and sprinkled directly on mulberry leaves, which were then fed to 5th instar larvae (variety name: Gunma 200) to mature silkworms and produce cocoons. The cocoons were boiled as usual, and the change in fineness of the cocoon filaments in the length direction from the outer layer to the inner layer was measured, resulting in the change in fineness shown in Figure 5. Cocoons were produced in which the fineness of the cocoon filaments decreased significantly from the outer layer to the inner layer. Comparative Example 2

[0013] Silkworms (variety: Gunma 200) were raised by feeding only mulberry leaves from the 4th to 5th instars, and allowed to mature and produce cocoons. The cocoons were boiled as usual, and the change in the lengthwise fineness of the cocoon filaments from the outer to the inner layer of the cocoon was measured, resulting in the change in fineness shown in Figure 6. Cocoons were obtained in which the fineness of the cocoon filaments gradually decreased from the outer to the inner layer.

Claims

1. Rice husks (rice husks) or rice stalks (rice straw) are physically crushed to obtain powder of said rice husks or rice stalks in which the X-ray diffraction peak at a diffraction angle of about 2θ = 35 degrees disappears in wide-angle X-ray diffraction measurement of the natural silica contained therein.

2. A silkworm breeding method for preventing viral diseases in silkworms by feeding the silkworms powder of rice husks (rice husks) or rice stalks (rice straw) containing natural silica in which the X-ray diffraction peak at a diffraction angle of 2θ = 35 degrees in wide-angle X-ray diffraction measurement as shown in claim 1 has disappeared.

3. This method for producing cocoon thread involves subjecting rice husks (rice husks) or rice stalks (rice straw) to heat treatment at 400°C to 600°C, and feeding the pyrolysis residue of the rice husks or rice stalks, in which the X-ray diffraction peak at a diffraction angle of about 2θ = 35 degrees generated in wide-angle X-ray diffraction measurement of the natural silica contained therein, to disappearance, to silkworms to modulate their spinning behavior, thereby making it possible to obtain finer cocoon thread from the same variety of silkworm.

Images