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昆虫の習性に基づく建築的防虫法


執筆者:高嶋聰(沖縄科学技術大学院大学



建築的防虫手法とは

生産施設(工場)や物流施設(倉庫)内の製品への昆虫異物の混入を防ぐ,物理的防除技術の研究がすすめられている.この技術は原則として,殺虫剤などの化学的防除技術を含まず,施設の新築や増改築時に,その建物の構造・設備などの建築手法により昆虫異物の混入を防ぐ技術である.昆虫の生態・習性を配慮し,建物への侵入経路や屋内での繁殖可能な場所に何らかの工夫・対策をすることで,昆虫異物の混入を防ぐ減らすことができる.

建物内部で繁殖する昆虫対策

建物内部での昆虫繁殖には建物の構造・設備などのハード面の対策だけでなく,日常の清掃と生息状況の監視を中心とした,管理・運用といったソフト面の対策も重要である.そこで,こういった昆虫繁殖を防ぐための建築的防虫対策の役割は,そういった清掃や監視などを容易に実行できるハード面を提供することである.具体的には壁と床の接合部に丸みをつけたり,窓枠に角度をつけたり照明を埋め込みにしたり,水平配管や凹凸の多い壁面構造を部屋内に露出させないことで,清掃を容易にしたり,昆虫の温床になりやすいゴミ溜りや粉溜りを解消することを目的としている.また,屋内での昆虫の繁殖には温度と湿度が重要な要因である.屋内で繁殖する昆虫の発育零点(昆虫の発育できないもっとも高い温度)は10℃前後から20℃前後の間に,また発育最適温度は25℃から30℃の間にある.そこで,屋内の温度をコントロールするコストも考慮して,昆虫の餌となりうる原材料を長期保管するところだけでも空調の負担の比較的少ない15℃前後に維持することで,昆虫の繁殖を抑制することができる.また湿度を60%以下に抑えることによって昆虫の餌となりうるカビの発生を抑えることによっても昆虫の繁殖をある程度抑制することができる.

外部からの侵入昆虫対策

建築的な防虫手法としては外部からの侵入昆虫対策により重大な責任を負っている.工場でも倉庫でも,建物内部の昆虫捕獲調査を実地すると,ユスリカやクロバネキノコバエなど外部から飛来する双翅目昆虫が圧倒的に優占している.そこで外部からの侵入昆虫対策としては,建物の気密性の向上,建物の空気圧の調節,照明方法と光源の選択が重要である.最近の工場や倉庫は気密性が高まり,かつてのように隙間風が吹き込むようなことは稀になった.しかし,人や物が出入りする開口部が不可欠であり,ここが昆虫侵入の最大の弱点である.倉庫開口部の防虫設備の代表的な物にはドックシェルターや高速シートシェルターがある.ドックシェルターは積荷の積み込み,積み降ろしの最中も開口部がトラックによりカバーされるため,高い気密性が保持される.高速シートシャッターは開閉速度が高速で防虫に不可欠なきめ細かい開閉管理に適している.扉は1枚ではなく,多重化すると 防虫効果は高まる.換気口などは気密性を損なうがメッシュの細かい網戸を付けることが不可欠である.また昆虫の施設への侵入には建物内外を往来する気流が強く影響する.建物に吹き込む気流にのり虫が侵入するのは容易に想像できるとして,さらに建物から吹き出す気流も虫の侵入を促進する可能性がある.虫に風上に向かって飛ぶ性質のものがいるからである.気流には建物内外の気圧が影響するが,建物の内部気圧を外より高くすると虫の侵入は減るようである.

光への昆虫誘引

昆虫には光に対し正の走性をもつものがいることは多くの人が知るところであるが,照明法と光源の選択は,昆虫の侵入を減らす大きな要因である.昆虫の個の性質を利用して多くの光源が開発されている.

建築的防虫の今後

建築的防虫法は近年,ヒトの経済活動の中で生まれた,実利的な技術分野であるが,薬剤などの化学的な防除によらない手法は,建築分野にとどまらず,環境保全や環境負荷の低い技術としてさまざまな分野に転用されていくことが期待される.



Further Reading


昆虫ミメティックス Insect Mimetics(2008),針山孝彦,下澤楯夫,pp.941-949

[/ja]

An architectural insecticide method based on insect traits


responsibility for wording of article: Akira Takashima (OIST)


What are architectural insecticide methods?

Physical technologies of insect control to protect against insect invasion of production facilities (factories) and logistic facilities (warehouses) are being developed. This technology is not based on using insecticides or similar chemical treatments in principle but based on architectural means such as designing structures and features when designing new buildings or restoring existing ones to protect against insect invasion. By considering insect behavioral traits and by intervening possible entrance pathways and breeding grounds in each room with appropriate countermeasures, it is possible to prevent or reduce insect invasions.

Suppressing propagation of insects inside buildings

Countermeasures against propagation of insects in buildings are not just a matter of the physical structure and equipment. Management and operation measures such as daily cleaning and monitoring of the inhabiting situation are also important.The role of architectural insect control countermeasures in combating propagation of insects is to provide physical structures that enable easier cleaning and monitoring. In particular, the junctions of walls and floors should be rounded, window frames should be angled, lighting should be embedded into the sealing and/or wall, and exposed horizontal pipes and rough wall surfaces are avoided inside rooms, thereby facilitating cleaning and eliminating potential insect hotbeds such as waste and dust reservoirs. The inside temperature and humidity are also major factors in propagation of insects. The development threshold temperature for insects inside buildings (the highest temperature at which the insects will not develop) ranges between approximately 10°C and 20°C. The optimal temperature for development is between 25°C and 30°C. Therefore, while considering the cost of temperature control, setting the air conditioning to a temperature of 15°C requiring relatively low energy should inhibit insect reproduction even in places only used for long-term storage of materials that insects could eat. Similarly, keeping the humidity lower than 60% inhibits the growth of molds that can serve as food for insects and will inhibit propagation of insects.

Countermeasures against insect invasion from outside

Architectural insecticide methods are largely dependent on countermeasures to prevent insect invasions from outside. Whether in a factory or in a warehouse, insect-trapping surveys have shown an overwhelming preponderance of chironomid and fungus gnat flies flying in from outside. Countermeasures against these invasions include keeping buildings airtight, regulating air pressure, and selecting suitable lighting methods and light sources. Modern factories and warehouses are airtight; hence drafty places have become uncommon. However, buildings need openings for people and goods to go in and out, and this is the main cause of insect invasions. Typical insect protection equipments for warehouse include dock shelters and high-speed sheet shutters. The dock shelters keep the entranceways covered by the truck during loading and unloading, and the interior stays airtight. High-speed sheet shutters protect against insects by ensuring rapid opening and closing and are suitable for precise open/close control essential for protection against insects. Protection against insects is improved if there is more than 1 door. Air can enter through ventilation openings; therefore it is essential to install fine mesh nets at the openings. The air flow in and out of the building affects insect invasions. It is easy to understand how insects can be transported in through airflow from outside the building. Air flowing out of the building can also facilitate insect invasions, given that some insects have propensity to fly upwind. Airflow is influenced by air pressure inside and outside the building. However, higher air pressure inside the building than outside appears to reduce insect invasions.

Attraction of insects to light

It is well known that insects have a positive phototaxis, and the choice of lighting regime and light source are a major factor to reduce insect invasions. Several light sources have been developed that exploit such a trait of insects.

Prospects of architectural insect control

The architectural insect control methodology is a practical technology field that has been recently established through human economic activity. It is highly expected that the insect control technology that does not rely on chemical reagents will be applicable to various other fields as an ecofriendly technology.



Further Reading


昆虫ミメティックス Insect Mimetics(2008),針山孝彦,下澤楯夫,pp.941-949


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