Physical modifications

Physical alteration of urban structures or other features of the habitat can reduce or prevent access by pest arthropods, or limit harborage and breeding sites. Methods such as the use of screens, caulking, removing moisture, limiting wood-soil contact, and other traditional methods are effective. Screening prevents flying insects and some soil-inhabiting insects, such as subterranean termites, from entering buildings. Screen specifications for excluding house flies and similar-sized species are: mesh #10, aperture length 2.27 mm excludes house flies; mesh#i6,aperturelengthi.3ommexcludesmostmosquitoes; and, mesh #20, aperture length 0.853 excludes ceratopogonid (Ceratopogonidae) flies. Traps based on light, ultraviolet light, carbon dioxide, pheromones, and other chemical scents can be used for local and area-wide insect control.

Ultraviolet (UV) light traps for flies and other insects utilize their sensitivity to this portion of the light spectrum. UV light is classified as light that has a wavelength between i00 and 400 nm. Blue light has a wavelength of 450-500 nm, green light 500-560 nm, orange 600-650 nm, and red 650-700 nm. The UV light bulbs used in insect light traps have an internal coating which gives off ultraviolet light when the tube is lit. The coating breaks down over time and eventually the UV light generated is notsufficientto attract insects. The tube, however, continues to give off normal, visible light. UV light is usually divided into three categories: UVA, which has light frequency of 315-400 nm; UVB, which has a frequency of 280-315 nm; and UVC, which has a frequency of 100-280 nm. UVC light is frequently used for its germicidal properties, and UVB is the sun-tanning light emitted by the sun. The UVA wavelengths are used in insect light traps, and are harmless to humans. The optimum range for attracting insects is 350-370 nm, but some insects are attracted to wavelengths near 500 nm. Some species of midges (Chironomidae) are attracted to light in the near-UV region of 300-390 nm. Many species, representative of most orders, are sensitive to UV light, and some significant behavioral responses are initiated by it. Some insects are negatively phototactic to UV light; for example, when given a choice, ants will congregate in a region not illuminated by UV.

Sound (wingbeat sounds) has been used as a component of insect traps, typically for mosquitoes and chironomids. Wavelengths are somewhat species-specific and may be combined with UV radiation to increase effectiveness in traps. Sinusoidal sounds 210-300 Hz are effective in attracting male Chironomus plumosus, a common chironomid pest around the world. Frequencies between 240 and 270 Hz are attractive to C. dissidens, and 150-180 Hz was attractive to males of Propsilocerus akamusi (Chironomidae).

Air currents have a long history of use as a barrier in preventing the entry of flying insects into buildings or other confined spaces. The house fly is the primary target, and velocities effective for this insect are generally effective for others. Effectiveness is achieved when air is discharged at a velocity in the range of457-670 m/min, ata 15° angle. For the house fly, 92% exclusion can be obtained when air is discharged at 546.5 m/min, and 80% exclusion is achieved with 529 m/min.

Volatile oils and other chemicals in personal-use mosquito repellents function as a chemical barrier to host-seeking females. Bednets treated with (pyrethroid) insecticides are an effective barrier between humans and the mosquito vectors of various diseases. Other barriers for mosquito control include the use of polystyrene beads in potable water supplies to reduce the potential breeding of Culex quinquefasciatus and Cx. pipiens.

Physical barriers can limit or prevent subterranean termites from entering structures from soil nests. Barriers consisting of soil particles of specific sizes can be used to prevent species ofsubterranean termites from tunneling through the material and gaining access to structural wood. Termites are unable to move particles larger than about 1 mm diameter; as particle size increases, so does the size ofthe space between the particles. Particles about 3 mm diameter provide interspaces large enough to allow workers to crawl through. Effective termite-barrier sand has particles 1-3 mm diameter, or no larger and no smaller than that able to pass through a 16-mesh screen. Sand smaller than 16-mesh can be carried away by workers, and larger particles can support tunnel construction. For Reti-culitermes hesperus the effective sand particle size is 1.6-2.5 mm; for R. flavipes the effective aquarium sand particle size is 1.4-3.35 mm; and for Coptotemesfomosanus sand blastparticles 1.4-2.36 mm are effective in establishing a barrier.

Stainless-steel screen, with a mesh of35-mesh material with an aperture size of 0.66 x 0.45 mm, in large continuous sheets and placed over building foundations, prevents movement of termites from soil to above-ground wood. To be effective the screen must be flexible to be molded around all potential entry points; a high-quality 316 marine-grade stainless steel is used. Similarly, insecticide-impregnated plastic sheeting that covers the subslab soil, or as a fitting around pipes and other building-construction features, forms a barrier to subterranean termites. It is placed as a continuous sheet beneath the foundation.

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