16.7. Physical control
Physical control refers to non-chemical, non-biological methods that destroy pests or make the environment unsuitable for the entry or survival of pests. Most of these control methods may be classified as passive (e.g. fences, trenches, traps, inert dusts, and oils) or active (e.g. mechanical, impact, and thermal treatments). Physical control measures generally are limited to confined environments such as glasshouses, food storage structures (e.g. silos), and domestic premises, although certain methods, such as exclusion barriers or trenches, can be employed in fields of crops. The best known mechanical method of pest control is the “fly swatter”, but the sifting and separating procedure used in flour mills to remove insects is another example. An obvious method is physical exclusion such as packaging of food products, semi-hermetic sealing of grain silos, or provision of mesh screens on glasshouses. In addition, products may be treated or stored under con- trolled conditions of temperature (low or high), atmospheric gas composition (e.g. low oxygen or high carbon dioxide), or low relative humidity, which can kill or reduce reproduction of insect pests. Ionizing radiation can be used as a quarantine treatment for insects inside exported fruit, and hot-water immersion of man-goes has been used to kill immature tephritid fruit flies. The use of certain physical control methods should be increased in order to replace methyl bromide, which is used as a fumigant for many stored and exported products but will be phased out by 2005 because it depletes ozone in the atmosphere.
Traps that use long-wave ultraviolet light (e.g. “insect-o-cutors” or “zappers” that lure flying insects towards an electrified metal grid) or adhesive surfaces can be effective in domestic or food retail buildings or in glasshouses, but should not be used outdoors because of the likelihood of catching native or introduced beneficial insects. One study of the insect catches from electric traps in suburban yards in the USA showed that insects from more than a hundred non-target families were killed; about half of the insects caught were non- biting aquatic insects, over 13% were predators and parasitoids, and only about 0.2% was nuisance biting flies.