Considerations of Soil-applied Insecticides for Termite Control
Residential real estate comprises some $12.5 trillion nationwide in the United States. Non-residential buildings, such as schools, retail businesses, hospitals, churches, factories and the like are not included in this total; the total value of structures in the United States is enormous. These investments are carefully designed for the climate in which they are built, and following construction are protected by such measures as fire suppression systems, anti-burglary protection and routine maintenance. In many parts of the United States, however, protection from subterranean termites is a primary concern, and such termite-prevention measures are in some cases required by state or local building codes. Although only a handful of subterranean termite species (about ten distributed among about five genera), and an even smaller number of dry wood and damp wood termite species, are found in the United States, recent estimates of termite damage and repair costs are roughly $5 billion per year, which is equivalent to the amount of damage caused by fires in 2004. Termites in the genus Reticulitermes are the most damaging because they are the most widespread. The northern limit of the native range of termites in North America extends from southern Maine, then westward to Duluth, MN, to Utah, and then northwest through Idaho and north into British Columbia. Termites are present in all fifty of the US states, including Alaska, where they have recently been found on the southern-most islands. Introduced Reticulitermes populations are reported from Toronto and in isolated pockets in southern Canada. Although the introduced Formosan subterranean termite Coptotermes formosanus has garnered much media attention it is not yet widespread and causes damage only in localised areas. The use of chemical insecticides is roughly one hundred years old, and soil application of insecticides for termite control was developed relatively late. The earliest reference to soil-applied termiticides (called at the time "soil poisons" or "chemical insulation") was a 1928 test in California for the protection of utility poles. Although adopted rapidly for use in structures, soil applications were thought to be less desirable than were good building practices (which minimise susceptibility) and wood treatments (which protect the wood directly). As recently as the 1960s some authorities considered soil-applied termiticides as useful only for temporary protection of structures of low value. Today, however, soil-applied termiticides are considered to be the standard protection method against which other methods must compete. The approach used in termiticide application is essentially the same today as it was over 80 years ago: provide a barrier of treated soil through which the termites must pass (and therefore succumb to the poison) between the termites' natural environment and a structure. This is done in two general ways: application to the soil prior to the pouring of the concrete slab and applications to the soil around the perimeter of either the slab or around exterior walls and interior supports (in wall-and-pier construction). Houses with basement construction are treated as a combination of these two methods: the soil beneath the basement slab is treated and the soil surrounding the walls is treated at the perimeter rate, often by using grouting rods to inject the insecticide to the top of the footing. Despite a long history of use, there is little information available regarding the distribution, mobility and longevity of termiticides in the soil, either initially or in the long term, in either application method. This paper reviews insecticide use and dissipation characteristics unique to sub-slab pretreatments and to perimeter treatments, and then concludes with a discussion of longevity considerations common to both methods.
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