Chlordane came on the market in the late 1950's and was soon accepted as a long-lasting, wide-spectrum insecticide. Applied to the outside foundation and adjacent foot of soil, it provided a barrier to keep out pests such as crickets, earwigs, and ground beetles for an entire growing season and was generally recommended as an annual treatment. In the 1960's it was available as a mop water additive to leave a film of insecticide across kitchen floors and along baseboards. In the 1980's, chlordane went the way of other long-lasting hydrochlorine insecticides, and most uses were eliminated by EPA. The last major use was in termite control. However, it was found that detectable residues of chlordane remained in the air of houses for years after proper application, and research animals developed cancer when exposed to chlordane. Termite uses were cancelled in 1987.
Diazinon and chlorpyrifos, organophosphate insecticides, replaced most chlordane uses in the 1970's and 1980's. Both were used as indoor baseboard treatments to control cockroaches, silverfish, and other indoor insect pests, lasting about a month. Killmaster was a commercially available chlorpyrifos formulation in a varnish that lasted for 6 months to one year, depending on content. The varnish base allowed a longer residual life and protected the residue from being washed away by daily mopping in commercial kitchens. Application was more precise than with chlordane and still provided a high level of control by treating those areas where these pests spend most of their time. This greatly reduced the amount of insecticide applied.
Outdoor foundation sprays used diazinon which lasted about one month. Rather than one application per year as with chlordane, recommendations changed to one or two fall applications when insects commonly invade houses. After the Food Quality Protection Act of 1996, usage of many pesticides was reduced due to modified risk analyses, including elimination of the use of diazinon and chlorpyrifos for residential uses except for chlorpyrifos in termite control.
Pyrethroid insecticides, which had been commonly used for much of this time, became the insecticides primarily used in general household insect control. Permethrin is the insecticide recommended for outdoor foundation treatment as it does not break down in contact with soil as quickly as other pyrethroids. Pyrethroids are the primary indoor crack and crevice indoor insecticides. However, indoor insect pest control shifted in the 1990's from baseboard and other crack and crevice treatments to baits that target specific pests using much less insecticide.
The increase in bed bugs has been linked to these changes in insecticide use. It is thought that the widespread use of organophosphate insecticides such as diazinon and chlorpyrifos indoors provided collateral control of bed bugs. The transition to baits from more widespread application apparently provided better survival options for them. Although other insects have become resistant to organophosphates, none has been found in bed bugs. In the 1940's and 1950's, heavy use of DDT resulted in bed bug resistance to this insecticide. Pyrethroids have a similar mode of action in killing pests, resulting in bed bugs quickly becoming resistant to them as well.
Dr. Phil Nixon, Extension Entomologist
Photo by Rhonda Feree