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  • Print publication year: 2007
  • Online publication date: June 2012

7 - Bacillus thuringiensis (Bt) Toxins: Microbial Insecticides


The concerted effect of the exponentially increasing costs of insecticide development, the dwindling rate of commercialization of new materials, and the demonstration of cross or multiple resistance to new classes of insecticides almost before they are fully commercialized makes pest resistance the greatest single problem facing applied entomology. The only reasonable hope of delaying or avoiding pest resistance lies in integrated pest management programs that decrease the frequency and intensity of genetic selection by reduced reliance upon insecticides and alternatively rely upon multiple interventions in insect population control by natural enemies, insect diseases, cultural manipulations, and host-plant resistance.

–Metcalf, R. L. (1980). Changing role of insecticides in crop protection. Annual Review Entomology, 25, 219–256.

The competition for crops between humans and insects is as old as agriculture, but chemical warfare against insects has a much shorter history. Farmers began to use chemical substances to control pests in the mid-1800s. Not surprisingly, the development of insecticides paralleled the development of chemistry: early insecticides were in the main inorganic and organic arsenic compounds, followed by organochlorine compounds, organophosphates, carbamates, pyrethroids, and formamidines, many of which are in use today. In 2001, global sales of chemical insecticides included more than 1.23 million pounds of active ingredients and reached about $9.1 billion a year.

There are disadvantages to relying exclusively on chemical pesticides. Foremost is that widespread use of single-chemical compounds confers a selective evolutionary advantage on the progeny of pests that have acquired resistance to the substances.

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