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ARS Researcher Finds Keys to Cockroach Resistance

By Jim Core
June 5, 2001

An Agricultural Research Service scientist has identified several key mechanisms responsible for insecticide resistance in one of the world's most intrusive cockroach species.

Steven M. Valles, an entomologist at the ARS Center for Medical, Agricultural and Veterinary Entomology (CMAVE) in Gainesville, Fla., has been studying strains of the German cockroach (Blattella germanica) to determine how they develop resistance to insecticides.

Valles identified the role that a previously unknown detoxification enzyme plays in conferring insecticide resistance in the German cockroach. He discovered that several strains of the German cockroach possess a unique membrane-bound substance, called esterase, that detoxifies certain insecticides. This enhanced ability greatly increases the amount of insecticide needed to kill cockroaches possessing the enzyme.

In related studies, Valles and Ke Dong of Michigan State University studied what's called knockdown resistance (kdr), an insecticide-resistance mechanism caused by mutations in nervous system proteins of some insects. They identified a gene mutation associated with kdr in 83 percent of German cockroach field populations they surveyed. The scientists later found two new mutations that were shown to make the roaches more resistant to pyrethroid and related insecticides.

Of more than 4,000 cockroach species in the world, only a few--most notably the German cockroach--dwell in homes. ARS scientists are interested in controlling cockroaches because they pose a threat to humans by contaminating harvested crops at processing plants, along with food products in supermarkets and homes. In addition, cockroaches carry pathogenic organisms that may be passed on to humans through surface and food contamination. And, cockroach feces, saliva, eggs and exoskeletons contain substances that are highly allergenic, especially among people with asthma or other respiratory conditions.

According to Valles, the research will be used in future studies to possibly develop kits capable of detecting insecticide resistance in field populations of German cockroaches (and possibly other insects). This would allow exterminators to choose the most effective control methods.

ARS is the U.S. Department of Agriculture's chief scientific research agency.

Scientific contact: Steven M. Valles, ARS Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Fla., phone (352) 374-5834, fax (352) 374-5818,