Bug Wars : UC Scientists Stumble Onto a Cockroach Killer

In the annals of tried and failed cockroach killers, people have heaved pesticides, ultrasonic waves, spiders and even cucumber peels at the seemingly invulnerable pests.

In many cases, the cockroaches quickly developed a resistance to the treatment and scuttled off to reproduce in greater numbers than before.

Now, a team of University of California, Riverside, entomologists has stumbled onto a new cockroach killer heralded as one of the most potent yet. Although they have no plans to market it soon, they see it having widespread commercial potential--provided that people wouldn’t mind spraying kitchen cupboards with fungus spores.

Entomologists Edwin Archbold, Michael Rust and Don Reierson, who have published their findings in the February issue of Environmental Entomology, say they accidentally discovered the fungus, thought to cause a deadly cockroach disease, after more than a million of their laboratory roaches died inexplicably.

They had been conducting research into the pesticide resistance of German cockroaches--the most common indoor pest in the world--collected at Southern California restaurants and reared in laboratory garbage cans when the first of several epidemics struck in 1980, said Rust, who has studied the insects for 15 years.

The symptoms were obvious. “They had broken and curled antennae and developed a rotten odor,” Rust said.

In an effort to save their cockroaches and research, Rust said, “we cleaned, washed jars and rearing facilities, sterilized food and water. . . . None of it was successful.”

In 1984, after losing $100,000 in time and research, Archbold isolated and identified the fungus that invades the insects’ circulatory system and robs them of nutrition. Rust said the fungus only seems to infect the German cockroach colonies. Other less-common cockroach species have been unaffected in the laboratory.

Since their discovery, Rust and the others have been able to grow the fungus in laboratory equipment and believe that they may have found a potentially powerful, biological means of controlling the almost universal pest.

Other roach experts, however, are cautious about the prospects.

“You need to have an awful lot of information on a microorganism before you reach the point where it can be of practical importance,” said Gary Bennett, a professor of entomology at Purdue University in Indiana. “Large populations and stresses upon them in laboratory conditions are different than what is found in field colonies. . . . That is not to say it (the fungus) won’t eventually prove useful.”

“You also have to deal with the public acceptance of it,” said William Robinson, professor of entomology at Virginia Polytechnic Institute and State University. “If you say we’ve got a fungus in this material, the public will wonder what it will do to their health.”

Even Rust said that a commercial product for use in the home--likely a spray or a treated bait trap--may not be available for another five years or more. His team has yet to gauge the effects of the fungus on cockroaches in field conditions and its safety to humans and animals.

But for laboratory cockroaches, especially young ones, the fungus means almost certain death, he said..

“Once a cockroach is infected with this disease, they don’t stand stress very well,” Rust said. “The most likely commercial use of the fungus is in a bait formula that would accompany reduced pesticide use.”

In the best-case scenario, he said, once in place, the fungus may be able to maintain itself indefinitely, keeping roach populations at barely noticeable numbers.

May Learn to Avoid It

In the worst case, he said, “maybe the cockroach will learn to avoid it or develop a resistance to it. So far it hasn’t in our laboratory.”

So why haven’t cockroaches around the world already succumbed to this disease?

Rust believes that the disease does not spread because cockroach colonies do not stray far from established foraging grounds, making it hard for diseased roaches to infect other colonies.

Meanwhile, “in California alone, the dollar amount spent on structural pest control and over-the-counter aerosols is $550 million a year,” Rust said. “Probably $200 million of that is spent in control of cockroaches.”

Seek Alternatives

In reaching for that market, Rust and his associates will join other scientists also searching for biological alternatives to chemical insecticides.

Last week, Carl Djerassi, who in 1951 invented Norethindrone, a synthesized hormone in the human birth control pill, announced the development of a birth-control spray for cockroaches that does not kill roaches but prevents them from reaching maturity and reproducing.

Djerassi, who led a team of scientists that invented the spray for his research company, Zoecon Corp. of Palo Alto said cockroaches ingest the insect growth regulator.