Research Into Cockroach Behavior Could Lead To Better Baits

April 30, 1998

GAINESVILLE—Take a left at the kitchen sink, a right at the toaster oven and then loop around the cookie jar and up the side to the lid that doesn’t quite close.

Those are the kinds of directions German cockroaches are leaving for each other when they navigate around your kitchen, say University of Florida researchers.

And in roach research, that’s big news, says entomologist Phil Koehler, of UF’s Institute of Food and Agricultural Sciences.

“For years, researchers thought that cockroaches randomly walked around your house looking for things to eat,” Koehler said.

“It turns out, as they move between food and water sources and their hiding places, they are laying down a chemical trail. And now we’ve discovered that other cockroaches will follow the trail back to food and water sources. It’s very intriguing.”

That’s only half the news from Koehler and his myth-busting graduate researchers, Dini Miller and Tim McCoy. They’ve also found that cockroaches, long thought not to use the sense of smell, also are following their noses, or antennae, to food sources.

“These advances are exciting because they could help us develop new baits, perhaps even a bait so effective that you could place just one and then all the cockroaches in the house would swarm over it, eat it and die,” Koehler said. “That’s exactly what we’re looking for.”

Anyone who has flipped a light switch in a dark kitchen and watched a roach run around can understand how the “random roach” theory got started. But in the quest for better methods of exterminating roaches, UF researchers have become quite familiar with the ins and outs of roach behavior.

“Cockroaches that are not stressed for food will do other things besides look for food,” Koehler said. “They are very curious animals. They like to run around and investigate everything. That’s always been interpreted as a non-response to food, when actually they are exhibiting other behaviors. They investigate, then they feed.”

Miller, who discovered cockroaches are following trails, said the idea that roaches forage randomly means they would have to come out of their hiding places every night and bump into food and water by accident. But roaches never seem to go hungry, so she theorized a chemical cue might guide their forays into the kitchens of the world.

Researchers already knew roaches emit a sex pheromone that helps them find mates and an aggregation pheromone that helps them find safe haven. Miller thought roaches might also use pheromones in scavenging for food.

She developed an extract from roach feces and began testing it at UF’s Urban Entomology Laboratory. First, she found roaches prefer to walk on fecal material rather than a clean surface. So she laid out trails and found roaches will, indeed, follow where other roaches have traveled before.

“The pheromones are communication devices between cockroaches,” Miller said. “If you have an infestation and have a lot of fecal material around, it advertises, ‘Hey, this is a good cockroach place.’”

The housekeeping ramifications have yet to be investigated, she said. She is not sure whether soap and water would be enough to disrupt the trails, and, of course, cleaning tight spaces between countertops and stoves might not be possible.

The fecal extract she has developed would be ideal in baits and traps because it eliminates any airborne residue, as with sprays, and is colorless and odorless.

“It’s an easy cockroach attractant to handle,” she said.

McCoy, too, challenged the assumption that roaches stumble into dinner.

In his experiments, he starved roaches so hunger would overcome their natural first instinct toward curiosity. He found they exited their hiding places, sampled the air, then moved steadily toward the food source, ignoring all visual cues.

“It’s clear they’re responding to something in the air, the odor,” McCoy said.

Koehler said McCoy’s research dovetails nicely with Miller’s because it, too, could lead to better baits. The baits currently on the market, for example, do not use odors because of the previous assumption that cockroaches could not use smell to find food.

Koehler said researchers next will try to determine which odors discriminating cockroaches likes best. So far, beer and bread seem to attract the most roaches, a finding with “implications for college towns,” he says.

“It’s taken a lot of effort to come up with a true picture of what the cockroach is doing,” Koehler said. “But if we can use odors to bait them or lay down trails to trap them, it will cut down on the amount of space you spray and on the amount of insecticide used in the home.”

And maybe, in a few years, the cockroach road map in your kitchen will lead to a dead end.