[Cockroach Control Issue] Rotation Application

Phil Koehler, a professor of entomology at the University of Florida, has been studying cockroach bait aversion and resistance for five years, trying to determine why three specific strains of cockroaches from around Florida just couldn’t be controlled when they were exposed to certain cockroach bait products.

The three strains of roaches — two found in restaurants and one in a house — that Koehler studies have shown aversion to several baits on the market, and even some resistance to them.

Koehler and his lab act as a sort of proving ground for chemical companies trying to stay one step ahead of the roaches. The manufacturers bring him new formulations of products — about a dozen to date — and he tests them on the three bait-averse roach strains.

The strains of cockroaches Koehler is testing come from all across the state of Florida. The Daytona strain, named after the city where it was discovered, was found in a Daytona Beach restaurant after “repeated failures” by pest control companies to eradicate it.

“We call it the Daytona Biker strain,” Koehler said, “because they’re tough.”

The second strain was found last year in a house in Lawtey, about 100 miles northwest of Daytona Beach. Koehler said the homeowner had contracted with three different pest control companies to take care of the roaches, but none could. Eventually, thousands of cockroaches were crawling all over the kitchen.

“There was so much bait put out, there were kind of bait icicles hanging from underneath the kitchen counters,” Koehler said. “There was no shortage of bait put out, but there was obviously not much consumed.”

The third strain, called Golden, also was found in 2006, this time infesting a Chinese restaurant in Gainesville.

Koehler said all three strains look identical to a normal German cockroach, and in each case, had to be eradicated by a new formulation of bait.

WHAT WORKS. Koehler and his assistant, Barbie Bayer, took the three strains of German roaches and bred them at his Florida lab. So far, he said, baits from Bayer Environmental Science, DuPont Professional Products and Whitmire Micro-Gen have proven effective cockroach products. But, he can’t be sure what, exactly, is working: The chemical companies won’t tell him what’s inside their pesticides.

“They don’t have to tell us,” he said. “All we can do is really look at them and see if they’re (effective).”

The first reports of bait-averse roaches came out of Miami in the early 1990s, Koehler said. The bugs there didn’t have a taste, it seemed, for glucose and baits sweetened with corn syrup were scrapped as the industry shifted to other kinds of sweeteners.

But shortly thereafter, cockroaches’ aversion to baits seemed to crop up across the country, first in commercial accounts, then in residential accounts as well.

“But now what we see is bait aversion to things maybe other than the sweeteners,” Koehler said. “Sometimes, even the active ingredient has been implicated.”

THAT’S NOT ALL. Incidences of cockroach bait aversion have been reported as far north as Michigan, Koehler said, but that aversion might not be the only problem for a PCO trying to keep cockroaches under control. Some roaches have shown a resistance to certain insecticides

“The issue isn’t just bait aversion,” he said. “There is low-level resistance to some of the active ingredients in baits. When you couple that with bait aversion, what you have is a tremendous failure.”

Koehler also is studying how roach baits change over time. He said something in the baits either becomes active, or becomes inactive, when the bait is left out for an extended period of time, which causes it to become displeasing to a cockroach.

“(Bait is) not always fresh. It’s going to be out there for some period of time,” he said. “It’s not necessarily stale, but perhaps the properties in the bait change.”

Koehler suggests a proactive approach to dealing with aversion. Instead of waiting for problems develop at an account, he said, PCOs should rotate regularly the baits they use, including newer formulations, effectively killing off the cockroaches that might be developing aversion or resistance.

“There’s a concept that you maybe want to do some rotation of baits so you don’t end up with a problem,” he said. “Use a variety of bait, not just one until it fails.” 

The author is assistant editor of PCT magazine. He can be reached at cbowen@giemedia.com.

Tips and Tricks

University of Florida professor Phil Koehler suggests some ways PCOs can handle — and even avoid — roach bait aversion or resistance.

• Use different kinds of baits, especially newer formulations.
• Rotate your baits regularly.
• Don’t wait until a particular formulation of bait stops working to try something new.
• Remove old bait when you put new bait down.