Roaches Take The Bait — Again

When it comes to controlling German cockroaches (Blatella germanica), cockroach baits are the No. 1 choice of pest management professionals and, among different bait formulations, gel baits have become the preferred solution (see "Staying Alive," January 2003 PCT). For many professionals, these gel baits play a vital role in effective integrated pest management (IPM) programs for this insect and have completely replaced residual sprays, dusts, aerosols and fogging.

Given the historical success of gel baits, a problem arose when pest management professionals began noticing control difficulties in field populations. Different degrees of aberrant feeding behavior, meaning cockroaches would not feed on insecticide baits with specific food ingredients, were identified and it was discovered the bait aversion trait could be passed on to offspring.

This was not the first time specific field strains of German cockroaches avoided bait placements, so pest management professionals and researchers at Bayer Environmental Science worked together to develop a new roach gel formula for finicky roaches.

BEHAVIOR HISTORY. Pest management professionals were first faced with aberrant cockroach behavior in German cockroaches in the early 1990s, when cockroach gel bait aversion was observed in Florida and reported to Maxforce field representatives. Maxforce researchers discovered that some strains of German cockroaches avoided foods containing glucose. Further investigation by Maxforce researchers and cooperating pest management professionals revealed small pockets of these aberrant feeding German cockroaches in several parts of the United States.

Research indicated the solution to the problem was to utilize a different sugar in the gel bait matrix. Maxforce Roach Killer Bait Gel was reformulated with fructose, instead of glucose and the problem was solved (see "How Sweet it Is," September 1993 PCT). The solution to the problem ended up being fairly simple. However, this was not the case when the issue came up again a few years ago.

In 1999, a few cases of cockroach bait aversion surfaced. The initial reports were isolated instances and locations were scattered in three distinct geographic locations: south central Florida; the Dallas-Fort Worth Metroplex; and the New York City-North New Jersey Metroplex. Within the year, instances would be found in other areas as well. Early in the current investigation, Maxforce researchers and cooperating professionals found sites where this behavior was reported had three common characteristics:

• They were food-handling establishments;

• The sanitation was poor; and,

• There was a heavy reliance (and in many cases total reliance) on cockroach gel baits for control.

"I was working with another pest control firm at a food-handling facility, a large corporate cafeteria in New York, and it was clear the roaches would not feed on the gel we put out," said Richard Cooper, Cooper Pest Control, Law-renceville, N.J. "In fact, it seemed as if it almost repelled them."

Upon receiving reports that control problems were once again becoming an issue, Maxforce researchers traveled with cooperating pest management professionals throughout the United States to observe and capture suspect German cockroach populations. Extensive field trials with cooperating pest management professionals were performed in locations where aversion was documented, as well as in locations with "normal" field strain populations. Captured roaches were sent to Dr. Tom Macom at Bayer Environmental Science’s research laboratory in Clayton, N.C., for observation and testing.

Since 1999, more than 30 different field strains with confirmed aberrant feeding behavior have been captured, maintained and studied at the Clayton facility. (It is important to note that not all captured roaches during the trials exhibited aberrant feeding behavior rather, in some accounts, a more thorough gel bait application solved the problem.)

"I’ve seen cases of aberrant feeding behavior on the East Coast from Baltimore to Richmond, Va.," said Bob Johnson, regional entomologist with Western Pest Services. "We tried all different types of gels and there was no acceptance of the bait. It got to a point that I thought we were going to have to go back to old treatment methods, which were time consuming and very labor intensive."

During this period of testing, the following observations were made:

• The aberrant feeding behavior occurs only in German cockroaches;

• Different strains display different levels of bait avoidance;

• This behavior can be inherited by offspring; and,

• These cockroaches avoided all commercially available cockroach gel baits tested.

LEARNING FROM THE FIELD. Estimates from pest management professionals across the country told Bayer ES researchers that finicky roaches are common in about 3 percent to 5 percent of commercial food-handling establishments. Recently, however, problems also have been reported and confirmed in some apartment buildings. It’s interesting to note aberrant feeding cockroaches have been discovered in some apartments and not others in the same complex.

This presents new challenges, as these aberrant roaches do not necessarily have the same biological and behavioral characteristics as the cockroaches with glucose aversion first investigated in the early 1990s.

Typically, these aberrant feeding roaches are slightly smaller, eat less and reproduce slower than normal roaches. Different field strains show different degrees of aberrant feeding behaviors and they avoid more than a single component of the gel bait matrix, indicating different mechanisms may be causing the problem.

Another key finding during this investigation was, that in general, technicians have stopped using bait stations. In many problem accounts, where aberrant feeding behavior toward gel baits was confirmed, the problem was solved with a thorough application of Maxforce Roach Killer Bait Stations. Stations, however, did not prove effective against all populations of aberrant feeding roaches, indicating that avoidance was due to more than one food ingredient.

Most professionals rely more heavily on gel than stations for controlling cockroaches, largely due to the cost difference. The best long-term approach, according to Bayer ES’ research, is to use bait stations in combination with gel. Bait stations contain a different bait matrix and have much better "long-term" bait acceptance when compared to gel. And the cost difference, "per gram of bait," is smaller than you may think. In most application sites, bait stations and gel placements are interchangeable, with each product having unique features and benefits (see table on page 66). Having both products in your arsenal allows you to select the most appropriate product for each specific micro-environment.

RECOMMENDATIONS. If you suspect one or more of your accounts contain aberrant feeding cockroaches, consider the following:

• Has enough bait been applied to the proper locations?

• Make sure new cockroaches are not being introduced into the account.

• Apply bait stations if you haven’t already.

• Improve sanitation if necessary and monitor cleaning procedures to make sure cleaning products are not contaminating bait placements.

• Incorporate non-chemical control procedures, such as sealing cracks and crevices and physically removing cockroaches with a vacuum cleaner.

• Watch how cockroaches react to fresh gel placements. Aberrant feeding cockroaches will be "repelled" by bait. Cockroaches with a high degree of avoidance will approach a bait placement and appear to be "shocked" before moving away.

• Monitor the cockroach population closely with visual inspections and sticky traps to assess the effectiveness of your control procedures.

As evidenced by the re-surfacing of this issue, the identification and development of an effective gel matrix to address this problem is not the end to this story. Bayer Environmental Science is committed to continuing research on the biological mechanisms behind this behavior in order to provide effective solutions now and in the future.

Authors’ note: A special thanks goes out to all of the pest management professionals who cooperated during the field investigations and trials, and contributed to this piece: Frank Meek, Orkin Pest Control; Bob Johnson, Western Pest Services; Richard Cooper, Cooper Pest Control; Pete Scala, Parkway Exterminating; Tom Aho, Allied Exterminating; Richard Berman, Waltham Services; and David Harrington, Smithereen Pest Control.

Gordon Morrison is marketing manager, Maxforce, for Bayer Environmental Science. Joe Barile is a field development and technical service representative, Professional Products, for Bayer ES. Dr. Thomas E. Macom is a research biologist for Bayer ES working on the development of cockroach and ant baits.