[Annual Cockroach Control Issue] Bait Rotation: Crucial to Control

The development of cockroach bait formulations more than 25 years ago revolutionized treatment protocols. No longer tasked with complex preparation and cleanup, PMPs reveled in the ease of use and increased efficacy of cockroach baits. However, overreliance on certain roach bait formulations has resulted in bait resistance and aversion to some popular insecticides, leaving PMPs asking questions about how to achieve and maintain high levels of efficacy. Scientists across the industry are looking to help.

“Cockroach gel baits have been the most effective product for German cockroach control for many years,” says Byron Reid, senior principle scientist at Bayer Environmental Science. “The danger is that we could ruin what has been a very effective tool by not paying attention to the science behind what cockroaches are telling us about baits.”

Reid, along with researchers across the nation, asserts that rotation is a vital component of cockroach treatment and “the only way we can preserve the long-term control of German cockroaches we’ve enjoyed with gel baits for the past 25 years.”

Joe Barile, technical service lead at Bayer Environmental Science, adds, “I was an applicator during that magical transition between liquid insecticide applications and baits. I was involved with Austin Frishman in the early development of these products. I don’t want our industry to go back to methodologies we used back then. Anything we can do to protect and preserve the continued use of bait formulations is paramount.”

What Bayer has done in recent months is to introduce a reduced-risk gel bait featuring a new bait active ingredient (AI), clothianidin. Maxforce Impact is part of the Maxforce Roach Control System developed by Bayer, which incorporates the rotation of gel baits with different active ingredients and bait matrices every 90 to 120 days (the typical German cockroach generational cycle). Bayer based development of this new product on the science that says resistance and aversion are growing among cockroaches, and the reality that says PMPs need a new plan.
 

What Science Says.

Coby Schal, the Blanton J. Whitmire Distinguished Professor at the Department of Entomology at North Carolina State University, describes two major forms of resistance: physiological resistance to the insecticide (the AI) and behavioral deterrence to the bait formulation (usually an aversion to a formulation ingredient other than the insecticide).

“Physiological resistance to the AI is common and very dynamic,” says Schal. “When any insecticide, in any formulation, is used extensively, cockroaches evolve resistance to it. So, we find resistance to AIs such as abamectin, hydramethylnon, fipronil and indoxacarb, which are widely used today. Cockroaches also developed relatively high levels of resistance to previously used insecticides such as sulfluramid and chlorpyrifos.”

Behavioral resistance — sugar aversion, for example — is much less prevalent, says Schal, but increasing in frequency. “In the past three years or so, we sampled about 20 populations and found glucose aversion in only a handful. But we are now finding some fructose aversion and possibly aversions to other sugars. As selection with sugar-containing baits continues, we expect to find more sugar-averse populations,” he explains.

How can PMPs minimize resistance? “The best strategy available is product rotations,” says Michael Scharf, professor and O.W. Rollins/Orkin Chair, Department of Entomology, Purdue University. “It is important to note that no formal research reports exist on this strategy for cockroaches, but in theory it is the most logical option available. Manufacturers are recommending product rotations for some of their products; we believe this is a very positive development for the industry.”

Schal echoes the need for bait rotation and recommends that PMPs alternate bait products based on their toxicological mode of action. “In other words, use a bait that targets target No. 1 in the nervous system for several months and then switch to a bait that targets a different system — mitochondrial respiration, for example — for the next several months, followed by a bait that targets target No. 2 in the nervous system, for several months,” he says.

Schal also suggests that PMPs use a variety of baits concurrently, with the intention of hitting multiple targets at the same time. This method also disrupts the associative learning process: Where cockroaches might have learned that certain aversive tastes are linked to certain smells, they will not be able to discern which smell is coming from which bait when a variety of baits are presented, and so will be more likely to feed.

“With any resistance management strategy, being familiar with the modes of action of bait products is imperative,” Schal adds. “It is also important to understand the behavior of cockroaches in your account. We often start a cockroach control program with a taste test: We place two or three small dabs of bait products side by side near a cockroach aggregation to see which one is most attractive to them. That is the bait we then start with in that account.”

Reid understands the need to appeal to the pest at hand. “Diet matters,” he says. “At different stages of their life cycles, cockroaches prefer to eat different things. Diet also matters based on their environment. If they’re living in a bakery, they’re dying for a steak but you’re just giving them more sugar. You need to be aware of their environmental conditions. It’s not just about what you’re feeding them, but what they’re feeding on in their environment as well.”

It comes back to knowing the pest’s behaviors inside and out — and that comes from having access to the latest research. Michael Rust, distinguished professor of entomology and the graduate division, Department of Entomology, University of California, Riverside, says, “Modern cockroach baits were a panacea for many years. It had become rare to even see a paper at national entomology meetings about German cockroaches. However, insects have that bad habit of evolving and defeating even our best efforts. Research remains a pivotal element of effective pest management.”

Scharf adds that his team at Purdue is testing a variety of resistance monitoring and management strategies, and he hopes to be able to share findings with the industry in the near future. “With the use of sound IPM approaches and widespread adoption of rotational management strategies (including rotation of mixture-based products), we feel that the industry will be able to combat resistance in a sustainable way,” he concludes.

Visit www.pctonline.com and click on “online extras” to see an infographic that outlines three easy steps for successful cockroach bait rotation.

 

About the author: Donna DeFranco is a frequent contributor to PCT.

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