[Technically Speaking] Cockroach resistance — How soon we forget

The other day I was thinking about how dramatically things have changed in our industry in the past 30 years. It brought back memories of a time when we were intensely focused on cockroach resistance and how to prevent and/or overcome control failures. I spent three years of my life along with another notable industry figure (Dr. Harold Harlan) at the U.S. Army Environmental Hygiene Agency — Regional Division South trying to figure out the most effective way to kill German cockroaches. We would periodically collect cockroaches from U.S. Army food service facilities by the hundreds, rear them through several generations until we had thousands, and then try to kill them with some oldies but goodies, e.g., chlorpyrifos, diazinon, propoxur, bendiocarb, malathion, etc.

BACK TO SCHOOL. At that time universities, such as Virginia Polytechnic Institute and State University (Dr. Don Cochran), University of Florida (Dr. Phil Koehler) and Purdue University (Dr. Gary Bennett) were leading the way in cockroach resistance research. Whenever you attended pest management training meetings and Entomological Society of America research meetings, one of the hottest topics was cockroach resistance. Today, except for the recent problems with bait aversion (behavioral resistance), we rarely hear anything discussed, read anything written or see any research on this topic.

The concerns of cockroach resistance changed in the late 1980s with the increased use of baits, reduction in the use of residual applications — due to the misperception that residual insecticides weren’t part of IPM — and the loss of many active ingredients due to re-registration issues. Other than the baits that, for the most part, were new active ingredients, the industry was left with a plethora of pyrethroids — many with similar detoxification mechanisms and cross-resistance issues related to chlorinated hydrocarbons.

Furthermore, baiting and the need for more intensive inspections and more directed treatments moved cockroaches to the No. 2 position behind ants as the No. 1 consumer pest. Today, for many pest management professionals and the consumer, our attention has taken on an entirely new dimension — bed bugs. This has probably moved cockroaches to the No. 3 position.

STILL A PROBLEM. Despite the cockroach’s diminished pest stature, it is one of the most resilient and adaptable pests and resistance remains a problem in some accounts. Another reason for resistance is that residual insecticide applications have remained a staple in some accounts, e.g., food service, clean-outs and other situations where populations are extremely high and there is a desire to reduce the numbers quickly. And finally we have mostly been relegated to the use of pyrethroids for residual applications, creating an increased probability of cross-resistance with these products. In our accounts where we are using residual pesticide applications we have increasingly found that pyrethroids are not performing as well as they have in the past, forcing us to explore other options.

HOW TO DO IT. Cockroach resistance testing and management has fallen on hard times — less than two pages in the current edition of the Mallis Handbook of Pest Control cover this topic. If you are thoroughly treating accounts with crack-and-crevice residual applications and are still finding low to moderate cockroach populations (as we are) it may be time to consider implementing a resistance management plan.

In the absence of resistance testing and when facing control failures, we can’t ignore resistance management. The good news is there are effective ways to address this problem.

Evaluate the problem

• Review records and visit affected accounts to determine the extent of the problem — this may involve an evening visit to determine where the pest activity is occurring.
• Evaluate all aspects of past treatments, thoroughness, proper mixing, appropriate formulation, etc.
• Residual applications with some pyrethroids, as with pyrethrin flushing in years past, force cockroaches into unusual areas, such as deep wall voids, equipment, and up walls into drop ceilings — this is a behavioral resistance problem, not a physiological one.
• Poor sanitation and clutter, providing food and harborage respectively, will sustain population growth.

Physical and mechanical interventions

• Heat is the most effective physical intervention — killing cockroaches by achieving a lethal temperature and maintaining it for an appropriate amount of time. The goal is to effect eradication — eliminating physiologically resistant populations. Because cockroaches are rarely exposed to this type of treatment, it is not likely they will exhibit any degree of tolerance. The limitations to this type of treatment are containing and maintaining the heat and preventing cockroaches from moving to cooler locations.
• Vacuuming is a tried-and-true technique for removing resistant populations, however this intervention is labor-intensive and often it is difficult to extricate cockroaches and their egg capsules from deep harborages, such as cracks and crevices and wall voids.

Insecticides

• All is not lost on insecticides — new products with new active ingredients and modes of action, such as chloronicotinyls and phenylpyrazoles, are finding their way into the marketplace and can be used for residual liquid applications. These novel active ingredients can be worked into a resistance management strategy involving rotation of products. When rotating products, be sure not to switch to the same class of insecticide, e.g., pyrethroids to pyrethroids.
• Don’t forget the insect growth regulators (IGRs) and chitin synthesis inhibitors (CSIs) — they can be very useful in managing resistant populations because they act at the cellular level and have different modes of action.

CONCLUSION. How soon we forget the challenges of the good old days. But in the days ahead, we can revel in the fact that there are many challenges — and opportunities — to be faced in pest management.

The author is president of Innovative Pest Management, Brookeville, Md.