"Nuts" to the Concept of German Cocokroach Resistance

During the Battle of the Bulge, one of the most famous conflicts in World War II, Allied forces found themselves completely surrounded by the German troops. When the Germans offered to allow them to surrender, the commander of the Allied forces responded with a one-word answer — "nuts." But then the Allies went on to break out of their predicament. A similar situation exists with resistance in German cockroaches, i.e., technicians often feel completely surrounded and overrun by this problem, yet we have in our arsenal the tools to simply say “nuts” and win the war.

The most recent issue of the Journal of Economic Entomology contained a research article by Steven M. Valles titled Lambda-cyhalothrin Resistance Detection in the German Cockroach (Blattodea: Blattellidae) that focused on methods of detecting resistance to this type of insecticide. The article reported significantly high resistance to lambda-cyhalothrin of field-collected populations of German cockroaches. This article serves as a reminder that resistance to some insecticide classes is readily present. On the surface, this news should be shocking considering that the active ingredient was only recently introduced into the urban pest management marketplace. However, in my opinion there is no need for surprise or alarm.

DON’T FEAR RESISTANCE. This apparently rapid onset of resistance is nothing new to the industry. When bendiocarb was first introduced to the cockroach control market in the mid-1970s, reports of resistance were almost immediate. It was ultimately determined that German cockroaches were predisposed to bendiocarb resistance due to their heavy and repeated exposure to the organo-chlorine insecticides during the 1950s and 1960s. This phenomenon typically is referred to as cross-resistance. By combining bendiocarb with a synergist piperonyl butoxide (PBO), this resistance pattern was overcome.

A similar situation has occurred with many pyrethroid insecticides (e.g., lambda-cyhalothrin) due to the extensive use of a wide variety of pyrethroid insecticides during the past 15 years. To some extent, resistance has been a problem with all the major classes of insecticides, i.e., chlorinated hydrocarbons, carbamates, organophosphates and pyrethroids. Now, use of chlorinated hydrocarbons has ceased, use of carbamates and organophosphates has declined and pyrethroids have become the main staple with regard to liquid insecticides for German cockroach control.

Only low levels of resistance have been reported for acephate, the lone organophosphate that has stood the test of time, in comparison to the two most widely used organophosphates, diazinon and chlorpyrifos. The reformulation of these products as baits raises some concern in my mind. However, the fact that these products are ingested may circumvent several of the resistance mechanisms that reside in the cuticle of cockroaches (e.g., thickening of the cuticle, thicker waxy layer, increased lipids, etc.). Only time will tell. As recent as five years ago, I never would have considered the possibility that resistance to insecticides in German cockroaches was of little consequence. Today, however, because we have new tools that allow us to effectively manage and, in many cases, exterminate cockroach populations, the future of cockroach control is bright and resistance should be of minimal concern. The key words in this discussion are German cockroach populations. Populations, not species, are managed and exterminated. Resistance is a problem in German cockroach populations, not in the species. In fact, through selection with insecticides, the industry has created strains of cockroaches that vary significantly in their resistance to insecticides.

For instance, the population in one apartment building might be significantly different from the one across the street based on the products used in the respective buildings. Population differences are less likely to be a problem among apartments in the same building due to similar exposure patterns and the ability of cockroaches to move more freely among units and interbreed.

COUNTERING RESISTANCE TENDENCIES. Resistance has been a major concern with German cockroaches but of little consequence with the other major domestic species (e.g., American, oriental and brown-banded cockroaches). This is due to the reproductive potential which is significantly greater in German cockroaches than in any of the other species. German cockroaches easily produce four to five generations per year as well as numerous egg capsules that contain twice as many eggs as other species. And although large populations of other species also might be encountered, they require a long time to grow. In addition, other species of cockroaches are less affected by resistance because populations typically are eradicated quickly without extensive pesticide applications. The key is applying an appropriate product in the right place.

I see no reason for alarm about controlling and eradicating cockroach populations because our industry has the tools (i.e., baits and boric acid) to do the job and these tools have not shown significant development of resistance. If you choose to use liquid insecticides, which also can be effective, there is no need for change. However, if liquid insecticides aren’t working, consider a few points about baits and boric acid. There’s no evidence of any significant resistance to any of the active ingredients used exclusively as baits, e.g., hydramethylnon, abamectin, fipronil and boric acid. Since these products are stomach poisons designed for ingestion, they are not subject to some of the resistance mechanisms that affect the insecticides applied as surface sprays and are absorbed through the cockroach’s cuticle.

TAKING THE BAIT. Baits are less likely to be abused. Because they are often visible, there are fewer tendencies to reapply them on a frequent basis. Sprays are not visible, so when cockroaches are still seen in an account, the tendency is to reapply the product. Baits are applied at fixed concentrations which precludes mixing the product at a reduced application rate in order to save money or at a higher rate in order to ensure that the product is strong enough to be effective. Both practices can result in development of resistance.

Research efforts currently focused on developing new active ingredients as baits (with less interest seen in development of new liquid residuals) for German cockroach control will lead to new products. These products will have different modes of action which then will circumvent the resistance problems currently found in German cockroach populations. Today, few technicians complain about resistance; many, however, express concern that we are putting ourselves out of business through the use of more effective tools, such as the baits. Fear not!

Dr. Richard Kramer is a board certified entomologist and serves as technical director of American Pest Management, Takoma Park, Md. He can be reached at 301/891-2600.