[Technically Speaking] Cockroach research--pest management implications

Following is a review of several published research reports that may help pest management professionals with their cockroach control practices.

Gore, J.C. and C. Schal. 2004. Laboratory evaluation of boric acid-sugar solutions as baits for the management of German cockroach infestations. J. Econ. Entomol. 97(2): 581-587.

The efficacy of boric acid in the control of German cockroaches was demonstrated 90 years ago by Vern Walter’s father. Since that time boric acid has been formulated as dusts, pastes, and gel baits in concentrations varying from 1 to 99 percent, however, boric acid’s use as a liquid bait has not been evaluated. This study examined the efficacy of borate bait solutions for the control of German cockroaches.

The results of the study indicated that boric acid was much more effective when used as a liquid than sodium tetraborate and sodium disodium octaborate tetrahydrate. Boric acid solutions (0.5 to 2.0 percent) mixed with simple sugars, such as fructose, glucose, maltose and sucrose rapidly killed German cockroaches.

Appel, A.G., M.J. Gehret, and M.J. Tanley. 2004. Effects of moisture on the toxicity of inorganic and organic insecticidal dust formulations to German cockroaches (Blattodea: Blattellidae). J. Econ. Entomol. 97(3): 1009-1016.

It’s amazing what we assume will happen with certain products only to find that when someone takes the time to evaluate our assumptions — they are found to be incorrect. I have heard it said many times and have repeated the information myself that wetting boric acid dust renders it ineffective and recommended the use of other dusts that are unaffected by the presence of moisture.

This study found that wet boric acid dust and silica aerogel with synergized pyrethrin formulations killed German cockroaches much more rapidly than when they were dry. For example, at the highest water amount tested, one product killed cockroaches almost 10 times faster than when it was used dry. The researchers suspected that increased toxicity resulted from increased penetration of the boric acid into cockroach tissues. It was speculated that the increased uptake of boric acid occurred through the digestive system and to a lesser extent the respiratory system.

The addition of water to several products noted for their durability in the presence of water did not significantly affect their toxicity to German cockroaches. Humidity had no apparent affect on any of the products tested.

Previously, other researchers reported that clumped and compacted boric acid deposits were less effective in controlling cockroaches; however, the authors of this article commented that the application of these dusts as a thin film in wet areas, such as kitchens, enhanced their toxicity, thus their use in wet environments should not be discouraged.

Appel, A.G. 2004. Contamination affects the performance of insecticidal baits against German cockroaches (Dictyoptera: Blattellidae). J. Econ. Entomol. 97(6): 2035-2042.

Typically control of German cockroaches involves a variety of products and depending on the account, e.g., food service, more than one product is typically used. Over the years there has been a great deal of interest in developing repellent products for cockroaches and mint oil has proven to be very effective. In addition, pyrethrin is known for its flushing properties and some pyrethroid insecticides exhibit varying degrees of repellency. This study examined the effects of two repellent materials on bait consumption.

Consumption of bait by German cockroaches was determined after solid and gel baits were contaminated with mint oil and silica aerogel. Direct repellent deposits on solid bait formulations caused decreased consumption and concurrently slower mortality. The consumption of gel baits contaminated with mint oil was not significantly affected, perhaps because the oil was absorbed into the gel, whereas consumption and toxicity of the dry formulations were reduced. The application of silica aerogel to solid baits significantly decreased their consumption and toxicity. In contrast, the gel baits were relatively unaffected by contamination with this product.

The study also examined the effects of these products when applied around baits. The consumption of bait and hence the toxicity was significantly reduced when the area around the bait was treated with mint oil. The study concluded that repellent treatment of the area around the bait was far more important in reducing bait effectiveness than direct contamination of the bait.

To optimize bait performance, Dr. Appel recommended:

· A visual survey (do not use flushing agents) of the area to be treated should be made to identify void areas that could be treated with conventional insecticide dusts and sprays (low pressure).

· Check cracks and crevices where baits could be applied for the presence of dusts and open containers of cleaning solutions and solvents. Prior to bait applications, dust should be removed with a damp cloth and cleaning agents sealed.

· Baits should be applied into cracks and crevices and other niches where cockroaches hide. He also recommended the application of baits to porous substrates, such as wood, rather than porcelain or metal.

· If dust must be applied around a bait, cover the bait deposits with a paper towel to prevent contamination.

Wang, C., M.E. Scharf, and G.W. Bennett. 2004. Behavioral and physiological resistance of the German cockroach to gel baits (Blattodea: Blattellidae). J. Econ. Entomol. 97(6); 2067-2072.

This study reported two more case histories of German cockroach behavioral resistance to gel bait formulations. Two field-collected strains of cockroaches were collected from apartment buildings with various treatment regimens. The strain collected from apartments where bait was used exclusively showed the greatest aversion to the gel baits. The other field-collected strain that was exposed to a variety of treatment regimens, including baits, pyrethroid sprays and boric acid dust exhibited bait aversion, however to a lesser extent. Although the aversion was associated with the presence of sucrose, glucose, fructose and maltose in the bait formulations tested, reformulation of the bait matrices overcame the aversion. The bothersome issue is how fast will aversion reoccur?

This study also examined the two strains’ physiological resistance to the active ingredients (fipronil and abamectin) used in two of the baits tested. It is disheartening to report that the strains demonstrated significant degrees of resistance to these active ingredients. While resistance was measured using topical applications of the active ingredients that circumvented their normal mode of entry, i.e., the digestive tract, it remains to be seen if someday physiological resistance to these active ingredients will be the cause of baiting failures.

When German cockroach populations persist, the issues raised by this study reinforce the need to periodically use other pest management strategies, e.g., residual liquids, dusts, vacuums to crash behaviorally and physiologically resistant populations.

Always remember to support those who provide this invaluable research to our industry.

The author is president of Innovative Pest Management, Brookeville, Md. He can be reached at 301/ 570-3900 or via e-mail at rkramer@giemedia.com.