Cockroaches 101

Haven’t heard much about today’s cockroach research? Here’s a summary of what researchers are currently studying at a variety of universities.

In 1984, I began my doctorate research at the University of Florida. At that time, a few students were researching ants, fleas, wasps and termites; however, almost everyone doing urban pest management research was working on cockroaches. But things have changed and priorities have shifted.

For instance, termite research, which lay fallow for almost 35 years, became a top priority in 1987, when it became apparent that the long-term workhorse of the termite industry, chlordane, would soon be gone. There was increased interest in other liquid termiticides, as well as baits and termiticide performance. As might be expected, manufacturers were funding a lot of this applied research in efforts to bring new products to the marketplace. Thus, as a result of this dramatic shift in university research and students’ increased interest in these pursuits, we have learned a lot about termite biology, habits and behavior.

Similarly, a significant amount of research is now being dedicated to pest management strategies for several ant species. Several factors brought this about: the use of chlordane (a product effective against ants outdoors) for turf and ornamental applications was discontinued in the 1970s; several pestiferous ant species have been introduced into the United States during the past decade; and the use of baits for cockroach control has increased. There has been a concurrent decrease in baseboard spraying, which impacted ants indoors.

Without a doubt, pest management practices for cockroaches have changed dramatically throughout the past five years. The shift to baits because of their success in reducing cockroach problems is having a significant impact on our industry. Cockroach problems are not what they used to be; in fact, cockroaches have been replaced by ants as the No. 1 pest in this country. Baits have unique properties that have contributed to their success. These include: inconsequential resistance problems; a food component that attracts cockroaches; insect growth regulators (IGRs) that enhance feeding activity; and, that some baits are translocated to other cockroaches.

My fear is that with these dramatic successes, the industry and, consequently, the research community, will become complacent as they did with termites and the result will be that we suddenly will find ourselves behind the research curve playing catch-up. One thing is for certain — cockroaches have adapted to and survived 350 million years of ecological changes. And pest management professionals, no matter how good we are, will not cause their downfall. It is imperative that research efforts continue so that we can better understand how cockroaches impact our health and find new ways to lessen these effects.

While it appears that cockroach research has fallen on hard times, some interesting things have come to light. This article highlights some of the current research initiatives on cockroaches and discusses their impact on the pest management industry.

COCKROACHES AND HEALTH. Cockroaches have always been suspected of being directly involved in disease transmission, however, a review of the literature on this subject finds only a few cases where circumstantial evidence has implicated them. There is no question that cockroaches carry microscopic organisms on their bodies, but it is uncertain what happens when they contact food and food-preparation surfaces. More recently, cockroaches have been found to play a significant role in childhood asthma, particularly in inner-city children.

For almost 15 years, Dr. Rick Brenner, Household Insects Research Leader, United States Department of Agriculture Center for Medical, Agricultural and Veterinary Entomology (USDA-CMAVE), has been in the forefront of research on cockroaches, their allergens and their impact on children with asthma. He has been involved in developing precision targeting techniques for mitigating cockroach populations and allergens in homes and has worked on the development of a polyclonal assay for detecting cockroach allergens. This work is continuing throughout the country and has received a great deal of attention and funding during the past year.

Deana Branscome, a doctoral student working with Dr. Phil Koehler at the University of Florida, is evaluating the potential of insects, particularly German cockroaches, to contaminate food-preparation surfaces with Escherchia coli and Salmonella spp. bacteria in food-service facilities. Ingested bacteria can be shed in the cockroach feces and since first instar nymphs feed almost exclusively on adult cockroach feces, she is attempting to determine if the nymphs will pick up the bacteria and, subsequently, whether the bacteria can be conveyed during molting.

There is an interesting dilemma posed by this information. As the pest management industry and consumers learn more about the direct effects of cockroaches on human health, this underscores the importance of pest management services and increases the demand for services. The other side of the issue is the customer’s expectation that the industry will provide them a pest-free environment, i.e., a healthy environment, and failure to do so creates a liability.

DESIGNING A BETTER TRAP. The importance of inspection and monitoring cannot be overemphasized, particularly in areas where there are recurrent cockroach problems. Trapping can provide information on the size and characteristics of the population, foci of infestation and other information that is essential in implementing effective pest management strategies. In addition, trapping can be an effective way of reducing populations in sensitive situations where other tools, such as pesticides, cannot be used. Thus, the type of trap may play a significant role in monitoring and control.

Dini Miller, assistant professor of entomology at Virginia Polytechnic Institute and State University, has been evaluating a variety of commercial cockroach traps during the past year. Her evaluation of the traps is based on the number of cockroaches trapped per cm2 of sticky surface area. Miller’s studies have found that the best traps have a large surface area, glue that keeps roaches stuck and a ramp that causes them to commit to the trap, i.e., they must jump onto the glue to be stuck. She has noted that cockroaches that do not commit to entering a flat edge trap can frequently pull themselves loose. She also reports that traps work better when reused, which indicates that pheromones can play an important role in trapping.

Miller, in earlier studies, evaluated the potential of German cockroach feces as an attractant and trailing mechanism. She found that cockroach feces were effective attractants, which could induce trailing activity and significantly enhance trap catches. The fecal extract used to induce trailing activity remained effective for three days. In a subsequent study of this behavior, she concluded that while German cockroaches exhibit trail-following activity, the fecal trails should not be viewed as having been intentionally deposited in order to lead other cockroaches to food. It is more likely that feces are randomly deposited as cockroaches forage through their home range; however, the deposition of feces along frequently traveled routes induces others to follow.

The benefit of this information to a pest management strategy should be obvious. If baits and crack and crevice applied pesticides are placed where feces are observed, there is a greater likelihood of affecting more cockroaches with such products.

ARE BAITS THE ONLY WAY? A good case can be made for almost exclusively shifting over to baits. Research within the past few years has begun to uncover added advantages of baits that were not observed with liquid insecticides. However, that being said, it may be that research was never conducted to evaluate similar effects of liquid and dust insecticide formulations. One of the major advantages of baits is that they have an attractant (food) component designed to attract cockroaches, an element lacking in liquids and dusts.

A frequently asked question about baiting is, "Which product is best?" There is no simple answer to the question because most products will do the job if placed in the appropriate areas. However, a number of noteworthy studies have found differences in baits.

Nalyanya, Kopanic and Schal (North Carolina State University) evaluated the attractiveness of four bait formulations (gel, paste, powder and station) containing one of the following active ingredients: boric acid, hydramethylnon, abamec-tin and chlorpyrifos. Avert powder (aba-mectin), the Maxforce station and gel (hydramethylnon) and Siege gel (hydra-methylnon) were attractive to German cockroach adults and nymphs. Aging the bait formulations for as little as seven days significantly reduced the attractiveness of Avert powder, indicating that the formulation is a critical element in the long-term effectiveness of the baits. Comparable responses were found in studies using brown-banded cockroaches.

Kopanic and Schal found in laboratory and field studies that hydramethylnon bait was horizontally transferred through the feces of foraging adult German cockroaches that was eaten (coprophagy) by the relatively sedentary first instar nymphs, causing significant mortality in both life stages. Coprophagy did not occur in other nymphal stages. Consideration should be given to this behavior when new bait toxicants and pathogens are in development for German cockroaches.

As if coprophagy was not enough, Buczkowski and Schal recently reported on emetophagy (an induced regurgitation of ingested materials) in German cockroaches that consumed fipronil bait. The excretion of fipronil coincided with the onset of fipronil-induced paralytic symptoms and 79 percent of the fipronil was excreted within 12 hours of bait consumption.

First instar nymphs were highly attracted to these secretions, which they readily consumed and which subsequently resulted in significant mortality. Emeto-phagy is another way in which bait toxicants can be distributed throughout a cockroach population.

Other methods of bait translocation in the environment were considered by Durier and Rivault (Universite de Rennes). In the laboratory, they found that bait, particularly fipronil, caused higher mortality in nonfeeding cockroaches because they either had direct contact with contaminated cockroaches and/or ate bait particles dropping off cockroaches (exposed to the bait) when they returned to their harborage.

A unique pest management strategy for German cockroaches was investigated by Godfrey Nalyanya, a Ph.D. student working with Dr. Colby Schal, professor of entomology at North Carolina State University. They used a "push-pull" behavioral strategy in combination with an insecticide to reduce cockroach populations. This technique involves using a repellent, i.e., methyl neo-decanamide, to force cockroaches away from an area to be protected and using an attractant, i.e., feces-contaminated surfaces, to lure cockroaches toward a baited area. This concept of luring cockroaches into specific areas that are treated, facilitates precision targeting and, consequently, reduced pesticide use.

FUNGUS + INSECTICIDE = MORTALITY. The use of biologicals, e.g., nematodes, fungus and parasites, for the control of cockroaches, has been tenuous at best. Some of the limitations to the biologicals are sustainment in the environment and/or population, slow action, consumer acceptance and other related issues.

Pari Pachamuthu and Dr. Shripat Kamble (professor of entomology at the University of Nebraska) investigated the effects of exposing German cockroaches to an entomopathogenic fungus, Metarhizium anisopliae, in combination with each of the following insecticides: chlor-pyrifos, cyfluthrin and propetamphos. The combination treatment produced significantly higher mortality rates than when either the fungus or the insecticide were used independently. They reported that there was an additive effect when combining the fungus with chlorpyrifos and cyfluthrin and a synergistic effect when the fungus was combined with propetamphos. In either case, the combination treatment reduces the amount of insecticide and fungus needed to produce a comparable effect when the products are used independently.

RESISTANCE: A PRIORITY? My bet is always on the cockroach. We are dealing with a pest that has endured, relatively unchanged, for 350 million years. Several species, including the German cockroach, have coevolved with humans. Guess what? They survived. Resistance has played a major role in the German cockroach’s success as a pest species. However, the active ingredients used in baits are standing the test of time and resistance has not reared its ugly head. Time will tell and it is far too early to let our guard down and ignore the potential for resistance to all baits.

More than a decade ago, the pest management industry expressed a need to have an expedient field test for insecticide resistance in German cockroaches. One of the leaders in this area has been Dr. Steven Valles (research entomologist for the USDA-CMAVE), who has spent many years developing detection methods that provide an immediate assessment of the presence and magnitude of insecticide resistance in field populations of the German cockroach.

To that end, he has spent much time investigating the biochemical and molecular mechanisms of insecticide resistance in cockroaches. He found that in field populations of German cockroaches, there is strong correlation between esterase (detoxification enzyme) activity and the degree of resistance exhibited toward cyper-methrin, cyhalothrin, permethrin and pro-poxur, (active ingredients widely used in liquid insecticide formulations). The isolation of this enzyme may ultimately lead to the development of a field resistance test and serve as a predictor of resistance to new active ingredients.

GERMAN AND AMERICAN ROACHES. Though not the rampant, excessive pest problem in the United States they were just a few years ago, German cockroaches, Blattella germanica, remain a constant and serious threat. The widespread use of baits appears to have reduced the severity of infestations and made insecticide resistance less of a relevant problem in terms of control.

However, Michael K. Rust and Donald A. Reierson, Department of Entomology, University of California, Riverside (UCR), have found that even though the numbers per infestation are generally lower, the incidence of German cockroaches has essentially remained unchanged. For instance, cockroaches are common in low-income housing and commercial kitchens but are usually found in lesser numbers than in years past. Also, German cockroaches continue to be the most economically important structural pest in developing countries and places where baits are not available.

Recent research by Rust and Reierson with German cockroaches involves studies to optimize control of this important pest using so-called low-impact or least-toxic chemicals. They are looking at the efficacy of old and new bait formulations, why baited populations of cockroaches are almost never eradicated, the relevant attractiveness of bait odors over distance, the effect of feeding patterns in relation to control, and the impact on control of low levels of remnant resistance. All of this with the intent of improving control with even less toxicants than is being used today. Along those same lines, Rust and Reierson are evaluating low-impact natural products like certain plant essential oils for contact toxicity and repellency to cockroaches. This introduces the concept of managing cockroaches with short-lived, highly repellent chemicals, an idea thought impractical up to now. Also, one of their projects involves looking at the synergistic effect of low rates of pyrethrins on pyrethroids and other natural products. They found that they can often lower rates and maintain efficacy if they combine novel spray solvents with low concentrations of pyrethrins.

Another serious pest that PCOs deal with is the American cockroach, Periplaneta americana. They frequently infest steam tunnels, storm drains and sewer systems. Populations frequently build to enormous numbers and subsequently invade nearby structures. Research at UCR nearly 10 years ago showed that low-volume sprays, such as chlorpyrifos and diazinon, could provide long-term control, especially in sewer systems. However, increasing concern about the contamination of watersheds, drainage and runoff water quality, and worker safety issues concerning insecticides has stimulated research into finding treatments with lower environmental impact.

Rust and Reierson’s latest research has primarily focused on using bait and parasites to control American cockroaches in sewers. Initial releases of special parasitic wasps that sting cockroach egg capsules were not successful. However, imidacloprid (Pre-Empt) and fipronil (Goliath) gel baits have provided excellent long-term control of American cockroaches.

In the first experiments, gels smeared on special plastic cards were suspended in sewers, but it was difficult to find reliable places to attach the cards. In subsequent tests, they applied the bait with a spatula under the rim of the manhole and this provided excellent results. Best overall control was achieved when all manholes connected to an infested manhole were baited, probably because this approach increases the likelihood of cockroaches finding bait. Area-wide baiting provided sustained control and helped reduce invasion from adjacent untreated sewers, and baiting near the top reduced chances of water contamination. Studies at UCR have found that similar strategies can be modified to control Oriental cockroaches and smokybrown cockroaches as well.

CONCLUSION. As you can see from this brief summary of research on cockroach pests, there is a lot going on out there that few of us are aware of or appreciate — and this is only the tip of the iceberg. It is important for us as pest management professionals and as an industry to take advantage of the information these and other scientists provide us because they do it willingly and without bias. Further, it is imperative that we support their efforts through industry funding, legislative mandate and any other means that sustain their efforts for the benefit of our industry.

The author is technical director of American Pest Management, Takoma Park, Md. He can be reached at rkramer@pctonline.com or 301/891-2600.