The German Cockroach - What You Need To Know About This Longtime Industry Nemesis
By Robert J. Kopanic Jr., Pest Control Technology, July 2006
Moving well into the first decade of 2000, the pest control industry is focusing on an increasing number of emerging urban pests, arthropod and non-arthropod alike. Let's take some time to review the basics of one pest that continues to hang in there regardless of what other "vogue" pests might be in the spotlight ... the German cockroach.
Gosh, a few years ago I heard rumors that we had the German cockroach (Blattella germanica) on the ropes.Researchers were having a difficult time finding apartments to conduct experimental trials, calls about infestations weren’t as frequent, and there was some dismay expressed from the industry. Was the elimination of one of our long-time most lucrative money bugs on the horizon? I think not, nor did I ever think so, just for the record. I was quite relieved to hear Dr. Coby Schal from North Carolina State University deliver the Arnold Mallis Memorial Award Lecture at the 2006 National Conference on Urban Entomology titled, "The German Cockroach: Reemergence of an Old Foe ... That Never Departed." The talk pointed out some excellent reasons why our good friend Blattella germanica is going to be here to stay ... at least for a while.
In addition, several companies have recently launched new cockroach gel bait products; targeting "bait-aversion," bait palatability and general resistance, acknowledging that PMPs continue to require the best formulations possible to fight this formidable pest. In honor of all of this, I would like to use this space to review some of the basics about the German cockroach.
Where did the German cockroach come from? To change Dr. Austin Frishman's common response to this question about invading species just a bit: "Who cares, they're everywhere [as opposed to here] now!" On a worldwide basis, the German cockroach has specialized in exploiting areas that humans inhabit.
Historical literature mentions two origins of the German cockroach. Cornwell (1968) suggests that this species originated from northeastern Africa, whereas Roth (1970) suggests that eastern Asia is a more likely estimation. As previously stated, regardless of where they came from, they are here now and got here by using humans as their primary means of dispersal. In modern time, the German cockroach has never been found far from humans or human activity; their sole existence depends upon humans wherever they are found.
The German cockroach is no doubt the most important cockroach pest species across the United States. They can be found in every state, and although they are not suited to surviving outdoors in those areas where ambient temperatures dip below freezing from time to time, they don’t need to because they have been able to thrive quite nicely in these less-than-perfect environmental situations by way of sharing the food, water, and shelter provided by homo sapiens. What are cockroaches after? What do they want with our home? Why do I have them in my bathroom, and why are they so difficult to battle in food preparation areas? I like to tell people in my training sessions that the German cockroach is a lot more like us (humans) than not. That usually results in at least one or two strange stares back from the audience. But after all, they are animals (just like us). Consequently they seek the same sorts of things from their surroundings: food, water and shelter.
Cockroach Reproduction - Power In Numbers
Like so many of our urban insect pests, one factor that has allowed the German cockroach to thrive is its amazing reproductive capacity. Commonly, consumers will say, “I’ve heard that when you see one, there are thousands of others behind the walls that you don’t see!” Now while this isn’t necessarily always true (although I’ve seen some case where it was), this roach is quite capable of producing huge numbers of offspring. As you all know, the German cockroach, like other insects that go through incomplete metamorphosis, have three distinct life stages: egg, nymph, and adult. The nymph is distinguished from the adult by its size, lack of wings, and inability to reproduce.
The nymphs generally go through five to seven molts depending on environmental conditions (temperature, availability of food and water) before reaching the adult stage, and the elapsed time from egg fertilization to adult is usually around 100 days, again depending on the environmental factors listed above. It is important to remember that each fertilized female can produce anywhere from two to six egg capsules, or ootheca, during her adult career that will each contain anywhere from 15-40 individuals (in a one-to-one, male-to-female ratio). This is what makes the pregnant female German cockroach such an important life state to consider. Given the food and water needed to survive, just one pregnant female stowed away in the bathroom or kitchen can result in a nice infestation within 100 days! What would happen if every one of these offspring survives and mates, and then those females produce offspring? Although it’s just theoretical, you do the math! Needless to say, the economic pest threshold for German cockroaches in homes or commercial establishments is different than the threshold of, say, aphids or corn earworms in our garden. Do you know what that threshold is? ZERO of course! Just one cockroach can result in an infestation that is going to result in a phone call to the PMP.
Shoes Were Made For Walking
We generally think of German cockroaches as nocturnal creatures, but studies have demonstrated that they do most of their exploring and foraging for food and water three hours before it is dark and again one hour before the light. In situations where humans are involved these patterns may be changed or not always necessarily observed. We’ve heard it before when discussing ant foraging behaviors: the best time to find certain ant species foraging is right at dusk or at night. Perhaps this isn’t a bad idea for locating cockroaches either! It’s not always feasible to get into accounts during these times, but where possible it could assist you in discovering where roach populations are concentrated.
There are a lot of accounts in the old literature about just what cockroaches will and won’t eat. Basically, there is the short story; they’ll TRY to survive on anything that has calories! Cockroaches haven’t been able to survive for hundreds of millions of years by being finicky eaters. Some of my favorites that are repeated over and over are cardboard, soap, hair, eyelashes and fingernails (of living humans!), not to mention each other (cannibalism), their fecal material (coprophagy), and regurgitated food (emetophagy). If you’ve been around long enough, you probably have a few favorites of your own. Bait manufacturers have created superior bait products by utilizing the aforementioned behaviors of cannibalism, coprophagy and emetophagy to their advantage. By incorporating active ingredients that are either slower acting, not metabolized or metabolized into other toxic (to the roaches) compounds, manufacturers have developed a deadly weapon against Blattella germanica. The theory is to use one cockroach that does wander into a bait placement as a carrier of material to other roaches that are in the colony. Several published studies have demonstrated the phenomenon of secondary kill or horizontal transfer. This allows the PMP to reach non-foraging or hiding individuals in an infestation without necessarily having to spray or treat directly deep into harborage areas. It also reduces the amount of material that has to be put down in an account. Furthermore, I think that most consumers or clients perceive baits as lower-impact pesticides. Bait placements should still be strategically placed as close to the harborage site as possible to maximize secondary/horizontal effects, so don’t skip that all-important step of inspection!
Just how little of a crumb is required for a German cockroach to survive? This depends on what survive means. There are plenty of studies on this topic, but first it is important to know that they can survive longer on water alone that on food alone. In the absence of both food and water, the mean survival time for adult females was shown to be 13 days and for males, eight days. However, if the proper amount and type of food (dog food being better than cardboard!) is available to them, it has been demonstrated that adult females could live for more than 300 days (that’s almost a year). Now just because the individual is alive, say in the case of the female roach above, doesn’t not mean that it is capable of reproducing. A diet with at least 5 percent available protein is required for the female to produce viable eggs. This is a bit of an academic point in must field cases as the food available to roaches in these conditions will likely have no problem meeting this protein requirement. Then again, it has also been demonstrated that in the absence of suitable protein sources, the German cockroach can compensate for this deficiency by eating larger amounts of lower protein food. Amazingly, but to their credit, cockroaches have been around for hundreds of millions of years! The thought that I’m hoping to trigger in your brain is the MOST important rule in German cockroach control: sanitation.
Sanitation Is Key
It doesn’t matter how attractive or palatable the particular bait you are using is, if you don’t take proper measures to insure that basic sanitation practices are followed, i.e. cleaning up the alternate food and water sources, your treatment program could be in jeopardy. I can see you shaking your heads out there, and I know, sanitation is easier said than done, but make every effort that you can to incorporate sanitation into your treatment programs. It will pay off with happy customers in the long run.
As stated earlier, water is a much more limiting factor for the German cockroach than is food (in facts it’s the same for us and all other animals as well), so managing sources of available water through sanitation practices is as important if not MORE important to your sanitation strategy. A suitable water source for a German cockroach doesn’t have to be much; it can be a small drip in a leaky faucet or pipe, condensation on a sink or toilet bowl, moisture around a commercial dish-washing area or even an extremely humid moist area underneath a kitchen sink. The German cockroach will also travel surprisingly great distances from the harborage to get to a water source. But when conducting those inspections, find the water leak or source of moisture and you’ll find the cockroaches if they are there. A pregnant female cockroach can stay in the harborage and go without water for as long as five days! When was the last time you went without a drink of water for five days? This to me is an amazing adaptive benefit to limiting the amount of time out in the open and therefore susceptibility to predators (or the bottom of a shoe!).
Have you ever noticed that in a large infestation of German cockroaches you tend to see more nymphs and adult males foraging (out of the harborage) than females? Adult male German cockroaches seem to require more frequent visits to water and food resources. There is at least one good explanation for this occurrence. Appel et al. (1983) demonstrated the water loss rate of adult male German cockroaches was three times higher than that of adult females. They lose water through their cuticle more rapidly than the more robust adult females and must therefore take in water more often. Silverman (1986) conducted laboratory studies demonstrating increased frequency and duration of feeding bouts when cockroaches had to travel to get to the food/water resources, particularly at higher population densities.
When resources were much closer to the harborage, frequency and duration of feeding bouts decreased in particularly high density populations. One suggested explanation for this is that increased competition for the same resource results in feeding disturbances. What does this mean for the PMP? You’ve heard it before: use more and smaller bait placements - i.e. dots - rather than fewer larger ones. You’re less likely to encounter the above cockroach behavior if you have more available food sources, especially in that one really tough account with thousands of roaches!
We have reviewed just some of the basic principles of cockroach biology and survival. There is, of course, a whole lot more to it than that we’ve discussed here. An excellent book dedicated entirely to the German cockroach, Understanding and Controlling the German Cockroach by Rust et al., is a great resource for those who want to learn more about the lowly but fascinating German cockroach. I hope this article has reminded you to think of some of these principles when you are out there baiting or spraying for cockroaches, and that you don’t rely on only the chemicals alone, but on a good understanding of what allows your enemy to survive as well as it does. Remember, you’re a lot more like a roach than you are different…