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.
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.
EATING MACHINES. 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!
CONCLUSION. 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…
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