Within a building, German cockroaches (Blattella germanica) tend to aggregate in kitchen areas, and they seem to travel between adjacent apartments, especially if management methods are incompletely applied—such as in one apartment but not in another. A new study shows how a building-wide integrated pest management program can decrease cockroaches’ movement between apartments. (Photo credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org)

By Andrew Porterfield

Andrew Porterfield

The German cockroach (Blattella germanica) has been a familiar part of European and American structural environments for several hundred years. One of the most common indoor insect pests, the cockroach (which originated from Southeast Asia, not Germany) is known for contaminating food, carrying pathogens, and triggering allergies and asthmatic reactions. It also adapts well to nearly every temperate environment, easily resists many pesticides, and is very difficult to eradicate.

Applying integrated pest management (IPM) methods against cockroach populations requires a knowledge of how the insects aggregate within—and between—buildings. Researchers have found that cockroaches disperse within apartment buildings, but rarely between them. Within a building, they tend to aggregate in kitchen areas, and they seem to travel between adjacent apartments, especially if insecticides were incompletely applied—such as in one apartment but not in another.

In a high-rise apartment building, researchers led by Changlu Wang, Ph.D., at Rutgers University, examined the spatial distribution of German cockroach (Blattella germanica) infestations among residential units. Prior to the application of a building-wide integrated pest management (IPM) program, the researchers found cockroach distribution in the building was not random or independent; instead, if one apartment was infested, so were neighboring apartments that were adjacent, across the hallway, or directly above or below. After a 12-month IPM program, the distribution correlations were weakened significantly. (Image originally published in Zha et al 2019, Journal of Economic Entomology)

To get a better idea of how IPM could be effectively applied to eliminate infestations in an entire building, Changlu Wang, Ph.D., an entomologist at Rutgers University in New Brunswick, New Jersey, and his team applied IPM techniques in a 13-story, 188-unit apartment building in urban Paterson, New Jersey. Their study uncovered cockroach dispersal patterns before IPM application and determined that IPM could eliminate infestations in a single apartment as well as reduce movement of the pests between apartment units. Their research was published May 23 in the Journal of Economic Entomology.

The researchers began by discontinuing current pesticide applications and then setting traps in 172 of the apartments. The IPM program was then initiated, starting with handing out one-page education sheets to residents with information on cockroach prevention and control and instructions on cleaning floors, reducing clutter, stowing pet food, and halting the use of consumer insecticides (which generally are ineffective). Any infested apartments received an initial treatment of Advion gel bait, and boric acid dust was used in 32 units that had more than 20 roaches in their traps after the first 14 days. A second building-wide monitoring effort took place at six months, and a third and final monitoring took place at 12 months.

Of the 172 apartments studied, 90 had cockroach activity in the set traps, 18 had heavy infestations (averaging 132 roaches), another 18 had medium infestations (averaging 21 roaches) and 31 had light infestations (averaging two roaches).

Initially, the team found that cockroach distribution in the building was not random or independent; instead, if one apartment was infested, neighboring apartments that were adjacent, across the hallway, or directly above or below were likely to be infested as well. Roaches were found in higher numbers beside stoves and refrigerators. The strong correlation of these initial distributions was unexpected. “We were surprised by the strong correlation between neighbors of all directions: sharing a wall, sharing a ceiling/floor, and across the hallway,” Wang says.

These distribution correlations began to weaken significantly after IPM applications. At six months, infestations among wall-sharing apartments became less frequent, and at 12 months, infestations in apartments across hallways and sharing walls were no longer correlated with each other. “Implementation of a building-wide cockroach IPM program for a 12-month period eliminated the correlations among infestations across the hallway as well as those sharing common walls,” the researchers wrote. In addition, any new infestations after six and 12 months were not connected to existing infestations at the beginning of the study, indicating that the new infestations were not triggered by previous populations.

In a high-rise apartment building, researchers led by Changlu Wang, Ph.D., at Rutgers University, examined the spatial distribution of German cockroach (Blattella germanica) infestations among residential units. These diagrams illustrate the infestation levels at the beginning (left) of the building-wide integrated pest management program, after six months (middle), and after 12 months (right). Units in red were heavily infested; orange had medium infestations, and yellow had light infestations. Units in white were free of cockroaches. (Images originally published in Zha et al 2019, Journal of Economic Entomology)

While the study showed that IPM within an entire building could suppress roach infestations between apartments, it also showed that only a comprehensive control approach, which left no apartment unit out, could be effective. It’s also likely that roaches could never be entirely eradicated, “due to the size of the building, frequent resident turnover, residents’ high level of tolerance to cockroaches, and poor sanitary conditions in a small proportion of the apartments,” Wang says. “This is why it is necessary to implement a continuous pest management program and keep the number of cockroach infestations as low as possible. On the other hand, it is possible to have cockroach-free apartment buildings when some or most of these conditions are not present.”

Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.