Tracking Bed Bug Infestations

Brett Smith for – Your Universe Online

Two studies published in the Journal of Medical Entomology this month have revealed new insights into the behavior of bed bugs and possibly shown new ways to deal with these tenacious pests.

One four-year study, from epidemiologists at the University of Pennsylvania’s School of Medicine, found that bed bug infestations around the city of Philadelphia tended to be at their highest in August and lowest in February.

“There is surprisingly very little known about seasonal trends among bed bug populations,” said study author Michael Z. Levy, assistant professor of epidemiology in the Center for Clinical Epidemiology and Biostatistics (CCEB) at Penn. “We found a steep and significant seasonal cycle in bed bug reporting, and suspect that bed bugs have different levels of mobility depending on the season, and that their population size may fluctuate throughout the year.”

He speculated that warm weather could encourage the bugs’ migration and breeding behaviors.

“We may be able to exploit this cycle: These seasonal trends could guide control programs to help reduce a city’s growing bug population,” he added.

In the study, researchers mapped phone calls reporting infestations to get the spatial and temporal patterns of the bugs. While bed bug reports came from all across Philadelphia, the south side of the city appeared to be the most affected.

Bed bug reports in Philadelphia gradually rose by 4.5 percent per month from 2008 to 2011, a nearly 70 percent increase from year to year. Almost half of all pest infestations reported over the study’s time period were for bed bugs, a total of 382. Reports peaked in August and bottomed out in February. The team said the bugs probably move and proliferate more often during warmer weather.

“We know the bug reports fluctuate over the year—what we need to figure out now is whether to treat when they are at their worst, in the summer months, or whether to wait until their numbers are down in the winter.” Levy said. “Seasonality, we noticed, is just one attribute that can eventually aid control measures, but it is one of many attributes we hope to uncover.”

In the other study, researchers found that bed bugs tend to grow faster when they live in groups. A study by researchers from North Carolina State University discovered that bed bug nymphs living in groups matured 2.2 days faster than solitary nymphs.

“Now that we found this social facilitation of growth and development, we can start asking what sensory cues are involved and how they contribute to faster growth,” said study author Coby Schal, a professor of entomology at NC State. “This should lead to some interesting experimental research on what sensory cues bed bugs use to grow faster in groups.”

The Carolina researchers also found that the effects of grouping are the same despite the age of individual bed bugs in the group. The researchers suggested that newly hatched bed bugs do not even need to interact with older bed bugs for faster development rates to occur.

“The observations that adults do not appear to contribute to nymph development suggests that eggs can survive and found new infestations without any adults,” Schal said.