[Bed Bug Supplement] Determining a Population’s Structure

Figure 1. Typical overnight catches in the First Response Bed Bug Trap (top) and Monitor (bottom) in a heavily infested location.

One of the most challenging aspects of bed bug control is determining the true extent of the infestation.

Estimating the total bed bug population based on the number of adults is notoriously unreliable. The portion of the population comprised of adults varies widely, based on a number of poorly understood environmental factors, including the age of the infestation. Previous studies have reported adults composing anywhere from 16 to 78 percent of mobile phases (that is, all life stages excluding eggs). It is likely that visual surveys are skewed towards the larger and easier-to-see adults. One survey using fumigation reported adults at 5 to 30 percent of mobile stages, which is a more realistic range, given recent studies of population-growth potential. Thus, new tools are needed to aid PCOs in their evaluations of bed bug infestations.

SpringStar has developed a line of kairomone-based bed bug capture devices: the First Response Bed Bug Trap (a durable device meant for long-term monitoring), and the First Response Bed Bug Monitor (a disposable unit intended for overnight use). (A kairomone is a chemical used for communication that is released by one species and used by an individual of another species.) The products are available to both professional and consumer customers.

Both devices use a three-fold combination of heat, carbon dioxide (CO2) and a proprietary, human-mimicking kairomone blend to attract host-seeking bed bugs (see Figure 1 above). Both devices use a white sticky surface to trap insects, which allows for quick identification in the field and easy classification later in the lab.

Two locations were used for initial field testing of the Trap and Monitor: a heavily infested, unoccupied room with no furniture (Location U); and a heavily infested, occupied apartment with two bedrooms (Location V). Both locations reported a bed bug infestation for at least one year with little to no prior treatment. Both populations were large and thoroughly established, each as close to a stable population as one can find outside of a lab. All trap catches from both the trap and monitor were counted and classified by life stage (N1-N5 and adult). Adult bed bugs were further classified by gender.

N1 nymphs, freshly hatched and unfed, made up about two-thirds of total catches. One might expect such results in a new or growing population, but not necessarily in a stable one. However, the observed population composition was virtually identical at both independent test locations. The population also closely matched one collected by fumigation in South African huts (see Figure 2 below), suggesting that the bed bug population composition as sampled by this trapping method accurately represents the entire infestation. The important conclusions to draw from this data is that adults may often make up a much smaller percentage of the population than previously reported.
 

In a stable population, such as a lab colony, males and females are present in approximately equal numbers. This 50:50 ratio has been supported by a number of field surveys. Location V contained essentially even numbers of both sexes. The main field site, Location U, showed a different result: over time, increasingly more male bed bugs than females were trapped. Based on the results from the other site, it does not appear to be a result of differential attraction by the traps to the sexes. Rather, an environmental stressor at Location U, such as a sudden lack of food, may be spurring emigration from the site.

“Location U” is a single room within a homeless shelter. There is no furniture, and (for the most part) no one slept in the room during the course of the study. However, people slept in adjacent rooms and hallways every night. Females compose a majority of migrating adults and thus a continuous stream of emigration could lead to an increasing imbalance between the sexes — as was observed (see Figure 3 below). No such change was seen at Location V, likely due to both the presence of hosts throughout the study and longer migration paths to new locations and hosts.

Final Thoughts. There is a lot left to learn about population composition and dynamics within different types of bed bug infestations, and how various factors, such as population age, access to hosts and different types of treatment affect each population. A durable, cost-effective trapping system, that is both powerful enough to capture a lone adult left after heat treatment and attractive enough to pull in many bed bugs of all life stages, will be a vital tool to illuminate these aspects of bed bug ecology. The population sample captured in a First Response Bed Bug Trap over a few days of trapping may be sufficient to describe the entire population, while discrepancies or changes in gender ratios of adults may indicate extensive emigration from the monitored location.

With widespread use of these devices in a variety of circumstances, a more detailed picture of bed bug populations can be assembled. Further studies with local pest control companies are currently being conducted to monitor before and after both heat and pesticide treatments in multiple locations and to compare the trapping efficacy against canine detection methods.

Editor’s note: Visit www.pctonline.com for a list of sources from this article.

Schaafsma is a research biologist and Hapke is an entomologist and research manager for SpringStar (www.springstar.net), Woodinville, Wash.