Since the U.S. bed bug resurgence of the 1990's, entomologists have been researching these elusive pests to better understand their behavior and improve control techniques. Despite progress, there is still much we don’t know about bed bug behavior. Entomologists, like Dr. Gail Ridge at the Connecticut Agricultural Experiment Station, are shedding some light on the habits and adaptations that make bed bugs so challenging to control. I had the opportunity to hear Dr. Ridge speak at a tribal housing conference in Augusta, Maine in June. The following represents just a small part of Dr. Ridge’s research.
Did you know young bed bug nymphs have been observed feeding on recently fed, older nymphs? They have a gene (pro-resilin) that allows bed bugs to expand when they feed and heal after traumatic insemination (males will basically poke a hole in the female’s abdomen to inseminate her). The gene allows for this additional, creepy bed bug adaptation. Clustering amongst younger nymphs allows nymphs to take a blood meal from a recently fed older nymph by piercing them in the abdomen through the exoskeleton. The pro-resilin gene allows the exoskeleton to be flexible enough to allow for these puncture wounds without killing the bed bugs. This means the young, vulnerable nymphs can stay safe in a hiding spot while the sturdier older nymphs venture out looking for a host and blood meal.
Another odd bed bug adaptation is adults survive past their reproductive usefulness. Most insects live just to reproduce, complete their life cycle, and die. These older, non-reproductive, bed bugs serve a seemingly altruistic purpose. Have you noticed bed bugs like to stack? Dr. Ridge observed the older bed bugs are usually on the outer layers of the stack. This provides protection for the younger nymphs who tend to hide under the bodies of older insects. Furthermore, young nymphs have been observed hitchhiking a ride on older bed bugs, aiding in the spread of an infestation. These older “grandparents” still play a role as caretakers of the nymphs despite having no reproductive role to play. Elders can protect the underlying insects from insecticide applications. This is another reason to use vacuuming as part of your bed bug control protocol.
Another key finding of Dr. Ridge’s research is pesticide resistance in bed bugs may be partially a behavioral adaptation in some cases, rather than biological. In order to test for pesticide resistance, she acquired a known pyrethroid-resistant strain of bed bugs to compare to non-resistant, lab-reared bed bugs. Resistant insects moved away from the pesticides, while those that were non-resistant freely walked over areas of pesticide application. This may be one way bed bugs elude chemical control and provide an explanation why infestations often become worse when chemical pesticides are used exclusively: another argument for an IPM approach, using multiple tools.
This insight into their behavior is important if we are to outsmart bed bugs. It can help us improve control tactics and understand control failures. Dr. Ridge promotes using these behavioral adaptations against them. Vacuuming dead bed bugs and skins is vital to exposing the nymphs to control techniques, but Dr. Ridge says leave the blood spots (bed bug droppings). These hold powerful pheromones that attract bed bugs to hiding spots. You can use their own scent as a lure and continue to vacuum and treat the area as long as the bed bugs continue to cluster there.
There’s still much to learn about bed bug biology and behavior, but researchers like Dr. Ridge are making great strides in increasing our understanding. The more we learn, the more we can apply this knowledge to our control tactics. To learn more about controlling bed bugs with IPM, take a look at what research is telling us about management at stoppests.org, the Connecticut Agricultural Experiment Station, Rutger's University Bed Bug information page, The Virginia Tech Bed Bug and Urban Pest Information Center, and the University of Minnesota's "let's Beat The Bug",