02 Apr Circadian rhythm of the bed bug and the best discoveries are accidental
A few years ago I was doing some dry ice (carbon dioxide attractant) experimentation with Susan Mcknight’s Climb up interceptors in a rental suite and found that the device really did work. Unfortunately the tenant complained that during periodic inspections the Interceptor was found to trap bugs but also lose bugs. There would be perhaps 3 bugs trapped one day and only 2 were left the next suggesting escape. In my own observations I had never noted this behaviour but I decided to do some video experimentation to confirm or refute the tenant’s observations. I put a new Interceptor under my own bed for a week to simulate ordinary use and then filled the pitfall portion with about 100 bed bugs I had harvested off a mattress and starved for a week. I then video taped the bugs for a week.
After a week of recording I noted that not a single bug had escaped so I confidently concluded that the tenant had been in error. The bugs simply walked around the inside the interceptor attempting to escape but could not escape. (please note I am now less sanguine about that confident determination after noting bed bugs periodically climbing my teflon pans and glass bowls). I did note, however, that the bugs followed the same Circadian rhythm patterns that K. Melanby documented in 1939 (quoted in Robert Usinger’s Monograph of Cimicidae, 1966). The bugs would follow a distinct “awake/sleep” pattern and be most active at dawn. A few weeks later I decided to repeat my experiment with a different batch of bed bugs and noted the same results except this time the awake/sleep pattern shifted about 4 hours with the most active time well into daylight hours!
The first batch of bugs came from a home with typical sleeping patterns – the bed bug hosts went to bed at night and were active during the day – much like human activity in England was like in 1939. The second batch of bugs came from a home where the host typically worked the evening shift (quitting time at 11PM) at a local store. Interesting!!
I have noted the same pattern during my apartment block inspections for bed bugs. Whenever I find even the most severe infestations the bugs are typically in their “sleep” mode on the bed. On one occasion, however, I woke a person at 2 PM from their sleep and asked to inspect their bed. The bed was literally shimmering with bed bug activity. The bedroom had south facing windows, the blinds were open, and the room was bright.
My theory, as it now stands, is that the bed bug does not rely on day/night cues for activity but rather will adapt its circadian rhythm to the host’s circadian rhythm – whatever that might be.
To test this theory further I have put out a request, through our local exterminator community, for large sample of bed bugs harvested from the bed of a true night shift worker. My hypothesis is that the awake/sleep pattern of these bugs will be exactly opposite of a day shift worker. Further questions would include: how do the bugs to adapt to shift workers constantly varying their schedules? Can we use the circadian rhythm to test which cues the bed bug uses to alter its own awake/sleep patterns? For example, one might repeat my initial experiments in a sealed room and mimic the vibration or sound a person might make and attempt to change the circadian rhythm. Perhaps we can discover cues other than heat and carbon dioxide the bed bugs use to find their hosts.