27 May Host cues and feeding patterns of bed bugs
We learned earlier that wild bed bugs starved for a week and subsequently placed in an open climb up interceptor (with zero harbourage available) would generally follow an awake / sleep pattern corresponding to the sleep patterns of the most recent host. I made a change to the structure of the experiment and collected 20 fresh bed bugs from a mattress and immediately placed them into my teflon experiment pan that contained an excellent harbourage in which to hide. The bugs scurried about for a short time and soon all bugs were invisibly hidden in the harbourage. I video taped these bugs for 15 days in my isolated experiment room.
The results were very interesting. The first few days there was absolutely zero movement in the pan. I assume this was due to the fact all the bugs had recently fed. After a few days a single bed bug would periodically wander the pan and then return to the harbourage. A few days after that a second bug would join the wandering. And a few days after that a third bed bug would periodically join the sojourn. The bugs usually wandered in the late evening early morning hours consistent with the original host sleep patterns but was not entirely consistent. Some wandering occurred at other hours as well. The interesting piece here was that never in the 15 days of recording was there ever more than 3 bed bugs active at any given time. If there was activity it was usually only 1 or two bugs moving.
On the 15th day at 1PM I entered the experiment room, sat in front of the experiment pan for 1.75 hours, and watched. I also turned on the carbon dioxide to represent about 1.5 additional people in the room. No additional heat was added. Within 1 hour at least 10 bed bugs were wandering the experimental apparatus (subject of future blog). Interestingly enough I observed 6 bugs remaining in the harbourage to be active and peeking out at me (I could not quite tell which part of the bugs were sticking out of the harbourage as I was not close enough but I assume it was the front) but refused to wander into the open despite the obvious host cues presented by my own body and the additional Co2.
I left the experiment room and let the experiment continue to run over night with only the additional Co2 source as an attractant. Several hours later two additional bugs entered the experiment area but a minimum of four bugs refused to enter the area. I entered the experiment room the next day and watched the pan the for about an hour and those bugs were again peeking out at me and again refused to enter the open area.
An interesting observation is how differently the bugs behaved in two different settings. When bed bugs were starved and then placed in an open climb up interceptor with zero harbourage available all the bugs moved every day to some extent. When bugs were freshly caught and immediately given a substitute harbourage only 15% moved on a daily basis after two weeks of starvation. Given that a natural bed bug habitat would include harbourage this second experiment would probably more closely resemble field conditions. Perhaps the interceptor/circadian rhythm observation included a search for harbourage which necessitated more movement. Or perhaps the movement of a few bugs constantly disturbed the entire group which got everyone moving. The current experiment does not negate the circadian rhythm observations, rather it adds another layer of knowledge.
One big lesson I observed here was that the circadian rhythm did not appear to cause movement for the vast majority of the bugs despite their being hungry (bugs generally feed every 5 to 7 days). It was not until host cues were added to the room that the bugs became physically active. In previous blogs I mentioned that bed bugs will remain in their harbourages on an infested mattress for months waiting for a host to return despite other potential hosts being available just a few feet over in the next room. I think this experiment inadvertently displayed that previously observed tendancy. It appears that the feeding behaviour of the bed bug, while partially influenced by circadian rhythms, is in large part stimulated by the presence of a host. What those host cues are exactly remains to be discovered. For a minimum of 4 of my bed bugs in this experiment, additional cues, beyond my presence and additional Co2, were required for them to leave the harbourage. I did not include additional heat in this experiment as it is generally thought to be a very short range cue. I suspect some of the cues the bugs were looking for involved a host going to sleep and presenting itself in a more accommodating fashion. This would then suggest an ability to identify sleep via reduced motion, vibration or sound levels.
This experiment also sheds light on the difficulty of chemically treating empty apartments. I have never successfully treated an empty apartment and other researchers have also commented on this difficulty. But some exterminators continue to treat empty suites and even recommend that the suites be vacated for a few weeks after treatment. This is a huge mistake. You will never get rid of bugs in an empty suite as the bugs simply hunker down in their harbourages waiting for the host cues to arrive. This experiment also reinforces the idea that one should never abandon an infested bedroom – the bugs will simply wait for you and attack you the next time you spend any appreciable amount of time in that room.