Ordinary bed bug behaviour is basically invisible. Bed bugs will typically feed when people are sleeping and stay out of harms way when there is human activity. After chemical treatments the bugs begin to lose control of brain function and and begin acting in very uncharacteristic manners such as wandering around during the day or feeding on a sensitive part of a person’s body such as the face. It is during these times that customers sometimes accuse the exterminator of doing a bad job because the customer now notices many more bugs than before. On the contrary – these bugs that are now so obvious will probably die eventually due to pyrethroid poisoning. It is the hidden/healthy bugs that are the problem.
As pyrethroid resistance becomes more pronounced the amount of time the bugs live after being poisoned becomes longer. It is important for the exterminator not to be psyched out by the activity and resist retreating too soon. It is better to allow some time for the chemical to do its work. Of course there is a sweet spot for retreatment intervals but it probably varies depending on the amount of resistance.
One interesting piece I have noticed is that bed bugs will survive the initial poisoning on the baseboards, climb the bed and take a blood meal, and then harbour in the folds of an encasement of the chemically untreated mattress. I suspect the bugs are avoiding returning to the baseboard because the baseboard is now chemically uncomfortable, the mattress has no chemical residual and therefore more comfortable, and there is now space for bugs on the mattress because the previous bugs were killed in the first treatment. When I begin treating these new bugs on the encasement I have found that many are already dead. I hypothesize that the bugs received a lethal dose on the baseboard but survived long enough to take a blood meal and find a new harbourage on the bed.
A good gauge for retreatment intervals is to analyze how many bugs are alive on the mattress during the second treatment. If most of the bugs are dead the retreatment interval is about right. If most of the bugs are alive the retreatment schedule needs to be tightened.
If climb up interceptors are used the exterminator can evaluate how many live bugs and how many dead bugs are in these devices. Adjust retreatment schedules accordingly.