Knockdown vs. Dead – Not what it used to be

Oh, the good ole’ days.   There was once a time when labs could combine their reps’ knockdown and dead counts.  So I frequently get concerned clients worry about why we don’t do this.  Here is how Snell Sci defines the 3 categories:

  1. Alive = an insect capable of ‘organized forward movement’… pretty simple but does become grey when things like roaches run in a hyper-active circle (which becomes a subjective decision on a case-by-case basis for the researcher)
  2. Dead = by EPA’s latest standards, ‘dead’ must be an insect with absolutely NO movement… no twitching, no antennae moving, no nothing. To further this, EPA needs us to document that we ‘probe’ each individual insect in some way (we have a specific method for this for each individual species that we work with)
  3. Knockdown (KD) = anything in-between dead and alive

In the distant past it was rather common for researchers to combine the KD and dead as the same group.   The assumption was that once the insect was affected by the chemical, it was ‘all over’ (and maybe with many of the older, more traditional actives, that was the case).   EPA no longer accepts combinations of KD and dead.   They realize that bugs DO come back to life (see future post on this topic).  In fact, for awhile EPA required that labs collect data 24 hours AFTER the point at which the bugs were all dead.  However, the combination of additional counts AND EPA’s requirement of 10% control death (see previous post), made it nearly impossible for anyone to get data on many of the sensitive species.

The Snell Sci staff is trained to record precisely what they see at the exact interval they see it. The easy thing to do is to ignore everything that had 10 ‘dead’ on the previous count and only look at cartridges that had something KD or alive from the previous count.  To ignore all cartridges once they show 100% dead is MUCH faster and MUCH easier, but this would also be unethical and should be ‘illegal’.  Instead we pick up each cartridge on each time interval and we record what we see.  If we were to instead just ‘transcribe’ the data from the previous entry into the next entry because ‘they were already dead,’ we would be falsifying data since we did not pick up the cartridge, probe the insects, and confirm their status.  We all know that insects fully recover from actives such as pyrethrin.

So … there is little we can do about how we record it.  If we look at an insect and there is absolutely no movement, we call it ‘dead’.   We don’t know if these insects might start twitching again or not.  We have to record them as we see them at that moment.  We can’t then go back and change the 5 minute data to ‘knockdown’ if we see them twitching at the 1 hour count.  Likewise, we train our staff not to even look at the previous data for each rep.   A common problem is that a researcher can look at the previous rep and see that 10 were dead and then not bother to look at the cartridge, just record it as 10 dead again, or ignore any twitching they see and keep the data set ‘clean and neat’.  If you are not used to seeing ‘dead’ come back to ‘knockdown’ it is because lots of other labs do just that… assume that ‘dead will stay dead’ or ignore what they see to keep the data set neat and tidy.   We don’t make that assumption and instead we ONLY look at the cartridge, NOT the previous count on the data sheet.   It is a critical piece of our training.  And frankly something I am proud of.  When data does not look perfect, it means we are doing our job.  If it looks perfect, someone probably ‘helped’ it to stay that way.  It is something all labs should show very regularly.  When data looks neat and tidy, I get concerned.