The ‘10% Control Death’ Factor:
Over the past few years, EPA has been requiring that all efficacy testing data stop once the average for the control treatment reaches 10%. This is a huge factor that has great repercussions on the results of your test product(s). First, let’s take the easy species… insects such as bed bugs and German cockroaches are not really a problem for this as they can often last 7-14 days in controls. Of course this is a major problem for some new actives as they can require 14-21 days to reach an acceptable level of mortality (by EPA standards this can be 85-90%, depending on the situation). However, even when you account for these new slow acting actives, the 10% control factor is not the end of the world for some species like cockroaches.
But what about the species that are NOT able to survive for such long times… such as mosquitoes, aphids, whiteflies, and many more? For these species it can be nearly impossible to expect only 10% control death even for 24 hours, but the idea that 90% of mosquitoes to survive for more than 48 hours is next-to-impossible. For direct contact sprays, it is reasonable (in our experience) that most products should easily provide 90% treatment mortality with your product within 24 hours, so control death is not of major concern. But this obsession EPA has over 10% control death is very unfair when it comes to residual exposures for these sensitive species such as some of the mosquitoes. First, EPA wavers on a regular basis as to how long is acceptable for insects to be exposed to such surfaces, but in this case the most logical expectation is that they won’t allow more than 4 hours of exposure on a treated surface before the mosquitoes need to be moved. This means that the mosquitoes will be stressed even further as we need to move them from the treated surfaces to untreated containers…. Putting more risk on the 10% factor. Then add to that, the problem that insects die MUCH slower when only exposed through tarsal contact of residual tests. This leaves a high probability that mosquitoes exposed through tarsal contact (i.e residuals) for only 2-4 hours are going to need more than 24 hours to show 90+% treatment mortality, particularly when the world needs eco-friendly formulas at super low rates for area-wide treatments of mosquitoes. This means 10% control death is a HUGE problem for residuals and mosquitoes, not to mention dozens of other species.
One of the few conditions EPA has in writing about testing methods for efficacy is the requirement to run statistical analysis and the requirement that all tests need to include an Abbotts correction formula of the data. First, Abbotts is a formula designed to correct for the level of control death (in a very loose interpretation, Abbotts essentially subtracts the control death from your treatment death). Second, any statistical analysis will also compare the probability of the treatment being different from the controls. Between these 2 forms of analysis, EPA has a built-in model to properly evaluate the performance of a new formulation. So what is the point of a black-and-white refusal to review any data past 10% control death? Certainly it is easier than reviewing the stats. Additionally Abbotts fails when the treatment reaches 100%. As with all unwritten policy from EPA, things regularly change and I would guess this factor may wane with time. Snell Sci will provide reports with as much as 15% control death when we see that the treatment will be rejected without that extra data (i.e. either we gamble the control death or the product has no chance). Maybe as labs clean up their procedures and stop dumping junk data into reports, EPA will also ease up on such black-and-white stances.