Droplet sampling of an oil-based and two water-based antievaporant ultra-low volume insecticide formulations using Teflon- and magnesium oxide-coated slides.

We estimated the diameters below which 50% and 90% of the volume of droplets exist (Dv50 and Dv90, respectively) of 1 oil-based (Permanone 30-30) and 2 water-based (AquaReslin, Aqua-K-Othrine) antievaporant aerosols (with the Film Forming Aqueous Spray Technology [FFAST]) using Teflon- and magnesium oxide (MgO)-coated slides and determined whether the aging of the droplets on the slides (up to 60 min) exhibited any significant effect on Dv50 and Dv90 calculations. There were no significant differences in either Dv50 or Dv90 estimates on MgO-coated slides at 0 min and 60 min for all 3 products tested. On Teflon-coated slides, the only product that showed significant difference between 0 min and 60 min in both Dv50 and Dv90 estimates was Aqua-K-Othrine, perhaps due to a difference in formulation components. Specifically, both values corresponding to Dv50 and Dv90 at 60 min decreased by approximately 50% when compared to the values at 0 min. For the other 2 products, AquaReslin and Permanone, aging of droplets on Teflon up to 60 min did not have any significant effect on Dv50 and Dv90 values. To further investigate the behavior of Aqua-K-Othrine droplets on Teflon-coated slides we observed the droplets immediately after spraying and at 10-min intervals under different conditions of temperature and humidity. The majority of the shrinkage occurred within the 1st 10 min after impaction on the slides under all conditions tested. So in most field situations where slides are read several hours or days after collection, this shrinkage would not be observed. The MgO-coated slides should be the preferred field method for sampling droplets of Aqua-K-Othirne with the FFAST antievaporant technology.