Table Of ContentDroplet Sampling of an Oil-Based and Two Water-Based
Antievaporant Ultra-Low Volume Insecticide Formulations
Using Teflon®- and Magnesium Oxide-Coated Slides
Author(s): Alexandra Chaskopoulou , Mark D. Latham , Roberto M. Pereira , and
Philip G. Koehler
Source: Journal of the American Mosquito Control Association, 29(2):173-176.
2013.
Published By: The American Mosquito Control Association
DOI: http://dx.doi.org/10.2987/12-6305r.1
URL: http://www.bioone.org/doi/full/10.2987/12-6305r.1
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2013 2. REPORT TYPE 00-00-2013 to 00-00-2013
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Droplet Sampling of an Oil-Based and Two Water-Based Antievaporant
5b. GRANT NUMBER
Ultra-Low Volume Insecticide Formulations Using Teflon- and
Magnesium Oxide-Coated Slides 5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
University of Florida,Department of Entomology,Building 970 Natural REPORT NUMBER
Area Drive,Gainesville,FL,32611-0620
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)
11. SPONSOR/MONITOR’S REPORT
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Approved for public release; distribution unlimited
13. SUPPLEMENTARY NOTES
14. ABSTRACT
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-KOthrine)
antievaporant aerosols (with the Film Forming Aqueous Spray Technology [FFASTTM]) using TeflonH-
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.
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Prescribed by ANSI Std Z39-18
JournaloftheAmericanMosquitoControlAssociation,29(2):173–176,2013
CopyrightE2013byTheAmericanMosquitoControlAssociation,Inc.
SCIENTIFIC NOTE
DROPLET SAMPLING OF AN OIL-BASED AND TWO WATER-BASED
ANTIEVAPORANT ULTRA-LOW VOLUME INSECTICIDE
FORMULATIONS USING TEFLONH- AND MAGNESIUM
OXIDE-COATED SLIDES
ALEXANDRACHASKOPOULOU,1,3MARKD.LATHAM,2ROBERTOM.PEREIRA1
ANDPHILIPG.KOEHLER1
ABSTRACT. We estimated the diameters below which 50% and 90% of the volume of droplets exist
(Dv and Dv , respectively)of 1 oil-based(Permanone 30-30) and 2 water-based(AquaReslin, Aqua-K-
50 90
Othrine) antievaporant aerosols (with the Film Forming Aqueous Spray Technology [FFASTTM]) using
TeflonH-andmagnesiumoxide(MgO)-coatedslidesanddeterminedwhethertheagingofthedropletsonthe
slides(upto60min)exhibitedanysignificanteffectonDv andDv calculations.Therewerenosignificant
50 90
differencesin eitherDv orDv estimates on MgO-coated slidesat 0 minand 60minforall 3 products
50 90
tested.OnTeflon-coatedslides,theonlyproductthatshowedsignificantdifferencebetween0minand60min
in both Dv and Dv estimates was Aqua-K-Othrine, perhaps due to a difference in formulation
50 90
components.Specifically,bothvaluescorrespondingtoDv andDv at60mindecreasedbyapproximately
50 90
50%whencomparedtothevaluesat0min.Fortheother2products,AquaReslinandPermanone,agingof
droplets on Teflon up to 60 min did not have any significant effect on Dv and Dv values. To further
50 90
investigate the behavior of Aqua-K-Othrine droplets on Teflon-coated slides we observed the droplets
immediatelyaftersprayingandat10-minintervalsunderdifferentconditionsoftemperatureandhumidity.
The majority of the shrinkage occurred within the 1st 10 min after impaction on the slides under all
conditionstested.Soinmostfieldsituationswhereslidesarereadseveralhoursordaysaftercollection,this
shrinkagewouldnotbeobserved.TheMgO-coatedslidesshouldbethepreferredfieldmethodforsampling
dropletsofAqua-K-OthirnewiththeFFASTantievaporanttechnology.
KEYWORDS Ultra-lowvolume,dropletsampling,Teflon-coatedslides,MgO-coatedslides
One of the factors affecting the efficacy of an evaporation and for that reason a magnesium
aerosolized, ultra-low volume (ULV) insecticidal oxide(MgO)slidecoatinghasbeenusedforwater-
spray (space spray) for targeting flying insects based insecticidal droplets (May 1945, 1950;
such as mosquitoes is the size of the droplets Rathburn 1970; Matthews 1975) because the
containedwithintheaerosolcloud(Mount1970). impressions that the droplets create upon impac-
One of the most commonly used methods to tion on the slide are measured, not the actual
sample droplets in the field is by impaction on droplets. These impressions are permanent and
rotating glass microscope slides; this method is allow for a more precise size determination, even
simple, affordabe, and easy to use. though droplets may shrink due to evaporation
The coating of the slides used for droplet (Rathburn1970).
impactionvariesbasedontheformulationcharac- In recent years, a new group of insecticidal
teristics of the insecticide. For oil-based insecti- formulations were developed as water-based
cides, TeflonH coating was found to be a suitable preformed emulsions utilizing an antievaporant
material for droplet impaction (Anderson and technology known as Film Forming Aqueous
Schulte 1971) because oil-based products are Spray Technology (FFASTTM) to slow droplet
relatively nonvolatile and retain their original evaporation (Groome et al. 1989). In the past,
diameter for extended periods of time (Anderson bothTeflonandMgOcoatingshavebeenusedto
andSchulte1971).Ontheotherhand,water-based sampledropletsofFFASTproducts(Brownetal.
insecticides are more prone to volatilization/ 1998, 2003; Mickle and Brown 1999, 2000, 2001;
Lothrop et al. 2007). However, experiments for
direct comparison of these 2 coatings in deter-
1DepartmentofEntomology,UniversityofFlorida, mining the volume median diameters (Dv s) of
50
Building 970 Natural Area Drive, Gainesville, FL FFASTH droplets are not known and the
32611-0620.
appropriateness of Teflon as a FFAST droplet
2Manatee County Mosquito Control District, 2317
impaction surface has not been investigated in
2ndAvenueW,Palmetto,FL34221.
3US Department of Agriculture–Agricultual Re- relationtodropletsizemeasurementsandshrink-
search Service European Biological Control Laborato- age.OurmainobjectivewastoestimatetheDv50
ry,Tsimiski43,54623,Thessaloniki,Greece. and the Dv of 1 oil-based and 2 water-based,
90
173
174 JOURNALOFTHEAMERICANMOSQUITOCONTROLASSOCIATION VOL.29,NO.2
antievaporant aerosols using Teflon- and MgO- product tested. For those droplets that did not
coated slides and to determine whether aging of have a spherical shape, 2 measurements were
the droplets on the slides (up to 60 min) has any made corresponding to the narrowest and widest
significant effect on Dv and Dv calculations. dimension of the droplet. The average of these 2
50 90
Three commercially available ULV formula- measurements was used as the droplet diameter.
tions registered for mosquito adulticiding were WhenestimatingtheDv andDv values,the
50 90
used in all experiments: 1 oil-based formulation, correction for volume diameter was done using
Permanone 30-30 (30% permethrin, Bayer Envi- the diameter (D) value rather than the volume
ronmentalScience,ResearchTrianglePark,NC), diameter (D3) associated with each droplet, as
and 2 water-based FFAST formulations, Aqua- suggestedbyYeomans(1949).Aspreadfactorof
Reslin (20% permethrin, Bayer Environmental 0.61 was used for the 3 compounds on Teflon;
Science,ResearchTrianglePark,NC)andAqua- spreadfactorsof0.86,0.8,and0.75wereusedfor
K-Othrine(2%deltamethrin,BayerEnvironmen- dropletsizes.20,15–20,and10–15mmonMgO
tal Science, Lyon, France). The latter product is coating, respectively (May 1945).
registered in the European Union but not Allstatisticalanalyseswereperformedwiththe
currently available for use in the USA. All SAS software package (version 8.01; SAS Insti-
compoundswereusedneat(undiluted).Anearlier tute,Cary,NC).Apairedt-testwasperformedto
version of the Colt 4 portable ULV-generator determine the effect of droplet aging on the
(LondonFoggerInc.,LongLake,MN)wasused calculation of droplet Dv and Dv values for
50 90
to atomize all compounds. The generator oper- droplets sprayed on MgO- and Teflon-coated
atedwithaflowrateofapproximately60ml/min. slides(P50.05).TheDv andDv valuesofthe
50 90
Battery-powered slide rotators (Compact droplets immediately upon impaction on the
Aerosol Droplet Sampler Model 312, John W. slides were calculated and compared with the
Hock Company, Gainesville, FL) were used for Dv and the Dv values of the droplets 60 min
50 90
droplet sampling. Rotators were operated at a postimpact.
speedof550rpmandwereplacedsidebysideto The mean Dv and Dv values of insecticide
50 90
create a sampling line on a stand approximately droplets at 0 and 60 min after impaction on
1 m from the ground. In order to create a Teflon- and MgO-coated slides were calculated
relatively uniform spray cloud, the handheld for all 3 products tested. There were no signifi-
generator was facing the rotators and moved at cant differences in either Dv or Dv estimates
50 90
the same height and alongside the sampling line on MgO slides at 0 min and 60 min for all 3
at a constant distance (approximately 2 m). products tested (Table 1). On Teflon-coated
Microscope glass slides (25 3 75 3 1 mm) were slides, the only product that showed significant
either coated with Teflon plastic film (BioQuip differencebetween0minand60mininbothDv
50
Products Inc., Rancho Dominguez, CA) or and Dv estimateswasAqua-K-Othrine.Specif-
90
purchased plain (Fisher Scientific Company, ically, both values corresponding to Dv and
50
Pittsburg,PA)andcoatedwithMgOasdescribed Dv at 60 min decreased by approximately 50%
90
by Chaskopoulou et al. (2011). Three rotators when compared to the initial readings. For the
were used containing 1 Teflon- and 1 MgO- other 2 products, AquaReslin and Permanone,
coated slide each. time did not have any significant effect on Dv
50
After spraying was completed the rotators, and Dv values.
90
with the slides still attached, were collected and TofurtherinvestigatethebehaviorofAqua-K-
transported to the laboratory. Once in the Othrine droplets on Teflon-coated slides we
laboratory the slides were removed from the observed the droplets immediately after spraying
rotators and placed on the microscope stage and at 10-min intervals for 60 min. Spray and
individually so the droplets could be measured. slide preparation was repeated as described
The droplets on both coating types were mea- above, except that this time the effects of 3
sured immediately after spraying each rotator different environmental scenarios on droplet
(within 3 min), and at 60 min postspraying for behavior were investigated. For the 1st scenario
bothcoatingtypes.Duringthe60-minperiod,the theslideswerekeptspinningattemperatures25–
slides were kept on their holding racks in the 27uC and humidity .80% RH, resembling
laboratory where the temperature and humidity spinning slides in the field during a night spray.
remainedrelativelyconstant(approximately20uC The 2nd scenario was identical to the 1st one
and 55% relative humidity [RH]). The droplet except that the slides were not spinning. For the
sizes were determined under a VanGuard com- 3rd scenario the slides were stationary in their
pound microscope (model 14867FLi, Vee Gee slideracksatconditionsoftemperatures18–20uC
Scientific, Kirkland, WA) at 2003 magnification andhumidity,55%RH,resemblingalaboratory
withanocularmicrometercalibratedsothateach whereslideswouldnormallybestoredfordroplet
division measured 4.5 mm. The diameters of at measurementafteranight-spraytrial.Inorderto
least 200 droplets were measured per slide for a observe droplet behavior, the slides were moved
total of 3 Teflon- and 3 MgO-coated slides per immediately to the laboratory after spraying and
JUNE2013 SCIENTIFICNOTE 175
Table1. MeanDv andDv valuesforPermanone,Aqua-K-OthrineandAquaReslindropletsonMgO-and
50 90
TeflonH-coatedslidesimmediately(0min)and60minafterimpactiontoslides.1
MeanDv 6SE MeanDv 6SE
50 90
Teflon MgO Teflon MgO
Product 0min 60min 0min 60min 0min 60min 0min 60min
Permanone 5.760.2 5.660.1 6.760.1 7.060.1 11.160.3 11.060.2 13.960.8 14.060.2
Aqua-K-Othrine 8.560.1 4.360.8* 6.260.3 5.960.2 25.865.0 9.461.4* 18.761.0 17.360.4
AquaReslin 7.260.5 6.260.4 7.460.2 7.860.3 18.964.2 11.960.8 14.960.2 15.060.2
1Dv50,volumemediandiameter;Dv90,volume90%diameter;MgO,magnesiumoxide.
*MeanDv andDv valuesat60minaresignificantlysmallerthancorrespondingvaluesat0min(P50.05,t-test).
50 90
observed by microscopy (2003 magnification). This study provided direct evidence that FFAST
Droplet behavior was recorded through time by droplets of Aqua-K-Othrine, despite containing
photographingasetfieldofapproximately10–20 antievaporantingredients,will shrinksignificant-
droplets every 10minfor 60min. The same field ly on Teflon-coated slides within 10 min after
ofdropletsoneachslidewascapturedeverytime. impaction and, therefore, MgO slides should be
This procedure was repeated over 8 different preferredoverTeflon.Ontheotherhand,despite
slides and a total of approximately 100 droplets
wererecordedforeachoneofthe3scenarios.The
slides were on the microscope stage only long
enough to capture the images and were immedi-
ately returned to the conditions described above.
A digital microscope camera (DCM500, Hang-
zhou Huaxin IC Technology Inc., Zhejiang,
China)withthecorrespondingcomputersoftware
(ScopePhoto 3.0 Image Processing, Hangzhou
HuaxinICTechnologyInc.,Zhejiang,China)was
usedtocapture,manage,andsavetheimagefiles.
The images of the droplet fields and of a
calibratedstagemicrometer(1division54.5mm)
were printed at the same scale on standard copy
paper or transparent acetate sheets (216 3
279 mm), respectively. The stage micrometer on
theacetatesheetwasusedtomeasurethedroplets
on the printed images of the droplet fields.
The diameter of Aqua-K-Othrine droplets
decreased significantly during all 3 experimental
conditions (dry environment/nonspinning slides,
moist environment/nonspinning slides, moist en-
vironment/spinning slides) (Fig. 1). The majority
of the shrinkage occurred during the 1st 10 min
after impaction on the slides under all 3
environmental conditions tested.
InpreviousstudieswithFFASTantievaporant
water-based products some inconsistencies be-
tweenDv estimatedusingTeflon-versusMgO-
50
coatedslideshavebeendemonstrated.TheTeflon
slides produced a measured Dv that was
50
approximately K the Dv measured by using
50
MgO slides (Mickle and Brown 2000, Brown et
al. 2003). Mickle and Brown (2001) showed that
characterizationoftheirnozzleusingalaserwind
tunnel in the laboratory yielded a Dv nearly 5-
50
fold greater than what was measured in the field
using Teflon slides. Findings by these authors
Fig. 1. Droplet diameter (in mm) distribution for
suggest that possible evaporation of the aqueous Aqua-K-Othrine(AKO)onTeflonH-coatedslidesat0,10,
formulation may have resulted into smaller 20,and60min.(A)Dry,nonspinningscenario.(B)Moist,
droplets being measured on the Teflon slides. nonspinningscenario.(C)Moist,spinningscenario.
176 JOURNALOFTHEAMERICANMOSQUITOCONTROLASSOCIATION VOL.29,NO.2
losingtheir spherical shape, AquaReslin droplets ChaskopoulouA,LathamMD,PereiraRM,Connelly
onTeflon-coatedslidesdidnotshrinksignificant- R, Bonds JAS, Koehler P. 2011. Efficacy of aerial
ly within 60 min postspraying. Although both ultra-low volume applications of two novel water-
Aqua-K-Othrine and AquaReslin formulations based formulations of unsynergized pyrethroids
against riceland mosquitoes in Greece. J Am Mosq
contain the same FFAST antievaporant technol-
ControlAssoc27:414–422.
ogy,theseformulationscontainacombinationof
Groome JM, Martin R, Slatter R. 1989. Advances in
ingredients (actives and/or solvents/synergists)
thecontrol of public health insects.IntPest Control
with variable physical properties (i.e., vapor 31:137–140.
pressure)resultingindifferentevaporationrates. Lothrop HD, Lothrop BB, Palmer M, Wheeler S,
Magnesium oxide slides also have several Gutierrez A, Gomsi DE, Reisen WK. 2007. Evalu-
disadvantages. Some of the most important ation of pyrethrin and permethrin ground ultra-low
disadvantages are the requirement of a long volume applications foradultCulexcontrol inrural
preparation time (Anderson and Schulte 1971) andurbanenvironmentsfortheCoachellaValleyof
and their high susceptibility to dust and other California.JAmMosqControlAssoc23:190–207.
airbornecontaminants,whichmayleaveimprints MatthewsGA.1975.Chemicalsandequipment.Deter-
mination of droplet size. Pest Art News Summ
on the slide surface. Although we currently
21:213–225.
recommend the use of MgO-coated slides, a new
May KR. 1945. The cascade impactor: an instrument
technologyisneededforamoreaccuratedroplet
for sampling coarse aerosols. J Sci Instrum 22:
sampling of FFAST antievaporant insecticides 187–195.
under field conditions. In the meantime, correc- MayKR.1950.Themeasurementofairbornedroplets
tion factors adjusted for each FFAST formula- by the magnesium oxide method. J Sci Instrum
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allow for the usage of Teflon-coated slides. Mickle RE, Brown JR. 1999. Aerial adulticide spray
We thank Jane Bonds (Barber), Roxanne trialscharacterizationandoptimizationresults,Crow-
Connelly, and Carol Thomas for useful editing ley Rice Research Station, LA. Report to Louisiana
MosquitoControlAssociation,
advice. We thank Gail Stout and Martin West
MickleRE,BrownJR.2000.Optimizationstrategiesfor
for their assistance during the experimentation.
theaerialapplicationofAqua-Reslin,Georgetown,SC
We thank the Deployed War-Fighter Protection
trials1999.ReporttoAventisEnvironmentalHealth.
Research Program for their support. Last, but
MickleRE,BrownJR.2001.Optimizationtrialsforthe
notleast,wethankBayerEnvironmentalSciences aerialapplicationofAqua-Reslinusingrotaryatomiz-
for providing us with samples of their products. ers, Easterwood, LA, 2000. Final report to Aventis
EnvironmentalHealth.
Mount GA. 1970. Optimum droplet size for adult
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