JournaloftheAmericanMosquitoControlAssociation,24(3):419–426,2008 CopyrightE2008byTheAmericanMosquitoControlAssociation,Inc. EFFECTS OF WIND SPEED ON AEROSOL SPRAY PENETRATION IN ADULT MOSQUITO BIOASSAY CAGES1 W.CLINTHOFFMANN,2BRADLEYK.FRITZ,3MUHAMMADFAROOQ3ANDMIRIAMF. COOPERBAND4 ABSTRACT. Bioassay cages are commonly used to assess efficacy of insecticides against adult mosquitoesinthefield.Tocorrelateadultmortalityreadingstoinsecticidalefficacyand/orsprayapplication parametersproperly,itisimportanttoknowhowthecageusedinthebioassayinteractswiththespraycloud containingtheappliedinsecticide.Thisstudycomparedthesizeofdroplets,windspeed,andamountofspray material penetrating cages and outside of cages in a wind tunnel at different wind speeds. Two bioassay cages,CenterforMedical,AgriculturalandVeterinaryEntomology(CMAVE)andCircle,wereevaluated. The screen materials used on these cages reduced the size of droplets, wind speed, and amount of spray materialinsidethecagesascomparedtothespraycloudandwindvelocityoutsideofthecages.Whenthe wind speed in the dispersion tunnel was set at 0.6m/sec (1.3mph), the mean wind speed inside of the CMAVE Bioassay Cage and Circle Cage was 0.045m/sec (0.10mph) and 0.075m/sec (0.17mph), respectively.Atairvelocitiesof2.2m/sec(4.9mph)inthedispersiontunnel,themeanwindspeedinsideof the CMAVE Bioassay Cage and Circle Cage was 0.83m/sec (1.86mph) and 0.71m/sec (1.59mph), respectively.Consequently,therewasaconsistent50–70%reductionofspraymaterialpenetratingthecages comparedtothespraycloudthatapproachedthecages.Theseresultsprovideabetterunderstandingofthe impactofwindspeed,cagedesign,andconstructiononultra-low-volumespraydroplets. KEYWORDS Sentinelmosquitocages,ULV,dropletdeposition,windtunnel,laserdiffraction INTRODUCTION antennae of mosquitoes flying through ULV aerosol clouds, and although droplets up to Theuseofultra-low-volume(ULV)insecticide 32 mm in diameter were found on slides, no droplets for adult mosquito control was devel- droplets larger than 16 mm were found on oped by the United States Department of mosquitoesexposed to thesame aerosol. Haile et Agriculture in the 1960s (Knapp and Roberts al. (1982) determined that mortality is optimized 1965), and is broadly used for controlling adult whendropletsarebetween10and15 mm,andthat mosquito populations today. Assessment of with increased distance downwind mortality of insecticide efficacy provides the foundation for caged mosquitoes was reduced. Confining adult pest management programs. In addition to mosquitoes in sentinel cages for bioassay tests insecticide concentration, dose, and release rate, continues to be used as a standard method for important considerations in ULV efficacy are dropletsizeandmeteorologicalinfluencessuchas evaluating the impact of insecticides on adult wind (Mount 1998). A considerable number of mosquitoes in the field (Boobar et al. 1988). studies have investigated the effects of the However,themortalityratesofconfinedmosqui- aforementioned factors on droplet entry into toes are not always well correlated with other sentinel cages, but few studies have investigated indicesformonitoringinsecticidalimpactonwild howvaryingwindspeedmayaffectULVdroplet mosquitopopulations(Boobaretal.1988).Barber entry into cages. etal.(2006)foundthatsignificantmortalitycould Several studies have found that for ULV to be be caused by spray material deposited on the efficacious the optimal droplet size is less than screen materials used in cage construction, and 20 mm in diameter. Using scanning electron that mosquitoes should be transferred to clean microscopy, Lofgren et al. (1973) found that containersassoonaspossibleaftertests.Boobaret droplets ranging from 2 to 16 mm in diameter al. (1988) suggested that filtering of droplets by were most likely to impinge on the wings and cagescreeningmayalsocontributetoinconsisten- ciesbetweenmortalityobservedincagedandfree- 1Mention of a trademark, vendor, or proprietary flying mosquitoes. Breeland (1970), using ultra- productdoesnotconstituteaguaranteeorwarrantyof low-volumespraysandcardsplacedinandaround the product by the USDA or US Navy, and does not cages of varying materials, found that droplet imply its approval to the exclusion of other products countwasreducedbyvaryingamountsdepending thatmayalsobesuitable. on the material used in the construction of the 2USDA-ARS-AreawidePestManagementResearch cages. Rathburn et al. (1989) did not find any Unit,2771F&BRoad,CollegeStation,TX77845. differences in the mortality of either Aedes 3USNavy,NavyEntomologyCenterofExcellence, taeniorhynchus Wiedemann or Culex quinquefas- Jacksonville,FL. 4USDA-ARS-Center for Medical, Agricultural and ciatusSay when the mosquitoeswere 1)confined VeterinaryEntomology,Gainesville,FL. in 2 cage types, 2) sprayed with 2 different 419 Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 3. DATES COVERED 2008 2. REPORT TYPE 00-00-2008 to 00-00-2008 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Effects of Wind Speed on Aerosol Spray Penetration in Adult Mosquito 5b. GRANT NUMBER Bioassay Cages 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 Navy Entomology Center of Excellence,Jacksonville,FL,32205 REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution unlimited 13. SUPPLEMENTARY NOTES U.S. Government or Federal Rights License 14. ABSTRACT see report 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF ABSTRACT OF PAGES RESPONSIBLE PERSON a. REPORT b. ABSTRACT c. THIS PAGE Same as 8 unclassified unclassified unclassified Report (SAR) Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 420 JOURNALOFTHEAMERICANMOSQUITOCONTROLASSOCIATION VOL.24,NO.3 volumes of the insecticides, or 3) sprayed with 2 the Terminator ULV Sprayer (Advanced Special differentinsecticides.Bunneretal.(1989)studied Technologies, Winnebago, MN). The Termina- aerosolpenetrationthroughmanyconfigurations tor’s 4.7 hp (219 cc) Yanamar diesel engine of solid and screened cages and found that a powers a direct-drive air compressor that pro- cylindrical screened cage, with the longitudinal duces the air blast that creates the pesticide axis perpendicular to the ground, provided a droplet spectrum at the dual venture style, consistent profile to the wind, regardless of wind stainless steel nozzles. This nozzle was selected direction.Boobaretal.(1988)studiedtheeffectof for this work as previous work by Hoffmann et screen materials on droplet size distribution of al. (2007) demonstrated that it produced a aerosols entering sentinel mosquito exposure volume median diameter of 20.4 mm and tubes. The cages used were solid, with different 21.7 mm for water-based and oil sprays, respec- meshesorscreensattheends.Althoughtheresults tively, which is typical to vector control applica- showed significant reduction in the number of tions. The nozzle was removed from the sprayer droplets penetrating the cages, the level of and plumbed to a shop compressor with a reduction varied with the different screening pressure regulator set at 690 kPa (100 psi). The materialstested. self-feed tube from the nozzle was attached to a To correlate adult mortality readings to spray plumbed graduated cylinder with an inline shut- application parameters better, it is important to off value. This allowed for a metered release of knowhowthecageusedinthebioassayinteracts 10 ml of the spray solution over approximately with the spray cloud containing the applied 10 sec, thereby constituting a spray run or insecticide. Due to the effects of the boundary replication. layer of the cage mesh, it is expected that differences in wind speed would result in differ- Spray solution encesindropletpenetrationintocages.Thisstudy explored this interaction with the following ThespraysolutionwasOrchex796mineraloil objectives: to evaluate the size of droplets that (CalumetLubricantsCo.,L.P.,Indianapolis,IN) entered the cages as compared to droplet size withUvitexfluorescentdyeattherateof1 g/liter presentedtothecage,tomeasurethewind speed ofoil.Theoilwasselectedbecauseitiscommonly inside of the cages as compared to wind speed used as a diluent in vector control applications. outside of the cages, and to measure the amount Duringeachsprayreplication,10 mlofthespray of spray material that penetrates the cages. solution was sprayed through the nozzle and released into the dispersion tunnel. Solution samples were analyzed in the laboratory to MATERIALS AND METHODS determine the exact amount of dye in solution Dispersion tunnel andusedtostandardizedepositionmeasurements across the various tests. A dispersion tunnel was constructed from standard lumber and plywood. The tunnel Cages cross-sectional area was a 0.9 3 0.9 m (3 3 3 ft)squarearea.Theoveralltunnelconsistsofa Twodifferentcagesusedinadultbioassaytests 2.4-m- (8 ft) long section where the spray nozzle were evaluated in these studies. The Center for ismountedenteringintoa1.831.836.7 m(63 Medical, Agricultural and Veterinary Entomolo- 6 312 ft) mixing chamber and a 7.3 m (24 ft) gy (CMAVE) Bioassay Cage was a cylindrical section(32.4 m[8 ft]sections)leavingthemixing cagethatcanbecollapsedduringstorageandwas chamber with a fan pulling air throughout fully described by Cooperband et al. (2007). The (Fig. 1). cage was framed by embroidery hoops that are The test portion of the tunnel is the center of approximately 26 cm in diameter and form the the last 2.4 m (8 ft) section before the fan. An top and bottom of the cage. Wooden dowels are access panel was created to allow for placement used as internal structural supports making the andrecoveryofcagesandsodastrawsusedinthis cage approximately 31 cm tall. The cage was study. Additionally, 2 holes were cut on oppos- coveredinnylontulle.The2ndcageisreferredto ing, vertical walls 1.8 m (6 ft) upwind of the as the Circle Cage and was based on a design sampling location to allow for placement of a provided to the authors by Tom Janasek and Sympatec Helos laser diffraction droplet sizing David Sykes. The cages were constructed by system (Sympatec Inc., Clausthal, Germany). forming a 60 3 6–cm paperboard strip into a circle approximately 18 cm in diameter and covering it with bridal veil material. The Circle Atomizer Cage was designed to be oriented vertically with Anair-assistednozzle(AdvancedSpecialTech- screen opening positioned into the wind. nologies, Winnebago, MN) was used in this Each of the screen materials used had fiber study. The nozzle was designed to be used on widths ofapproximately0.075 mmandopenings SEPTEMBER2008 SPRAYENTRYINTOCAGES 421 Fig.1. SpraydispersiontunnelwithspraynozzleandSympatecHeloslaserdiffractionsysteminplace. of approximately 1 mm. Teitel and Shklyar 20 mm) was calculated for all tests. The term (1998) defined screen porosity, a, as (%Vol,20 mm)isanindicatoroftheportionof ðm{dÞðn{dÞ the applied material that will most likely stay a~ , ð1Þ aloftafteranapplicationandpotentiallyimpinge mn on a flying insect. where m and n are distances between 2 adjacent weft (horizontal) and warp (vertical) fibers, Droplet size tests respectively, and d is the diameter of the fiber. The purpose of the droplet size tests was to Therefore, the 2 screen materials had a screen comparethesizeofdropletsthatpenetratedthe2 porosity of 85.5%. However, the bridal veil screen materials to the size of droplets presented screens tended to be of a looser weave than the tothem.Awoodenteststandwasconstructedto nylon tulle screen. span the width of the tunnel to facilitate testing andchangingofscreen materials.Holeswerecut intheverticalsidesoftheframetoallowthelaser Droplet size equipment beam to pass through the frame unobstructed. A Sympatec Helos laser diffraction droplet The screen material was stretched taut over both sizing system (Sympatec Inc., Clausthal, Ger- upstream and downstream faces of the frame many)wasusedtomeasurethedropletsizeofthe (0.9 m wide 3 0.3 m high). The screen material spray material in the dispersion tunnel and was replaced with new screen material after 3 presented to the cage and screen samples. The replications at a given air velocity. Evaluations Helos system utilizes a 623-nm He-Ne laser and were made with and without the screening was fitted with a lens (denoted by manufacturer materialacrossthetunnel(referredtoinTables 1 as R5)with a dynamic size rangeof 0.5–875 mm, and 2 as Screen in Place and Open Tunnel, which is divided across 32 sizing bins. The laser respectively). The air velocities tested were 0.6, system has 2 components, the emitter and the 0.9, 1.3, 2.2, and 4.5 m/sec. receiver, which were positionedacross from each other and outside of the wind tunnel. Holes that Air velocity and spray deposition measurement were slightly largerthanthelaseroptics werecut into the tunnel at a height of 0.36 m (1.2 ft) as a Each cage was suspended in the center of the precautionary measure to minimize air-flow wind tunnel and away from the ceiling and floor disruption in the wind tunnel and to allow (Fig. 2). Two hot-wire anemometers (Extech measurementofthespraycloudacrosstheentire Instruments, Model 407119A, Waltham, MA) tunnel. were used to measure air velocities. One ane- Themostcommontermusedtodescribespray mometer was positioned outside of the cage, droplet size spectra is volume median diameter whereas the other was positioned inside of the (D ).D isthedropletdiameter(mm)where cage. Simultaneous readings of the 2 anemome- V0.5 V0.5 50% ofthesprayvolume ormass is contained in tersweremadeduringeachofthe3replicatesfor droplets smaller than this value. D and D each of the air velocities tested. Although the 3 V0.1 V0.9 values,whichdescribetheproportionofthespray replicates were completed during 1 air velocity volume(10%and90%,respectively)containedin setting, the air velocities were randomized droplets of the specified size or less, were also throughout the testing. calculated. The percent of spray volume con- Concurrent with air velocity tests, soda straws tained in droplets less than 20 mm (%Vol , (19.1 cm long 3 0.6 cm diameter) were used to 422 JOURNALOFTHEAMERICANMOSQUITOCONTROLASSOCIATION VOL.24,NO.3 Table1. EffectofthescreenmaterialusedintheCMAVEBioassayCageonthedropletsizeparametersinthe opentunnelversuspassingthroughthescreenmaterial. Windspeed (m/sec) Laseropticalpath D (mm6SD)1 D (mm6SD) D (mm6SD) %Vol,20mm V0.1 V0.5 V0.9 0.6 Opentunnelscreenin 11.060.0 18.560.2 34.261.0 57.261.1 place 10.260.4 17.760.2 33.160.3 60.960.5 P50.02*,2 P50.007** P50.16(ns) P50.007** 0.9 Opentunnelscreenin 11.660.0 20.260.2 40.860.5 49.260.7 place 11.160.9 19.760.1 40.860.1 51.460.5 P50.001** P50.01** P50.77(ns) P50.01** 1.3 Opentunnelscreenin 11.760.1 20.860.2 43.760.7 46.460.9 place 11.260.1 20.160.0 42.760.4 49.760.1 P50.002** P50.003** P50.09** P50.003** 2.2 Opentunnelscreenin 11.660.1 20.760.2 44.560.5 47.360.7 place 11.360.1 20.460.6 44.761.9 48.462.3 P50.02* P50.43(ns) P50.88(ns) P50.42(ns) 4.5 Opentunnelscreenin 11.160.0 19.760.1 44.360.3 51.460.3 place 10.760.1 18.960.0 43.160.1 54.960.1 P50.002** P50.001** P50.003** P50.001** 1DV0.1,DV0.5,andDV0.9valuesdescribethemediandiameterforthespecifiedvolumetricproportionofthespray(10%,50%,and 90%,respectively)thatfallsbelowthesizeinmicrometersgiveninthetable. 2Meanswithineachdatapairforthedifferentdropletsizeparameterswereanalyzedforstatisticaldifferenceswiththeuseofthe pairedStudent’st-test(ns5notsignificant). *Significantata50.05. **Highlysignificantata50.01. collect spray deposits in order to measure the laboratory for processing. After pipetting 20 ml spray flux or amount of material that passed by. of hexane into each bag, the bags were agitated, Two straws were used, 1 straw positioned inside and 6 ml of the effluent was poured into a eachcagetomeasuretheamountofmaterialthat cuvette. The cuvettes were then placed into a penetrated the cage, and a 2nd straw positioned spectrofluorophotometer (Shimadzu, Model outsideeachcagetomeasureamountofmaterial RF5000U, Kyoto, Japan) with an excitation presented to each cage (Fig. 2). After each wavelength of 372 nm and an emission at replication, the straws were carefully placed in 427 nm. These wavelengths optimized the fluo- individuallylabeledplasticbagsandstoredoutof rescence of the Uvitex dye. The fluorometric the light to prevent any photodegradation of the readingswereconvertedtomg/cm2withtheuseof dye. The bags were brought back to the a projected area of the straw of 11.6 cm2. The Table2. EffectofthescreenmaterialusedintheCircleCageonthedropletsizeparametersintheopentunnel versuspassingthroughthescreenmaterial. Windspeed (m/sec) Laseropticalpath D (mm6SD)1 D (mm6SD) D (mm6SD) %Vol,20mm V0.1 V0.5 V0.9 0.6 Opentunnelscreenin 10.760.2 18.960.2 36.460.6 54.761.0 place 10.560.1 18.560.4 36.461.0 56.962.1 P50.11(ns)2 P50.14(ns) P50.96(ns) P50.18(ns) 0.9 Opentunnelscreenin 11.460.1 20.260.1 41.160.3 49.060.6 place 11.160.1 19.760.0 41.460.2 51.160.2 P50.006** P50.004** P50.21(ns) P50.004** 1.3 Opentunnelscreenin 11.760.1 20.960.3 43.460.9 46.561.2 place 11.260.1 20.260.3 42.960.9 49.461.2 P50.001** P50.04* P50.55(ns) P50.04* 2.2 Opentunnelscreenin 11.760.1 20.960.2 44.960.7 46.060.9 place 11.260.1 19.960.2 43.060.7 50.360.8 P50.002** P50.004** P50.03* P50.003** 4.5 Opentunnelscreenin 11.160.0 19.760.1 44.360.3 51.460.3 place 10.760.0 19.160.1 43.460.7 54.060.4 P50.001** P50.001** P50.12(ns) P50.001** 1DV0.1,DV0.5,andDV0.9valuesdescribethemediandiameterforthespecifiedvolumetricproportionofthespray(10%,50%,and 90%,respectively)thatfallsbelowthesizeinmicrometersgiveninthetable. 2Meanswithineachdatapairforthedifferentdropletsizeparameterswereanalyzedforstatisticaldifferenceswiththeuseofthe pairedStudent’st-test(ns5notsignificant). *Significantata50.05. **Highlysignificantata50.01. SEPTEMBER2008 SPRAYENTRYINTOCAGES 423 across the 0.9-m width of the dispersion tunnel. The modified cages were stretched across the length of the wind tunnel so that the laser beam would passthrough thecenterofthecagesalong the longitudinal axis (i.e., center line). Each end of the screen material was secured to the wall of the tunnel to prevent any droplets from passing through the laser beam without first passing through the screen. The resulting data were inconsistent, probably due to buildup of the spray material on the screens during the testing. Therefore, the testing stand presented was devel- oped to allow the screen material to be easily changed between tests. Differences in droplet sizes (i.e., ,0.3–3 mm) measured with and without screening material fromeachcageweresignificant(Tables 1and2). Nearly all trials resulted in a significant decrease in the size of the droplets passing through the screens as compared to the open tunnel, indicat- ingthatlargerdropletswerebeingfilteredbythe screenmaterial.Allofthedropletsizeparameters (D ,D ,D ,and%Vol,20)increasedas V0.5 V0.1 V0.9 the air velocity was increased from 0.6 m/sec to 2.2 m/sec. This was expected, as there was more energy at the higher wind speeds to pull larger dropletsdownthedispersiontunneltothetesting section before they settled out. However, the Fig.2. CenterforMedical,AgriculturalandVeter- droplet size parameters slightly decreased when inary Entomology and Circle Bioassay Cages in the the air velocity was increased to 4.5 m/sec in the wind tunnel during the air velocity measurements and tunnel. This may be due to higher air speeds strawdepositionstudies. resultinginincreasedcollectionefficienciesofthe screen material, thus removing more droplets minimumdetectionlevelforthedyeandsampling from the air stream and decreasing the droplet technique was 7.0 3 1025 mg/cm2. size of the penetrating spray. The percent reduction of the D inside and V0.5 Statistical analysis outsideofthecageswascalculatedforthescreen materials used in the 2 cages. The percent All tests were replicated at least 3 times and reductions of D for the CMAVE materials statistically analyzed. Droplet size data were V0.5 were 4.3, 2.5, 3.4, 1.5, and 4.1% for the 0.6, 0.9, analyzed with the use of the PROC GLM 1.3,2.2,and4.5 m/secairspeeds,respectively.The procedure in SAS (SAS Institute 2001). Linear percent reductions of D for the Circle Cage regression equations were developed for the air V0.5 were 2.1, 2.5, 3.4, 4.8, and 3.1% for the 0.6, 0.9, velocity studies in Microsoft Excel (Microsoft 1.3,2.2,and4.5 m/secairspeeds,respectively.The 2003) with the airspeed in the tunnel considered overall averages were 3.14 and 3.15% for the the dependent variable and the airspeed in the CMAVEandtheCircleCages,respectively.Both bioassay cages the independent variable. The screen materials essentially have the same collec- deposition inside and outside of the cages was tioneffectonthespray,whichwouldbeexpected analyzed with the Student’s t-test (SAS Institute giventhattheybasicallyhavethesamestructure. 2001).Thelevelofsignificanceforalltestswasset at a 5 0.05. Air velocities inside and outside of cage RESULTS Thereweresignificantdecreasesinairvelocities inside the cages as compared to the air velocities Droplet sizes inside and outside of the cages in the wind tunnel. When the wind speed in the The spray dispersion tunnel used in these dispersion tunnel was set at 0.6 m/sec (1.3 mph), studies generated repeatable droplet sizing data. themeanwindspeedinsideoftheCMAVECage Therewasgenerallyonly0.5–2%variancewithin and Circle Cage was 0.045 m/sec (0.1 mph) and the D values for a given test. In preliminary 0.075 m/sec (0.17 mph), respectively (Fig. 3). At V0.5 experiments, the 2 cages were modified so that air velocities of 2.2 m/sec (4.9 mph) in the each cage and screen material would extend dispersion tunnel, the mean wind speed inside of 424 JOURNALOFTHEAMERICANMOSQUITOCONTROLASSOCIATION VOL.24,NO.3 Fig. 3. Air velocities inside versus outside of the Center forMedical, Agriculturaland VeterinaryEnto- mologyandCircleBioassayCages. the CMAVE Cage and Circle Cage was 0.83 m/ sec (1.86 mph) and 0.71 m/sec (1.59 mph), re- spectively.Theimplicationofthesemeasurements is that if these cages are used in low wind speeds (i.e.,,0.67 m/sec[1.5 mph]verylittleofthespray beingcarriedbythewindislikelytopenetratethe cage.Basedontheregressionequationsfromthe data collected, no spray-laden air would be Fig.4. Depositiononsodastrawsplacedinsideand expected to penetrate the cages at ambient wind outside of the Center for Medical, Agricultural and speedsof0.25 m/sec(0.56 mph)(R250.986)and Veterinary Entomology (A) and Circle (B) Bioassay 0.17 m/sec (0.38 mph) (R2 5 0.968) for the Cages.Differentletterswithineachcolumnforagiven CMAVE Cage and Circle Cage, respectively. windspeedindicatesignificantdifferences. The reduction in air velocity inside the cages correlatedtolowerlevelsofspraypenetratingthe penetrate the cages, and the amount of spray cages. filtered by the cage screening material. The influenceofthescreeningmaterialontheairspeed inside and outside of the cages was also Deposition on soda straws measured. The 2 types of screening evaluated in Significantly lower deposition values were this study were found to reduce the size of measured inside the CMAVE Cage and Circle droplets, air velocity, and amount of spray Cage than measured in the open tunnel at all 4 material inside as compared to outside of the wind speeds tested (Fig. 4). There was a consis- cages similarly. tent 50–70% reduction of spray material pene- The movement of a fluid (in this case air) tratingthecagecomparedtothespraycloudthat flowingpast anobjectis described byanobject’s approached the CMAVE Cage and Circle Cage. Reynolds number, which takes into account the The amount of spray penetrating the cage viscosity and velocity ofthe fluid, and the length increased as the wind speed increased for both of the object (in this case the diameter of the theCMAVECageandCircleCage.Theseresults mesh) (Patel et al. 1985). The creation of a suggest that lethal dosages of insecticides as boundary layer likewise reduces the flow of a determined by bioassay cages may be overesti- viscous fluid past a surface. Consequently, the matingtheamountofinsecticideneededtocause fiber diameter and the porosity of the mesh are mortalityinthewild.Althoughthisstudydidnot the 2 main features of a screening material that include bioassays, the methods and techniques affect airflow through that material (Wakeland described here could be adapted for bioassay and Keolian 2003). As predicted, because of studies. effects of the boundary layer and Reynolds number produced by a wire mesh (Livesey and Laws1973),thewindspeedmeasuredinsidecages DISCUSSION was significantly slower than wind speed outside Two cages (CMAVE Cage and Circle Cage) ofcages,whichwouldalsoresultinareductionin used in adult mosquito bioassays were tested to ULV droplets entering cages, especially at lower measure their effects on the size of droplets that wind speeds. SEPTEMBER2008 SPRAYENTRYINTOCAGES 425 Fig. 5. Regression lines of wind speeds inside Center for Medical, Agricultural and Veterinary Entomology BioassayCage,CircleCage,andoutsideofcages,andpercentreductioninwindspeedincagescomparedtooutside cages.Lightgrayregionindicatesthewindspeedatwhichultra-low-volumesprayisusuallyapplied. As wind speed outside cages increased, the cages compared to the spray cloud that ap- percent reduction of wind speed inside cages proached the cages. The highest deposition of decreased. With tunnel wind speeds of 2.2 and dropletsonstrawsoccurredoutsideofcagesatthe 0.6 m/sec,arespective63–93%reductionofwind highest wind speed tested. The accumulation of speed was observed inside cages. Figure 5 shows dropletsonstrawsoutsideacageat1.5 m/secwas linear regressions of wind speeds inside the more similar to the droplet deposition on straws tunnel, and both cages extrapolated to higher inside the cage at 2.2 m/sec. The largest droplets wind speeds, as well as the percent reduction in were most likely to be filtered by the screening windspeedthatwouldbeexpected.Atalowwind material on the cages. A statistically significant speed, there would be less opportunity for reduction occurred in the volume of droplets less droplet-ladenairtoentercages,becausethewind than20 mmindiameter(thedropletsmostlikelyto speed inside cages would reach 0 when the wind persist in the air and impinge on flying mosqui- speed outside of cages was roughly between 0.4 toes) entering cages. Again, this indicates that and 0.5 m/sec. This has important implications lethal dosages of insecticides as determined by when caged sentinel mosquitoes are used to bioassaycagesmaybeoverestimatingtheamount monitor spray success in the field. With all other ofinsecticideneededtocausemortalityinthewild. factors being equal, at low wind speeds much Although there were significant differences in the size of droplets entering cages at different wind more spray would be needed to realize the same speeds,thebiologicalrelevanceofthesedifferences rate of droplet entry into cages, and perhaps infieldapplicationsmustbetested.Futurestudies mortality rates of caged mosquitoes, than at toaddresshowthesedifferencesinsideandoutside higher wind speeds. Additionally, when Circle of cages affect mortality could be conducted by Cages, which have solid sides, were used, small adaptingthesetechniquesandmethodsforbioas- shifts in wind direction could further reduce saystudies. droplet entry into the cages during ULV spray application.Thiswouldresultinfieldestimations CONCLUSIONS ofmortality beinghighlyvariableand inaccurate when they are based on mosquito mortality in Forthe2cages(CMAVEandCircle)evaluated sentinel cages, as suggested by Boobar et al. in these studies, the average reduction in droplet (1988). It is likely that the amount of spray sizes inside the cages as compared to outside of requiredtoattainthedesiredmortalityinthefield the cages were 3.14 and 3.15% for the CMAVE hasbeenoverestimatedbasedonmortalityfigures and the Circle Cages, respectively. At 0.6 m/sec for caged sentinel mosquitoes, because of the (1.3 mph), the mean wind speed inside of the amount of spray that is filtered out by the cage CMAVE Bioassay Cage and Circle Cage was before the spray enters the cage. 0.045 m/sec (0.1 mph) and 0.075 m/sec (0.17 Corresponding to the reduction of wind speed mph), respectively. At 2.2 m/sec (4.9 mph), the observed inside cages, there was a consistent 50– meanwindspeedinsideoftheCMAVEBioassay 70% reduction of spray material penetrating the Cage and Circle Cage was0.83 m/sec (1.86 mph) 426 JOURNALOFTHEAMERICANMOSQUITOCONTROLASSOCIATION VOL.24,NO.3 and 0.71 m/sec (1.59 mph), respectively. There Haile DG, Mount GA, Pierce NW. 1982. Effect of was a consistent 50–70% reduction of spray droplet size of malathion aerosols on kill of caged material penetrating the cages compared to the adultmosquitoes.MosqNews42:576–583. spray cloud that approached the CMAVE HoffmannWC,WalkerTW,MartinDE,BarberJAB, Gwinn T, Szumlas D, Lan Y, Smith VL, Fritz BK. Bioassay Cage and Circle Cage. 2007.Characterizationoftruckmountedatomization equipment typically used in vector control. J Am ACKNOWLEDGMENTS MosqControlAssoc23:321–329. Knapp FW, Roberts LL. 1965. Low volume aerial applicationoftechnicalmalathionforadultmosquito This study was supported in part by a grant control.MosqNews25:46–47. from the Deployed War-Fighter Protection Livesey JL, Laws EM. 1973. Simulation of velocity (DWFP) Research Program, funded by the U.S. profilesbyshapedgauzescreens.AIAAJ11:184–188. Department of Defense through the Armed Lofgren CS, Anthony DW, Mount GA. 1973. Size of Forces Pest Management Board (AFPMB). The aerosol droplets impinging on mosquitoes as deter- authors would like to thank Phil Jank for his mined with a scanning electron microscope. J Econ assistance during data collection and processing. Entomol66:1085–1088. Microsoft. 2003. Microsoft Office Excel. Redmond, WA:MicrosoftInc. REFERENCESCITED MountGA.1998.Acriticalreviewofultralow-volume Barber JAS, Greer M, Coughlin J. 2006. The effect of aerosols of insecticide applied with vehicle-mounted pesticideresidueoncagedmosquitobioassays.JAm generators for adult mosquito controls. J Am Mosq MosqControlAssoc22:469–472. ControlAssoc14:305–334. Boobar LR, Dobson SE, Perich MJ, Darby WM, Patel VC, Rodi W, Scheuerer G. 1985. Turbulence Nelson JH. 1988. Effects of screen materials on models for near-wall and low Reynolds number dropletsize frequency distribution ofaerosolsenter- flows—Areview.AIAAJ23:1308–1319. ing sentinel mosquito exposure tubes. Med Vet Rathburn CB Jr, Floore TG, Boike AH Jr. 1989. A Entomol2:379–384. comparison of mosquito mortality obtained in BreelandSG.1970.Theeffectoftestcagematerialson cardboard and metal cages with ground applied ULVmalathionevaluations.MosqNews30:338–342. ULVsprays.JFlaAnti-MosqAssoc60:1–3. BunnerBL,PosaSG,DobsonSE,BroskiFH,Boobar SAS Institute. 2001. SAS Software Release 8.2. Cary, LR. 1989. Aerosol penetration relative to sentinel NC:SASInstitute. cage configuration and orientation. J Am Mosq TeitelM,ShklyarA.1998.Pressuredropacrossinsect- ControlAssoc5:547–551. proofscreens.TransASAE41:1829–1834. Cooperband MF, Clark GG, Spears BM, Allan SA. Wakeland RS, Keolian RM. 2003. Measurements of 2007. An economical, cylindrical, and collapsible resistance of individual square-mesh screens to fieldcageformosquitoresearch.JAmMosqControl oscillating flow at low and intermediate Reynolds Assoc23:484–487. numbers.JFluidsEng125:851–862.