DTIC ADA499780: Effects of Wind Speed on Aerosol Spray Penetration in Adult Mosquito Bioassay Cages

0.69 MB·English

by  Defense Technical Information Center

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.