Droplet size and efficacy of an adulticide-larvicide ultralow-volume formulation on Aedes aegypti using different solvents and spray application methods

Abstract

When cases of dengue are reported or the density of adult Aedes aegypti (L.) becomes too high, ultralow-volume (ULV) application of insecticides is the recommended control method. The droplet size of an aerosol insecticide influences its efficiency in killing adult mosquitoes. Many studies have been carried out to determine the optimum droplet size that maximises vector control efforts, but only a few have determined droplet-size spectra for specific equipment using different solvents and comparing thermal and non-thermal aerosols.
The present study showed that the droplet size for a water-based adulticide-larvicide formulation was larger than for the same formulation diluted in gasoil or biodiesel. No significant differences in adult mortality were observed between sprayers and solvents, but efficacy decreased with distance from the sprayer nozzle. Adult emergence inhibition was more than 90% when using water as a solvent for both thermal and cold foggers, and the efficacy did not decrease with distance from the sprayer nozzle. On the other hand, oil-based solvents became less effective with distance.
The use of water as a solvent with both thermal and cold foggers improves the efficacy of the studied formulation containing permethrin as adulticide and pyriproxyfen as larvicide in scaled-up assays. Moreover, it reduces the environmental impact and costs of spraying by comparison with formulations using oil solvents.

Full text

137
Research Article
Received: 30 August 2010 Revised: 15 April 2011 Accepted article published: 16 May 2011 Published online in Wiley Online Library: 28 June 2011
(wileyonlinelibrary.com) DOI 10.1002/ps.2237
Droplet size and efficacy of an adulticide–
larvicide ultralow-volume formulation
on Aedes aegypti using different solvents
and spray application methods
Laura Harburguer,aEmilia Seccacini,aSusana Licastro,aEduardo Zerbaa,b
and H´
ector Masuh∗a,b
Abstract
BACKGROUND: When cases of dengue are reported or the density of adult Aedes aegypti (L.) becomes too high, ultralow-volume
(ULV) application of insecticides is the recommended control method. The droplet size of an aerosol insecticide influences its
efficiency in killing adult mosquitoes. Many studies have been carried out to determine the optimum droplet size that maximises
vector control efforts, but only a few have determined droplet-size spectra for specific equipment using different solvents and
comparing thermal and non-thermal aerosols.
RESULTS: The present study showed that the droplet size for a water-based adulticide–larvicide formulation was larger than
for the same formulation diluted in gasoil or biodiesel. No significant differences in adult mortality were observed between
sprayers and solvents, but efficacy decreased with distance from the sprayer nozzle. Adult emergence inhibition was more than
90% when using water as a solvent for both thermal and cold foggers, and the efficacy did not decrease with distance from the
sprayer nozzle. On the other hand, oil-based solvents became less effective with distance.
CONCLUSION: The use of water as a solvent with both thermal and cold foggers improves the efficacy of the studied formulation
containing permethrin as adulticide and pyriproxyfen as larvicide in scaled-up assays. Moreover, it reduces the environmental
impact and costs of spraying by comparison with formulations using oil solvents.
c
2011 Society of Chemical Industry
Keywords: droplet size; cold fogger; thermal fogger; water; oil solvents; Aedes aegypti
1 INTRODUCTION
Aedes aegypti (L.) is the main vector of dengue virus. Rigorous en-
vironmental sanitation and source reduction are used as control
methods against Ae. aegypti, but these methods are neither rou-
tinely nor uniformly practised. During the mid-twentieth century,
the health authorities of American countries, together with the
Pan American Health Organisation (PAHO), carried out important
Ae. aegypti eradication campaigns; eradication was achieved in Ar-
gentinain 1965.1However, by the endof the 1980s, the countrywas
reinfested by the mosquito, and since 1997 it has suffered a series
of small dengue epidemic outbreaks almost every year until 2009,
when a large outbreak occurred involving more than 20 000 cases.2
When cases of dengue/DHF are actually reported, or when
adult Aedes densities pose a potential risk of transmission,
ultralow-volume (ULV) application of various adulticides is the
recommended control method in the Americas.3
There are two main types of fogging machine: thermal foggers
and cold foggers. Thermal fogging is a space treatment in
which the fog is produced by a device that uses heat to break
up the insecticide into very small droplets (5–30 microns in
diameter) that disperse in the air. When the chemical formulation,
generally diluted in oil-based carriers, is heated, it is vaporised
in a combustion chamber and expelled to form a dense cloud.
Applications should be carried out early in the morning before
thermal convection currents lift the fog from ground level.4The
active ingredient in cold foggers is mechanically broken up into
small droplets by a special device that uses a high-pressure pump
and a fine nozzle. The cold fogger can dispense formulations and
generate the droplets precisely, but does not penetrate dense
foliage or obstacles as well as thermal fogging does.
Droplet size influences the efficiency of an aerosol insecticide
in killing adult mosquitoes, mainly because droplet movement
in the environment and impingement on mosquitoes depend on
size.5In addition to a decrease in insecticidal efficacy, inadequate
∗Correspondence to: H´
ector Masuh, Centro de Investigaciones de Plagas e
Insecticidas, CIPEIN (CITEFA/CONICET), JB de La Salle 4397, (1603) Villa Martelli,
Buenos Aires, Argentina. E-mail: hmasuh@citedef.gob.ar
aCentro de Investigaciones de Plagas e Insecticidas (CIPEIN-CITEFA/CONICET),
Villa Martelli, Buenos Aires, Argentina
bInstituto de Investigaciones e Ingeniería Ambiental (3IA), Universidad Nacional
de San Martín, San Martín, Buenos Aires, Argentina
Pest Manag Sci 2012; 68: 137 –141 www.soci.org c
2011 Society of Chemical Industry

138
www.soci.org L Harburguer et al.
droplet size may cause an unnecessary contamination of the
environment, especially when using oil solvents. Many studies
have aimed to determine optimum droplet size to maximise
vector control efforts,6–8 but few have detailed specific droplet-
size spectra for determined equipment using different solvents,
or compared thermal and non-thermal aerosols for controlling
mosquitoes.9,10
Simultaneous control of adult and larval stages is ideal in
mosquito vector control programmes in order to reduce the
overall vector mosquito population and subsequently decrease or
disrupt the transmission of diseases. Outdoor ULV spray tests using
a mixture of chemical adulticides with larvicides11,12 have recently
been carried out. A ULV formulation containing permethrin as
an adulticide and pyriproxyfen as a larvicide recently developed
in the present authors’ laboratory yielded excellent results in an
initial field trial.13 The present study was designed to measure
droplet size and evaluate the efficacy of this larvicide– adulticide
ULV formulation using three different solvents (water, biodiesel
and gasoil) and two different methods of application (a thermal
and a cold fogger) in scaled-up assays.
2 MATERIALS AND METHODS
2.1 Biological material
An insecticide-susceptible CIPEIN strain of Ae. aegypti originating
from the Rockefeller strain in Venezuela and maintained in the
authors’ laboratory since 1996 was used. The strain was reared
as described in previous reports.14 Adults between 2 and 3 days
old and late third- or early fourth-instar Ae. aegypti larvae of both
sexes were used for the study.
2.2 Insecticide formulation and equipment
A mixture of permethrin 15% (3-phenoxyphenyl)methyl
3-(2,2-dichloroethenyl)-2,2-(dimethyl cyclopropane car-
boxylate) and pyriproxyfen 3% {2-[1-methyl-2-(4-
phenoxyphhenoxy)ethoxy]pyridine}used as an emulsifiable
concentrate (EC) was formulated by Chemotecnica SA (Argentina).
Polyethylene glycol 1000 (Química Oeste) was used as an
antievaporant for ULV treatments. Water, gasoil and biodiesel
(soybean oil) (Cocoil SA) were used as solvents for the EC.
A Swingtec SwingfogSN 50 (Swingtec GmbH, Isny, Germany)
thermal fogger was used. The SN 50 is a handheld machine with
a net weight of 9 kg, designed to disperse oil- and water-based
chemicals. The cold fogger, also a handheld machine, was a
portable Swingtec (formerly known as Motan) Starlet (Swingtec
GmbH, Isny, Germany) with a net weight of 12 kg, which can be
used with oil- or water-based chemicals.
The SN 50 discharge rate using a No. 1 nozzle was 20.5 L h−1;
water, gasoil and biodiesel were used as solvents. The Starlet
discharge rate using a No. 68 nozzle was 3 L h−1, and only water
was used as a solvent.
2.3 Droplet size
Droplet size was measured with a hot-wire anemometer. This
instrument uses a hot-wire probe as the sensing element for
counting and sizing droplets. Each droplet that contacts the probe
cools a length of wire proportional to the droplet’s diameter
and thus reduces the probe’s electrical resistance by an amount
proportional to the size of the droplet. The system was developed
by KLD Industries (Huntington Station, NY). A KLD Industries model
DC-III system was used, and measurements were taken according
to the standard operating procedures provided with the unit. The
probe was located 3 m in front of the machine nozzle, with a
wind speed of 1.5–2.5 m s−1. Four independent replications were
conducted for each combination of sprayer and solvent.
DC-III software for Windows 2000/XP was used to compute the
volume median diameter (VMD), DV0.5, as well as diameters DV0.1
and DV0.9.TheDV0.5is the droplet diameter (µm) where 50% of
the spray volume is contained in droplets smaller than this value.
Similarly, DV0.1and DV0.9are the diameters at which 10% and 90%
of the spray volume are contained in droplets of similar size or less.
The percentage of spray volume contained in droplets less than
20 µm (%Vol <20 µm) was calculated for all tests. This term allows
the user of the equipment or solvent to determine the amount of
material that will most likely remain aloft after an application and
potentially impinge on flying insects. This software was also used
to record the number of droplets greater than 32 µm; these are
interesting data because most insecticide providers recommend
that users comply with droplet sizes between 8 and 30 µm.15
2.4 Fogging operations and assessment of bioefficiency
Trials were carried out in a large shed, 15 m ×4.7 m ×3.2 m
(225 m3volume), which had some openings near the ceiling. The
recommended dose is 700 mL of EC in 5 L of solvent, using 250 mL
of the diluted formulation per 1000 m3. A solution 10 times more
diluted (70 mL in 5 L) was used to provide a low discriminating
dose for measuring the effects of the machines and solvents.
Owing to differences in nozzle size, and hence differences in flow,
the SN50 fogger was turned on for 1 min and the Starlet fogger for
7 min. When water was used as solvent, 5% of polyethylene glycol
1000 was added to the mixture.
Cylindrical screened sentinel cages built with 18-mesh nylon,
15 cm long ×3 cm in diameter, were used to assess fumigation
efficacy according to WHO protocols with minor modifications.16
Sixteen adults (50% each sex), between 1 and 3 days old and
fed on raisins, were transferred to the cages suspended by a
rope 1.5 m above ground level and were placed at 3, 6 and
9 m from the spraying machine. In addition, 500 mL plastic jars
(7.5 cm in diameter) containing 15 late third- or early fourth-
instar larvae and 250 mL tap water were placed on the ground
at the same distances. After spraying, the mosquitoes were kept
in the shed for 1 h, and then both adults and larvae were taken
to the laboratory and maintained at 26 ±2◦C under a 12 : 12 h
photoperiod. Adult mortality was assessed after 24 h, and the
plastic jars were inspected daily until death or adult emergence
of all the individuals to determine adult emergence inhibition
(EI). EI was calculated as shown below and adjusted for larval or
pupal mortalities in the corresponding controls according to Mulla
et al.:17
EI (%) =100 −100(T/C)
where Tis the percentage of emergence in treated containers and
Cis the percentage of emergence in control containers.
Three replicates were conducted for each combination of
sprayer and solvent. In each test, a cage with adults and a jar
with larvae were kept outside the shed as controls; the entire assay
was discarded if control mortality exceeded 15%.
2.5 Statistical analysis
Droplet size data were analysed using a one-way analysis of
variance (ANOVA), with an accepted level of significance for all
comparisons of P<0.05 (Statistica, 1995).18
wileyonlinelibrary.com/journal/ps c
2011 Society of Chemical Industry Pest Manag Sci 2012; 68: 137 –141

139
Efficacy of an adulticide– larvicide ULV formulation on A. aegypti www.soci.org
Table 1. Spray droplet spectra data of permethrin and pyriproxyfen aerosol EC dispersed from portable generators [Swingtec (Motan) Starlet and
SN 50] using different solvents
Droplet dataa,b,c
Sprayer Solvent DV0.1(µm±SD) DV0.5(µm±SD) DV0.9(µm±SD) %Vol <20 µm%<32 µm
Swingtec (Motan) Starlet Water 7.0±0.8a 23.8±2.5a 44.3±2.8a 38.8±4.8a 99.0±0.4a
Swingtec SN 50 Water 6.5±3.0a 25.1±2.9a 37.7±9.3a 30.8±6.9a 99.2±0.6a
Swingtec SN 50 Gasoil 2.0±0.6b 11.8±2.3b 18.9±4.4b 81.2±22.1 b 100 a
Swingtec SN 50 Biodiesel 3.2±0.8b 13.3±4.1b 19.4±4.4b 81.4±13.9 b 100 a
aData are the mean of four replicates.
bDV0.1,DV0.5and DV0.9are the droplet diameters (µm) when 10, 50 and 90%, respectively, of the spray volume is contained in droplets smaller than
this value; %Vol <20 µm is the percentage of spray volume contained in droplets of <20 µm.
cDiameters followed by the same letter within the same column are not significantly different (ANOVA, P<0.050).
Figure 1. Percentage mortality (±ES) of caged adult Ae. aegypti exposed to thermal or cold aerosols of permethrin and pyriproxyfen using water, gasoil
or biodiesel as solvent. Cages were placed 3, 6 and 9 m from the fogger nozzle, 1.5 m above ground level. Treatments with the same letter were not
significantly different (P>0.05) in Duncan’s multiple range test.
Adult mortality, 48 h larval mortality and EI were corrected
with Abbott’s formula19 and subjected to an arcsine square root
transformation before the analyses. Adult mortality data were
compared using two-way analysis of variance (ANOVA); differences
between means were compared using Duncan’s multiple range
test. The accepted level of significance for all comparisons was
P<0.05 (Statistica, 1995).18
Data on 48 h larval mortality and EI were analysed individually
because the authors wanted to compare the efficacy between
sprayers and solvents at different distances and not for each
machine. A two-way analysis of variance (ANOVA) was used where
the factors were distance (3, 6 and 9 m) and the sprayer/solvent
combination (thermal/cold, water/gasoil/biodiesel).
3 RESULTS AND DISCUSSION
3.1 Droplet size
Table 1 shows the results of the sprayer droplet spectra. There
were differences in droplet size spectra between treatments in
DV0.1(F=9.2; df =12; P<0.01), DV0.5(F=20.6; df =12;
P<0.001), DV0.9(F=19.9; df =12; P<0.001) and %Vol
<20 µm(F=15.6; df =12; P<0.001). As can be seen, there
was a significant difference between water-based and oil-based
sprays (Duncan’s multiple range test, P<0.05). Droplet size
for water-based EC was larger than for sprays diluted in gasoil or
biodiesel. However, there were no significant differences in droplet
size between cold and thermal foggers when water was used as
solvent. The percentage of spray volume contained in droplets of
<20 µm was more than 80% for oil-based formulations, a value
considerably greater than that of the water-based formulation of
approximately 40%. Therefore, most of the spray volume of oil
formulations is contained in droplets smaller than 20 µm, which
implies that these sprays will most likely remain airborne after an
application instead of falling to the ground. Moreover, as 99% of
the droplets were smaller than 32 µm for all the solvents used, the
spraying can be considered as ULV.
Several studies5,8,20 have determined optimum droplet size for
adult mosquito control. Haile et al.21 found that the optimum
droplet diameter was between 10 and 15 µm, although little
difference in efficacy on adults using malathion was indicated for
sizes between 7 and 25 µm.
The droplet size results obtained were in accordance with the
results of Hoffmann et al.,15 where DV0.5values for sprays diluted
in diesel were usually smaller than for sprays diluted in water and
%Vol <20 µm ranged between 12 and 100% for diesel-diluted
sprays and only reached 30% for water-diluted sprays.
Pest Manag Sci 2012; 68: 137 –141 c
2011 Society of Chemical Industry wileyonlinelibrary.com/journal/ps

140
www.soci.org L Harburguer et al.
Figure 2. Adult emergence inhibition (%) and larval mortality (%) 48 h after treatment with thermal or cold aerosols of permethrin and pyriproxyfen using
water, gasoil or biodiesel as solvents in late third-/early fourth-instar larvae. Plastic 500 mL jars with 250 mL of tap water were placed on the ground at
different distances (3, 6 and 9 m) from the fogger nozzle. Treatments with the same letter were not significantly different (P>0.05) in Duncan’s multiple
range test for EI. The asterisk (∗) denotes significant difference (P<0.05) from the other treatments for 48 h larval mortality (Duncan’s multiple range
test).
3.2 Adult mortality
Mortality of caged Ae. aegypti adults showed no significant
differences between sprayers and solvents (F=0.14; df =27;
P>0.05) but significant differences between distances (F=4.3;
df =27; P=0.024). Interaction between these factors was also
non-significant (F=0.12; df =27; P>0.05). Duncan’s multiple
range test for distance showed that there were differences in
adult mortality between the cages located at 3 and 9 m, but not
between the cages at 6 m and the other two distances tested
(Fig. 1). Adult mortality at 3 m was 100% and decreased to values
of approximately 90% at 9 m.
In spite of the differences in DV0.5and %Vol <20 µm for water-
based and oil-based formulations, there were no differences in the
mortality of caged adults. These results are consistent with the
work of Yap et al.,22 who compared the efficacy of a Pesguard
FG 161 formulation using a thermal fogger and water and diesel
as solvents and found 100% adult mortality at 24 h with both
solvents. On the other hand, Chung et al.,23 using a formulation
containing Actellic50 EC plus Vectobac12AS with a thermal
fogger and water as solvent, found that the efficacy on adults
decreased with distance, obtaining an adult mortality of 100% at
3 m and less than 30% at 9 m. However, the difference with the
results obtained in this study may be due to differences in droplet
size, as the DV0.5in the work of Chung et al.23 was 57 µm for water-
based solvents, whereas here it is around 25 µm. This means that
the larger droplets fall onto the ground within a few metres of the
sprayer nozzle without impinging on the mosquitoes at distances
greater than 3 m; on the other hand, droplets reaching larger
distances do not have the required dose of pesticide to produce
significant mortality. This was not the case with the machines and
solvents tested in this study. Although efficacy decreased with
distance, adult mortality was still higher than 90% 9 m away from
the sprayer nozzle.
3.3 Larval mortality
Larval mortality (%) 48 h after treatment showed significant
differences among sprayers and solvents (F=12,9; df =27;
P<0.05) and between distances (F=4,33; df =27; P<0.05). The
interaction between these factors was also significant (F=5.87;
df =27; P>0.05).
As shown in Fig. 2, when the thermal fogger was used with
water as a solvent, larval mortality at 48 h was nearly 100% at
a distance of 3 m. This value is significantly different (P<0.05,
Duncan’s multiple range test) from the other treatments at 48 h,
where mortality values were less than 30% and there were no
differences between distances and sprayers when using gasoil
and biodiesel as solvents or when using the cold fogger.
Figure 2 also shows that EI was more than 90% when water was
used as a solvent for both thermal and cold foggers. Moreover,
efficacy did not decrease with distance from the sprayer nozzle.
On the other hand, the efficacy of oil-based solvents decreased
with distance and ranged from 80% EI at 3 m to less than 20% at
9 m. This decrease was greater when using biodiesel instead of
gasoil. In fact, when comparing all treatments at a distance of 3 m,
all of them were equally effective, with the exception of the EI for
biodiesel, which was significantly lower, although still comparable
with that of gas oil (Fig. 2).
Differences between larval mortality after 48 h and EI show
that, at the doses used in this work (10 times lower than the
recommended doses), permethrin does not produce significant
larval mortality, except in the case of the thermal fogger using
water as a solvent, and therefore the EI was produced by
pyriproxyfen.
The difference in efficacy on larvae at 48 h between the cold
and thermal sprayers when water was used as solvent could be
determined by the difference in droplet size. While not statistically
significant, the difference was noteworthy on its effectiveness. As
DV0.5was slightly higher for the thermal fogger, the larger droplets
wileyonlinelibrary.com/journal/ps c
2011 Society of Chemical Industry Pest Manag Sci 2012; 68: 137 –141

141
Efficacy of an adulticide– larvicide ULV formulation on A. aegypti www.soci.org
may contain more insecticide, causing larval mortality as they fall
into the jars at a short distance.
The larvicidal effect of pyriproxyfen (measured as EI) decreases
with distance for oil-based solvents but not for aqueous solvents.
These results are in accordance with previous results by Yap et al.,22
where a water-based thermal fogging formulation of Pesguard
FG 16l seemed to achieve a significantly better larvicidal effect than
a diesel-based spray. This could be due to the difference in droplet
size between the two types of solvent found in this work, where
oil-based solvents had a significantly lower DV0.5.AstheDV0.5is
low, the droplets remain suspended for longer and are less likely
to fall into the jars with larvae. However, by remaining suspended,
they are just as effective on Ae. aegypti adults as aqueous solvents.
This explanation agrees with the results of Mount et al.,24 who
found a much lower mortality in caged Ae. taeniorhynchus at
ground level (14%) than at 1.5 m above the ground using fuel oil
as solvent and fenthion or naled as insecticide. Similarly, using
ULV applications of ground aerosols of synergised pyrethrins and
resmethrin against caged Cx. quinquefasciatus, Womeldorf and
Mount25 obtained a higher mortality of mosquitoes in cages
placed 1.5 m above ground level than in others placed at 0.15 m.
Only Chung et al.23 used jars with larvae to assess the larvicidal
efficacy of a formulation containing Bti and pirimiphos-methyl
applied with a thermal fogger and water as solvent. The jars
were placed on the floor and, as observed in this study, efficacy
decreased with distance. However, contrary to the results of the
present study when using oil solvents, the loss of effectiveness
in the work by Chung et al.23 was due to the large droplet size
(57 µm) limiting the distance the insecticide could reach.
Finally, the lower larvicidal effect observed when using oil
solvents could also be due to a better settlement of the spraying
droplets on exposed water surfaces in the water-based spray
formulation compared with the oil-based sprays, as suggested by
Yap et al.22
4 CONCLUSIONS
Droplet size is a crucial factor modulating the trajectory of aerosols
generated by thermal or cold foggers. Although significant
differences in droplet size were observed between water and
oil solvents, they were all equally effective on Ae. aegypti adults.
However, this was not the case with larvae, where sprays using
water as a solvent were significantly more effective than the
oil-based formulations.
These results show that a water-based formulation is more
effective than an oil-based formulation (gasoil or biodiesel).
Therefore, the use of water as solvent, with both thermal or
cold foggers, not only improves the efficacy of the formulation
containing permethrin and pyriproxyfen but also reduces the
environmental impact and costs of spraying compared with
the use of oil solvents. Further research on the performance
of this formulation, using different solvents and sprayers in field
conditions and at the recommended dose, is needed to determine
its specific efficacy on Ae. aegypti adults and larvae.
REFERENCES
1 Ousset JH, De Ustar´
an KJ and Lombardo B, Erradicaci´
on del Aedes
aegypti en la Rep ´
ublica Argentina (infestacion inicial – adaptaci ´
on
de procedimientos). Segundas Jornadas Entomoepidemiologicas
Argentinas 2:81– 88 (1965).
2 Masuh H, Re-emergence of dengue in Argentina: historical
development and future challenges. Dengue Bull 32:44 –54 (2008).
3 Pan American Health Organization, Dengue in Americas. Epidemiol
Bull 2:1– 4 (1981).
4 Gratz NG, Space sprays for control of Aedes aegypti in South-East Asia
and the Western Pacific. Dengue Bull 23:80 –84 (1999).
5 Mount GA, Pierce NW and Baldwin KF, Droplet size of aerosols
dispersed by portable and truck-mounted generators. Mosq News
35:195– 198 (1975).
6 Himel CM, The optimum size for insecticide spray droplets. JEcon
Entomol 62:919– 926 (1969).
7 Lofgren CS, Anthony DW and Mount GA, Size of aerosol droplets
impinging on mosquitoes as determined with a scanning electron
microscope. J Econ Entomol 66:1085 –1088 (1973).
8 Curtis GA and Beidler EJ, Influence of ground ULV droplet spectra on
adulticide efficacy for Aedestaeniorhynchus.JAmMosqControlAssoc
12:368– 371 (1996).
9 Hoffmann WC, Walker TW, Martin DE, Barber JA, Gwinn T, Smith VL,
et al, Characterization of truck-mounted atomization equipment
typically used in vector control. J AmMosq Control Assoc 23:321– 329
(2007).
10 Brown JR, Steinke WE, Zhai J and Sykes D, Aqua-Reslindroplet
analysis. J Am Mosq Control Assoc 14:467 –469 (1998).
11 Yap HH, Chong ASC, Adanan CR, Chong NL, Rohaizat B, Abdul Mailk Y,
et al, Performance of ULV formulations (Pestguard102/Vectobac
AS 12) against three mosquito species. J Am Mosq Control Assoc
13:384– 388 (1997).
12 Yap HH, Chong ASC, Chong NL, Adanan CR, Abdul Mailk Y, Lim SY,
et al, ULV field studies of combined spraying of Aqua Resigenand
VectobacAS 12 against Aedes aegypti, Aedes albopictus and Culex
quinquefasciatus.Trop Biomed 14:57 –63 (1997).
13 Lucía A, Harburguer L, Licastro S, Zerba E and Masuh H, Efficacy of a
new combined larvicidal– adulticidal utralow volume formulation
against Aedes aegypti (Diptera: Culicidae), vector of dengue.
Parasitol Res 104:1101 –1107 (2008).
14 Seccacini E, Masuh H, Licastro S and Zerba E, Laboratory and scaled
up evaluation of cis-permethrin applied as a new ultra volume
formulation against Aedes aegypti (Diptera: Culicidae). Acta Trop
97:1– 4 (2006).
15 Hoffmann WC, Walker TW, Fritz BK, Gwinn T, Smith VL, Szumlas D, et al ,
Spray characterization of thermal fogging equipment typically used
in vector control. J Am Mosq Control Assoc 24:550 –559 (2008).
16 Reiter P and Nathan MB, Report of the WHO informal consultation on
the evaluation and testing of insecticidas – Guía para la evaluaci ´
on
de la eficacia del rociado espacial de insecticidas para el control del
vector del dengue, (WHO/CTD/WHOPES/IC/96.1), WHO, Geneva,
Switzerland (2006).
17 Mulla MS, Darwazeh HA and Norland RL, Insect growth regulators:
evaluation procedures and activity against mosquitoes. JEcon
Entomol 67:329– 332 (1974).
18 STATISTICA for Windows ’99 Edition. [Online]. Statistica StatSoft Inc.,
Tulsa, OK (1995). Available: http://www.statsoft.com/support/free-
statistica-10-trial/download/ [June 22 2011].
19 Abbott WS, A method of computing the effectiveness of an insecticide.
J Econ Entomol 18:265 –267 (1925).
20 Mount GA, A critical review of ultralow-volume aerosols of insecticide
applied with vehicle-mounted generators for adult mosquito
control. J Am Mosq Control Assoc 14:305 –334 (1998).
21 Haile DG, Mount GA and Pierce NW, Effect of droplet size of malathion
aerosols on kill of caged adult mosquitoes. Mosq News 42:576 –583
(1982).
22 Yap HH, Lee YW, Zairi J, Jahangir K and Adanan CR, Indoor thermal
fogging application of PesguardFG 161, a mixture of d-
tetramithrin and cyphenothrin, using portable sprayer against
vector mosquitoes in the tropical environment. J Am Mosq Control
Assoc 17:28– 32 (2001).
23 Chung YK, Lam-Phua SG, Chua YT and Yatiman R, Evaluation of
biological and chemical insecticide mixture against Aedes aegypti
larvae and adults by thermal fogging in Singapore. Med and Vet
Entomol 15:321– 327 (2001).
24 Mount GA, Pierce NW, Lofgren CS and Gahan JB, Fog oil and fuel oil as
diluents of fenthion, naled, and malathion in thermal aerosols used
to control adult stable flies and salt-marsh mosquitoes. Mosq News
26:249– 253 (1966).
25 Womeldorf DJ and Mount GA, Control of adult Aedes nigromaculis
(Ludlow) with aerosols of pyrethrins and synthetic pyrethroids II.
Field evaluations. Proc Calif Mosq Vector Control Assoc 45:154 –156
(1977).
Pest Manag Sci 2012; 68: 137 –141 c
2011 Society of Chemical Industry wileyonlinelibrary.com/journal/ps