ArticlePDF Available

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


Abstract and Figures

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.
Content may be subject to copyright.
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
( 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 Masuha,b
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 adulticidelarvicide 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.
2011 Society of Chemical Industry
Keywords: droplet size; cold fogger; thermal fogger; water; oil solvents; Aedes aegypti
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 (530 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:
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 c
2011 Society of Chemical Industry
138 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
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.
2.1 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 SwingfogSN 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 h1;
water, gasoil and biodiesel were used as solvents. The Starlet
discharge rate using a No. 68 nozzle was 3 L h1, 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 1.52.5 m s1. 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 ±2C 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 c
2011 Society of Chemical Industry Pest Manag Sci 2012; 68: 137 –141
Efficacy of an adulticide– larvicide ULV formulation on A. aegypti
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).
3.1 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
140 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
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 Actellic50 EC plus Vectobac12AS 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
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 c
2011 Society of Chemical Industry Pest Manag Sci 2012; 68: 137 –141
Efficacy of an adulticide– larvicide ULV formulation on A. aegypti
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
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.
1 Ousset JH, De Ustar´
an KJ and Lombardo B, Erradicaci´
on del Aedes
aegypti en la Rep ´
ublica Argentina (infestacion inicial adaptaci ´
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
10 Brown JR, Steinke WE, Zhai J and Sykes D, Aqua-Reslindroplet
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 (Pestguard102/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 Resigenand
VectobacAS 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 ´
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:
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
22 Yap HH, Lee YW, Zairi J, Jahangir K and Adanan CR, Indoor thermal
fogging application of PesguardFG 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
Pest Manag Sci 2012; 68: 137 –141 c
2011 Society of Chemical Industry
... A test is defined as a single-pass of an operator (man)-held Colt-4 ULV Handheld Fogger Sprayer (London Fog, Minneapolis, MN) applying Permanone 31-66, with the direction of the pesticide treatment being perpendicular to the walking path (Fig 2); this is a cold fogger that produces droplets of less than 15 μm, which is considered optimal for Ae. aegypti control [37]. A typical test used approximately 350 female mosquitoes, of which 20% were of the Orlando strain. ...
... In a similar study with susceptible Ae. aegypti Rockefeller strain and comparing applications of permethrin + pyriproxyfen, the cold fogging resulted in 95% mortality at 6 m and about 90% at 9 m, while thermal fogging resulted in 100% mortality. The output of a cold fogger, such as the one used here, provides excellent droplet size but does not penetrate obstacles (i.e., cages) as the thermal fogging does [37]. Wind direction and speed and local thermal inversion also influence the spread of the insecticide application. ...
Full-text available
Aedes aegypti (L.) is an important mosquito vector of emerging arboviruses such as Zika, dengue, yellow fever, and chikungunya. To quell potential disease outbreaks, its populations are controlled by applying pyrethroid insecticides, which selection pressure may lead to the development of insecticide resistance. Target site insensitivity to pyrethroids caused by non-synonymous knockdown resistance ( kdr ) mutations in the voltage-gated sodium (Na V ) channel is a predominant mechanism of resistance in mosquitoes. To evaluate the potential impact of pyrethroid resistance on vector control, Ae . aegypti eggs were collected from eight mosquito control operational areas in Harris County, Texas, and emerged females were treated in field tests at four different distances from the pyrethroid Permanone 31–66 source. The females were genotyped by melting curve analyses to detect two kdr mutations (V1016I and F1534C) in the Na V channel. Harris County females had higher survivorship rates at each distance than the pyrethroid-susceptible Orlando strain females. Survivorship increased with distance from the pyrethroid source, with 39% of field-collected mosquitoes surviving at 7.62 m and 82.3% at 22.86 m from the treatment source. Both the V1016I and F1534C pyrethroid resistant genotypes were widely distributed and at high frequency, with 77% of the females being double homozygous resistant (II/CC), this being the first report of kdr mutations in Ae . aegypti in Harris County. Analysis of the probability of survival for each mutation site independently indicated that the CC genotype had similar probability of survival as the FC heterozygous, while the II genotype had higher survival than both the VI and VV, that did not differ. The double homozygous resistant genotype (II/CC) had the highest probability of survival. A linear model estimated probability of survival for areas and genotypes. The high frequency and widespread distribution of double-homozygote pyrethroid-resistant Ae . aegypti may jeopardize disease vector control efforts in Harris County.
... Six studies were written in Spanish, and the others in English. The studies came from many regions including South America (30%), North America (28%), Asia (17%), Europe (9%), Caribbean (17%), Middle east (5%), • Use of PPF ultra low volume, thermal fogging, and fumigant technologies (15 studies) [67][68][69][70][71][72][73][74][75][76][77][78][79][80]; ...
... Studies investigating the use of PPF in ULV, thermal fogging (TF) and fumigant techniques found IE declining from 100%-50% for 4-6 weeks respectively in treated areas and steadily decreasing with the distance from the sprayer, the length of time from treatment, and type (cold/thermal) of fogging (Fig 3) [67,68,[73][74][75][76][77][78][79]. Beyond simply having an effect on larval mortality, the sublethal dose of PPF was found to have effects on the fertility and fecundity of adult females who were exposed at the adult stage. ...
Full-text available
Background Dengue is the most rapidly spreading arboviral disease in the world. The current lack of fully protective vaccines and clinical therapeutics creates an urgent need to identify more effective means of controlling Aedes mosquitos, principally Aedes aegypti, as the main vector of dengue. Pyriproxyfen (PPF) is an increasingly used hormone analogue that prevents juvenile Aedes mosquitoes from becoming adults and being incapable of transmitting dengue. The objectives of the review were to (1) Determine the effect of PPF on endpoints including percentage inhibition of emergence to adulthood, larval mortality, and resistance ratios; and (2) Determine the different uses, strengths, and limitations of PPF in control of Aedes. A systematic search was applied to Pubmed, EMBASE, Web of Science, LILACS, Global Health, and the Cochrane database of Systematic Reviews. Out of 1,369 records, 90 studies met the inclusion criteria. Nearly all fit in one of the following four categories 1) Efficacy of granules, 2) Auto-dissemination/horizontal transfer, 3) use of ultra-low volume thermal fogging (ULV), thermal fogging (TF), or fumigant technologies, and 4) assessing mosquito resistance. PPF granules had consistently efficacious results of 90–100% inhibition of emergence for up to 90 days. The evidence is less robust but promising regarding PPF dust for auto-dissemination and the use of PPF in ULV, TF and fumigants. Several studies also found that while mosquito populations were still susceptible to PPF, the lethal concentrations increased among temephos-resistant mosquitoes compared to reference strains. The evidence is strong that PPF does increase immature mortality and adult inhibition in settings represented in the included studies, however future research should focus on areas where there is less evidence (e.g. auto-dissemination, sprays) and new use cases for PPF. A better understanding of the biological mechanisms of cross-resistance between PPF, temephos, and other insecticides will allow control programs to make better informed decisions.
... Spray quality depends largely on the spray nozzle; different pesticide atomization methods can produce droplets of varying sizes; however, for a particular organism or part of the organism, only a certain droplet size can be captured to produce an effective toxic effect. This was discovered in the 1950s, and after extensive research, it was gradually accepted and recognized by researchers (Mount, 1970;Johnstone, 1971;Harburguer et al., 2012). Studies have shown that the optimum particle size is 10−50 mm for flying pests, 30−150 mm for cotton bollworms, 30−150 mm for treating diseases, and 100−300 mm for weeds. ...
Full-text available
To clarify the effect of droplet size on solution deposition and powdery mildew control on greenhouse cucumber leaves, the effect of volume median droplet diameter (VMD) on solution deposition and maximum retention, as well as the effect of flusilazole on powdery mildew control on cucumber, was determined using the stem and leaf spray method. The VMD of the typical fan nozzles (F110-01, F110-015, F110-02, F110-03) of the selected US Tee jet production differs by approximately 90 μm. The results showed that the deposition of flusilazole solution on cucumber leaves decreased as the VMD of the droplets increased and that the deposition of the solution in the treatments with VMD of 120, 172, and 210 μm decreased by 22.02%, 10.37%, and 46. 97%, respectively, compared to that observed with treatment with 151 μm VMD. The deposition of the solution on cucumber leaves showed the highest deposition efficiency of 63.3% when the applied solution volume was 320 L/hm ² , and the maximum stable retention of the liquid on the leaves was 6.6 µl/cm ² . The control effects of different concentrations of flusilazole solution on cucumber powdery mildew differed significantly, and the best control effect was achieved at the dosage of 90 g/hm ² of the active ingredient, which was 15%−25% higher than that observed at the dosage of 50 and 70 g/hm ² of the active ingredient per hectare. A significant difference in the effect of droplet size on the control of cucumber powdery mildew was observed at any specific liquid concentration. Nozzle F110-01 showed the best control effect when the dosage of the active ingredient was 50 and 70 g/hm ² per hectare, which did not differ significantly from that observed with nozzle F110-015 but differed significantly from those observed with nozzles F110-02 and F110-03. Hence, we concluded that the use of smaller droplets with VMD of 100−150 μm, i.e. the choice of F110-01 or F110-015 nozzles, for application on the leaf parts of cucumber in the greenhouse under conditions of high liquid concentration, can significantly improve the effective use of pharmaceuticals and the disease control effect.
... First, we found high frequencies of the V410L kdr mutation associated with pyrethroid resistance, manifested as higher than expected survivorship at 7.62 m in most operational areas investigated (Figs 1 and 2). In similar trials with susceptible Aedes aegypti 95-100% mortality is expected at 6 m [44]. This is the first detection of the V410L kdr mutation in Texas, which was found frequently in combination with the V1016I and F1534C genotypes ( Table 2 and Fig 1). ...
Full-text available
Harris County, TX, is the third most populous county in the USA and upon detection of arboviruses Harris County Public Health applies insecticides (e.g., pyrethroid-based Permanone 31–66) against adults of Culex quinquefasciatus to prevent disease transmission. Populations of Aedes aegypti , while not yet a target of public health control, are likely affected by pyrethroid exposure. As this species is a vector of emerging arboviruses, its resistance status to Permanone and the kdr mutations in the voltage-gated sodium channel (VGSC) associated with pyrethroid resistance were investigated. We examined females of known genotype at the V1016I and F1534C sites (N = 716) for their genotype at the 410 amino acid position in the VGSC, and for the influence of their kdr genotype on survival to Permanone at three different distances from the insecticide source in field tests. Most females (81.8%) had at least one resistant L allele at the 410 position, being the first report of the V410L mutation in Ae . aegypti for Texas. When only genotypes at the 410 position were analyzed, the LL genotype exhibited higher survivorship than VL or VV. Out of 27 possible tri-locus kdr genotypes only 23 were found. Analyses of the probability of survival of tri-locus genotypes and for the V410L genotype using a multivariate logistic regression model including area, distance, and genotype found significant interactions between distance and genotype. When only the most common tri-locus genotypes were analyzed (LL/II/CC, 48.2%; VL/II/CC, 19.1%; and VV/II/CC, 10.1%) genotype had no effect on survival, but significant interactions of distance and genotype were found. This indicated that the V410L kdr allele increased survival probability at certain distances. Genotypes did not differ in survivorship at 7.62-m, but LL/II/CC had higher survivorship than VL/II/CC at 15.24- and 22.86-m. The model also identified differences in survivorship among the operational areas investigated.
... Esto último se puede conseguir mediante la reducción de los posibles criaderos y a través de la aplicación de larvicidas. El control de adultos es recomendado solo en casos de brotes o epidemias 51 . Debido a las ventajas que poseen en comparación con otros insecticidas, los productos habitualmente elegidos para controlar mosquitos contienen piretroides, aunque a veces se usan otros como el organofosforado temefós. ...
The Triatoma infestans bedbug (known in Argentina as “vinchuca”) and four species of mosquitoes (Aedes aegypti, Culex pipiens quinquefasciatus, Anopheles pseudopunctipennis and An. darlingi) are the main insect vectors of disease in Argentina. Since 1977, the Argentine Pest and Insecticide Research Center (CIPEIN) has been doing research on these insects and developing products for their control that have a low impact on human health and the environment. Recognized as a Reference Center by the Pan American Health Organization and the World Health Organization, CIPEIN was a pioneer in the development of insecticide products in Latin America. The aim of this article is to review the status of the health issues involving kissing bugs and mosquitoes in Argentina and to describe the main contributions of CIPEIN to their study and control.
... The Birchmeier had the smallest mean droplet size, but all 3 produced droplets within the range of a barrier spray application. Usually smaller droplets linger longer in the air, drift more effectively through air and vegetation, and cover more surface area with insecticides (Harburguer 2012). More tests should be done on the Birchmeier to analyze the flow rate for different nozzles at different pressures and operating time for the fully charged battery at different pressures. ...
... Large Ae. aegypti populations in urban areas most often require the employment of mosquito control strategies to artificially reduce its populations by, among other things, insecticide spraying. The combined use of larvicide and adulticide has been used in the attempt to control populations of vector mosquito species [33][34][35][36]. However, controlling Ae. aegypti populations in urban environments is problematic, relying on many critical steps that logically build on each other [37]. ...
Full-text available
Current management and control of Aedes aegypti populations in urban areas are based on the spraying of insecticides. Here, we evaluated the effectiveness of spraying larvicide (Bacillus thuringiensis israelensis) using a truck-mounted Buffalo Turbine and adulticide (Deltamethrin) using a Grizzly ULV Sprayer in an urban area with high densities of Ae. aegypti and many cryptic and difficult to reach aquatic breeding habitats. Experiments were conducted in a tire shop located in Miami-Dade County, Florida with approximately 100,000 used airplane tires. Insecticide interventions were performed after a baseline survey consisting of 3 weeks of collections, followed by two insecticide interventions: (i) application of the adulticide followed by the application of larvicide on the subsequent week; and (ii) application of both adulticide and larvicide on two consecutive weeks. The first insecticide intervention resulted in a non-significant decrease in the relative abundance of Ae. aegypti. On the other hand, the second insecticide intervention significantly reduced the Ae. aegypti relative abundance (P < 0.002). Our results demonstrated that the combined insecticide interventions on two consecutive weeks significantly reduced the relative abundance of Ae. aegypti. This result indicated that the larvicide was successfully propelled reaching cryptical and difficult to reach aquatic habitats. However, even though the number of mosquitoes was greatly reduced, it was still greatly above the 10-mosquito threshold by trap night used by the Miami-Dade Mosquito Control Division to deploy an inspector to survey the area. Considering the lack of new and effective mosquito control tools, efficient and mobile insecticide propellers such as Buffalo Turbine can be of great help to manage mosquito populations in urban areas.
... Each dot represents the average effect at a location relative to naled residues on the co-located filter paper sampler Data from the present study indicate that naled aerially applied by ULV sprays will drift from target areas on the Refuge into the no-spray zones. The small droplet sizes typical of ULV sprays enhance efficacy of the sprays against mosquitoes (Sugiura et al. 2011;Harburguer et al. 2012) but also enhance drift (Teske et al. 2000;Lothrop et al. 2007; reviewed in Hilz and Vermeer 2013). Drift was a concern for resource managers responsible for conservation of sensitive species in the no-spray zones, because it could adversely affect those species. ...
Full-text available
Natural resource managers are concerned about the impacts of aerial ultra-low volume spray (ULV) of insecticides for mosquito control (i.e., mosquito adulticides) and seek science-driven management recommendations that reduce risk but allow vector control for nearby human populations. Managers at the National Key Deer Refuge (Florida Keys, FL) are concerned for ULV effects upon conservation efforts for imperiled butterflies (Florida leafwing [Anaea troglodyta floridalis] and Bartram’s hairstreak [Strymon acis bartrami] butterflies). No-spray zones were designated for protection of those butterflies, but their effectiveness for mitigation is unclear. To address this uncertainty, cholinesterase activity (ChE) and mortality were monitored for caged butterflies gulf fritillary [Agraulis vanilla] and great southern white [Ascia monuste]) deployed on the Refuge during three aerial ULV applications of the insecticide naled. Residue samplers also were deployed to estimate butterfly exposure. Spray efficacy against mosquitoes was assessed by deploying caged mosquitoes at the same locations as the butterflies. Average naled residue levels on filter paper samplers in the target area (1882–2898 µg/m2) was significantly greater than in the no-spray zone (9–1562 µg/m2). Differences between the no-spray zone and target area for butterfly mortality and ChE were inconsistent. Average mortality was significantly lower, and average ChE was significantly higher in the no-spray zone for larvae of one species but not for larvae of the other species. Mosquito mortality did not differ significantly between the two areas. Data from the present study reflect the inconsistent effectiveness of no-spray zones on the Refuge using standard methods employed at the time by the vector control agency in the Florida Keys and possibly by other vector control agencies in similar coastal environments. Furthermore, these findings helped to guide the design and to improve the conservation value of future no-spray zone delineations while allowing for treatment in areas where mosquito control is necessary for vector-borne disease reduction.
... Also, adult control using spatial sprays with adulticides is recommended when dengue outbreaks occurs [1]. Because adult emergence from container habitats is continuous, conventional adult insecticides spraying generally achieves inadequate and merely transient control [2][3][4][5][6]. ...
Full-text available
Background: Aedes aegypti (L.) is the main vector of dengue, yellow fever, Zika and chikungunya viruses. A new method for controlling this mosquito has been developed based on the possibility that wild adult mosquitoes exposed to artificial resting sites contaminated with a larvicide, can disseminate it to larval breeding sites, is named "auto-dissemination". The present study was undertaken to evaluate if a chitin synthesis inhibitor like lufenuron can be disseminated to larval breeding sites and prevent adult emergence and also if forced contact of Ae. aegypti females with treated surfaces can affect its fertility, fecundity, and blood intake capacity. Methods: Larval susceptibility to lufenuron was measured through EI50 and EI90. On the other hand, gravid females were exposed by tarsal contact to lufenuron-treated papers, we used the WHO susceptibility test kit tube to line the papers, and 1, 3 or 5 females for the transference. We also evaluated if the exposure of female mosquitoes to lufenuron-treated papers (0.4 and 1 mg a.i./cm2) has an effect on their fertility, fecundity or in the ability to feed on blood. In each assay 12-15 female mosquitoes were exposed to lufenuron for 1 h, 24 h before blood meal (BBM) or 24 h after a blood meal (ABM). Results: Lufenuron proved to be very active against Ae. aegypti larvae with an EI50 of 0.164 ppb and EI90 of 0.81 ppb. We also found that lufenuron can be transferred by females from treated surfaces to clean containers causing the inhibition of emergence of the larvae (between 30 and 50%). This effect was dependent on the concentration applied on the paper and the number of females added to each cage. Conclusions: This study introduces an innovation by first exploring the possibility that an insect growth regulator (IGR) belonging to the group of benzoylphenyl ureas, such as lufenuron, can be transferred by gravid females to breeding sites and that at the same time can have an effect on fertility, fecundity and blood intake capacity of adult mosquitoes.
For the indoor and outdoor pest controls, various types of insecticide formulations are available including aerosols, sprays, electric vaporizers, mosquito coils, and traps. In the present study, the insecticidal activity of aerosols, the most commonly used formulation of household insecticides for mosquito control, against Aedes albopictus (Skuse) was assessed using seven commercial products and some attributes which can affect the efficacy of aerosol were investigated as well. The products had difference in their chemical composition of active ingredients, propellant/liquid phase ratios, solvent types, and nozzle orifice sizes, and these characteristics seem to affect the overall insecticidal activity. In general, solvent type dominantly determined the insecticidal activity, where four products in oil-based solvent system showed greater mortality (97.5% in average) than water-based aerosols (38.3% in average) against the mosquitoes located at the far side of the test chamber. The contribution of solvent type and nozzle orifice size were further examined with the sample aerosols, and the orifice size were determined more influential to the spray distance. Regardless of solvent types, the sample products attached to a bigger actuator (0.96 mm in diameter) showed greater knock-down activity (>98%) than the smaller ones (0.48 mm, 62.5% in average) to the back panel in the chamber. On the other hand, solvent system significantly affected the residual activity, as the oil-based and water-based aerosols showed 2.3- and 4.8-fold decrease in KT50 values, respectively, between 1 and 10 min after the spray.
Full-text available
A new ultralow volume formulation (ULV) containing permethrin as an adulticidal active ingredient and the insect growth regulator (IGR) pyriproxyfen as a larvicide was developed and its efficacy evaluated in a field trial in Wanda, Misiones (Argentina). Two separate study areas were sprayed: one with a ULV formulation of permethrin 15% plus pyriproxyfen 3% and the other with permethrin 15% only. A third untreated area was kept as a control. Sentinel cages containing adult mosquitoes and jars containing Aedes aegypti larvae III/IV were placed in treated and control areas. The residual activity of the formulations was tested using 20 L water containers. The adulticide effect of permethrin 15% + pyriproxyfen 3% formulation was similar to the permethrin 15% formulation, however, the inhibition of adult emergence in the treatment with permethrin 15% never exceeded 20%, whereas the inhibition of adult emergence in the treatment with permethrin 15% plus pyriproxyfen 3% showed initial values of 96% maintaining this high level of inhibition up to 35 days after ULV spraying. Larval indexes (House and Breteau indexes) showed that a greater, long-lasting effect was obtained with the permethrin 15% plus pyriproxyfen 3% formulation.
After 82 years of the absence of dengue in Argentina, a dengue outbreak occurred in the northern provinces of the country in 1998. Aedes aegypti, the vector mosquito, was eradicated in the 1960s, mainly due to the use of residual insecticides at an enormous cost of resources and through a vertical health programme. Since then, the country has gradually become reinfested due to the deterioration of the surveillance system and vector control programmes. At present, DENV-1 to 3 have been found in circulation and 3162 cases of dengue fever (DF) have been reported in the country. However, as autochthonous cases have been recorded during this epidemic only, the disease is still not considered endemic in the country, although there is a regular occurrence of outbreaks in neighbouring countries. The control strategies currently being used are the same ones as used in the past century although socioeconomic and demographic conditions have greatly changed. Consequently, alternative methods are proposed as potential tools to establish new ways of controlling the vector, which is the only way of preventing new outbreaks in the region.
The optimum size for insecticide spray droplets is that size which gives maximum control of the target insect with minimum insecticide and minimum ecosystem contamination. Spray droplets found to be efficient in delivery of insecticide to the target insect are those with size range allowing them to be airborne and to be transported to the target by atmospheric transport and diffusion. Therefore, optimum-size droplets are those sizes small enough to be produced in maximum numbers for maximum coverage and large enough to have an optimum critical impingement velocity for optimum impingement on the target insect. Field research data which trace the point of deposition of spray droplets by size in insect ecosystems have been obtained from the fluorescent particle spray droplet tracer method. Data obtained indicate that the optimum size for insecticide spray droplets is in the range of 20µ diameter. No data were found that spray droplets larger than 100µ diameter have any substantial probability of efficient delivery of insecticide to the target insect or to its proximate foliage (where spray residues could act by secondary foliage contact). Spray droplets of 50-100µ diameter were marginal in efficiency.
Droplet size spectra from different sprayers used to generate insecticide-laden fogs for controlling flying insects were measured by a laser diffraction instrument and Teflon-coated slides. The objectives of this work were to present not only information on spray-system droplet size generated by different sprayers, but to compare methodologies by which other similar systems can be evaluated and give applicators sprayer-system performance data. Data from 45 replicated spray tests, comprising 11 sprayers and 5 pesticides, showed a wide range in the droplet size spectra produced. The volume median diameter measurements ranged from 2.6 to 75.5 microm for diesel-diluted sprays and from 27.9 to 59.9 microm for water-diluted sprays. Similarly, the percent volume <20 microm ranged between 12.0-100% and 8.5-30.7%, for diesel- and water-diluted sprays, respectively. The droplet sizes measured by the swinging slide and laser diffraction methods were not consistent. The information presented aids users in sprayer selection and operation to produce the specific droplet size spectra required for a particular application.
In the laboratory, 10 insect growth regulators (IGR) were evaluated against 4th-instars and 4 IGR’s were evaluated against 1st-instal’s and pupae of Culex pipiens quinquefasciatus Say. The latter 4 IGR’s also were evaluated against 4th-instars of Anopheles albimanus Wiedemann. One IGR, TH-6040 [1-(4-chlorophenyl)-3(2,6-difluoro-benzoyl)-urea], showed outstanding activity against all stages of the 2 species. The 4 most active and readily available IGR’s were evaluated against asynchronous populations of Culex tarsalis Coquillett in the field. RO-20-3600 (6,7-epoxy-3-methyl-7-ethyl-1-[3,4-(methylenedioxy)-phenoxy] cis/trans-octene) suppressed emergence of adults for ca. 3–5 days at the rates of 0.25 and 0.5 lb AI/acre. HE-24108 [3-Butyn-2-yl N-(p-chlorophenyl)carbamate] inhibited adult emergence only at the high rate of 0.5 lb/acre, 1 day posttreatment. R-20458 [1-(4′-ethylphenoxy)-6,7-epoxy-3,7-dimethyl-2-octene] yielded complete inhibition of adult emergence from isolates 1 day posttreatment but not 5 days. TH-6040 was the most effective compound evaluated, producing high to complete inhibition of adult emergence 5–15 days posttreatment. An EC and a WP formulation of this compound were equally effective.
A procedure was developed whereby aerosol droplets of soybean oil (used to simulate undiluted insecticide) that impinged on Aedes taeniorhynchus Wiedemann were observed and photographed with a scanning electron microscope. Few droplets occurred on mosquitoes exposed outdoors, but mosquitoes exposed in wooden chambers had droplets on all sections of their body surface. Highest concentrations were on the wings and antennae. On mosquito wings, droplets ranging in size from two to 16 microns impinged with more efficiency than smaller or larger droplets. All droplets of soybean oil on mosquitoes exposed outdoors measured one to eight microns.