Efficacy of Various Larvicides against Aedes aegypti Immatures in the Laboratory

Article · July 2013with145 Reads
DOI: 10.7883/yoken.66.341 · Source: PubMed
Abstract
We conducted a laboratory study to evaluate the efficacy of control agents against small larvae, large larvae, and pupae of Aedes aegypti to determine an appropriate larvicide regime to employ in emergency dengue control programs. The control agents included Bacillus thuringiensis var. israelensis (Bti), pyriproxyfen (an insect growth regulator), a larvicidal oil, Aquatain AMF (polydimethylsiloxane, a monomolecular film), and temephos at the recommend application dosages and rates. Our results showed that Bti, pyriproxyfen, and temephos were efficacious (100% mortality) against larvae, irrespective of the instar stage, but not against pupae of Ae. aegypti (1.5-7.8% mortality). Aquatain AMF, on the other hand, was very effective at controlling the pupal stage (100% mortality), but had limited efficacy against small larvae (38.0% mortality) and large larvae (78.0% mortality). The larvicidal oil was effective against all immature stages (93.3-100% mortality). Therefore, we concluded that for effectively interrupting the dengue transmission cycle, larvicides that kill the pupal stage (Aquatain AMF or larvicidal oil) should be included in an emergency dengue control program in addition to Bti, pyriproxyfen, or temephos.
341
*
Corresponding author: Ma iling address: Research and
Diagnostic Center, Centers fo r Disea se Control, 1 61
Kun-Yang Street, Nankang, Taipei 11561, Taiwan
(R.O.C.). Tel:
118862-26531075, Fax:
11886-
26519632, E-mail: hjteng
cdc.gov.tw
341
Jpn. J. Infect. Dis., 66, 341-344, 2013
Short Communication
Efficacy of Various Larvicides against
Aedes aegypti
Immatures in the Laboratory
Chih-Yuan Wang
1
,Hwa-JenTeng
1
*
,Si-JiaLee
1
,
Cheo Lin
1
,Jhy-WenWu
2
, and Ho-Sheng Wu
1
1
Research and Diagnostic Center and
2
2nd Divisio n, Centers f or D isea se Control, Taipei, Taiwan
(Received October 22, 2012. Accepted April 26, 2013)
SUMMARY : W e conducted a laboratory study to evaluate the efficacy of control agents against small
larvae, large larvae, and pupae of
Aedes aegypti
to determine an appropriate larvicide regim e to employ
in emergency dengue control programs . T he contro l agents included
Bacillus thur ingiensis
var.
israelen-
sis
(Bti), pyriproxyfen (an insect growth regulator), a larvicidal oil, Aquatain AMF (poly dimethyl-
siloxane, a monomolecular film), and temephos at the recommend application dosages a nd rates. Our
results showed that Bti, pyriproxyfen, and temephos were ef ficacious (100
z
mor tality) against larvae,
irrespective of the instar stage, but n ot against pupae of
Ae. aegypti
(1.5–7.8
z
mortality). Aquatain
AMF, on the other hand, was very effective at controlling the pupal stage (100
z
mortality), but had
limited efficacy again st small larvae (38.0
z
mortality) and larg e larvae (78.0
z
mortality). The larvici-
dal oil was effective against all immature stages (93.3–100
z
mortality). Therefore, w e concluded that
for effectiv ely interrupting the dengue transmis sion cycle, la rvicides that kill the pupal stage ( Aquatain
AMF or larvicidal oil) should be included in an emergency dengue control program in addition to Bti,
pyriproxyfen, or temephos.
In Taiwan, dengue fever is considered a travel-related
disease b ecause the cau sative viruses are introduce d in
the early summer by travelers from dengue-endemic
countries (1,2). These viruses are subsequently passed to
local dengue vectors and then transmitted to local
human populations, resulting in s mall to medium-sized
outbreaks. Proactive and em e rgency strate gie s (source
reduction and the use of insecticide sprays) to con trol
dengue outbreaks have been launched each year for the
past decade in Taiwan. The principal methods include
the application of adulticides, removal of s m all contain-
ers, the application of l arvicides to stagnant water, and
the release of mosquito-eating f ish su ch as
Macropodus
opercularis
Ahl and
Poecilia r eticula ta
Peters.
The most commonly used larvicides to control
Aedes
aegypti
L. worldwide include
Bacillus thurin giensis
var.
israelensis
(Bti), pyriproxyfen (an insect growth regu la-
tor), temephos (an organophosphate), larvicid al oils,
and Aquatain anti-mosquito film (AMF ; a mo no-
molecular film) (3,4). These larvicides kill immatur e
stages of mos quitoes throug h diff erent m ech anisms.
For example, one such mechanism is larval poison ing
over a short duration, with a toxin, such as Bti and
temephos, which kill all
Ae. aegypti
larvae within 24 h
(5). A second mechanism is to delay larval development
and prevent the emergence of adults. For example, the
sand formulation of pyriproxyfen caused 1 00
z
mortali-
ty in larvae and pupae at 0.2 ppm (5). A third mechan-
ism is physical, as illust rated by Aquatain AMF and
larvicidal oils that spread across the water surface and
form a very thin film that suffocates larvae and pupae
(6). Aquatain AMF treatment (1 mL/m
2
)causes48
z
mortality of
Ae. aegypti
larvae a fter 48 h of exposure
and 100
z
mortality of pupae after 3 h of exposure in
the labora tory (7). In Taiwan, Bti, pyriproxyfen, and
temephos a re commonly used in field applications t o kill
Ae. aegypti
larvae and, to date, no resis tance to these
pesticides has been reported (8,9). However, A quatain
AMF and larvicidal oils are not approved f or pesticidal
use in Taiwan a nd thus are not available for dengue
fever control in field a pplications.
Most trials conducted to evaluate the efficacy of
mosquito control a gents hav e f ocused on m ature larvae
and pupae or ha ve compared only 2– 3 la rv icid es. T o
rapidly stop a dengue fever outbreak, fast-acting c on-
trol agents should be used against all mosquito life
stages , includin g small larvae, large larvae, pupae, and
adults. Therefor e, the objective of this study was to
evaluate the efficacy of five agents against various
mosquito life stages in the laboratory to determine the
appropriate uses of these larvicides in emergency dengue
fever cont rol programs.
A colony of
Ae. aegypti
was established from larvae
that were collected in Tainan City, Taiw an, in 1987 and
maintained in an insectary a t 20–30
9
C for an unknown
number of generations. Females were fed mouse blood
andprovidedwitha10
z
sucrose solution. Eggs were
collected on white filter paper and placed within a cup
that was part ia lly filled with water. Then, t he eggs were
dried and stored in a closed jar until used for experimen-
tation. Batches of eggs w ere hatched in a nutrient broth
containing yeast powder. The small (stage I–II instars)
and large (stage III–IV instars) larvae use d in these ex-
periments were 1 and 4 da ys old, respectively. The tested
pupae were less than 1 day old.
342
Table 1. The dosages of the tested larvicides (temephos, pyriproxyfen,
Bacillus thuringiensis
var.
israelensis
[Bti], larvicida l oil, and Aquatain
AMF) used in each replicate
Mosquito
stage
Replicate
Bti (mg) Temephos (mg) Pyriproxyfen (mg)
Larvicidal oil
(
m
L)
Aquatain AMF
(
m
L)Formulation
weight
AI weight
Formulation
weight
AI w eight
Formulation
weight
AI wight
I–II instars 1 21.0 0.588 31.3 0.313 2.2 0.011 190.5 8.7
2 13.4 0.375 30.1 0.301 2.3 0.012 190.5 8.7
3 12.8 0.358 30.1 0.301 2.2 0.011 190.5 8.7
4 13.3 0.372 30.8 0.308 1.9 0.010 190.5 8.7
III–IV instars 1 14.8 0.414 30.0 0.300 2.0 0.010 190.5 8.7
2 25.4 0.711 30.3 0.303 2.3 0.012 190.5 8.7
3 5.7 0.160 30.1 0.301 2.9 0.015 190.5 8.7
4 9.9 0.277 29.6 0.296 2.3 0.012 190.5 8.7
Pupae 1 8.8 0.246 30.2 0.302 2.9 0.015 190.5 8.7
2 1.2 0.034 30.5 0.305 3.3 0.017 190.5 8.7
3 21.4 0.599 30.8 0.308 2.1 0.011 190.5 8.7
4 19.6 0.549 30.1 0.301 2.2 0.011 190.5 8.7
AI, active ingredient; AMF, anti-mosquito film.
Table 2. Larvicidal effects of temephos, pyriproxyfen,
Bacillus thuringiensis
var.
israelensis
(Bti), Aquatain AM F, and a larvicidal oil on
Aedes aegypti
larvae in the laboratory
Mosquito
stage
Treatment No.
Cumulative immature mortality
±
SD Mean larval
survival
rate
±
SD
Mean
pupation
rate
±
SD
Mean
emerging
rate
±
SDDay1 Day4 Day7 Day10 Day14
I–II insta rs Bti 4 100.0 ————0.0
Temephos 4 100.0 ————0.0
Larvicidal oil 4 97.3
±
5.5 99 .3
±
1.5 100.0 0.0
Pyriproxyfen 4 0.5
±
1.0 10 .0
±
4.7 55.5
±
33.6 9 3.3
±
7.4 99.8
±
0.5 81.8
±
6.5 81.8
±
6.5 0.2
±
0.5
Aquatain AMF 4 0.3
±
0.5 13 .3
±
18.1 2 2.3
±
20.1 3 0.0
±
21.6 38.0
±
21.4 62.0
±
21.4
*
*
Control 4 3.3
±
6.5 9.5
±
13.3 1 4.5
±
13.5 1 5.3
±
12.7 15.8
±
13.1 85.7
±
13.3 85.5
±
13.0 84.2
±
13.1
III–IV instars Bti 4 100.0 ————0.0
Temephos 4 100.0 ————0.0
Larvicidal oil 4 97.5
±
5.0 100.0 0.0
Pyriproxyfen 4 0.0 24.5
±
29.0 7 3.0
±
30.7 9 9.3
±
1.5 100.0 91.3
±
8.4 91.3
±
8.4 0.0
Aquata in AM F 4 10.0
±
4.5 40 .3
±
7.6 54.3
±
9.8 66.3
±
7.6 78.0
±
11.2 22.0
±
10.9 0.3
±
0.5
*
Control 4 0.0 5.5
±
1.3 9.5
±
6.0 10.3
±
6.3 10.3
±
6.3 90.5
±
5.2 90.5
±
5.2 89.7
±
6.0
*
Experiments were te rmi nated on day 14, and all surviving larvae were in the larval stag e.
342
The larvicides tested in this study included one mono-
molecular film product, Aquatain AMF (Aquatain
Products Pty Ltd., Dandenong Sou th, A ustra lia ), one
larvicidal oil (H anwai general cleaner; Hanwai Chemi-
cal Products Co., Hong Kong, China), Bti (Vectobac G;
active ingredient [AI], 2.8
z
; 200 international toxic
units/mg; Abbott Laborator ies, North Chicago, Ill.,
USA), pyriproxyfe n (Sumilarv 0.5G; AI, 0.5
z
;
Sumitomo Chemical Co., Tokyo, Japan), and temephos
(Antimos 1.0
z
SG; AI, 1.0
z
;The Wei Erdeng Co.,
Taiwan). Aquatain AM F , the larvicida l oil, Bti,
pyriproxyfen, and temephos were tested at the recom-
mend application dosages based on the formulatio n
weights, which were 1.0 mL/m
2
(8.7
m
L/300 mL), 22.0
mL/m
2
(190.5
m
L/300 mL), 1 granule per 100 cm
2
(0.28
granule/300 mL), 2.0–1 0.0 g/m
3
(0.6–2.9 mg/300 mL),
and 100 mg/L (30 mg/300 mL), respectively. However,
the commercial granule products of B t i, pyriproxyfen,
and temephos were diff icult to breakdown; therefore,
the dosage formulations of A I us ed in each replicate
slightly varied (Table 1).
For each trial (five tested lar vicides an d one control),
100 sm all larvae, large lar va e or pupae were placed in a
6
×
10 cm (diameter
×
height) paper cup con taining
300 mL of distille d water for e ach larvicid e, resulting in
a total of 600 larvae or pupae per trial. Each trial was
replicated 4 times. The live larvae and/or pupae in ea c h
cup were counted daily for up to 14 days. When pupae
developed, the cups w ere placed inside of a cage. All
cups and cages were stored in a growth chamber at
28
9
C, in a relative hum idity of 75
z
, and under a 12-h
light:dark cycle. Sufficient food was provided at the
beginning of the experiments.
Control effects w ere evaluated for all tested larvicides
applied to the small
Ae. aegypti
larvae (Table 2). The
mean total mortality rates (
±
standard deviation [SD])
of the small instars up to day 14 after treatment with
temephos, Bti, and la rvicid al oil w ere 100
z
, followed
by pyripr oxyfen (99.8
±
0.5
z
), Aquatain AMF (38.0
±
21.4
z
), and the control (15.8
±
13.1
z
). On day 1
after the trea tm ent, Bti, temephos, and the larvicidal oil
killed small la rvae more effectively than Aquata in
343
Table 3. Larvicidal effects of temephos, pyriproxyfen,
Bacillus thuringiensis
var.
israelensis
(Bti), Aquatain A MF, and a larvici dal oil on
Aedes aegypti
pupae in the laboratory
Treatm ent No.
Cumu lative p upa l mo r tal ity rate
±
SD Mean
emerging
rate
±
SDDay1 Day2 Day3
Aquatain AMF 4 1 00.0
Larvicidal o il 4 92.3
±
8.1 93.3
±
6.8 93.3
±
6.8 7.7
±
6.8
Temephos 4 1.3
±
1.3 7.8
±
10.2 7.8
±
10.2 92.2
±
10.2
Pyriproxyfen 4 1.0
±
0.8 3.0
±
1.4 3.0
±
1.4 97.0
±
1.4
Control 4 1.5
±
1.3 2.0
±
1.6 2.3
±
2.1 97.7
±
2.1
Bti 4 1.0
±
1.2 1.0
±
1.2 1.5
±
1.9 98.5
±
1.9
343
AMF, pyriproxyf en , and the control. Em erging adults
were observ ed in the control and py riproxyfen groups
with mean emerging rates of 84.2
±
13.1
z
and 0.2
±
0.5
z
, respectively. In the Aquatain AMF treatment
group, 62.0
±
21.4
z
of the individuals remained in the
larval stages on day 14 a fter the treatment.
Control effects were evalua ted for all tested larvicides
appliedtolarge
Ae. aegypti
larvae (Table 2). The mean
total mortality rates (
±
SD) of large larvae up to day 14
after treatment with Bti, pyri prox yfen, temepho s, and
the l arvicidal oil were 100
z
, followed by Aquatain
AMF (78.0
z
±
11.2
z
) and the control ( 10.3
±
6.3
z
).
On day 1 after the treatment, Bti, temephos, and the la r-
vicidal oil killed large larvae more effectively than
Aquatain AMF, pyr iprox yf en, or the contro l; howev er,
Aquatain AMF and pyriproxyfen eventually inhibited
the growth of all emerging adults. The mean emerging
rates of the control was 89.7
±
6.0
z
.Furthermore,
22.0
±
10.9
z
of larg e larvae in the Aquatain AMF
treatment group remained in the larval stage until day
14 after the treatment.
When the la rvicides were applied to
Ae. aegypti
pu-
pae, good control effects were a ch ieved by Aquatain
AMF and the larvicidal oil, but not the other larvicides
(Table 3). T he mean pupal mortality rate for the
Aquatain A MF treatment group was 100
z
, follow ed by
the larvicidal oil (93.3
±
6.8
z
), temephos (7.8
±
10.2
z
), pyriproxyfen (3.0
±
1.4
z
), control (2.3
±
2.1
z
), and Bti (1.5
±
1.9
z
) treat ment groups. On day
1 a fter treatment, the Aquatain and the larvicidal oil
treatment groups exhibited higher mortality ra tes
against pupae than the other tested larv icides or the con -
trol. All surviv ing pupa e successfully emerged into
adults (mean emerging rate, 7.7–98.5
z
)andthemean
emerging rate of control was 97.7
±
2.1
z
.
In the pre se nt study, all t e sted larvicides were suffi-
ciently effective for use in emergency programs to con-
trol dengue f ever vectors, bu t with som e restrictions.
Bti, temephos, a nd pyriproxyfen were found to be effec-
tive against all larval instar stages, but not agains t pupae
of
Ae. aegypti
. T he Aquatain AMF, on the other hand,
effectively controll ed growth within the pupal stage, but
had only limited effects on the larval s tage. The larvici-
dal oil was effective again st all immature stages of
Ae.
aegypti
.
Our results were similar to those of oth er studies, in
which Bti and temephos killed al l small a nd large
Ae.
aegypti
larvae (5,10). Pyriproxyfen killed all late instar
Ae. aegypti
larvae and exhibited residual activity for 1
month against eggs and l arvae (5,11). Aquatain AMF
killed 100
z
of
Ae. aegypti
pupae, but only 33.6
z
of
lateinstars(7).However,thislarvicidewasmoreeffec-
tive against
Anopheles
and
Culex
spp. and was success-
fully evaluated in the field for control of
Anopheles
larvae (3). In addition, they found that Aquatain AMF
had no negative effect on rice pla nts or o n various non-
target organisms with the exception of backswimmers.
Aquatain AMF had a limit ed effect on t he larval st age ,
but i t continued to delay larval dev elopment after the
experiments were discontinued. These results indicated
that even though this lar vicide did not kill all the larvae
within a short period of time, it can kill the remaining
larvae at a later time or when they develop into pupae ,
which are also susceptible to this larvicide. Incidentally,
the larvicidal oil was not miscible with water, thus this
character ist ic may have affe c t e d our results w he n we
applied the oil b y hand as opposed to usin g a sprayer.
Three spray applications with intervals of 7 days are
required to kill a dult mosquitoes, particularly infectious
females, and to interrupt the transmission in a particu-
lar focal area (12). However, in reality, only 1 or 2 spray
applications are often applied. Therefor e, the applica-
tion of larvicides to kill all imma ture sta ges dur ing an
outbreak remains an important iss ue. A study to in-
crease the residual effect of Bti in small temporary
containers is warranted and recommended (13). Fu r-
thermore, the dengue viruse s pe rsist in viremic patients
during an outbreak; therefore, it is also critical to
decrease the risk of female mosquitoes becoming infec-
tious females by killing the pupae. Therefore, in an
emergency control program, Aqua tain A MF or larvici-
dal oil to kill pupae should be included in addition to the
application of Bti, pyriprox yfen, or temephos.
Acknow ledgments
This st udy was sup po rted by scien tific resea rc h
grants from the Centers for Disease Co ntrol, Taiwan, in 2011
(DOH100-DC-2014).
Conflict of interest
None to declare.
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    Full-text · Article · Nov 2014
  • [Show abstract] [Hide abstract] ABSTRACT: Although silicone-based monomolecular film (MMF) has been accepted as larvicide in several countries, its mosquito control potential has never been investigated in Thailand. Laboratory assessment in this study was conducted to determine the MMF efficacy against Aedes aegypti. At the recommended dosage (1mL/m(2) of water surface), mortality of pupae (99.17±0.83%) was significantly greater than mortality of old and young larvae (73.33±9.13, 11.67±3.47%; respectively). Pupicidal activity was rapidly exhibited within hours while larvicidal activity took at least one day. Interestingly, among the survived mosquitoes after MMF exposure, larval length (3.6±0.18mm), pupation (0%) and adult emergence (0%) were significantly less than the control group. Gravid females also avoided laying eggs in MMF-treated oviposition cups. There was no influence of physical factors on MMF efficacy and no toxic effects on fish and plants. These results indicated the MMF is promising to provide not only larvicidal and pupicidal activity but also inhibition of larval development as indicated by both larval length and stage transformation.
    Article · Jul 2016
  • [Show abstract] [Hide abstract] ABSTRACT: There is increasing concern to control Aedes aegypti mosquito exposure in developing countries such as Brazil. Thus, integrated approaches using a combination of chemical, pyriproxyfen larvicide, and biological, Xiphophorus maculatus, larvivorous fish species approaches are necessary and important to initiate more effective control against mosquito borne diseases. This study describes the toxicological effects of pyriproxyfen larvicide on the fish Xiphophorus maculatus, the larvivorous fish species employed to destroy A. aegypti larvae mosquito species. The toxicological profile of pyriproxyfen was evaluated to determine compatible concentrations for the use of this chemical in conjunction with X. maculatus as an integrated approach against A. aegypti mosquito larvae. According to the behavioral responses of fish, the no-observed-effect concentration (NOEC) and lowest-observed-effect concentration (LOEC) of pyriproxyfen were determined to be 2.5 and 5 µg/L, respectively. Bioassays indicated that although pyriproxyfen was not lethal to X. maculatus, the application of this compound at a concentration reported to control the emergence of A. aegypti larvae may decrease the swimming performance of larvivorous fish and their ability to ingest A. aegypti L4 larvae. Data show that integration of biological larvivorous fish and chemical larvicides is more effective when the appropriate larvicide concentration is utilized.
    Full-text · Article · Jul 2016
  • [Show abstract] [Hide abstract] ABSTRACT: Silicone-based surfactants have become of interest for mosquito control in Thailand. When this non-ionic surfactant is applied in mosquito habitats, a monomolecular film (MMF) forms on the water surface and disrupts the ability of larvae and pupae to breathe. In this study, a laboratory bioassay was conducted to determine the mosquito control potential of MMF against Aedes aegypti (L.) and Anopheles minimus (Theobald), and to compare its efficacy with other larvicides consisting of temephos (an organophosphate), Bacillus thuringiensis israelensis (Bti) and pyriproxyfen (an insect growth regulator). It was determined that the percentage mortality of Ae. aegypti and An. minimus treated with MMF at a recommended dosage of 1 mL/m² was significantly greater in pupae (99.2% and 100%, respectively) than old stage larvae (L3-L4, age 46 d; 70.8% and 97.5%, respectively) and young stage larvae (L1-L2, age 1–2 d; 8.3% and 58.0%, respectively). Small larvae and prolonged stage transformations indicated MMF growth inhibition activity. MMF also displayed oviposition deterrence behavior and caused female mosquitoes to drown during egg laying. In comparison, temephos and Bti were highly effective in larval control while pyriproxyfen and MMF provided excellent control effects against the pupal stage. Based on the results, MMF showed promise as an alternative larvicide for mosquito control in Thailand. Further studies on the environmental effects of MMF are needed.
    Full-text · Article · Jan 2017
  • [Show abstract] [Hide abstract] ABSTRACT: Background: Government-administered adulticiding is frequently conducted in response to dengue transmission worldwide. Anecdotal evidence suggests that spraying may create a "false sense of security" for residents. Our objective was to determine if there was an association between residents' reporting outdoor spatial insecticide spraying as way to prevent dengue transmission and both their reported frequency of dengue prevention practices and household entomological indices in Hermosillo, Mexico. Methodology/principal findings: A non-probabilistic survey of 400 households was conducted in August 2014. An oral questionnaire was administered to an adult resident and the outer premises of the home were inspected for water-holding containers and presence of Ae. aegypti larvae and pupae. Self-reported frequency of prevention practices were assessed among residents who reported outdoor spatial spraying as a strategy to prevent dengue (n = 93) and those who did not (n = 307). Mixed effects negative binomial regression was used to assess associations between resident's reporting spraying as a means to prevent dengue and container indices. Mixed effects logistic regression was used to determine associations with presence/absence of larvae and pupae. Those reporting spatial spraying disposed of trash less frequently and spent less time indoors to avoid mosquitoes. They also used insecticides and larvicides more often and covered their water containers more frequently. Their backyards had more containers positive for Ae. aegypti (RR = 1.92) and there was a higher probability of finding one or more Ae. aegypti pupae (OR = 2.20). Survey respondents that reported spatial spraying prevented dengue were more likely to be older and were exposed to fewer media sources regarding prevention. Conclusions/significance: The results suggest that the perception that outdoor spatial spraying prevents dengue is associated with lower adoption of prevention practices and higher entomological risk. This provides some support to the hypothesis that spraying may lead to a "false sense of security". Further investigations to clarify this relationship should be conducted. Government campaigns should emphasize the difficulty in controlling Ae. aegypti mosquitoes and the need for both government and community action to minimize risk of dengue transmission.
    Full-text · Article · May 2017
Project
In this project, we focus on the investigation of insect-vectors including sandflies, blackflies, midges, blood-sucking triatomine and body lice. We will collect these insects and identify the spec…" [more]
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