The Effect of Mosquito Magnet® Liberty Plus Trap on the Human Mosquito Biting Rate under Semi-Field Conditions

Article (PDF Available)inJournal of the American Mosquito Control Association 26(3):287-94 · September 2010with93 Reads
DOI: 10.2987/09-5979.1 · Source: PubMed
Abstract
This study evaluated the efficacy of a commercially available mosquito trap, the Mosquito Magnet Liberty Plus (MM), in reducing human biting rates under semi-field conditions when used alone or with different types of repellents. The MM trap significantly reduced the human biting rate with both laboratory-reared Culex quinquefasciatus and Anopheles gambiae sensu stricto. The MM trap catch did not increase when a mosquito coil was burned but did significantly increase when a skin repellent was applied to the human bait. Microencapsulated repellent ankle bands did not increase the MM trap catch with either Cx. quinquefasciatus or An. gambiae s.s., although its combination with the trap was more effective at reducing bites by Cx. quinquefasciatus. The absence of the commercial attractant Lurex3 in traps significantly lowered the catch efficiency of Cx. quinquefasciatus even when the skin repellent was applied to volunteers. The results from this study showed that the use of a skin repellent and an attractant-baited trap can significantly reduce the human biting rate of both nuisance biting mosquitoes and malaria vectors. Further work is required to investigate how this push-pull system would work in a field environment.
THE EFFECT OF MOSQUITO MAGNETH LIBERTY PLUS TRAP ON THE
HUMAN MOSQUITO BITING RATE UNDER SEMI-FIELD CONDITIONS
JOVIN KITAU,
1,6
HELEN PATES,
2
THEOPHIL R. RWEGOSHORA,
3,7
DIONIS RWEGOSHORA,
3
JOHNSON MATOWO,
1,6
ELININGAYA J. KWEKA,
4
FRANKLIN W. MOSHA,
1,6
KAREN M
C
KENZIE
5
AND
STEPHEN M. MAGESA
3,6
ABSTRACT. This study evaluated the efficacy of a commercially available mosquito trap, the Mosquito
MagnetH Liberty Plus (MM), in reducing human biting rates under semi-field conditions when used alone or
with different types of repellents. The MM trap significantly reduced the human biting rate with both
laboratory-reared Culex quinquefasciatus and Anopheles gambiae sensu stricto. The MM trap catch did not
increase when a mosquito coil was burned but did significantly increase when a skin repellent was applied to
the human bait. Microencapsulated repellent ankle bands did not increase the MM trap catch with either Cx.
quinquefasciatus or An. gambiae s.s., although its combination with the trap was more effective at reducing
bites by Cx. quinquefasciatus. The absence of the commercial attractant Lurex3
TM
in traps significantly
lowered the catch efficiency of Cx. quinquefasciatus even when the skin repellent was applied to volunteers.
The results from this study showed that the use of a skin repellent and an attractant-baited trap can
significantly reduce the human biting rate of both nuisance biting mosquitoes and malaria vectors. Further
work is required to investigate how this push-pull system would work in a field environment.
KEY WORDS Anopheles gambiae s.s., Culex quinquefasciatus, Mosquito MagnetH Liberty Plus trap,
attractants, repellents, semi-field experimental structures
INTRODUCTION
Several commercially available mosquito traps
that use various chemical attractants have shown
promising results in effectively attracting a large
number of mosquitoes while eliminating the need
for live bait (Kline 1998, 2002; Ritchie et al. 2003,
Dennett et al. 2004, Siphiprasasna et al. 2004, Bell
et al. 2005, Njiru et al. 2006). These traps have
potential as both a tool for mosquito control as
well as routine surveillance. The Mosquito Mag-
netH (MM) trap (American Biophysics Corpora-
tion, currently owned by Woodstream Corpora-
tion, Lititz, PA) is battery operated and runs on
propane gas that is catalytically converted to
produce carbon dioxide (CO
2
), heat, and water
vapor. A thermoelectric generator uses excess heat
from combustion to produce electricity to power
the trap (Kline 1999, Johansen et al. 2003). The
trap is based on counterflow geometry technology
whereby a fan produces a down-flow plume of
CO
2
through a central pipe and an updraft
through a larger surrounding pipe that draws in
mosquitoes attracted to the CO
2
(Kline 1999).
Different MM trap models have been evaluated
against a variety of mosquito species (Kline 2002,
Ritchie et al. 2003, Bell et al. 2005) and biting
midges (Mands et al. 2004, Cilek and Hallmon
2005) for both trapping and surveillance. Field
removal-trapping experiments on biting midges
have shown inconsistent reductions, which were
attributed to overwhelming abundance of adult
host-seeking midges in the target zones (Cilek et al.
2003, Cilek and Hallmon, 2005). Repellents could
be used to enhance removal trapping efficiency
while also providing personal protection.
Repellents (synthetic and plant-based) in the
form of vaporizers or skin repellents are used for
personal protection against mosquitoes and other
biting arthropods (Sharma and Ansari 1994,
Lindsay et al. 1996, Tawatsin et al. 2001, Malebo
et al. 2005, Kweka et al. 2008a, 2008b). Deet (N,N-
diethyl-toluamide) is an effective, broad-spectrum
synthetic repellent used as an active ingredient in
various formulations and a gold standard repellent
against which candidate repellents are compared
(Gupta and Rutledge 1989, Rutledge and Gupta
1996, Fradin 1998). Pyrethroids have been very
effectively used as space repellents, in coils (Mosha
et al. 1992), kerosene oil lamps (Sharma et al. 1993,
Pates et al. 2002, Msangi et al. 2010), and
vaporized in electric mats (Hewitt et al. 1996). In
all cases, however, uniform protection is not
guaranteed, and furthermore, repellents tend to
push mosquitoes to nonrepellent users, subjecting
them to relatively more bites.
A more effective way of exploiting the use of
repellents may be to remove the repelled mosqui-
toes by trapping, thus creating a ‘‘push-pull’’
6
Pan-African Malaria Vector Research Consortium,
www.pamverc.org.
7
Deceased.
1
Kilimanjaro Christian Medical College of Tumaini
University, PO Box 2240, Moshi, Tanzania.
2
Vestergaard-Frandsen SA, Chemin de Messidor
5-7, 1006 Lausanne, Switzerland.
3
National Institute for Medical Research, Amani
Centre, PO Box 81, Muheza, Tanzania.
4
Tropical Pesticides Research Institute, Division of
Livestock and Human Disease Vector Control, PO Box
3024, Arusha, Tanzania.
5
TyraTech Inc., 111 West New Haven Avenue,
Melbourne, FL 32901.
Journal of the American Mosquito Control Association, 26(3):287–294, 2010
Copyright
E
2010 by The American Mosquito Control Association, Inc.
287
system. In this strategy pests are targeted and/or
repelled to reduce their abundance on a protected
resource (push) and are simultaneously attracted
using stimuli (pull) to areas such as traps (Cook
et al. 2007). This strategy has been used in
management of agricultural pests (Miller and
Cowles 1990) and was shown to be effective
against instars and adults of laboratory-reared
cockroaches (Nalyanya et al. 2000). The present
study evaluates the effect of the MM trap, used
with or without an attractant chemical, on human
mosquito biting rates under semi-field conditions.
Semi-field systems act as an intermediate envi-
ronment between the laboratory and open field
conditions, thus providing a suitable environment
for testing a variety of vector control interven-
tions prior to more extensive field testing.
MATERIALS AND METHODS
Study site
Experiments were carried out in 3 semi-field
structures located at National Institute for
Medical Research, Amani Research Centre
(05u1092200S, 38u4697330E), in Muheza, Tanza-
nia. The area experiences 1,000 mm average
annual rainfall with 2 seasonal peaks; the main
peak is between March and May, and a less
pronounced peak occurs from November to
December. The mean temperature is 26uCwith
cooler months between June and September and
warmer months between October and May.
Experimental semi-field environment
The semi-field experimental environment
(sphere) has been constructed to simulate a local,
outdoor outlook (Knols et al. 2002). Each sphere
(12.2 m long and 8.2 m wide; Fig. 1) is covered with
shade cloth (90%)permittingentryofwindand
precipitation and creating similar climatic condi-
tions to ambient conditions. Entrance into the
sphere is through a double door system; a wooden
door provides entrance to the sphere, after passing
through a small corridor (3.0 m long and 2.2 m
wide) covered with shade cloth, with a screened
door to the outside. This prevents escape of released
mosquitoes and entry of wild ones. Each sphere
contains some vegetation and a traditional mud hut
(2.74 3 2.74 3 1.83 m) with its roof (2.56 m at the
apex) made of grass thatch. The house has a single
door, 2 open windows, and a single Zanzibari-style
rope bed inside that is occupied by a volunteer
during experiments. Mud huts and rope beds are
common in coastal village areas of Tanzania.
Test products
Four products were used with the MM trap in
the study:
a) A commercial attractant lure, Lurex3
TM
(Amer-
ican Biophysics Corporation, currently owned
by Woodstream Corporation), consisting of L-
lactic acid (2-hydroxy propionic acid) in gelatin
and ammonium bicarbonate in solid. The
attractant was used by fixing and plugging the
sachet in a carrier brace inside the plume tube
according to the manufacturer’s instructions.
b) HatariH, a repellent mosquito coil (Star Import
and Export, Surabaya, Indonesia) containing
0.1% d-Allethrin. The mosquito coil was
placed inside the mud hut close to the person
performing the human landing catch and left
to burn. One coil lasted 6–7 h; therefore, a total
of 2 coils were burned per test night.
c) A roll-on skin repellent, NO BITEH (Man-
soor Daya Chemicals Limited, Dar es
Salaam, Tanzania) containing 15% deet and
5% dimethyl phthalate. The repellent was
applied to each exposed leg of the volunteer
by making 4 stripes on each exposed leg from
the toes to the knee and rubbed onto each leg
using the palm of the hand. Two repellent
applications were made per test night.
d) MozawayH wrist and ankle repellent bands
(Mozaway, United Kingdom), containing
micro-encapsulated deet (90%) and citronella
(10%). Two repellent bands were stretched
twice according to manufacturer’s instruc-
tions, and 1 band was placed around the ankle
of each exposed leg.
Trapping methods
In the course of study, 2 assessment tools were
used to collect mosquitoes. The MM trap was
operated according to the manufacturer’s instruc-
tions.
Human landing catch was performed to
directly measure the number of biting mosquitoes
attracted to human bait throughout the study.
Volunteers were stationed inside the mud hut of
each sphere, equipped with a torch, an aspirator,
and labeled paper cups. Volunteers removed
shoes and socks to expose the feet and legs from
the knee down. The volunteer then aspirated the
biting mosquitoes into labeled paper cups.
Test mosquitoes
Two species of mosquito, Anopheles gambiae
Giles s.s. (IFAKARA strain) and Culex quinque-
fasciatus Say (Bandari strain), were used for the
experiments; both colonies were maintained
under laboratory conditions in an insectary at
the site. The An. gambiae colony was established
from colony-reared gravid females from the
Ifakara Centre for Health Research and Devel-
opment in October 2004. The Cx. quinquefascia-
tus colony was initiated in October 2006 using
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eggs collected from water outlets at the Bandari
residential flats (05u0495430S, 39u0697210Eand
23.5-m altitude) in Tanga, Tanzania.
For each experiment, 300, 4–9 day-old adult
female Cx. quinquefasciatus and An. gambiae
were collected from their cages using an aspirator,
placed in a small cage, and starved for 10–12 h
before releasing them into the spheres.
Experimental procedure
A series of 4 experiments were performed to
investigate efficacy of the MM trap with and
without attractant lure and using different types
of repellents as shown in Table 1.
The baited MM traps were set by plugging a
Lurex3 cartridge in the plume tube according to
the manufacturer’s instructions and placing a
trap close to the entrance in each of the 2
mosquito spheres; the remaining mosquito sphere
served as a control and did not contain a MM
trap. The traps were started at 1800 h. Fifteen
minutes later, 300 starved females (An. gambiae
and Cx. quinquefasciatus) were released from the
center of each sphere. One volunteer was assigned
to each sphere and stationed inside the mud hut,
Fig. 1. Semi-field experimental spheres: outer surfaces (a), mud hut inside (b), and a Mosquito MagnetH trap
close to the entrance (c).
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where he performed a whole night human landing
catch. Traps were switched off at 0600 h, and the
collections from traps and human landing catches
placed in the freezer to kill mosquitoes, ready for
identification and counting. A 30-min resting
catch was done in each sphere at daybreak of
every test day to recover any mosquitoes left inside
the sphere. Individuals equipped with mouth
aspirators and labeled paper cups collected mos-
quitoes resting at different places (inside the mud
hut, on the shade cloth, and on plant leaves) within
each sphere. The number of mosquitoes caught in
each sphere with each method (MM trap, human
landing catch) was recorded. In each of these
experiments the procedure was repeated for 9 test
nights, during which treatments and volunteers
were rotated so that each treatment was tested in
each sphere 3 times following a 3 3 3 Latin Square
design to limit the effects of differences between
volunteers, test nights, and sphere location. A
HOBOH PRO data logger (Onset Computer
Corporation, Cape Cod, MA) was set up (accord-
ing to the manufacturer’s instructions) on poles
close to the entrance inside each sphere, approx-
imately 1.5 m above the ground. This instrument
recorded temperature (uC) and relative humidity
(%) at hourly intervals throughout each day of
each experiment.
Data analysis
Analyse-it
TM
for Microsoft Excel statistical
software was used to analyze the results. Counts
of mosquitoes recovered from each treatment were
checked for normality using the Shapiro-Wilk (W)
test. Parametric datasets were compared for
homogeneity of variance and either subjected to
analysis of variance (ANOVA) or an independent
t-test (using Welch’s approximation for unequal
variances) to investigate the difference between
the mean numbers of each species caught with
each treatment. The Mann-Whitney (U) test was
used for nonparametric data to determine any
significant differences between treatments.
Ethical consideration
Full verbal explanation of the study was given
to volunteers who participated in the night study
collections. Verbal consent was then obtained
from the volunteers before commencement of the
study. A nominal fee for participation in the
study was also paid to volunteers.
RESULTS
A total of 32,400 mosquitoes of each Cx.
quinquefasciatus and An. gambiae s.s. were
released in the 4 experiments. Only recovered
mosquitoes in each trial were used in statistical
analysis. In total, 84.2% Cx. quinquefasciatus and
76.1% An. gambiae s.s. were recovered. There was
no significant difference in the daily internal
temperature (ANOVA, P . 0.05) and humidity
(t-test, P . 0.2) between each sphere. However,
the temperature was generally higher outside than
inside the spheres (ANOVA, P , 0.0001), while
external humidity was lower (t-test, P , 0.0001)
than the humidity inside the spheres.
Efficacy of the un-baited MM trap
The MM trap significantly reduced human
landing rates of both Cx. quinquefasciatus (t-test,
P , 0.0001) and An. gambiae (ANOVA, P ,
0.0001; Fig. 2a) when compared with the controls
(no trap). The combination of skin repellent and
unbaited MM trap resulted in significantly lower
human landing rates of both Cx. quinquefasciatus
(t-test, P , 0.0001) and An. gambiae (ANOVA,
P , 0.0001) when compared with a MM trap
alone or the control (no MM trap and no skin
repellent). The mean catch rate of both species
with the unbaited MM trap was significantly
higher (t-test, P , 0.001; Fig. 3a) in the presence
of the skin repellent.
Performance of the MM trap with an attractant
and repellent mosquito coil
The use of a MM trap significantly reduced
human landing rates of both Cx. quinquefasciatus
(t-test, P , 0.0001) and An. gambiae (t-test, P 5
0.0096; Fig. 2b). The combination of a mosquito
coil with a MM trap resulted in significantly
lower human landing rates with An. gambiae (t-
test, P 5 0.0005) but not with Cx. quinquefascia-
tus (Mann-Whitney test, P 5 0.0939; Fig. 2b)
when compared with a MM trap alone or the
control (no MM trap and no mosquito coil). The
Table 1. Summary of the treatments used in each experiment.
Experiment
Treatments
1
12 3
I MM (without Lurex3) No MM MM (without Lurex3) and skin repellent
II MM (with Lurex3) No MM MM (with Lurex3) and mosquito coil
III MM (with Lurex3) No MM MM (with Lurex3) and skin repellent
IV MM (with Lurex3) No MM MM (with Lurex3) and repellent ankle bands
1
MM 5 Mosquito MagnetH Liberty Plus trap.
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mean MM trap catch rate with both Cx.
quinquefasciatus (t-test, P 5 0.8312; Fig. 3b) and
An. gambiae (Mann-Whitney test, P 5 0.3401)
was not affected by the use of mosquito coils.
Performance of the MM trap with an attractant
and skin repellent
The MM trap significantly reduced the human
landing rates of both Cx. quinquefasciatus (t-test,
P , 0.0001) and An. gambiae (t-test, P 5 0.0137;
Fig. 2c) when compared with the control (no
MM trap). The combination of a skin repellent
and a MM trap resulted in significantly lower
landing rates with Cx. quinquefasciatus (t-test, P
, 0.0001; Fig. 2c) and with An. gambiae (Mann-
Whitney test, P , 0.0003; Table 1) when
compared with a MM trap alone or the control
(no MM trap and no skin repellent). The mean
MM trap catch rate with both Cx. quinquefascia-
tus (Mann-Whitney test, P 5 0.0002; Fig. 3c) and
An. gambiae (Mann-Whitney test, P 5 0.0142)
was significantly higher in the presence of the skin
repellent. More Cx. quinquefasciatus than An.
gambiae were caught in the traps (t-test, P ,
0.0001).
Performance of the MM trap with attractant and
repellent ankle bands
The MM trap significantly reduced the human
landing rates of both Cx. quinquefasciatus and
An. gambiae when compared with the control (no
MM trap) (ANOVA, P , 0.0001). The combi-
nation of the repellent ankle band and a MM trap
resulted in a significantly lower landing rate with
Cx. quinquefasciatus (t-test, P 5 0.0029; Fig. 2d),
but not with An. gambiae s.s. (t-test, P 5 0.4129)
when compared with the MM trap alone; however,
results from MM trap catches showed that the
mean catch rate with both Cx. quinquefasciatus
(Mann-Whitney test, P 5 0.1359; Fig. 3d) and
An. gambiae (t-test, P 5 0.1861) was not affected
by the use of repellent ankle bands.
DISCUSSION
Performance of baited and unbaited MM traps
The use of a MM trap without a commercially
available attractant effectively reduced human
landing rates with An. gambiae and Cx. quinque-
fasciatus, and an addition of lactic acid and
ammonia containing Lurex3 significantly in-
Fig. 2. Culex quinquefasciatus (gray) and Anopheles gambiae s.s. (diagonal lines) caught per night by human
landing catch in different experiments. Histograms with the same letter are not significantly different from each
other (P , 0.05). Error bars represent standard error.
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creased catches of Cx. quinquefasciatus.The
significance of carbon dioxide (Dekker et al.
2005), lactic acid (Bernier et al. 2003), and
ammonia (Smallegange et al. 2005) in host
location and attraction is well established. The
smaller An. gambiae catch in MM traps, which
may be due to carbon dioxide being less attractive
to this species than Cx. quinquefasciatus,isin
agreement with prevailing literature (Pates et al.
2001). The low An. gambiae catch in MM traps
may as well be due to their higher propensity to
feeding on humans, or else Lurex3 may not be as
active for An. gambiae as Cx. quinquefasciatus
because it lacked many other key components
known to be attractive to mosquitoes (Syed and
Leal 2009).
Compared to the MM trap alone, combining
the MM trap and mosquito coils reduced the
biting rate with An. gambiae but not with Cx.
quinquefasciatus; the use of coils did not enhance
the trap catches of either species. Smoke from the
allethrin-containing mosquito coils interfered
with flight and/or host-seeking behavior, resulting
in mosquitoes going for shelter. The difference in
the response of Cx. quinquefasciatus compared
with An. gambiae is probably due to the well-
known resistance of Cx. quinquefasciatus to
pyrethroids in the area (Khayrandish and Wood
1993, R. Malima, unpublished data).
The combination of a skin repellent and a MM
trap resulted in significantly lower landing rates
with Cx. quinquefasciatus and with An. gambiae.
Skin repellent kept off (‘‘pushed’’) hungry mos-
quitoes from landing and accessing blood, which
were subsequently removed by the attractant-
baited MM trap. Application of repellents has
previously been shown to create a ‘‘push’’ effect
such that mosquitoes are diverted to the nearby
alternative blood meal sources (Moore et al.
2007). However, relatively little is known about
the mode of action of repellents, the effect of
which depends on the method of application.
Recent evidence suggests that deet is detected by
specific olfactory-receptor neurons on the anten-
nae to which mosquitoes respond by avoiding
treated surfaces (Syed and Leal 2008) rather than
masking/disrupting sensory reception of odor-
ants.
The repellent ankle bands successfully repelled
and subsequently lowered human landing rates of
Cx. quinquefasciatus but not of An. gambiae. The
MM trap catch rate, however, did not increase
with either species. The bands contained micro-
encapsulated deet and citronella, and stretching
of the band prior to wearing and movements of
the ankle are meant to burst a few capsules each
time to release the active ingredients. This forms a
protective halo extending a few centimeters from
Fig. 3. Baited and unbaited MM trap catches for Culex quinquefasciatus (gray) and Anopheles gambiae s.s.
(diagonal lines). Histograms with the same letter are not significantly different from each other (P , 0.05). Error
bars represent standard error.
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the site of the band. However, most of the
exposed skin remains unprotected from landing
mosquitoes. Poor performance of repellent bands
has also been shown by Jensen et al. (2000), who
found that the repellent effect of wrist bands was
limited to areas close to the bands and that other
exposed areas encountered frequent mosquito
bites. Differential responses of mosquito species
to repellent bands may be due to differences in
host-seeking behavior, sensitivity to different host
cues, and/or repellents.
The use of a mosquito attractant (in this case
Lurex3) in a trapping system and a repellent item is
an example of a ‘‘push-pull’’ system. Mosquitoes
repelled by the repellent item on one end (push)
were subsequently attracted and trapped by the
baited MM traps (pull). In the present study, this
strategy worked with the application of a skin
repellent. Smoke from mosquito-repellent coils
interfered with mosquitoes normal flight/host-
seeking behavior, and as a result they could not be
trapped, rendering the ‘‘pull’’ end ineffective.
Repellent ankle bands had relatively little or no
effect that was exerted on the ‘‘push’’ end. The
present study shows a significant reduction in
numbers of mosquitoes landing on humans when
mosquito traps are used relative to the control.
These results emphasize that within a confined
area and with a known mosquito population size,
a reduction in human landing rates could be
achieved by the use of MM traps. Furthermore, in
an integrated system where MM traps are used
with repellents, the synergy of the system is highly
dependent on the type of repellent.
In conclusion, this study suggests in conformity
with existing literature that Cx. quinquefasciatus
more so than An. gambiae are more attracted to
carbon dioxide, a basic attractant produced by
the MM traps from a catalytic combustion of
propane. Lurex3 is a more suitable lure for Cx.
quinquefasciatus than it is for An. gambiae.A
different chemical combination is required to
increase the trapping efficiency of the highly
anthropophilic malaria vector An. gambiae.With
the right trap/repellent combination, a repellency
(‘‘push’’) and attractiveness (‘‘pull’’) system can
successfully work to reduce mosquitoes landing
on humans and, therefore, subsequent bites by
increasing the efficiency of the individual compo-
nents. In this study, skin repellents worked
effectively to increase catches with the MM traps,
but mosquito coils and repellent ankle bands did
not.
ACKNOWLEDGMENTS
This work is dedicated to the late Rehumbiza
Theophil Rwegoshora, who died in a tragic car
accident in the Serengeti on December 17, 2006.
Special thanks to Martin Mkufya and Omary
Mohammed, who volunteered their participation
in the night study collections. Many thanks to all
workers, colleagues, and fellows at Amani
Medical Research Centre in Ubwari for their
invaluable advice and support. This study re-
ceived financial assistance from American Bio-
physics Corporation and the National Institute
for Medical Research.
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    • "Nonetheless, preliminary work has been encouraging. For example, Kitau et al. showed in a semifield environment that the combined use of personal repellents (topically applied) and mosquito traps could reduce the biting rates of laboratory reared Anopheles gambiae more than the use of traps alone [17] and Menger et al., also working with An. gambiae in a semifield setup, recently showed that a combination of spatial repellents and baited traps can be used to reduce mosquito house entry [19] . Additionally, a number of re- searchers222324 have made progress towards defining the parameters of a push-pull intervention for the control of the dengue vector Aedes aegypti, including studies demonstrating local interest in and community acceptance of the concept in both Latin America and South East Asia [16]. "
    [Show abstract] [Hide abstract] ABSTRACT: Campaigns for the continued reduction and eventual elimination of malaria may benefit from new and innovative vector control tools. One novel approach being considered uses a push-pull strategy, whereby spatial repellents are used in combination with outdoor baited traps. The desired effect is the behavioural manipulation of mosquito populations to elicit movement of vectors away from people and into traps. Here, a prototype push-pull intervention was evaluated using an experimental hut methodology to test proof-of-principle for the strategy against two natural vector populations, Anopheles albimanus and Anopheles vestitipennis, in Belize, Central America. A Latin square study design was used to compare mosquito entry into experimental huts and outdoor traps across four different experimental conditions: 1) control, with no interventions; 2) pull, utilizing only outdoor traps; 3) push, utilizing only an indoor spatial repellent; and 4) push-pull, utilizing both interventions simultaneously. For An. vestitipennis, the combined use of an indoor repellent and outdoor baited traps reduced average nightly mosquito hut entry by 39% (95% CI: [0.37 - 0.41]) as compared to control and simultaneously increased the nightly average densities of An. vestitipennis captured in outdoor baited traps by 48% (95% CI: [0.22 - 0.74]), compared to when no repellent was used. Against An. albimanus, the combined push-pull treatment similarly reduced hut entry, by 54% (95% CI: [0.40 - 0.68]) as compared to control; however, the presence of a repellent indoors did not affect overall outdoor trap catch densities for this species. Against both anopheline species, the combined intervention did not further reduce mosquito hut entry compared to the use of repellent alone. The prototype intervention evaluated here clearly demonstrated that push-pull strategies have potential to reduce human-vector interactions inside homes by reducing mosquito entry, and highlighted the possibility for the strategy to simultaneously decrease human-vector interactions outside of homes by increasing baited trap collections. However, the variation in effect on different vectors demonstrates the need to characterize the underlying behavioral ecology of target mosquitoes in order to drive local optimization of the intervention.
    Full-text · Article · Apr 2015
    • "In SFS vegetation was allowed to grow as in natural environment with a small hut inside (2.74 × 2.74 × 1.83 m). SFS has dimensions of 12.2 m length and 8.2 m width262728. SFS is covered with strong netting material allowing free wind flow and precipitations to mimic the natural climatic conditions. "
    [Show abstract] [Hide abstract] ABSTRACT: Effective malaria vector control initiatives need a clear understanding of mosquito behaviour and its ecology. This study compared larvae development to adult emergence in insectary and malaria-sphere (SFS). This is the preliminary study which gives an insight to forthcoming studies. Anopheles gambiae sensu stricto eggs were hatched in insectary and transferred in densities of 20 and 50 per microhabitat with twenty replicates of each density. Both densities of larvae were reared in semifield structure and in insectary from the same batch of eggs. They were provided with tetramin fish food. In both densities of 20 and 50, pupation rate and time were found to be similar in SFS and insectary, but, in survivorship from larvae to pupae at density of 50, more larvae survived significantly to pupae stage in SFS than in insectary(𝑃 = 0.002). The adult emergence rates were similar for densities of 20 and 50 between SFS and Insectary. There was a significant difference between SFS and insectary in light intensity (𝑃 = 0.001) and temperatures (𝑃 = 0.001), with SFS having higher rates than insectary. The findings of this study have shown that larvae development rates are encouraging having semifield structures for malaria vector rearing for behavioural studies toward malaria control.
    Full-text · Article · Jan 2015
    • "Studies of the insect olfactory system have led to identification and development of synthetic chemical compounds that attract insects to hosts [10]. This knowledge is successfully applied in the agricultural sector for the control of crop pests [11] and tsetse flies [12, 13, 14] as well as the control of mosquitoes [15, 16, 17]. Other volatile compounds, commonly known as repellents, interfere with mosquitoes' host finding ability. "
    [Show abstract] [Hide abstract] ABSTRACT: Malaria vector control relies on toxicity of insecticides used in long lasting insecticide treated nets and indoor residual spraying. This is despite evidence that sub-lethal insecticides reduce human-vector contact and malaria transmission. The impact of sub-lethal insecticides on host seeking and blood feeding of mosquitoes was measured. Taxis boxes distinguished between repellency and attraction inhibition of mosquitoes by measuring response of mosquitoes towards or away from Transfluthrin coils and humans. Protective effective distance of coils and long-term effects on blood feeding were measured in the semi-field tunnel and in a Peet Grady chamber. Laboratory reared pyrethroid susceptible Anopheles gambiae sensu stricto mosquitoes were used. In the taxis boxes, a higher proportion of mosquitoes (67%-82%) were activated and flew towards the human in the presence of Transfluthrin coils. Coils did not hinder attraction of mosquitoes to the human. In the semi-field Tunnel, coils placed 0.3 m from the human reduced feeding by 86% (95% CI [0.66; 0.95]) when used as a "bubble" compared to 65% (95% CI [0.51; 0.76]) when used as a "point source". Mosquitoes exposed to coils inside a Peet Grady chamber were delayed from feeding normally for 12 hours but there was no effect on free flying and caged mosquitoes exposed in the semi-field tunnel. These findings indicate that airborne pyrethroids minimize human-vector contact through reduced and delayed blood feeding. This information is useful for the development of target product profiles of spatial repellent products that can be used to complement mainstream malaria vector control tools.
    Full-text · Article · Dec 2014
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