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online | memorias.ioc.fiocruz.br
Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 108(2): 229-232, April 2013
Detection of chemical cues emitted by vertebrate
hosts is important for the host-finding behaviour of
mosquitoes. Carbon dioxide (CO2) is a known attractant
for mosquitoes and f luctuations in the atmospheric con-
centration of the gas can indicate the presence of a host
(Reeves 1990, Dekker et al. 2005). CO2 also activates
the host-seeking behaviour of mosquitoes, including Ae-
des aegypti (L.) (Eiras & Jepson 1991). CO2-baited traps
have been widely used to increase catch rates of mosqui-
toes, including for monitoring of Ae. aeg ypti with Cen-
ters for Disease Control (CDC) traps in the United States
of America (Service 1992, Canyon & Hii 1997).
In Brazil, the National Dengue Control Program
recommends monitoring of Ae. aegypti based on larval
surveys (MS/FUNASA 2002). Nevertheless, traps for
capturing adult mosquitoes such as the MosquiTRAP®
(Gama et al. 2007) and the BG-Sentinel® (Kröckel et al.
2006) have been evaluated as new monitoring technolo-
gies for dengue vectors in Brazil.
The Biogents-Sentinel™ trap (BGS) (Biogents AG,
Regensburg, Germany) attracts mosquitoes by visual
cues, by the imitation of convection currents of human
beings and by olfactory baits which are released through
a dispenser [BG-Lure (BGL)] which is placed inside of
the trap (Kröckel et al. 2006). The BGL contains sub-
stances that are found on human skin, such as ammo-
nia, lactic acid and caproic acid that also attracts for host
seeking females Ae. aegypti (Geier et al. 1999, Bosch et
al. 2000).
The BGS has been used for capturing Culicidae, es-
pecially Ae. aegypti, Aedes albopictus and Culex spp
(Williams et al. 2006, 2007), including studies with par-
ity rates (Maciel-de-Freitas et al. 2007) and detection of
new infestations with mosquitoes (Ritchie et al. 2006).
In these studies, BGS traps were used without addition
of CO2, which is cost and labour-intensive, as dry ice is
not available everywhere and CO2 cylinders are heavy
to carry. Other suction traps for mosquitoes, such as
CDC traps, are routinely used with CO2 in order to ob-
tain sufficient collections (McNelly 1989). In direct trap
comparisons it was shown that BGS traps without CO2
capture significantly more female Ae. aegypti than CO2-
baited encephalitis vector surveillance traps (Williams
et al. 2006) and significantly more female Ae. albopictus
than CO2-baited CDC traps (Meeraus et al. 2008), but
the effect of CO2 on catch rates of BGS traps for urban
mosquitoes, mainly Ae. aegypti and Culex spp, has not
been investigated in Brazil.
The objective of the present paper is to compare the
effectiveness of BGS traps for capturing urban Culici-
dae, such as Ae. aegypti and Culex quinquefasciatus
when used with and without CO2 in an urban area in
Brazil. Additionally, the physiological state of female
Ae. aegypti was determined.
The study was conducted in 15 urban areas within
the neighbourhood Cidade Nova, in the northern re-
gion of the city of Manaus, state of Amazonas, Brazil
(3º6′0′′S 60º1′0′′W ). Cidade Novais t he most populat-
ed neighbourhood of Manaus, with more than 300,000
Financial support: World Bank, CNPq, UEA, FAPEAM
+ Corresponding author: tatimingote@hotmail.com
Received 17 October 2012
Accepted 15 January 2013
The impact of CO2 on collection of Aedes aegypti (Linnaeus) and
Culex quinquefasciatus Say by BG-Sentinel® traps in Manaus, Brazil
Tatiana Mingote Ferreira de Ázara1/+, Carolin Marlen Degener1, Rosemary Aparecida Roque2,
Jörg Johannes Ohly3, Martin Geier4, Álvaro Eduardo Eiras1
1Laboratório de Ecologia Química de Insetos Vetores, Departamento de Parasitologia, Universidade Federal de Minas Gerais,
Belo Horizonte, MG, Brasil 2Universidade Nilton Lins, Manaus, AM, Brasil 3Centro de Estudos dos Trópicos Úmidos,
Universidade do Estado do Amazonas, Manaus, AM, Brasil 4Institute of Zoology, University of Regensburg, Regensburg, Germany
Carbon dioxide (CO2) is an important component for activating and attracting host-seeking mosquitoes. The BG-
Sentinel® trap is a well-established monitoring tool for capturing Culicidae, but CO2 role for the trap effectiveness
has not been evaluated in highly urbanised areas. The objective was to evaluate the effectiveness of BG-Sentinel
traps baited with and without CO2 for capturing urban mosquitoes. Fifteen areas were selected within the city
of Manaus, Brazil, where four BG-Sentinels were operated for 24 h, two of them with CO2 and two without CO2.
Captured Aedes aegypti females were dissected for the determination of their parity status. A significantly higher
proportion of traps (from 32-79%) were positive for female Ae. aegypti when using the BG-Sentinel with CO2 (χ2 =
11.0271, p < 0.001). Catches of female Culex spp were six times higher in CO2 traps (Mann-Whitney U test = 190.5; p
= 0.001). Parity rates were similar for both traps. This study showed that CO2 has primarily an enhancing effect on
the efficacy of BG-Sentinel for capturing Culex spp in Manaus. For Ae. aegypti, the positivity rate of the trap was
increased, when CO2 was added.
Key words: adult mosquitoes - dry ice - urban area
Role of CO2 in BG-Sentinel traps • Tatiana Mingote Ferreira de Ázara et al.
230
inhabitants, and was chosen as a study site because of
high larvae indices and regular sanitation in most of the
houses. All 15 areas were at least 250 m apart from each
other and included four-seven quarters with a total of
approximately 120 houses.
The BGS traps were supplied with approximately 3
kg of pulverised dry ice (CARBOMAN Ltda, Manaus).
Bottles of 5 L PET were adapted for being used as recipi-
ents for the dry ice. A hole of 4 mm was drilled in the lid
of the bottle and a polyethylene tube of 4 mm diameter
and 1 m of length was pulled through. The connection of
the tube and the lid was closed air-tight with the help of
hot glue. The bottle was isolated with a double layer of
bubble foil and placed inside of a 20 L-Styrofoam box.
The polyethylene tube was connected to a Biogents-
CO2-nozzle and this nozzle was attached to the end of a
mounting pole of the trap (bg-sentinel.com/bilder/BG-
Sentinel_Manual_Addition_of_CO2.pdf) (Figure).
In each of the 15 areas, four houses were randomly
chosen (flipping of a coin) to receive BGS traps with
BGL. Two of the four traps per area were additionally
baited with CO2. The traps were installed in the perido-
mestic area of houses, sheltered from sunlight and rain.
All traps were installed in the morning and operated
for a 24 h period. Catch bags were identified and sent
to the Entomology Department of the Tropical Medi-
cine Foundation of Amazonas (FMT-AM) in Manaus.
Three of the 60 traps were excluded from the trial, be-
cause inhabitants were absent at the end of the trapping
period, or the traps were turned off. Trap catches were
performed in January 2009.
Captured mosquitoes were counted and sexed under
a stereomicroscope. Aedes were identified to species and
other Culicidae were identified to genus with the help of
a dichotomic identification key (Consoli & Lourenço-de-
Oliveira 1994). Female individuals of Ae. aegypti were
dissected and the parity status (parous, nulliparous) was
evaluatedforfemalesineggdevelopmentstage≤Chris-
topher’s stage II (Detinova 1962, Reiter & Nathan 2001).
Females in Christopher’s stage >II were documented as
“late ovarian development stages”.
For Ae. aegypti and Culex mosquitoes, statistical
differences between the catches of BGS traps with and
without CO2 were assessed using the nonparametric
Mann-Whitney U test. For Ae. aegypti, the chi-square
test was used to investigate if the proportions of positive
catch rates differ between the two trap types. Parity rates
were compared by Fisher’s exact test. Due to the low Ae.
albopictus catch rates, comparisons between traps were
not statistically evaluated. Statistical analysis was per-
formed using the statistical software R 2.12.2 (r-project.
org) (The R Foundation for Statistical Computing, 2010).
The Ethical Research Committee (CEP) of studies in-
volving human beings from the FMT-AM approved this
project (approbation 1906 - registration CEP 1024-08).
BGS traps (n = 57) collected 2,924 Culicidae, where
2,699 (92.3%) belonged to the genus Culex and 225 (7.7%)
to the genus Aedes. Of the 225 Aedes mosquitoes, 197
(88%) were identif ied as Ae. aeg ypti and 28 (12%) as Ae.
albopictus. BGS traps baited with BGL and CO2 (n = 29)
captured significantly higher mean numbers of female
(Mann-Whitney, p = 0.03) and sum of male and female
Ae. aeg ypti (Mann-Whitney, p = 0.04), than traps baited
with BGL only (n = 28), but no significant difference was
observed for males (Mann-Whitney, p = 0.07) (Table I).
For BGS traps without CO2, nine out of 28 traps (32%)
were positive for the presence of female Ae. aegypt i and
for traps with CO2, 23 out of 29 traps (79%) were positive
(χ2 = 11.0271, p < 0.001). Interestingly, BGS traps without
CO2 collected the highest maximum number of female
and male Ae. aegypti per 24 h trapping period.
Traps with CO2 captured six times more female
and almost four times more male Culex spp, than traps
without CO2. Significant difference between two differ-
ent trap configurations was only observed for females
(Mann-Whitney U test: Culex females: U = 190.5; p =
0.001; Culex males: U = 302; p = 0.095) (Table I).
Addition of CO2 slightly increased the catch rates of
Ae. aegypti females and males (by 23% and 9%, respec-
tively). The better performance of the traps with CO2 is
more pronounced in the comparison of the proportions
of positive trapping periods, which was significantly
higher, when CO2 was used.
Many trap types are routinely used with CO2 in order
to obtain sufficient trapping efficacies. The CDC trap
was shown to catch significantly higher numbers of Ae.
aegypti in French Polynesia when it was used with CO2
(Russel 2004).
Although the BGS trap was especially developed
for capturing Ae. aegypti, catches of Culex mosquitoes
have been reported (Kröckel et al. 2006, Williams et al.
2006). This might be due to the BGS trap’s imitation
A: filled PET-bottle with 3 Kg of dry ice and carbon dioxide (CO2)-
nozzle, surrounded by bubble foil; B: sealed 20L-Styrofoam box with
CO2-nozzle; C: BG-Sentinel® trap with CO2-nozzle (arrow) which is
connected by a plastic tube to the dry ice-filled PET-bottle.
231
Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 108(2), April 2013
of human odour plumes. In the present study, six times
higher number of female Culex spp were captured by the
traps that were operated with CO2. This suggests that
this kairomone might be an important attractant for this
mosquito genus. Similar results were described before
for the CDC trap (Russel 2004). The high catch rates of
up to 272 Culex females with CO2 and up to 57 Culex
females without CO2 (mainly Cx. quinquefasciatus, per-
sonal observation of TMF de Ázara) per 24 h shows that
the BGS trap might be a useful tool for the monitoring of
diseases that are transmitted by the species in urban ar-
eas in Brazil, like Oropouche fever or Bancroftian Filari-
osis. The high catch rates of Culex mosquitoes in both
BGS configurations demonstrate that these mosquitoes
are predominant in our study area. This information
was confirmed by the Foundation of Health Vigilance in
Manaus (L Mustafa, unpublished observations).
It is interesting to note that the positive effect of CO2
on the collection rate of the traps is most pronounced in
mosquito species that occur in high densities, less pro-
nounced in mosquito species that occur in low densities.
It might be that in urbanised areas with a high density of
human hosts and a high background level of atmospheric
CO2, the CO2 signals from the trap attract mosquitoes
only over a short-range distance.
These results may have a practical importance for
monitoring programs in urban areas. For instance, for
monitoring Ae. aegypti with BGS traps in urban areas,
CO2 is not necessarily required, which minimizes costs
and labour. Even if positivity of the BGS trap for Ae. ae-
gypti females was higher when CO2 was used, the high
costs and operational labour of using CO2 from cylinders
or dry ice might not to be worth it. Instead, the number
of traps could be increased in order to capture a suffi-
cient number of individuals. As conditions can vary con-
siderably between different geographic areas, we sug-
gest evaluating the traps performance with and without
CO2, before a bigger experiment with BGS traps is being
started. For researchers who work with Culex however, it
is highly recommendable to add CO2, if very high catch
rates are required.
Dissections were performed with 104 of the 105 cap-
tured Ae. aegypti females. The traps with and without
CO2 captured 59 and 45 females, respectively (Table II).
The presence of fresh blood was detected in three out
of the 27 females in early ovarian development stages
that were captured by traps with CO2 and in eight out
of the 17 females in early ovarian development stages
that were captured by the traps without CO2 (Table II).
The parous rate [parous/(nulliparous + parous)] of Ae.
aegypti was 92.6% and 82.4% for traps with and without
CO2, respectively and 88.6% for all traps together. The
proportions of parous and nulliparous females did not
differ significantly between the two trap types (Fisher’s
exact test: p = 0.359).
Theoretically, the BGS with BGL should be especial-
ly attractive for host-seeking female mosquitoes. Maciel-
de-Freitas et al. (2006) found the highest percentage of
recaptured individuals in to be in initial stages of ovarian
development, what reflects that these females were host
seeking. In contrast to this, we found almost 60% of Ae.
aegypti females collected to be in ovarian development
stages > II, what means that this females have taken a
blood meal recently and are developing a batch of eggs.
Morais (2009) found similar results in field studies con-
ducted in the urban area of Belo Horizonte, Brazil, where
71% of female Ae. aegypti captured with BGS traps were
gravid. As Ae. aegypti is known to take more than one
blood meal during a single gonotrophic cycle (Barata et
TABLE I
Aedes aegypti and Culex spp [mean ± standard error (SE)]
in BG-Sentinel traps (BGS) baited with BG-Lure (BGL)
and with or without carbon dioxide (CO2) in Manaus,
state of Amazonas, Brazil
BGS + BG L + CO2BGS + BGL
Ae. aegypti
Female Mean 2.0 -1.6
SE 0.39 -0.81
p - 0.038a-
Sum 59 -46
Male Mean 1.6 -1.5
SE 0.43 -0.94
p - 0.07 -
Sum 49 -43
Culex spp
Female Mean 42.7 -7.3
SE 12.23 -2.26
p - 0.001a-
Sum 1282 -205
Male Mean 32.0 -9.0
SE 12.06 -2.38
p - 0.095 -
Sum 961 -251
a: statistical difference (Mann-Whitney U test) between catch-
es of female for the same specie and male also for the same
specie of the two different trap configurations.
TABLE II
Physiological status of female Aedes aegypti
captured with BG-Sentinel traps (BGS) baited with
BG-Lure (BGL) and with or without carbon dioxide (CO2)
in Manaus, state of Amazonas, Brazil
Ae. aegypti
BGS + BGL + CO2
n (%)
BGS + BGL
n (%)
Total
n (%)
Nulliparous 2 (3.4) 3 (6.7) 5 (4.8)
Parous 25 (42.4) 14 (31.1) 39 (37.5)
> stage III 32 (54.2) 28 (62.2) 60 (57.7)
Total 59 (100) 45 (100) 104 (100)
Engorged 3 (0.5) 8 (18) 11 (10.6)
Role of CO2 in BG-Sentinel traps • Tatiana Mingote Ferreira de Ázara et al.
232
al. 2001), our observation could indicate that some of the
females were seeking for a host or that the BGS traps
are not only attractive for host-seeking mosquitoes. The
visual cue of the black funnel for example could be at-
tractive to gravid females looking for oviposition sites.
The observation that 88.6% of the Ae. aegypti females
were parous could reflect high survival rates in Manaus
and thus a high transmission risk of dengue viruses.
ACKNOWLEDGEMENTS
To Maria das Graças Vale Barbosa and the students of the
FMT-AM, for the processing of the field material, to Luzia
Mustafa and the field workers from the FVS-AM, for the con-
duction of the fieldwork, to the inhabitants of Cidade Nova,
for their permissions to install the traps in their homes, and
to Claudia T Codeço and Aline A Nobre, to the help with the
statistical data analysis.
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