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Field Efficacy of VectoMax FG and VectoLex CG Biological Larvicides for Malaria Vector Control in Northwestern Brazil

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Pablo Secato Fontoura at University of São Paulo
Pablo Secato Fontoura
Anderson S da Costa
Anderson S da Costa
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Francismar S Ribeiro
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Marcílio S Ferreira
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Abstract

Despite historical and contemporary evidence of its effectiveness, larval source management with insecticides remains little used by most malaria control programs worldwide. Here we show that environmentally safe biological larvicides under field conditions can significantly reduce anopheline larval density in fish farming ponds that have became major larval habitats across the Amazon Basin. Importantly, the primary local malaria vector, Anopheles darlingi Root (Diptera: Culicidae), feeds and rests predominantly outdoors, being little affected by interventions such as long-lasting insecticidal bed net distribution and indoor residual spraying. We found >95% reduction in late-instar density up to 7 d after the first application of VectoMax FG or VectoLex CG (both from Valent BioSciences), and up to 21 d after larvicide reapplication in fish ponds (n = 20) situated in the main residual malaria pocket of Brazil, irrespective of the formulation or dosage (10 or 20 kg/ha) used. These results are consistent with a substantial residual effect upon retreatment and support the use of biological larvicides to reduce the density of anopheline larvae in this and similar settings across the Amazon where larval habitats are readily identified and accessible.
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Short Communication
Field Efficacy of VectoMax FG and VectoLex CG
Biological Larvicides for Malaria Vector Control in
NorthwesternBrazil
PabloS. Fontoura, 1 AndersonS. daCosta, 1 FrancismarS. Ribeiro, 1
MarcílioS. Ferreira, 1 MarciaC. Castro, 2,† and MarceloU. Ferreira1,3,†,
1Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, Av. Prof. Lineu Prestes 1374, 05508-
900 São Paulo, SP, Brazil2Department of Global Health and Population, Harvard T.H. Chan School of Public Health, Boston, MA
021153Corresponding author, e-mail: muferrei@usp.br
†These authors contributed equally to this work.
Subject Editor: Ary Faraji
Received 29 August 2019; Editorial decision 29 October 2019
Abstract
Despite historical and contemporary evidence of its effectiveness, larval source management with insecticides re-
mains little used by most malaria control programs worldwide. Here we show that environmentally safe biological
larvicides under field conditions can significantly reduce anopheline larval density in fish farming ponds that have
became major larval habitats across the Amazon Basin. Importantly, the primary local malaria vector, Anopheles
darlingi Root (Diptera: Culicidae), feeds and rests predominantly outdoors, being little affected by interventions
such as long-lasting insecticidal bed net distribution and indoor residual spraying. We found >95% reduction in late-
instar density up to 7 d after the first application of VectoMax FG or VectoLex CG (both from Valent BioSciences), and
up to 21 d after larvicide reapplication in fish ponds (n=20) situated in the main residual malaria pocket of Brazil, ir-
respective of the formulation or dosage (10 or 20kg/ha) used. These results are consistent with a substantial residual
effect upon retreatment and support the use of biological larvicides to reduce the density of anopheline larvae in
this and similar settings across the Amazon where larval habitats are readily identified and accessible.
Key words: Anopheles, Bacillus thuringiensis serovar israelensis, Lysinibacillus sphaericus, larviciding, vector control
Anopheles darlingi Root (Diptera: Culicidae), a widely distributed
Neotropical mosquito, is the most efcient malaria vector in the
Amazon (Sinka etal. 2010). Larval habitats of this species include
natural water bodies with clear water and partially shaded edges
covered with vegetation and articial habitats such as sh farming
ponds used for commercial aquaculture (Maheu-Giroux etal. 2010,
Barros and Honorio 2015, dos Reis etal. 2015).
Adult An. darlingi mosquitoes have gradually changed their
biting and resting behavior over the past decades (Hiwat and Bretas
2011). They now typically feed and rest outdoors (e.g., Gil et al.
2003), with more intense human biting activity at dusk, and some-
times a minor peak at dawn (Conn and Ribolla 2016, Martins etal.
2018). This behavior introduces major challenges for core vector
control strategies that rely on long-lasting insecticidal net distribu-
tion and indoor residual spraying (Ferreira and Castro 2016). First,
early-evening biting is unlikely to be prevented by bednet use, ex-
cept for infants. Second, the efcacy of indoor residual spraying is
limited against mosquitoes that bite and rest mostly outdoors. Even
in areas where indoor transmission still occurs, emerging insecticide
resistance and the poor quality of local houses constitute additional
challenges for indoor residual spraying.
Targeting aquatic immature stages is among the much-needed al-
ternative strategies to control outdoor feeding and outdoor resting
mosquito populations with well delineated, easy to nd, and readily
accessible larval habitats. Indeed, larval source management can be
achieved by permanent or recurrent habitat modication, biological
control with natural predators, and chemical or biological larviciding
(World Health Organization 2013). However, these measures have
not been incorporated in the agenda of most national malaria con-
trol programs (Fillinger and Lindsay 2011), despite historical (Keiser
et al. 2005) and contemporary (Maheu-Giroux and Castro 2013)
evidence of their effectiveness.
The eld efcacy of biological larvicides against An. darlingi
remains little studied, despite promising preliminary results with
Lysinibacillus sphaericus application in Brazil (Galardo etal. 2013,
Ferreira etal. 2015), Peru, and Venezuela (reviewed by Conn and
Ribolla 2016). To address this gap, we evaluated the efcacy of
biological larvicides in reducing anopheline larval density in sh
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Journal of Medical Entomology, 57(3), 2020, 942–946
doi: 10.1093/jme/tjz220
Advance Access Publication Date: 21 November 2019
Short Communication
Downloaded from https://academic.oup.com/jme/article-abstract/57/3/942/5637486 by guest on 05 May 2020
943Journal of Medical Entomology, 2020, Vol. 57, No. 3
farming ponds in Juruá Valley, the main residual malaria pocket in
Brazil, accounting for 18.5% of the country’s malaria burden. Here,
we report the results of a eld trial of two biological larvicide formu-
lations as a measure to reduce the proliferation of anopheline larvae
in sh farmingponds.
Materials and Methods
The study area is located in the rural community of Nova Cintra
(07°49′17ʺS, 72°39′54ʺW), situated along Juruá River, that experi-
ences year-round malaria transmission. Nova Cintra (population,
371)is part of the municipality of Rodrigues Alves, Acre State, close
to the Brazil–Peru border. Average monthly rainfall estimates during
the study period were obtained from the Climate Hazards group
Infrared Precipitation with Stations (CHIRPS) dataset, which uses
modeled satellite-based infrared data (http://chg.geog.ucsb.edu/data/
chirps). The annual parasite incidence in Rodrigues Alves, estimated
at 343.4 cases per 1,000 inhabitants in 2016, is the second highest for
a municipality in Brazil (Ministry of Health of Brazil, unpublished
data). Nova Cintra has been targeted for free insecticide-treated
bednet replacement within the past 3 yr; indoor residual spaying
with pyrethroids is irregularly carried out and reported to meet with
frequent refusals, mostly due to allergic reactions. The main malaria
vector is An. darlingi, although larvae of An. albitarsis s.l. (Galvão
and Damasceno) are also abundant in water bodies across the region
(dos Reis etal. 2015, Martins etal. 2018).
Two granular formulations of biological larvicides donated
by Valent BioSciences LLC (Libertyville, IL) were evaluated: a)
VectoMax FG (lot number, 277444N830), which combines toxins
from Bacillus thuringiensis serovar israelensis (Bti; strain AM65-52)
and Lysinibacillus (formerly Bacillus) sphaericus 2362 (Ls; strain
ABTS-1743) in a single microparticle, with a potency of 50 interna-
tional toxin units; and b) VectoLex CG (lot number, 276440N830),
which has Ls 2362 (strain ABTS-1743) toxins attached to the bac-
terial spores in corncob granules, with a potency of 50 international
toxin units. These products were applied using an 18-liter capacity
knapsack power mistblower (Guarany, Itu, Brazil) operating at a
walking speed of 0.5 m/s, with a reach of 10 m, covering a surface
area of 5 m2/s.
The trial aimed to examine the eld efcacy and residual activity
of VectoMax FG and VectoLex CG, and to determine their optimum
application dosage in sh farming ponds. We georeferenced all 24
sh ponds, most of them articial, situated in the community of
Nova Cintra. Their surface areas ranged from 200 to 12,000 m2, or
0.02 to 1.2 hectares (ha). Field activities were carried out between
27 September and 4 December 2017. On September 27, we assessed
the baseline larval density using a standard dipping technique for
sampling water bodies (World Health Organization 1992); 2–3 dips
were taken, using a 500-ml ladle, every 3 m along the edges of the
sh pond. Larvae were classied as rst (L1), second (L2), third (L3),
or fourth (L4) instar, and then as early (L1 and L2) or late (L3 and
L4) instars. The presence and number of pupae were recorded but
not used in the analysis due to the impracticability of morphological
differentiation under eld conditions. Larval density in each water
body was calculated as the average count per dip. At baseline all
ponds were positive for immature anopheline stages and supported
active sh farming.
We used stratied block randomization to allocate sh ponds to
different treatments. Briey, we ranked sh ponds according to base-
line larval density and excluded from randomization the four ponds
with the lowest densities. The remaining ponds were stratied into
larval density quartiles; within each quartile, habitats were randomly
allocated to one of the following four treatments: a) VectoLex CG,
10 kg/ha; b) VectoLex CG, 20 kg/ha; c) VectoMax FG, 10kg/ha;
d) VectoMax FG, 20kg/ha. Five additional sh ponds, with similar
surface areas and larval densities, were selected as controls and re-
mained untreated throughout the trial period. To avoid contamina-
tion, controls were chosen in a rural community named Vila Assis
Brasil (07°35′30ʺS, 72°48′29ʺW), situated 27 km from the main
studysite.
Larval density was monitored within 48h and 72h after the rst
larvicide application, and then weekly until the prevalence of L4 was
similar in treated and untreated habitats. Fish ponds were retreated
21 d after the rst application, following their original allocation
to products and dosages, and further monitored for larval density
within 48h, 72h, 7 d, 14 d, 21 d, 35 d, and 42 d after retreatment.
Main outcome variables were: a) anopheline larval density, total
and by instar stage, in treated and control sh ponds, and b) percent
reduction in larval density (%RLD) relative to untreated controls,
total and by instar stage, calculated using Mulla’s formula (Mulla
etal. 1971):
%
RLD =100
ïÅC
1
T1ã×ÅT
2
C2ãò×
100,
where C1 and C2 are the baseline and posttreatment average number
of larvae per dip in the control habitats, respectively, while T1 and
T2 are the baseline and posttreatment average number of larvae per
dip in the treated habitats. When %LDR was negative (i.e., larval
density was higher in treated compared with untreated sh ponds),
the value was taken as zero. The mean numbers of anopheline larvae
per dip in treatment and control habitats were compared using the
nonparametric Kruskal–Wallis test. When individual Kruskal–Wallis
tests indicated a signicant difference (P<0.05) among treatment
groups, posthoc Dunn’s tests for multiple comparisons were carried
out with each pair of habitats to determine whether differences in
habitats were observed. Comparisons were separately made for each
sampling day using Stata 14.1 (StataCorp, College Station,TX).
The study was approved by the Institutional Review Board of
the Institute of Biomedical Sciences, University of São Paulo, Brazil
(CAAE number 6467416.6.0000.5467).
Results and Discussion
At baseline, water pH in the treated sh ponds ranged between 4.96
and 6.59, with water temperatures between 30.3 and 32.1°C. The
study period partially overlapped with the rainy season, and average
monthly rainfall estimates were 179mm in September, 151mm in
October, 288mm in November, and 282mm in December2017.
All treated ponds remained free of L2, L3, and L4 larvae until
day 7, although L1 larvae were already present in 16 (80%) ponds
on day 7.We note that newly hatched L1 larvae have a much lower
feeding rate and thus ingest lower amounts of larvicides, potentially
leading to an underestimation of larvicide efcacy. By days 14 and
21 after treatment, L4 larvae were found in 11 of 20 (55%) and 17
of 20 (85%) treated ponds, respectively. Table 1 shows the average
number of anopheline larvae per dip in treated and untreated sh
ponds, at baseline and following the rst application of biological
larvicides. Until day 7 after treatment, average late instar densities
were signicantly lower in all treated ponds, compared with control
ponds, with %LDR >95% irrespective of the larvicide formulation
and dosage. Indeed, the different products and dosages were simi-
larly effective in reducing larval density between 48h and 7 d after
treatment (Dunn’s tests, P=0.500 for all comparisons).
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944 Journal of Medical Entomology, 2020, Vol. 57, No. 3
Ponds were retreated on day 21, following the original allocation
to formulations and dosages as in the rst application. Time points
shown in Table 2 were dened considering day 21 of the primary
treatment as day 0 (baseline) of retreatment. Until day 14 after lar-
vicide reapplication, early and late instars were not found in any sh
pond, regardless of the product and dosage used. Interestingly, all
ponds remained free of L4 larvae until day 21 after reapplication,
and most of them remained negative for L4 until days 28 (16 of
20, 80%) and 35 (12 of 19, 58%), consistent with some prolonged
residual effect of the larvicides upon reapplication. One of the ve
ponds treated with 20kg/ha of VectoMax was empty after day 28
after reapplication, hence a total of 19 ponds were monitored at
days 35 and42.
On day 21 after reapplication, overall differences in mean L3+L4
density across groups were of borderline signicance (Kruskal–
Wallis test, P=0.056), but %LDR for late instars remained >95%
for all products and dosages. Pairwise comparisons with Dunn’s tests
still revealed signicant differences between control and treatment
groups on day 21 for L3+L4 density, with P values ranging between
0.0001 and 0.0009. Average %LDR for late instars ranged between
85 and 100% on day 28, but differences in L3+L4 density across
groups were no longer signicant beyond day 21 after reapplication
(Kruskal–Wallis tests, P values between 0.090 and 0.481).
Commercial aquaculture represents a major challenge for ma-
laria control in the Amazon Basin (Maheu-Giroux et al. 2010,
Barros and Honorio 2015, dos Reis etal. 2015). Indeed, sh farming
Table 2. Larval density (LD), estimated as the mean number of larvae per dip, and percent larval density reduction (%LDR)
after retreatment of fish ponds in Juruá Valley, northwestern Brazil, with either 10 or 20kg/ha of VectoLex CG and VectoMax
FG biolarvicides
Treatment Group
None (control) VectoLex CG 10kg/ha Vectolex CG 20kg/ha VectoMax FG 10kg/ha Vectomax FG 20kg/ha
Time L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total
48 h LD 0.44 0.46 0.90 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
72 h LD 0.39 0.49 0.88 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
7 d LD 0.36 0.40 0.76 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
14 d LD 0.29 0.59 0.88 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
21 d LD 0.81 1.01 1.82 0.01 0.01 0.02 0.06 0.01 0.07 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 95.6 96.5 96.1 83.2 96.5 89.1 100.0 100.0 100.0 100.0 100.0 100.0
28 d LD 0.70 0.97 1.67 0.00 0.00 0.00 0.07 0.04 0.11 0.01 0.01 0.02 0.01 0.03 0.04
%LDR — — — 100.0 100.0 100.0 77.3 85.4 81.3 90.4 95.9 94.2 92.1 88.9 89.9
35 d LD 0.19 0.27 0.46 0.04 0.01 0.05 0.04 0.03 0.07 0.03 0.03 0.06 0.1 0.05 0.15
%LDR — — — 24.7 86.9 61.4 52.3 60.7 56.7 0.0 55.6 36.8 0.0 33.5 0.0
42 d LD 0.22 0.25 0.47 0.18 0.07 0.25 0.08 0.07 0.15 0.09 0.09 0.18 0.08 0.06 0.14
%LDR — — — 0.0 1.1 0.0 17.5 1.1 9.1 0.0 0.0 0.0 0.0 13.8 0.0
Average densities in bold are signicantly different from those in the control group (P<0.05) for the same larval stages (L1+L2, L3+L4, or all), and
on the same day of monitoring (Kruskal–Wallis test followed by posthoc Dunn′s tests).
Table 1. Larval density (LD), estimated as the mean number of larvae per dip, and percent larval density reduction
(%LDR) after the first treatment of fish ponds in Juruá Valley, northwestern Brazil, with either 10 or 20kg/ha of VectoLex
CG and VectoMax FG biolarvicides
Treatment Group
None (control) VectoLex CG 10kg/ha Vectolex CG 20kg/ha VectoMax FG 10kg/ha Vectomax FG 20kg/ha
Time L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total
0 h LD 0.85 0.97 1.82 0.65 1.11 1.76 0.48 1.22 1.70 0.54 1.21 1.75 0.55 1.29 1.84
48 h LD 0.29 0.78 1.07 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
72 h LD 0.17 0.81 0.98 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
7 d LD 0.44 1.33 1.77 0.07 0.00 0.07 0.08 0.00 0.08 0.02 0.00 0.02 0.09 0.00 0.09
%LDR — — — 78.5 100.0 95.9 66.0 100.0 95.1 92.6 100.0 98.8 67.3 100.0 94.9
14 d LD 0.63 1.05 1.68 0.12 0.09 0.21 0.25 0.16 0.41 0.19 0.13 0.32 0.14 0.16 0.30
%LDR — — — 74.8 93.3 87.6 27.4 88.0 73.7 49.4 90.8 80.1 65.3 88.5 82.2
21 d LD 0.81 1.06 1.87 0.23 0.30 0.53 0.36 0.30 0.66 0.12 0.27 0.39 0.14 0.30 0.44
%LDR — — — 62.4 75.3 70.5 18.7 77.7 62.0 76.4 79.6 78.2 71.0 79.4 76.6
Average densities in bold are signicantly different from those in the control group (P<0.05) for the same larval stages (L1+L2, L3+L4, or all) and on
the same day of monitoring (Kruskal–Wallis test followed by posthoc Dunn′s tests).
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945Journal of Medical Entomology, 2020, Vol. 57, No. 3
Table 2. Larval density (LD), estimated as the mean number of larvae per dip, and percent larval density reduction (%LDR)
after retreatment of fish ponds in Juruá Valley, northwestern Brazil, with either 10 or 20kg/ha of VectoLex CG and VectoMax
FG biolarvicides
Treatment Group
None (control) VectoLex CG 10kg/ha Vectolex CG 20kg/ha VectoMax FG 10kg/ha Vectomax FG 20kg/ha
Time L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total
48 h LD 0.44 0.46 0.90 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
72 h LD 0.39 0.49 0.88 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
7 d LD 0.36 0.40 0.76 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
14 d LD 0.29 0.59 0.88 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
21 d LD 0.81 1.01 1.82 0.01 0.01 0.02 0.06 0.01 0.07 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 95.6 96.5 96.1 83.2 96.5 89.1 100.0 100.0 100.0 100.0 100.0 100.0
28 d LD 0.70 0.97 1.67 0.00 0.00 0.00 0.07 0.04 0.11 0.01 0.01 0.02 0.01 0.03 0.04
%LDR — — — 100.0 100.0 100.0 77.3 85.4 81.3 90.4 95.9 94.2 92.1 88.9 89.9
35 d LD 0.19 0.27 0.46 0.04 0.01 0.05 0.04 0.03 0.07 0.03 0.03 0.06 0.1 0.05 0.15
%LDR — — — 24.7 86.9 61.4 52.3 60.7 56.7 0.0 55.6 36.8 0.0 33.5 0.0
42 d LD 0.22 0.25 0.47 0.18 0.07 0.25 0.08 0.07 0.15 0.09 0.09 0.18 0.08 0.06 0.14
%LDR — — — 0.0 1.1 0.0 17.5 1.1 9.1 0.0 0.0 0.0 0.0 13.8 0.0
Average densities in bold are signicantly different from those in the control group (P<0.05) for the same larval stages (L1+L2, L3+L4, or all), and
on the same day of monitoring (Kruskal–Wallis test followed by posthoc Dunn′s tests).
ponds are among the main larval habitats in Juruá Valley, currently
the area with the highest malaria transmission levels in Brazil (dos
Reis etal. 2015, Martins etal. 2018). These are relatively small, easy
to nd, and readily accessible water bodies that constitute ideal tar-
gets for larviciding (World Health Organization 2013).
Here we show that commercially available biological larvicides
can signicantly reduce anopheline larval density in sh farming
ponds under eld conditions, with substantial residual effect. We
found >95% reduction in late instar density up to 7 d after the rst
application and up to 21 d after reapplication of the same products.
Importantly, the study period overlapped the rainy season in the
Amazon, when heavy rainfall may potentially raise the water level
of larval habitats, diluting the products and washing away oating
toxins. Percent larval density reduction was similar across treatment
groups, irrespective of the formulation (VectoMax FG or VectoLex
CG) or dosage (10 or 20kg/ha) used.
Taken together, these results support the use of biological larvi-
cide formulations to reduce anopheline larval density in areas where
larval habitats can be easily identied and treated. However, whether
decreased larval density will translate into reduced local malaria
transmission remains to be determined. To address this gap, we re-
cently started a 1-yr eld trial of monthly treatment with 20kg/ha
of VectoMax FG of 170 sh farming ponds in Juruá Valley, which
is expected to help dene the role of larvicide-based larval source
management in malaria control in this and similar settings across
the Amazon Basin.
Table 1. Larval density (LD), estimated as the mean number of larvae per dip, and percent larval density reduction
(%LDR) after the first treatment of fish ponds in Juruá Valley, northwestern Brazil, with either 10 or 20kg/ha of VectoLex
CG and VectoMax FG biolarvicides
Treatment Group
None (control) VectoLex CG 10kg/ha Vectolex CG 20kg/ha VectoMax FG 10kg/ha Vectomax FG 20kg/ha
Time L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total L1+L2 L3+L4 Total
0 h LD 0.85 0.97 1.82 0.65 1.11 1.76 0.48 1.22 1.70 0.54 1.21 1.75 0.55 1.29 1.84
48 h LD 0.29 0.78 1.07 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
72 h LD 0.17 0.81 0.98 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
%LDR — — — 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0
7 d LD 0.44 1.33 1.77 0.07 0.00 0.07 0.08 0.00 0.08 0.02 0.00 0.02 0.09 0.00 0.09
%LDR — — — 78.5 100.0 95.9 66.0 100.0 95.1 92.6 100.0 98.8 67.3 100.0 94.9
14 d LD 0.63 1.05 1.68 0.12 0.09 0.21 0.25 0.16 0.41 0.19 0.13 0.32 0.14 0.16 0.30
%LDR — — — 74.8 93.3 87.6 27.4 88.0 73.7 49.4 90.8 80.1 65.3 88.5 82.2
21 d LD 0.81 1.06 1.87 0.23 0.30 0.53 0.36 0.30 0.66 0.12 0.27 0.39 0.14 0.30 0.44
%LDR — — — 62.4 75.3 70.5 18.7 77.7 62.0 76.4 79.6 78.2 71.0 79.4 76.6
Average densities in bold are signicantly different from those in the control group (P<0.05) for the same larval stages (L1+L2, L3+L4, or all) and on
the same day of monitoring (Kruskal–Wallis test followed by posthoc Dunn′s tests).
Downloaded from https://academic.oup.com/jme/article-abstract/57/3/942/5637486 by guest on 05 May 2020
946 Journal of Medical Entomology, 2020, Vol. 57, No. 3
Acknowledgments
We thank Maria José Menezes for excellent administrative support; Dr.
José Bento P. Lima and Prof. Maria Anice Sallum for helpful suggestions;
and Hélio Cameli, Muana Araújo, Francisco Menezes, and José Wilson for
their invaluable logistical support. Financial support was provided by the
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Brazil
(grant 2016/18740–9). P.S.F. receives a FAPESP post-doctoral fellowship
(grant 2016/25617–9), and M.U.F. receives a senior research scholarship
from the Conselho Nacional de Desenvolvimento Cientíco e Tecnológico
(CNPq), Brazil. Valent BioSciences LLC supplied the biological larvicides
and one mistblower. Dr. Peter DeChant (Global Technical Manager at Valent
BioSciences) provided technical expertise in eld trial implementation. The
funders had no role in data collection and analysis, decision to publish, or
preparation of the manuscript.
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... However, very few data are available on vegetated larval sites. In polluted water ditches in India, Cx. quinquefasciatus larval and pupal densities were significantly reduced for 8-15 days at dosages of both 500 and 1,000 mg/m 2 (WHO 2016); in Brazilian fishponds, Anopheles darlingi (Root) larval abundance was reduced for up to 7 days after an application of Bti þ Bs (Fontoura et al. 2020). Notably, the shorter time of the residual effect reported in Brazilian fishponds may potentially be due to the overlapping of the rainy season in the Amazon, when heavy rainfall raises the water level of larval habitats, diluting the product. ...
... larvae and pupae for up to 28 days posttreatment (Dritz et al. 2011). We estimated a higher efficacy for Bti þ Bs compared with a previous evaluation in Brazilian fishponds (Fontoura et al. 2020), where a single application (10 kg/ha) substantially reduced (.95%) anopheline larval densities for 7 days. However, Fontoura et al. (2020) reported residual effects for up to 21 days after reapplication of Bti þ Bs (20 kg/ha). ...
... We estimated a higher efficacy for Bti þ Bs compared with a previous evaluation in Brazilian fishponds (Fontoura et al. 2020), where a single application (10 kg/ha) substantially reduced (.95%) anopheline larval densities for 7 days. However, Fontoura et al. (2020) reported residual effects for up to 21 days after reapplication of Bti þ Bs (20 kg/ha). Our results, obtained from rural ditches, estimated Bti þ Bs to be less effective with respect to other studies conducted in different settings, such as a septic tank in Turkey (Cetin et al. 2015) and urban catch basins in the USA (Anderson et al. 2011) and Switzerland (Guidi et al. 2013). ...
Evaluation of Bacillus thuringiensis Subsp. Israelensis and Bacillus sphaericus Combination Against Culex pipiens in Highly Vegetated Ditches
Article
  • Mar 2022
Among the few mosquito larvicides available in the market, Bacillus thuringiensis subsp. israelensis (Bti) and B. sphaericus (Bs) represent the most environmentally safe alternatives. The combination of the 2 products is known to overcome their specific limitations by producing a synergistic effect. The aim of the study was to assess the effect and persistence of a single treatment with a granular Bti + Bs formulation on highly vegetated ditches in northeastern Italy that represents the primary rural larval sites for Culex pipiens, the primary vector of the West Nile virus in Europe. The analysis takes into account the nonlinear temporal effects on the population dynamics of larvae and pupae. The results showed a dramatic reduction in mosquito larval abundance 24 h posttreatment (93%) and was effective against larvae up to 22 days (100%). The residual effect after 28 days was 99.5%, and a limited residual effect was observed after 39 days (31.2%). A reduction in pupal density was observed after 4 days (70%) and was >98% from days 14 to 28 posttreatment, persisting for up to 39 days (84% after 39 days). The results demonstrate the effective use of the Bti + Bs formulation against Cx. pipiens in vegetated ditches in rural areas. Our modeling framework provides a flexible statistical approach to predict the residual effect of the product over time, in order to plan a seasonal intervention scheme.
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... To address this critical knowledge gap, we assess the impact on malaria prevalence and incidence of community-wide larviciding of fish farming ponds in a peri-urban transmission hotspot in Brazil. We use an environmentally safe biological larvicide with robust residual activity (90-100% reduction in larval density) lasting for 35 days after retreatment of water habitats [19] and negligible effects on non-target populations, such as other invertebrates, fish, and humans. We tested whether larviciding at monthly intervals might reduce larval density in fish farming ponds leading to decreased malaria incidence in the intervention community, compared with untreated communities in the same region. ...
... These toxins, once ingested by larvae, lead to lysis of the insect's gut epithelium. VectoMax FG (Valent Bio-Sciences, Libertyville, IL, USA) at the concentration of 20 kg/ha was applied using 18-l capacity knapsack power mistblowers (Guarany, Itu, Brazil) operating at a walking speed of 0.5 m/s, with a reach of 10 m, covering a surface area of 5 m 2 /s [19]. Based on the extended residual effect of VectoMax FG applied to fish ponds described in the region [19], habitats were retreated monthly; the only exception was May 2019, when treatment failed due to an unexpected delay in the shipping of larvicides to the field site. ...
... VectoMax FG (Valent Bio-Sciences, Libertyville, IL, USA) at the concentration of 20 kg/ha was applied using 18-l capacity knapsack power mistblowers (Guarany, Itu, Brazil) operating at a walking speed of 0.5 m/s, with a reach of 10 m, covering a surface area of 5 m 2 /s [19]. Based on the extended residual effect of VectoMax FG applied to fish ponds described in the region [19], habitats were retreated monthly; the only exception was May 2019, when treatment failed due to an unexpected delay in the shipping of larvicides to the field site. As a consequence, there was a 2-month interval between the treatment applied in April 2019 and the next treatment in June 2019. ...
Monthly biological larviciding associated with a tenfold decrease in larval density in fish farming ponds and reduced community-wide malaria incidence in northwestern Brazil
Article
Full-text available
  • Sep 2021
Background: Larvicides are typically applied to fixed and findable mosquito breeding sites, such as fish farming ponds used in commercial aquaculture, to kill immature forms and thereby reduce the size of adult malaria vector populations. However, there is little evidence suggesting that larviciding may suppress community-wide malaria transmission outside Africa. Here, we tested whether the biological larvicide VectoMax FG applied at monthly intervals to fish farming ponds can reduce malaria incidence in Amazonian Brazil. Methods: This study was carried out in Vila Assis Brasil (VAB; population 1700), a peri-urban malaria hotspot in northwestern Brazil with a baseline annual parasite incidence of 553 malaria cases per 1000 inhabitants. The intervention consisted of monthly treatments with 20 kg/ha of VectoMax FG of all water-filled fish ponds in VAB (n ranging between 167 and 170) with a surface area between 20 and 8000 m2, using knapsack power mistblowers. We used single-group interrupted time-series analysis to compare monthly larval density measurements in fish ponds during a 14-month pre-intervention period (September 2017-October 2018), with measurements made during November 2018-October 2019 and shortly after the 12-month intervention (November 2019). We used interrupted time-series analysis with a comparison group to contrast the malaria incidence trends in VAB and nearby nonintervention localities before and during the intervention. Results: Average larval densities decreased tenfold in treated fish farming ponds, from 0.467 (95% confidence interval [CI], 0.444-0.490) anopheline larvae per dip pre-intervention (September 2017-October 2018) to 0.046 (95% CI, 0.041-0.051) larvae per dip during (November 2018-October 2019) and shortly after the intervention (November 2019). Average malaria incidence rates decreased by 0.08 (95% CI, 0.04-0.11) cases per 100 person-months (P < 0.0001) during the intervention in VAB and remained nearly unchanged in comparison localities. We estimate that the intervention averted 24.5 (95% CI, 6.2-42.8) malaria cases in VAB between January and December 2019. Conclusions: Regular larviciding is associated with a dramatic decrease in larval density and a modest but significant decrease in community-wide malaria incidence. Larviciding may provide a valuable complementary vector control strategy in commercial aquaculture settings across the Amazon.
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... aegypti and Cx. quinquefasciatus, with a lower risk of resistance selection [35,44,45]. ...
... We believe that the uninterrupted permanence of traps throughout the evaluation period may have favored the high maintenance of this index, in addition to the already known high density of the species in the area. Other studies have also demonstrated the traps' positivity above 90%, indicating a very high degree of sensitivity in ovitrap monitoring [45][46][47]. Regarding the density of eggs removed from the environment, results just like ours have been observed by other authors [32,48]. Several studies, performed in different regions, demonstrated a greater sensitivity for detecting the Ae. ...
Integrated Strategies for Aedes aegypti Control Applied to Individual Houses: An Approach to Mitigate Vectorial Arbovirus Transmission
Article
Full-text available
  • Feb 2024
Aedes aegypti and Culex quinquefasciatus mosquitoes are vectors of different arboviruses that cause a large burden of disease in humans worldwide. A key step towards reducing the impact of arboviruses on humans can be achieved through integrated mosquito surveillance and control approaches. We carried out an integrated approach of mosquito surveillance and control actions to reduce populations of these insects along with a viral surveillance in a neighborhood of Recife (Northeastern Brazil) with high mosquito densities and arbovirus transmission. The actions were carried out in 40 different houses in the Nova Descoberta neighborhood. The area was divided into two groups, the control group using tools to monitor the mosquito density (1 OVT; 1 Double BR-ovt; monthly capture of alates) and the experimental group with control actions using surveillance tools in an intensified way (2 OVTs; 2 Double BR-ovts; fortnightly capture of alates; toxic baits). We evaluated the study’s impact on the mosquito density via the Egg Density (ED) and Adult Density (AD) over a period of 12 cycles of 28 days each. The collected adult mosquitoes were processed via RT-qPCR for DENV, CHIKV and ZIKV and, subsequently, the Minimum Infection Rate (MIR) was calculated. After 12 cycles, we observed a 91% and 99% reduction in Aedes ED and AD in the monitored properties, as well as a 76% reduction in the AD of Cx. quinquefasciatus in the same properties. Moreover, we detected circulating arboviruses (DENV and ZIKV) in 19.52% of captured adult mosquitoes. We show that enhancing entomological surveillance tools can aid in the early detection of possible risk areas based on vector mosquito population numbers. Additionally, the detection of important arboviruses such as ZIKV and DENV raises awareness and allows for a better selection of risk areas and silent virus spread. It offers supplementary information for guiding emergency mosquito control measures in the target area. The goal is to minimize human–vector interactions and, subsequently, to lower the risk of transmitting circulating arboviruses.
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... 30,35-37 These easily located breeding habitats are suitable targets for LSM. Accordingly, we have shown that the monthly application of environmentally safe biologic larvicides with extended residual activity, such as commercially available granular formulations of toxins from Bacillus thuringiensis serovar israelensis and Lysinibacillus (formerly Bacillus) sphaericus, 38 is an effective way of reducing larval density in fish-farming ponds, 38,39 with a potential impact on malaria transmission. 39 Importantly, these products do not appear to impact biodiversity or interfere with the safety of the water and food sources. ...
... 59 Fish-farming ponds, which are now commonly found in the periphery of cities and towns across the Brazilian Amazon, offer a perfect fit for these criteria. 30,[35][36][37][38][39] Last, cluster-randomized controlled trials are needed to evaluate the effectiveness of focal mass drug administration to reduce P. vivax transmission in selected transmission hotspots. The pre-elimination phase of the MZP has incorporated targeted antimalarial drug administration as a key strategy in Peru (Figure 2), although locally generated evidence is currently lacking to support its use in public health campaigns across the Amazon. ...
Evidence-Based Malaria Control and Elimination in the Amazon: Input from the International Center of Excellence in Malaria Research Network in Peru and Brazil
Article
Full-text available
  • Oct 2022
  • AM J TROP MED HYG
Malaria remains endemic in 17 countries in the Americas, where 723,000 cases were reported in 2019. The majority (> 90%) of the regional malaria burden is found within the Amazon Basin, which includes nine countries and territories in South America. Locally generated evidence is critical to provide information to public health decision makers upon which the design of efficient and regionally directed malaria control and elimination programs can be built. Plasmodium vivax is the predominant malaria parasite in the Amazon Basin. This parasite species appears to be more resilient to malaria control strategies worldwide. Asymptomatic Plasmodium infections constitute a potentially infectious reservoir that is typically missed by routine microscopy-based surveillance and often remains untreated. The primary Amazonian malaria vector, Nyssorhynchus (formerly Anopheles) darlingi, has changed its behavior to feed and rest predominantly outdoors, reducing the efficiency of core vector control measures such as indoor residual spraying and distribution of long-lasting insecticide-treated bed nets. We review public health implications of recent field-based research carried out by the Amazonia International Center of Excellence in Malaria Research in Peru and Brazil. We discuss the relative role of traditional and novel tools and strategies for better malaria control and elimination across the Amazon, including improved diagnostic methods, new anti-relapse medicines, and biological larvicides, and emphasize the need to integrate research and public health policymaking.
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... The primary local vector, Anopheles (Nyssorhynchus) darlingi, thrives in water habitats that were opened or modified for fish farming. Importantly, anopheline larval density can be drastically reduced by treating fish farming tanks and ponds periodically with biological larvicides [19,20]. P vivax malaria incidence in VAB and other sites in the region was already declining in the preintervention period, between September 2017 and November 2018, and it decreased further in VAB-but not in nearby sites-until December 2019 ( Figure 1A), during and shortly after the larviciding intervention described in the supplementary methods [20]. ...
Changing Clinical Epidemiology of Plasmodium vivax Malaria as Transmission Decreases: Population-Based Prospective Panel Survey in the Brazilian Amazon
Article
Full-text available
  • Feb 2024
  • J INFECT DIS
Background Malarial infections are often missed by microscopy, and most parasite carriers are asymptomatic in low-endemicity settings. Whether parasite detectability and its ability to elicit symptoms change as transmission declines remains unclear. Methods We performed a prospective panel survey with repeated measurements on the same participants over 12 months to investigate whether Plasmodium vivax detectability by microscopy and risk of symptoms upon infection varied during a community-wide larviciding intervention in the Amazon basin of Brazil that markedly reduced vector density. We screened 1096 to 1400 residents in the intervention site for malaria by microscopy and quantitative TaqMan assays at baseline and twice during intervention. Results We found that more P vivax infections than expected from their parasite densities measured by TaqMan assays were missed by microscopy as transmission decreased. At lower transmission, study participants appeared to tolerate higher P vivax loads without developing symptoms. We hypothesize that changes in the ratio between circulating parasites and those that accumulate in the bone marrow and spleen, by avoiding peripheral blood microscopy detection, account for decreased parasite detectability and lower risk of symptoms under low transmission. Conclusions P vivax infections are more likely to be subpatent and remain asymptomatic as malaria transmission decreases.
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... Microbial larvicides containing crystals from L. sphaericus and Bti are effective tools used as part of integrated mosquito control programs, due to their high larvicidal action associated with environmental safety and an overall low risk of resistance selection [12][13][14][15]. Resistance to the Bin toxin has nevertheless been reported in Cx. quinquefasciatus and it remains a major concern. ...
Culex quinquefasciatus Resistant to the Binary Toxin from Lysinibacillus sphaericus Displays a Consistent Downregulation of Pantetheinase Transcripts
Article
  • Jan 2024
Citation: Rezende, T.M.T.; Menezes, H.S.G.; Rezende, A.M.; Cavalcanti, M.P.; Silva, Y.M.G.; de-Melo-Neto, O.P.; Romão, T.P.; Silva-Filha, M.H.N.L. Culex quinquefasciatus Resistant to the Binary Toxin from Lysinibacillus sphaericus Displays a Consistent Downregulation of Pantetheinase Transcripts. Abstract: Culex quinquefasciatus resistance to the binary (Bin) toxin, the major larvicidal component from Lysinibacillus sphaericus, is associated with mutations in the cqm1 gene, encoding the Bin-toxin receptor. Downregulation of the cqm1 transcript was found in the transcriptome of larvae resistant to the L. sphaericus IAB59 strain, which produces both the Bin toxin and a second binary toxin, Cry48Aa/Cry49Aa. Here, we investigated the transcription profiles of two other mosquito colonies having Bin resistance only. These confirmed the cqm1 downregulation and identified transcripts encoding the enzyme pantetheinase as the most downregulated mRNAs in both resistant colonies. Further quantification of these transcripts reinforced their strong downregulation in Bin-resistant larvae. Multiple genes were found encoding this enzyme in Cx. quinquefasciatus and a recombinant pantetheinase was then expressed in Escherichia coli and Sf 9 cells, with its presence assessed in the midgut brush border membrane of susceptible larvae. The pantetheinase was expressed as ã 70 kDa protein, potentially membrane-bound, which does not seem to be significantly targeted by glycosylation. This is the first pantetheinase characterization in mosquitoes, and its remarkable downregulation might reflect features impacted by co-selection with the Bin-resistant phenotype or potential roles in the Bin-toxin mode of action that deserve to be investigated.
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... However, in this study each catch basin was treated only once, which does not represent the reality of periodically repeated treatments done in the field. For example, a study on the field efficacy of VectoMax® FG applied to fish ponds for the control of malaria vector Anopheles (Nyssorhynchus) darlingi Root, 1926 showed a possible prolonged residual effect upon reapplication of the larvicide (Fontoura et al., 2020). The results presented here are rather to be interpreted as focussing on the effect and duration after a single treatment. ...
Efficacy of biological larvicide VectoMax® FG against Aedes albopictus and Culex pipiens under field conditions in urban catch basins
Article
Full-text available
  • Sep 2023
The invasive Asian tiger mosquito Aedes albopictus appeared in southern Switzerland in 2003 and is currently well established in most of its urban regions. In public areas, the control measures against the mosquito focus on its aquatic phase with removal of breeding sites and applications of larvicides at sites that cannot be eliminated. Larvicidal products are applied mainly to catch basins, one of the major sites of oviposition for both Ae. albopictus and Culex pipiens in urban areas. We evaluated the efficacy of a larvicidal formulation (i.e. VectoMax® FG), combing the action of spore-forming bacteria Bacillus thuringiensis var. israelensis and Lysinibacillus sphaericus, against Ae. albopictus, Cx. pipiens and non- target organisms present in urban catch basins. We used floating adult emergence traps to compare the number of adults emerging from 38 catch basins treated once during the study period with ten untreated (control) catch basins. The catch basins were monitored for 21 weeks and the efficacy was evaluated fitting a Generalised Additive Mixed Model (GAMM). The efficacy of the treatment varied among species. It was high against Cx. pipiens (100% reduction in emerging adults at maximal efficacy) and lower against Ae. albopictus (60% reduction). This suggests that it is important to examine target species separately when evaluating the efficacy of larvicidal products. The product showed a long residual larvicidal activity with the number of emerging adults still being reduced by 75% for Cx. pipiens and 60% for Ae. albopictus at ten weeks after the treatment. We also observed that the maximal efficacy of the product was reached about two weeks after the treatment. The effect on non-target organisms, specifically, chironomids, was also strong (80% reduction). However, their numbers raised again rather quickly (i.e. after two weeks), and the effect vanished around week 11.
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... darlingi adult profiles in nearby households. Tailored LSM strategies accounting for this heterogeneity, such the use of biological larvicides [69], need to be routinely incorporated in malaria integrated control to reduce transmission in Mâncio Lima, and in other cities of Vale do Jurua region. ...
Ecology and larval population dynamics of the primary malaria vector Nyssorhynchus darlingi in a high transmission setting dominated by fish farming in western Amazonian Brazil
Article
Full-text available
Vale do Rio Juruá in western Acre, Brazil, is a persistent malaria transmission hotspot partly due to fish farming development that was encouraged to improve local standards of living. Fish ponds can be productive breeding sites for Amazonian malaria vector species, including Nyssorhynchus darlingi , which, combined with high human density and mobility, add to the local malaria burden.This study reports entomological profile of immature and adult Ny . darlingi at three sites in Mâncio Lima, Acre, during the rainy and dry season (February to September, 2017). From 63 fishponds, 10,859 larvae were collected, including 5,512 first-instar Anophelinae larvae and 4,927 second, third and fourth-instars, of which 8.5% (n = 420) were Ny . darlingi . This species was most abundant in not-abandoned fishponds and in the presence of emerging aquatic vegetation. Seasonal analysis of immatures in urban landscapes found no significant difference in the numbers of Ny . darlingi , corresponding to equivalent population density during the rainy to dry transition period. However, in the rural landscape, significantly higher numbers of Ny . darlingi larvae were collected in August (IRR = 5.80, p = 0.037) and September (IRR = 6.62, p = 0.023) (dry season), compared to February (rainy season), suggesting important role of fishponds for vector population maintenance during the seasonal transition in this landscape type. Adult sampling detected mainly Ny . darlingi (~93%), with similar outdoor feeding behavior, but different abundance according to landscape profile: urban site 1 showed higher peaks of human biting rate in May (46 bites/person/hour), than February (4) and September (15), while rural site 3 shows similar HBR during the same sampling period (22, 24 and 21, respectively). This study contributes to a better understanding of the larvae biology of the main malaria vector in the Vale do Rio Juruá region and, ultimately will support vector control efforts.
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... Larval source management with biological larvicides represents a logical approach to malaria control in urbanized spaces where breeding sites are relatively few, easy to find and readily accessible. It has been successful in African cities [52,53] and can drastically reduce anopheline larval density in fish farming ponds in the Amazon [54]. ...
Human mobility and urban malaria risk in the main transmission hotspot of Amazonian Brazil
Article
Full-text available
Malaria in the Amazon is often perceived as an exclusively rural disease, but transmission has been increasingly documented within and near urban centers. Here we explore patterns and causes of urban-to-rural mobility, which places travelers at risk of malaria in Mâncio Lima, the main malaria hotspot in northwestern Brazil. We also analyze rural-to-urban mobility caused by malaria treatment seeking, which poses an additional risk of infection to urban residents. We show that the rural localities most frequently visited by urban residents–typically farming settlements in the vicinity of the town–are those with the most intense malaria transmission and also the most frequent source localities of imported malaria cases diagnosed in the town. The most mobile urban residents are typically poor males 16 to 60-years old from multi-sited households who lack a formal job. Highly mobile residents represent a priority target for more intensive and effective malaria control interventions, that cannot be readily delivered to the entire community, in this and similar urbanized endemic settings across the Amazon.
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Bacterial Toxins Active against Mosquitoes: Mode of Action and Resistance
Article
Full-text available
  • Jul 2021
Larvicides based on the bacteria Bacillus thuringiensis svar. israelensis (Bti) and Lysinibacillus sphaericus are effective and environmentally safe compounds for the control of dipteran insects of medical importance. They produce crystals that display specific and potent insecticidal activity against larvae. Bti crystals are composed of multiple protoxins: three from the three-domain Cry type family, which bind to different cell receptors in the midgut, and one cytolytic (Cyt1Aa) protoxin that can insert itself into the cell membrane and act as surrogate receptor of the Cry toxins. Together, those toxins display a complex mode of action that shows a low risk of resistance selection. L. sphaericus crystals contain one major binary toxin that display an outstanding persistence in field conditions, which is superior to Bti. However, the action of the Bin toxin based on its interaction with a single receptor is vulnerable for resistance selection in insects. In this review we present the most recent data on the mode of action and synergism of these toxins, resistance issues, and examples of their use worldwide. Data reported in recent years improved our understanding of the mechanism of action of these toxins, showed that their combined use can enhance their activity and counteract resistance, and reinforced their relevance for mosquito control programs in the future years.
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Diversity of Anopheles mosquitoes from four landscapes in the highest endemic region of malaria transmission in Brazil
Article
Full-text available
  • Sep 2018
  • J VECTOR ECOL
Malaria transmission in South America is overwhelmingly located in the Amazon region with limited cases outside that biome. A key factor in the mitigation of malaria transmission is the determination of vector diversity and bionomics in endemic areas. Anopheles mosquitoes were collected in four different landscapes of Cruzeiro do Sul-Acre, the current area with highest malaria transmission in Brazil. We performed adult mosquito collections every three months over two years and associated vector occurrence with local abiotic factors. A total of 1,754 Anopheles belonging to nine species were collected, but only four of them (An. albitarsis s.l. Lynch-Arribalzaga, An. braziliensis Chagas, An. peryassui Dyar and Knab, and An. triannulatus Neiva and Pinto) represented 77.1% of the total. Vector density and diversity was uneven across field sites and collection periods. Higher Anopheles abundance (54.8%) and richness were observed in a deforested palm tree area (IFC), with An. braziliensis the most frequent mosquito (40.5%). Only 7.3% of mosquitoes were collected in the SAB village, but 66.4% of them were An. darlingi and An. oswaldoi, species often regarded as primary and secondary vectors of malaria in the Amazon region. A distinct biting preference was observed between 18:00-19:40. The distance from the nearest breeding site and minimum temperature explained 41.6% of the Anopheles community composition. Our data show that the Anopheles species composition may present great variation on a microgeographic scale. Journal of Vector Ecology 43 (2): xxx-xxx. 2018.
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Challenges for malaria elimination in Brazil
Article
Full-text available
  • May 2016
  • MALARIA J
Brazil currently contributes 42 % of all malaria cases reported in the Latin America and the Caribbean, a region where major progress towards malaria elimination has been achieved in recent years. In 2014, malaria burden in Brazil (143,910 microscopically confirmed cases and 41 malaria-related deaths) has reached its lowest levels in 35 years, Plasmodium falciparum is highly focal, and the geographic boundary of transmission has considerably shrunk. Transmission in Brazil remains entrenched in the Amazon Basin, which accounts for 99.5 % of the country's malaria burden. This paper reviews major lessons learned from past and current malaria control policies in Brazil. A comprehensive discussion of the scientific and logistic challenges that may impact malaria elimination efforts in the country is presented in light of the launching of the Plan for Elimination of Malaria in Brazil in November 2015. Challenges for malaria elimination addressed include the high prevalence of symptomless and submicroscopic infections, emerging anti-malarial drug resistance in P. falciparum and Plasmodium vivax and the lack of safe anti-relapse drugs, the largely neglected burden of malaria in pregnancy, the need for better vector control strategies where Anopheles mosquitoes present a highly variable biting behaviour, human movement, the need for effective surveillance and tools to identify foci of infection in areas with low transmission, and the effects of environmental changes and climatic variability in transmission. Control actions launched in Brazil and results to come are likely to influence control programs in other countries in the Americas.
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Contribution of fish farming ponds to the production of immature Anopheles spp. in a Malaria-Endemic Amazonian town
Article
Full-text available
  • Nov 2015
  • MALARIA J
Background: In the past decade fish farming has become an important economic activity in the Occidental Brazilian Amazon, where the number of new fish farms is rapidly increasing. One of the primary concerns with this phenomenon is the contribution of fishponds to the maintenance and increase of the anopheline mosquito population, and the subsequent increase in human malaria burden. This study reports the results of a 2-year anopheline abundance survey in fishponds and natural water bodies in a malaria-endemic area in northwest Brazil. The objective of this study was to investigate the contribution of natural water bodies (rivers, streams, creeks, ponds, and puddles) and artificial fishponds as breeding sites for Anopheles spp. in Mâncio Lima, Acre and to investigate the effect of limnological and environmental variables on Anopheles spp. larval abundance. Methods: Natural water bodies and fishponds were sampled at eight different times over 2 years (early, mid and late rainy season, dry season) in the Amazonian town of Mâncio Lima, Acre. Anopheline larvae were collected with an entomological dipper, and physical, chemical and ecological characteristics of each water body were measured. Management practices of fishpond owners were ascertained with a systematic questionnaire. Results: Fishponds were four times more infested with anopheline larvae than natural water bodies. Electrical conductivity and the distance to the nearest house were both significant inverse predictors of larval abundance in natural water bodies. The density of larvae in fishponds raised with increasing border vegetation. Fishponds owned by different farmers varied in the extent of anopheline larval infestation but ponds owned by the same individual had similar infestation patterns over time. Commercial fishponds were 1.7-times more infested with anopheline larvae compared to fishponds for family use. Conclusions: These results suggest that fishponds are important breeding sites for anopheline larvae, and that adequate management activities, such as removal of border vegetation could reduce the abundance of mosquito larvae, most importantly Anopheles darlingi.
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Effect of Bacillus sphaericus Neide on Anopheles (Diptera: Culicidae) and associated insect fauna in fish ponds in the Amazon
Article
Full-text available
  • Jul 2015
  • REV BRAS ENTOMOL
We analyzed the effects of Bacillus sphaericus on Anopheles larvae and on the associated insect fauna in fish farming ponds. Five breeding sites in the peri-urban area of the city of Manaus, AM, Brazil, were studied. Seven samples were collected from each breeding site and B. sphaericus was applied and reapplied after 15 days. The samples were made at 24 h before application, 24 h post-application and 5 and 15 days post-application. We determined abundance, larval reduction and larval density for Anopheles, and abundance, richness, Shannon diversity index and classified according to the functional trophic groups for associated insect fauna. A total of 904 Anopheles larvae were collected and distributed into five species. Density data and larval reduction demonstrated the rapid effect of the biolarvicide 24 h after application. A total of 4874 associated aquatic insects belonging to six orders and 23 families were collected. Regression analysis of diversity and richness indicated that the application of the biolarvicide had no influence on these indices and thus no effect on the associated insect fauna for a period of 30 days. B. sphaericus was found to be highly effective against the larvae of Anopheles, eliminating the larvae in the first days after application, with no effect on the associated insect fauna present in the fish ponds analyzed.
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Deforestation and Malaria on the Amazon Frontier: Larval Clustering of Anopheles darlingi (Diptera: Culicidae) Determines Focal Distribution of Malaria
Article
Full-text available
  • Sep 2015
  • AM J TROP MED HYG
We performed bimonthly mosquito larval collections during 1 year, in an agricultural settlement in the Brazilian Amazon, as well as an analysis of malaria incidence in neighboring houses. Water collections located at forest fringes were more commonly positive for Anopheles darlingi larvae and Kulldorff spatial analysis pinpointed significant larval clusters at sites directly beneath forest fringes, which were called larval "hotspots." Remote sensing identified 43 "potential" hotspots. Sampling of these areas revealed an 85.7% positivity rate for A. darlingi larvae. Malaria was correlated with shorter distances to potential hotpots and settlers living within 400 m of potential hotspots had a 2.60 higher risk of malaria. Recently arrived settlers, usually located closer to the tip of the triangularly shaped deforestation imprints of side roads, may be more exposed to malaria due to their proximity to the forest fringe. As deforestation progresses, transmission decreases. However, forest remnants inside deforested areas conferred an increased risk of malaria. We propose a model for explaining frontier malaria in the Amazon: because of adaptation of A. darlingi to the forest fringe ecotone, humans are exposed to an increased transmission risk when in proximity to these areas, especially when small dams are created on naturally running water collections.
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Impact of Community-Based Larviciding on the Prevalence of Malaria Infection in Dar es Salaam, Tanzania
Article
Full-text available
The use of larval source management is not prioritized by contemporary malaria control programs in sub-Saharan Africa despite historical success. Larviciding, in particular, could be effective in urban areas where transmission is focal and accessibility to Anopheles breeding habitats is generally easier than in rural settings. The objective of this study is to assess the effectiveness of a community-based microbial larviciding intervention to reduce the prevalence of malaria infection in Dar es Salaam, United Republic of Tanzania. Larviciding was implemented in 3 out of 15 targeted wards of Dar es Salaam in 2006 after two years of baseline data collection. This intervention was subsequently scaled up to 9 wards a year later, and to all 15 targeted wards in 2008. Continuous randomized cluster sampling of malaria prevalence and socio-demographic characteristics was carried out during 6 survey rounds (2004-2008), which included both cross-sectional and longitudinal data (N = 64,537). Bayesian random effects logistic regression models were used to quantify the effect of the intervention on malaria prevalence at the individual level. Effect size estimates suggest a significant protective effect of the larviciding intervention. After adjustment for confounders, the odds of individuals living in areas treated with larviciding being infected with malaria were 21% lower (Odds Ratio = 0.79; 95% Credible Intervals: 0.66-0.93) than those who lived in areas not treated. The larviciding intervention was most effective during dry seasons and had synergistic effects with other protective measures such as use of insecticide-treated bed nets and house proofing (i.e., complete ceiling or window screens). A large-scale community-based larviciding intervention significantly reduced the prevalence of malaria infection in urban Dar es Salaam.
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Larval control of Anopheles (Nyssorhinchus) darling using granular formulation of Bacillus Sphaericus in abandoned gold-miners excavation pools in the Brazilian Amazon Rainforest
Article
Full-text available
  • Apr 2013
Introduction: Use of a Bacillus sphaericus based mosquito larvicide was evaluated as an intervention for malaria vector control at a mining site in Amapá, Brazil. Impacts on larval and adult densities of the primary vector Anopheles darlingi were measured over the course of a 52 week study period. Methods: In Calçoene, State of Amapá, gold mining activity occurs in 19 mining sites in gold-miners of Lourenço. Large pools are formed in mining sites and naturally colonized by Anopheles darlingi. During one year, the impact of applications of VectoLex® CG to these larval sources was evaluated. Applications of 20kg/ha were made as needed, based on 10 immature (3rd, 4th instars and pupae) surveillance of health and established thresholds. Results: One hundred percent initial control was observed 48h after each treatment. The pools received from 2-10 (5.3±1.6) treatments during the year. The average re-treatment interval in productive pools was 9.4±4.3 weeks. During weeks 3-52 of the study, mean density of late stage larvae was 78% and pupae were 93% lower in the treated pools than in untreated pools (p< 0.0001, n=51) while reduction of adult mosquitoes was 53% in comparison to the untreated area during the last five months of the study, which were the rainy season (p<0.001). Conclusions: VectoLex® CG reduced immature Anopheles darlingi infestation levels during the entire study period, and reduced adult mosquito populations during the rainy season.
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Ecology of Anopheles darlingi, the Primary Malaria Vector in the Americas and Current Nongenetic Methods of Vector Control
Chapter
  • Dec 2016
Anopheles darlingi is the primary malaria vector throughout most of its distribution from Mexico to Argentina. Depending on the environment, it displays a range of behaviors: anthropophily, opportunism, endo-exophagy, and endo-exophily. It readily colonizes anthropogenic sites and is susceptible to Plasmodium vivax and Plasmodium falciparum. Anopheles darlingi displays moderate variability and significant population structure between Central America plus northwestern South America; and the Amazon. Within the Amazon region, it consists of multiple clusters or putative species, each with partial barriers to gene flow. The other significant malaria vector in northern South America and the Caribbean is Anopheles albimanus, consisting of three distinct lineages with limited gene flow among them. Because most Neotropical vectors are opportunistic, exophagic, and exophilic, the vector control mainstays of long-lasting insecticide-treated nets and indoor residual spraying are not effective alone, and integrated vector control methods, tailored to specific transmission hot spots, will be needed to improve the probability of malaria elimination.
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Control of Chironomid Midges1 in Recreational Lakes2,3
Article
  • Feb 1971
  • J ECON ENTOMOL
Several commonly available and experimental insecticides were evaluated for control of chironomid midge larvae, Chironomus spp., Proclaideus spp., and Tanytarsus spp. in 2 recreational lakes. In Lake Calabasas, where the bottom has a thin layer of mud on a surface of cement, standard midge larvicides such as Abate® (O, O-dimethyl phosphorothioate O, O-diester with 4,4′-thiodiphenol) and fenthion proved highly effective. Fenthion at 0.5 Ib per surface acre controlled the larvae for more than 7 weeks. At this rate of application very slight mortality of the mosquito fish Gambusia affinis (Baird & Girard) was observed. Abate at 0.75 pounds per acre controlled the midges for about 4–5 weeks and caused slight mortality of the fish. Dursban® (O, O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate) at the rate of 0.2 Ib/acre yielded long-lasting control of midge larvae, the suppression lasting for almost 5 months. In Westlake (about 10 miles from Lake Calabasas), with a natural bottom, where small portions were treated, fenthion at 0.5 lb/acre yielded little or no control of the midge larvae. Abate at 0.5 pounds per acre produced similar results. Carbaryl at 0.5 and 1.0 pounds per acre yielded good control, but its longevity was for only 2-3 weeks. Dursban insecticide applied as granules or sprays at 0.2 pounds per acre yielded excellent control of midge larvae. The granular formulations produced better and longer-lasting larval control than an emulsifiable concentrate formulation. The latter formulation at 0.2 lb/acre or higher rate caused slight kill of blugill, Lepomis macrochirus Rafinesque; largemouth bass, Micropterus salmoides Lacépède; and black crappie, Pornoxis nigromaculatus (Le Sueur) in the lake. No mortality of fish was observed in plots treated with a granular formulation of Dursban at the same rate.
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