Factors affecting the size of a
mosquito population in a favourable
environment
P. Cailly1, A. Tran2, T. Balenghien3, C. Toty4,5, P. Ezanno1 1INRA,Oniris, UMR1300 Bio-agression, Epidémiologie et Analyse de Risques,
2CIRAD, UPR AGIRs Animal et Gestion Intégrée des Risques, 3CIRAD, UMR Contrôle des maladies,
4IRD, UR016 Caractérisation et Contrôle des Populations de Vecteurs,
2 Pathogenic agents of major vector born diseases
viruses (e.g. West Nile virus), parasites (e.g. Plasmodium falciparum)
largely distributed across the world
public health & animal health
health, ecological, socioeconomic & political consequences
active vectors necessary for the epidemiological cycle of these diseases
Why mosquitoes?
Aedes aegypti dengue vector www.eplp.asso.nc Anopheles gambiae malaria vector faculty.vetmed.ucdavis.eduCulex pipiens West
3 Efficient anti-vector fight strategies require to well know:
mosquito life cycle & behaviour
related to their biotope (breeding site, ...)
related to the variation of climatic factors (temperature, humidity,
…)
Mosquitoes brave these strategies up to now: malaria and dengue do not weaken
An integrative approach by modelling proves to be necessary for better:
understanding the dynamics of a mosquito vector population
describing the mosquito abundance
identifying the most influential parameters = potential control
points of the population
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Identifying by modelling the factors affecting
the size of a mosquito population located in
a favourable environment
5 Mechanistic model
Adapted to Anopheles of Camargue region, France
Driven by climate
Lasting several years
Modelling approach
France © IRD N.Rahola Anopheles hyrcanus Emerging adults Death Eggs Larvae Pupae Death Death Diapause Hatching Pupation Oviposition Parous engorged Parous searching oviposition sites Nulliparous searching oviposition sites Host-seeking nulliparous Nulliparous engorged Host-seeking parousMigration Death during host or Death oviposition site-seeking Emergence Death Emerging adults Death Eggs Larvae Pupae Death Death Diapause Hatching Pupation Oviposition Parous engorged Parous searching oviposition sites Nulliparous searching oviposition sites Host-seeking nulliparous Nulliparous engorged Host-seeking parous
Migration Death during host or Death oviposition site-seeking
Pupa
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Larva
Nulliparous into diapause during winter
Development parameters
& mortality rates depend on temperature
Model output
General output:
Dynamic abundance in adults over time
Aggregated output:
Modelling approach
Attack rate Time Ad ou Ah year n Peak date Adult peak Number of mosquitoes Emergence date threshold of emerging adults -10 +10 year n+1 Attack rate Time Ad ou Ah year n Peak date Adult peak Number of mosquitoes Emergence date threshold of emerging adults -10 +10 year n+17 Quantify the influence of input values on the outputs
describe the model parameters for which the model is the most sensitive
Influent parameters are potential control points of the biological system
Confront different methods to identify influential parameters in a robust way
Sensitivity analysis of the model
Model
Inputs Outputs
ex: parameters, functions or model structure
ex: attack rate, adult peak
8 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Feb-05 May-05 Aug-05 Nov-05 Feb-06 May-06 Aug-06 Nov-06 Time (month) R e la ti v e a b u n d a n c e ( % )
Model confrontation to independent field data
Number of host-seeking females
Results
G. L’Ambert C.TotyAn. hyrcanus a favourable area
one trap
sum of the 8 traps of 2005
model Cross-correlation=0.8
Our model predicts correctly a mean dynamics of mosquito populations
9 Sensitivity analysis No interaction Influent parameters:
Results
Emerging adults Death Eggs Larvae Pupae Death Death Diapause Hatching Pupation Oviposition Parous engorged Parous searching oviposition sites Nulliparous searching oviposition sites Host-seeking nulliparous Nulliparous engorged Host-seeking parousMigration Death during host or Death oviposition site-seeking Emergence Death Emerging adults Death Eggs Larvae Pupae Death Death Diapause Hatching Pupation Oviposition Parous engorged Parous searching oviposition sites Nulliparous searching oviposition sites Host-seeking nulliparous Nulliparous engorged Host-seeking parous
Migration Death during host or Death oviposition site-seeking Emergence Emerging adults Death Eggs Larvae Pupae Death Death Diapause Hatching Pupation Oviposition Parous engorged Parous searching oviposition sites Nulliparous searching oviposition sites Host-seeking nulliparous Nulliparous engorged Host-seeking parous
Migration Death during host or Death oviposition site-seeking
Bio-larvicide, similar to Bti, persistent during 7 days
Different proportions of the sprayed surface & 2 strategies tested
Sprayed at regular time intervals
Sprayed when mosquito abundance exceeds a threshold value
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Scenario of control strategies
proportions of the zone sprayed = 0.45 Nb of treatment = 5 1000 2000 300 250 200 150 100 3000 4000 5000 6000 7000 8000 0 time (days) n u m b e r o f h o s t-s e e k in g f e m a le s threshold
date of treatments for regular time regular time
reference
date of treatments for threshold
80% reduction of the average number of host-seeking females 60% reduction of the average number of host-seeking females 5 Treatments, Sprayed surface=0.45
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Contribution of our model of mosquito population dynamics
Knowing the influential parameters of the model orientates future
research efforts on the control of mosquitoes
The model is a tool to test control strategies
Valid results for a homogeneous environment
Not restricted in hosts, rest shelters, breeding sites
Environmental factors can be heterogeneous
Population can be spatially structured
In these conditions:
Spatial model is the next step
Discussion & perspectives
Rush wetland Rice field Reeds
Hosts An. hyrcanus
Breeding site
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Thank you for your attention …
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1.0 24 21 18 15 12 9 0 3 6 0.9 0.8 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.7 0.9 0.8 0.9 0.5 0.8 1.0 0.0 0.3 P e rc e n ta g e o f re d u c ti o n o f h o s t s e e k in g a d u lt s ( A h ) b sprayed surface n u m b e r o f t re a tm e n ts
Sprayed when mosquito
abundance exceeds a threshold value Scenario corresponding to sprayed surface= 0.45 , number of treatment=5 12 sprayed surface 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1.0 18 15 9 0 3 6 n u m b e r o f t re a tm 0.8 0.9 0.6 0.4 0.3 0.2 0.7 0.5
