Factors affecting the size of a mosquito population in a favourable environment

Transcription

1 EDEN th May Montpellier, FRANCE Factors affecting the size of a mosquito population in a favourable environment P. Cailly 1, A. Tran 2, T. Balenghien 3, C. Toty 4,5, P. Ezanno 1 1 INRA,Oniris, UMR1300 Bio-agression, Epidémiologie et Analyse de Risques, 2 CIRAD, UPR AGIRs Animal et Gestion Intégrée des Risques, 3 CIRAD, UMR Contrôle des maladies, 4 IRD, UR016 Caractérisation et Contrôle des Populations de Vecteurs, 5 Centre de Recherche et de Veille sur les maladies émergentes dans l'océan Indien

2 Why mosquitoes? 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 Culex pipiens West Nile virus vector faculty.vetmed.ucdavis.edu Aedes aegypti dengue vector Anopheles gambiae malaria vector active vectors necessary for the epidemiological cycle of these diseases 2

3 Why mosquitoes? 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 3

4 Objective Identifying by modelling the factors affecting the size of a mosquito population located in a favourable environment 4

5 Modelling approach Mechanistic model Adapted to Anopheles of Camargue region, France Driven by climate Lasting several years Diapause Migration during host or oviposition site-seeking Anopheles hyrcanus Emerging adults Host-seeking nulliparous Nulliparous engorged Parous searching oviposition sites IRD N.Rahola Nulliparous searching oviposition sites Host-seeking parous Parous engorged Emergence Oviposition Pupae Pupation Larvae Hatching Eggs France 5

6 Modelling approach Nulliparous into diapause during winter Development parameters & mortality rates depend on temperature Model output General output: Dynamic abundance in adults over time Number of mosquitoes Attack rate Ad ou Ah year n Adult peak Larva Pupa year n+1 Aggregated output: threshold of emerging adults Emergence date Peak date Time 6

7 Sensitivity analysis of the model Quantify the influence of input values on the outputs Inputs ex: parameters, functions or model structure Model Outputs ex: attack rate, adult peak 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 7

8 Results G. L Ambert C.Toty Model confrontation to independent field data Number of host-seeking females Relative abundance (%) 100% one trap 90% sum of the 8 traps of % model 70% 60% 50% 40% 30% 20% 10% 0% Feb-05 May-05 Aug-05 Nov-05 Feb-06 May-06 Aug-06 Nov-06 Time (month) Cross-correlation=0.8 An. hyrcanus a favourable area Our model predicts correctly a mean dynamics of mosquito populations 8

9 Results Sensitivity analysis No interaction Influent parameters: Diapause Migration during host or oviposition site-seeking Emerging adults Host-seeking nulliparous Nulliparous engorged Parous searching oviposition sites Nulliparous searching oviposition sites Host-seeking parous Parous engorged Emergence Oviposition Pupae Pupation Larvae Hatching Eggs 9

10 Scenario of control strategies 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 number of host-seeking females reference regular time date of treatments for regular time threshold date of treatments for threshold 5 Treatments, Sprayed surface=0.45 proportions of the zone sprayed = 0.45 Nb of treatment = 5 60% reduction of the average number of host-seeking females 80% reduction of the average number of host-seeking females time (days) 10

11 Discussion & perspectives 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 Reeds Rice field Breeding site An. hyrcanus Rush wetland Hosts An. hyrcanus 11

12 Thank you for your attention Questions? 12

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14 a number of treatments b number of treatments sprayed surface Sprayed at regular time intervals Sprayed when mosquito abundance exceeds a threshold value Scenario corresponding to sprayed surface= 0.45, number of treatment= Percentage of reduction of host seeking adults (Ah) sprayed surface