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Habitat  Suitability  for  Mosquito  Larvae  and  Its  Implica;ons  for  the  Hamilton  Region   Heather  Bonn,  Rebecca  Englert,  Kira  Moor   McMaster  University,  Advanced  Raster  GIS  

Introduc;on  

Methods  

Sensi;vity  Analysis  

Mosquitoes  are  prominent  disease  vectors  and  are  responsible  for  the   transmission  of  many  diseases  harming     human  popula;ons  worldwide     (Figure  1)1.  Of  par;cular  concern  to     North  America  is  the  West  Nile  Virus,     which  first  emerged  in  Canada  in  2001     and  con;nues  to  appear  annually  in  the     summer  and  fall  months2.  Specific     condi;ons  are  required  for  mosquito   Figure  1:  A  mosquito  blood  feeding3   breeding  and  larvae  survival  making  them  essen;al  to  sustaining   mosquito  popula;ons.  Mapping  mosquito  larvae  habitat  suitability  can   be  used  to  determine  the  vector  capacity  of  an  area  and  the  impact  this   has  on  nearby  human  popula;ons.  

ESRI  ArcMap  10.2  GIS  soaware  was  used  to  conduct  a  mul;-­‐criteria  analysis   to  generate  a  habitat  suitability  model  for  mosquito  larvae.  The  values  of   each  criterion  were  standardized  using  a  linear  scale  transforma;on  score   range  procedure.  Each  criterion  was  weighted  to  reflect  rela;ve  importance   by  piece-­‐wise  comparison  and  combined  using  a  weighted  linear  combina;on   to  produce  the  resul;ng  map  (Figure  3).  

Ra;o  es;ma;on  and  ranked  reciprocal  methods  were  used  to  evaluate   the  sensi;vity  of  the  model  to  different  weigh;ng  schemes.  Both   methods  produced  a  slight  decrease  in  habitat  suitability  in  specific   loca;ons,  which  was  more  significant  in  the  ra;o  es;ma;on  method.   However,  this  varia;on  between  the  habitat  suitability  depicted  by   each  method  (Figures  4  &  5)  was  minimal.  This  represents  the  accuracy   of  the  model.            

Results  &  Implica;ons  

Study  Area     .  

Figure  2:  West  Nile  Virus  incidence  in  Canada  for  2013  as  of  November7.  

Decision  Criteria   Criterion    

Desired  Condi,on  

Water  Body  Proximity   The  closer  the  beLer   Wind  Speed  

The  lower  the  beLer  

Precipita;on  

The  greater  the  beLer  

Slope  

The  flaLer  the  beLer  

Temperature  

The  higher  the  beLer  

Eleva;on  

The  lower  the  beLer  

The  area  under   inves;ga;on  in  this   study  is  the  region   of  Hamilton  (Figure   2).  This  area  was   selected  because   of  its  large   popula;on  and   close  proximity  to   several  water   bodies  with  the   poten;al  to  serve   as  breeding   grounds.  

Figure  4:  Sensi-vity  analysis  using  rank  reciprocal.   Figure  5:  Sensi-vity  analysis  using  ra-o  es-ma-on.  

Model  Improvements   Figure  3:  Habitat  suitability  for  mosquito  larvae  in  the  Hamilton  region  using  pairwise  comparison.  

Habitat   suitability   was   greatest   around   Hamilton   Harbour   (Figure   3).   These   areas  are  at  the  highest  risk  for  infec;on  of  mosquito  transmiLed  diseases  and   have   the   greatest   vector   capacity   in   the   Hamilton   region.   It   is   recommended   that  local  mosquito  control  strategies,  such  as  spraying  and  sampling,  should   be   primarily   focused   on   these   areas.   This   will   allow   for   more   effec;ve   treatment   and   more   appropriate   resource   alloca;on   in   an   effort   to   prevent   disease   dissemina;on.   The   final   model   could   be   used   to   not   only   help   prevent   the  spread  of  West  Nile  Virus,  but  to  aid  in  managing  future  outbreaks  of  other   mosquito   transmiLed   diseases.   As   mosquitoes   also   prey   on   a   host   of   other   animals   and   birds,   preventa;ve   measures   may   also   serve   to   protect   na;ve   wildlife  as  well  as  human  health.     Ra,onal  

Method  

Shallow  standing  water  is  required  for   Euclidean   breeding4.   Distance   Interferes  with  mosquito  movement  and   Spline   creates  disturbances  in  water  bodies5.   Interpola;on   Creates  damp  condi;ons  for  larvae  and  excess   Spline   water  forms  puddles5.     Interpola;on   Low  slopes  are  favourable  for  water  reten;on   DEM   and  pooling6.   Larvae  prefer  hot  and  humid  climates5.   Spline   Interpola;on   Greater  chance  of  water  pooling6.     DEM  

Rank  

Pairwise  Comparison   Weight  

1  

0.404  

2  

0.279  

3  

0.141  

4  

0.098  

5  

0.051  

6  

0.027  

There  are  several  adjustments  that  could  improve  the  overall  accuracy   of  this  model:   1.  More   factors   such   as   vegeta;on,   soil   types,   preda;on,   and   rate   of   water   flow   could   be   taken   into   account   to   enhance   the   model’s   predic;ve  ability.   2.  Decision   criteria   could   be   specific   to   the   species   of   mosquitoes   known  to  carry  West  Nile  Virus  instead  of  general  condi;ons  for  all   mosquitoes.   3.  Finer  resolu;on  and  more  recent  data  would  provide  more  realis;c   results.   4.  The   study   could   be   expanded   to   encompass   a   greater   area   so   comparisons   could   be   made   over   the   province.   Addi;onally,   this   offers  the  poten;al  for  correla;ng  data  with  infec;on  incidence.    

Data  Sources  &  References    

Data  Sources:     •  •  •  •  • 

DMTI  Spa;al  Inc.  –  Digital  Eleva;on  Model   Environment  Canada  –  Canadian  Wind  Energy  Atlas   Na;onal  Hydro  Network  –  Hamilton’s  Hydro  Network  2012   Government  Canada  –  Climate   Sta;s;cs  Canada  –  Hamilton  Region  Boundary  

References:    

1.  Fradin,  M.  S.  (1998).  Mosquitoes  and  Mosquito  Repellents:  A  Clinician’s  Guide.  Annals  of  Interna-onal  Medicine,  128(11),  931  –  940.   2.  Canadian  Endangered  Species  Conserva;on  Council  (CESCC).  (2010).  Wild  Species  2010.  Retrieved  October  9,  2013,  from  hLp:// publica;ons.gc.ca/collec;ons/collec;on_2011/ec/CW70-­‐7-­‐2010-­‐eng.pdf.   3.  Gathany,  J.  (2003).  Culix  Nil,  [Photograph].  Retrieved  November  22,  2013  from:  hLp://commons.wikimedia.org/wiki/File:CulexNil.jpg   4.  Vanwambeke  et  al.,  (2007).  Landscape  and  land  cover  factors  influence  the  presence  of  Aedes  and  Anopheles  larvae,  Journal  of  Medical   Entomology,  44(1),  133-­‐144.     5.  Dohm,  D.  J.,  O’Guinn,  M.  L.,  &  Turell,  M.  J.  (2002).  Effect  of  Environmental  Temperature  on  the  Ability  of  Culex  pipiens  (Diptera:  Culicidae)  to   Transmit  West  Nile  Virus.  Journal  of  Medical  Entomology,  39(1),  221-­‐225.     6.  Cooke,  W.  H.,  Grala,  K.,  &  Wallis,  R.  C.  (2006).  Avian  GIS  models  signal  human  risk  for  West  Nile  virus  in  Mississippi.Interna-onal  Journal  of   Health  Geographics,  5(36),  na.     7.  Public  Health  Agency  of  Canada.  (2013).West  Nile  Virus  MONITOR  Surveillance  Maps,  [image].  Retrieved  November  23,  2013  from:  hLp:// www.phac-­‐aspc.gc.ca/wnv-­‐vwn/map-­‐carte/index-­‐eng.php  


Mosquito larvae