four cylindrical metal traps , each 
 containing a single chicken or rabbit ( average weight = 1.5 kg ) , were used ( 2 with 
 chickens and 2 with rabbits ) ( service 1993 ) . the traps were put in place at the same 
 time ( 12 total traps ) in three types of environments ( sites ) : urban ( resistencia ) 
 ( 2730 's 59w ) , semi - urban ( monte alto ) ( 2726'38 ' 's 5855'3''w ) and wild 
 ( kil - ometer 1,031 ) ( 2710 's 5858'w ) . the chickens and rabbits were immobilised and 
 enclosed in wire and metal mesh , respectively , to avoid mosquitoes being eaten or 
 killed by the bait animals . the cylindrical metal traps were separated by a distance of greater than 50 m 
 and set at a height of 1.5 m above the ground . the trapped mosquitoes were aspirated mechanically 
 using battery operated aspirators ( service 1993 ) . additionally , two operators at the 
 semi - urban site used battery aspirators to capture mosquitoes during the first 15 
 min of exposure within the following time intervals : from 09:00 am-11:00 am , 01:00 
 pm-03:00 pm , 05:00 pm-07:00 pm and 09:00 pm-10:00 pm . the specimens captured on both 
 the animal and human bait were stored in labelled glass bottles lined with porous 
 paper . processing of the specimens in the laboratory - the collected 
 specimens were asphyxiated with ethyl acetate , identified and counted . specimen 
 identification was based on examination of adults following the characteristics 
 outlined in lane ( 1953 ) , forattini ( 1962 , 1965a , b ) , ronderos and 
 bachmann ( 1962 ) , bram ( 1967 ) , darsie ( 1985 ) and consoli and loureno - de - oliveira ( 1994 ) . the specimens were 
 deposited into the entomological collections of the regional institute of medicine , 
 national university of the northeast ( chaco ) and the entomology research center , 
 building for biological research and technology , faculty of exact , physical and 
 natural sciences , national university of crdoba ( crdoba ) . 
 data analysis - a pearson 's chi - square test was used to compare the 
 differences in the relative abundance of species between mosquitoes collected on 
 chicken and rabbit bait and between mosquitoes collected on animal and human bait . contingency tables were also generated to test the differences between blood - fed and 
 unfed females collected on the same bait . the type of bait ( rows ) was used as a 
 classification variable ( chicken or rabbit ) and the response variable was blood - fed 
 vs. unfed females ( columns ) . the odds ratio ( or ) was estimated for each species to 
 quantify the association between the two variables ( bait and feeding ) . pearson 's 
 chi - square was also applied to compare the relative abundance of the mosquito 
 species captured in different habitats on animal bait and the activity intervals on 
 human bait . the obtained data were analysed with the statistical software program 
 infostat ( di rienzo et al . william 's mean was used as a measure of the 
 central tendency to calculate the monthly average values of the mosquito species on 
 different bait types . animal bait - a total of 14,044 specimens were captured on the 
 animal bait ( 60.45% on rabbits and 39.55% on chickens ) in the present study . a total 
 of 45 species ( 42 on rabbits and 36 on chickens ) belonging to eight genera were 
 identified . aedeomyia squamipennis ( lynch arribalzaga ) ( 0.16% ) , 
 anopheles albitarsis lynch arribalzaga ( 0.02% ) , 
 coquillettidia albicosta ( peryassu ) ( 0.02% ) and 
 mansonia flaveola coquillett ( 0.02% ) were caught only with 
 chicken bait . coquillettidia shannoni lane & antunes ( 0.01% ) , 
 culex saltanensis dyar ( 0.08% ) , mansonia 
 pseudotitillans theobald ( 0.01% ) , ochlerotatus 
 albifasciatus macquart ( 0.01% ) , ochlerotatus crinifer 
 theobald ( 0.01% ) , psorophora cingulata fabricius ( 0.05% ) , 
 psorophora confinnis arribalzaga ( 0.13% ) , psorophora 
 pallescens edwards ( 0.05% ) and psorophora varinervis 
 edwards ( 0.05% ) were captured only with rabbit bait . the genus 
 culex contributed 87.25% of the specimens captured on chickens 
 and 59.74% of those captured on rabbits . twenty - two species showed significant 
 differences between the females captured using chicken vs. rabbit bait ( p < only culex quinquefasciatus say and culex 
 chidesteri dyar were significantly more abundant in the chicken - baited 
 traps ( x 
  = 1,204.43 , p < 0.0001 ; x 
  = 13.55 , p blood - fed mosquitoes captured on animal bait - no analyses of the 
 blood contents of captured mosquitoes were performed . nevertheless , mosquitoes 
 containing red blood ( freshly engorged ) in their abdomen were considered to have fed 
 on the animal bait because once they were in the trap they could not escape . 
 following this criterion , 85.31% of the specimens collected using chicken bait were 
 found to be blood - fed , but only 66.95% of those captured on rabbit bait were 
 blood - fed . the proportion of fed females in relation to the total number of females 
 captured is shown in fig . 2 . eight species 
 exhibited significant differences between the number of blood - fed and unfed 
 specimens on both types of animal bait ( fig . 
 2 ) . for this analysis , we considered only species with a sample size of 
 more than 10 females found on each type of bait . culex bidens dyar 
 was captured mostly on rabbit bait , but presented an or  ( 1 = chicken , 2 = rabbit ) 
 equal to 2.43 [ p < 0.001 ; confidence interval ( ci ) = 95% ] , indicating that it was 
 more likely to feed on chicken bait . conversely , culex coronator 
 dyar & knab , culex lahillei bachmann and casal and 
 culex maxi dyar did not show statistically significant 
 differences in their rates of capture on the different types of animal bait , but 
 they were more likely to feed on chicken bait [ or ( 1/2 ) = 3.2 , 33 and 7.2 , 
 respectively , p < 0.0001 ] . quinquefasciatus were more likely to feed on chicken bait ( or ( 1/2 ) = 
 3.5 and 75.3 , respectively , p < 0.0001 ] . only psorophora ferox 
 ( von humbolt ) and wyeomyia diabolica lane and forattini showed a 
 greater likelihood of feeding on rabbit bait [ or ( 2/1 ) = 2.24 and 3.7 , respectively , 
 p < 0.05 ] . 2percentages of mosquitoes ( by species ) in traps that engorged on 
 chicken and rabbit bait in the province of chaco , argentina . data are 
 presented only when sample size was > 10 females on each bait . maxi were captured in higher proportions using chicken 
 bait , whereas at semi - urban and wild sites they were more often captured in 
 rabbit - baited traps ( x 
  = 128.79 and x 
  = 163.56 , respectively , p < 0.0001 ) ( fig . no significant differences or associations between the 
 environments and bait types were found for the other species . 3mosquitoes captured on chicken and rabbit bait at urban , semi - urban 
 and wild sites in province of chaco , argentina . data are presented only 
 when sample size was > 10 females at a site . 0.001 . 
 
 seasonal distribution analysis and host selection - no collections 
 were conducted in january . in november and february consequently , only data on the most frequent species 
 obtained in the collections conducted from march - december are shown ( fig . ferox 
 showed similar behaviours in all months in which collections were performed on both 
 bait species ( fig . diabolica 
 and wyeomyia muelhensi fed on both bait species equally from 
 june - october , but fed only on the rabbit bait from march - may ( fig . in contrast , ochlerotatus fulvus 
 ( wiedemann ) and ochlerotatus stigmaticus edwards fed only on the 
 rabbit bait between july - october and fed on both types of bait between march - may 
 ( fig . 4number of mosquitoes captured on chicken and rabbit bait between june 
 2001 - 2002 in province of chaco , argentina . ln : natural log ; n : number of mosquitoes ; 
 n / c : no capture was done . human bait - a total of 5,386 specimens were captured on human 
 bait , belonging to nine genera and 42 species ( supplementary data ) . a high 
 percentage ( 82% ) of species was captured on both human and animal bait . titillans ( 10.60% ) , anophe - les triannulatus neiva and 
 pinto ( 8.80% ) , ps . ferox ( 5.80% ) , psorophora 
 albigenu peryassu ( 5.02% ) , ochlerotatus hastatus 
 ( 2.50% ) , mansonia humeralis dyar & knab ( 2.43% ) , cx . 
 bidens ( 2.09% ) , oc . the remaining species were captured at rates 
 of less than 1% ( supplementary 
 data ) . anopheles galvaoi causey ( 0.07% ) , 
 anopheles neomaculipalpus curry ( 0.36% ) , haemagogus 
 spegazzini brethes ( 0.05% ) , psorophora albipes 
 theobald ( 0.04% ) , uranotaenia nataliae arribalzaga ( 0.02% ) and 
 wyeomyia melanocephala dyar & knab ( 0.13% ) were captured 
 only on human bait . albigenu showed a strong preference for human 
 bait ( p < 0.0001 ) ( supplementary data ) . timing of activity - the time interval showing the greatest 
 abundance of mosquitoes was 05:00 pm-07:00 pm ( x ) . 5 
 most ochlerotatus and psorophora species were 
 more abundant during the day and declined abruptly or became almost absent after 
 09:00 pm ( fig . 5 ) . most anopheles , 
 coquilletidia , culex and mansonia species were more 
 abundant during the evening and night intervals ( fig . 5 ) . albigenu were captured in all of the investigated time 
 intervals ( 09:00 am-10:00 pm ) , though there were intervals showing higher activity 
 of these species ( fig . 5mosquitoes species captured on human bait at different interval time 
 in semi - urban environment in province of chaco , argentina . seasonal variations on human bait - the greatest abundance and 
 variety of mosquito species captured on human bait were recorded in june , october , 
 november and april ( fig . species of ochlerotatus and psorophora were mainly 
 caught between october - december ( spring ) and between march - may ( autumn ) , with the 
 exception of oc . albifasciatus , which was more abundant in the 
 winter ( fig . 6 ) . half of the species were 
 only captured in one , two or three months during the study . albicosta , coquilletidia shanonni , coquilletidia clarki , culex eduardoi , culex 
 mollis , ps . albipes , ps . cingulata and ur . nataliae 
 were caught in only one month . 6number of mosquitoes captured on human bait between june 2001-may 
 2002 in province of chaco , argentina . ln : natural log ; n : number of 
 mosquitoes ; n / c : no capture was done . the results presented here are in agreement with studies that have 
 concluded that culex species show selection for birds , while the 
 ochlerotatus , psorophora and wyeomyia genera 
 show a preference for mammals ( tempelis et al . 
 1967 , mitchell et al . 1985 , 
 loureno - de - oli - veira & heyden 1986 , loureno - de - oliveira et al . these studies also mention the preference of 
 coquillettidia and mansonia species for 
 mammals . maxi were attracted by both 
 animal hosts , but they are more likely to feed on chicken bait . the chances of 
 feeding on one of the types of animal bait did not differ significantly for the 
 other species belonging to the culex , mansonia , ochlerotatus and 
 psorophora genera , which were attracted by both bait species . bait poor selectivity was also observed for the most culex 
 specimens from the melanoconium subgenus . we believe that these 
 species feed on both types of bait , in agreement with their designation as 
 euritrophic mosquitoes ( natal 1981 ) . ( 1987 ) found that 
 culex ( melanoconion ) species fed on both 
 birds and mammals . in studies using different types of bait , loureno - de - oliveira and heyden ( 1986 ) captured cx . bidens mainly on humans , but classified this species as showing a 
 tendency to bite birds . bidens , respectively ( edman & downe 1964 , loureno - de - oliveira 1984 , loureno - de - oliveira & heyden 1986 , forattini et al . quinquefasciatus is known for its high anthropophily ( charlwood 1979 ) and its ability to adapt to 
 the anthropic environment ( almirn & brewer 
 1996 , oria et al . 2002 ) . in the present study , as 
 in the reports of other authors , cx . 1960 
 , forattini 1965a , loureno - de - oliveira & 
 heyden 1986 , forattini et al . 2008 , garcia - rejon et al . 2010 ) and it is possible 
 that this species was not captured on human bait because sampling was only conducted 
 on humans in the semi - urban environment , where cx . in contrast with our findings , almirn and brewer ( 1995 ) captured a high percentage of cx . flaveola were only 
 captured on chickens , in agreement with the findings of other authors ( gabaldon et al . titillans and oc . 
 scapularis are the species that have presented the highest capture 
 frequencies on human bait in other studies ( hack et 
 al . 1978 , loureno - de - oli - veira 1984 , loureno - de - oliveira & da 
 silva 1985 , loureno - de - oliveira & heyden 
 1986 ) . ma . titillans can be attracted by different 
 types of bait , including poikilothermic animals , but it appears to show a preference 
 for large mammals , such as horses and cows ( loureno - de - oliveira & heyden 1986 ) . inside houses in rural areas 
 of brazil , this species is more abundant than cx . quinquefasciatus 
 and comparative studies have shown that it is attracted to humans ( loureno - de - oliveira & heyden 1986 ) . oc . scapularis has been identified as a species that is adapting to 
 the anthropic environment ( forattini et al . 
 1987 , 1995 ) . other notable hosts of this species are horses and cows 
 ( loureno - de - oliveira & heyden 1986 ) . ( 1985 ) identified the 
 blood of birds , marsupials , horses , felidae , canidae , bovidae , cervidae and 
 hominidae in oc . scapularis specimens , indicating the broad host 
 preference of this species . in this study , oc . scapularis was more 
 attracted to humans than to rabbits or chickens . our results regarding oc . albifasciatus showed 
 differences and similarities compared with other studies . in the present study , this 
 species showed almost exclusive selection for humans , in agreement with prosen et al . ( 1985 ) used horse , chicken and human bait and 
 obtained the highest percentage of specimens from horses and only a single specimen 
 from human bait in the province of santa f . in crdoba , almirn and brewer ( 1995 ) obtained high capture percentages of 
 oc . albifasciatus on chickens and rabbits and showed that this 
 species preferentially feeds on chickens . albifasciatus in different climatic 
 regions of argentina , but we can conclude that it utilises a variety of hosts . bidlingmayer ( 1985 ) demonstrated that each 
 environment has specific characteristics that make it unique when considering the 
 physiological needs of each mosquito species . triannulatus is considered to be essentially zoophilic , 
 although it may bite humans indoors ( loureno - de - oliveira & luz 1996 , brochero et al . albitarsis on birds and loureno - de - oliveira and heyden ( 1986 ) captured this species on 
 horses and cows in higher percentages than on humans . analyses of mosquitoes 
 collected in chaco , corrientes and santa f by mitchell et al . ( 1985 ) identified bovidae blood in an . many environmental factors may act in combination with the innate 
 preferences of a mosquito species to affect its final selection of a host . moreover , 
 the absence of a host or an increase in the mosquito population may favour those 
 mosquitoes with an innate preference for a variety of hosts or could induce 
 phenotypic plasticity to modify host selection patterns , without changing innate 
 preferences ( tempelis et al . 1967 , lefvre et al . 2009 ) . in the united states of 
 america ( usa ) , culex pipiens undergoes a shift in its host 
 preference from birds to humans at the end of summer . this change coincides with the 
 migration of its preferred host ( the american robin ) ( kilpatrick et al . quinquefasciatus feed mainly on rabbits in the summer and 
 on chickens during both the spring and summer . in the same study , oc . albifasciatus was more often captured on rabbits in the summer and on 
 chickens in the autumn and spring ; however , the authors did not offer any 
 explanation for these observations ( almirn & 
 brewer 1995 ) . in the present study , oc . stigmaticus were mostly caught on rabbit bait , but when 
 there was an explosion of both species in the autumn ( march - may ) , the percentages of 
 females on chickens increased considerably . in venezuela , berti et al . ferox showed strong selection for rabbit bait and , in agreement 
 with other studies , was also very abundant on human bait ( gomes et al . however , wy . 
 melanocephala was captured only on human bait and this species has been 
 observed biting humans in brazil ( forattini 1965b ) . ( 1987 ) observed three 
 specimens of uranotaenia lowii on birds , amphibians and humans . lowii to be the most abundant species captured in cdc light 
 traps that did not use any type of bait . in nueva pompeya ( chaco ) , 
 uranotaenia was reported to be the most abundant genus captured 
 with cdc light traps ( ramrez pg 2008 ) . in the present study , no specimens of this 
 species or culex ( microculex ) species were captured on the 
 presented hosts , despite the significant percentages of larvae that have been found 
 in nearby larval habitats ( stein et al . 1986 ) also found 
 recorded high percentages of mosquito larvae , but did not observe adults of the same 
 species on any type of bait ( which included humans , horses , cows , cats , sheep and 
 frogs ) ( 
 loureno - de - oliveira & heyden 1986 
 ) . they classified these species as haematophagous on poikilothermic 
 animals , such as amphibians and reptilians . our results do not allow us to confirm the existence of changes in host 
 selection patterns among different environments . only cx . maxi showed significant habitat - associated host selection , 
 as they were more attracted to chickens in the urban habitat , but preferred rabbits 
 in the semi - urban and wild habitats . with respect to temporal activity , our findings showed similarities to 
 studies conducted in argentina , brazil and venezuela ( hack et al . 1978 , loureno - de - oliveira et al . 1985 , mendez et al . 2001 ) . ochlerotatus , psorophora , 
 wyeomyia and haemagogus species are predominantly 
 diurnal , while anopheles , culex , mansonia and 
 coquillettidia species are crepuscular and nocturnal ( forattini 
 1965 a , b , hack et al . 1978 , loureno - de - oliveira et al . 1985 , brochero et al . 2006 ) . in colombia , some species recorded in the present study are involved in the 
 transmission of diseases to humans or have been found to be naturally infected with 
 different arboviruses ( gabaldon et al . albifasciatus is often found to be naturally infected with 
 the western equine encephalitis ( wee ) virus . this species presents a wide 
 distribution in argentina and shows a preference for mammals , particularly horses 
 and cattle . in addition , laboratory studies have found that it is a competent vector 
 for the wee virus ( avils et al . vertical transmission of the japanese 
 encephalitis virus has also been demonstrated in this species ( loureno - de - oliveira 
 & da silva 1985 , johansen et al . ( 1985 ) isolated three different 
 viruses { the par , wee and rio negro [ venezuelan equine encephalitis ( veev ) , subtype 
 vi ] viruses } from cx . ocossa mosquitoes captured in antequeras and 
 near the negro river in chaco . the epidemic and enzootic cycles of virus 
 transmission involving mosquitoes belonging to the melanoconion 
 subgenus also involve rodents and birds ( calisher 
 et al . ferox have 
 been found to be naturally infected with the veev virus , rocio virus and una virus , 
 respectively ( forattini et al . ferox after the first major outbreak recorded in birds , horses and 
 people ( cdc 2000 ) . albitarsis play a secondary role in malaria transmission in 
 south america when they are present at high densities ( curto et al . several authors have observed that the species found in the present study 
 show a wide host selection range . it is also noteworthy that a high percentage of 
 species were common to both the animal and human bait , indicating that these 
 mosquito species could transmit arboviruses to humans in this region . the identified 
 species also revealed certain patterns of host selection , different degrees of 
 anthropophilia or zoophilia and , within the latter , different degrees of feeding 
 preferences for birds or mammals . an increased versatility of a species ' feeding 
 pattern increases its potential to serve as a vector to spread a zoonotic pathogen 
 ( tempelis et al . similarly , as 
 several species were detected throughout the year and throughout the day , these 
 behavioural patterns contribute to their contacting different hosts and affect a 
 mosquito 's vector status . knowledge of the issues outlined here could be useful for 
 developing control strategies for diseases transmitted by mosquitoes in this 
 region .
studies were conducted to determine the selection of humans , chickens 
 and rabbits by culicidae in three different environments in the province of 
 chaco , argentina . 
 mosquitoes were collected fortnightly using cylindrical metal 
 traps containing animal bait ( chickens and rabbits ) . 
 the mosquitoes were 
 collected between june 2001-may 2002 . during the same period and with the same 
 frequency , 
 mosquitoes biting the human operators of the traps were collected 
 during the first 15 min of exposure within different time intervals : from 09:00 
 am-11:00 am , 01:00 pm-03:00 pm , 05:00 pm-07:00 pm and 09:00 pm-10:00 pm . a total 
 of 19,430 mosquitoes of 49 species belonging to 10 genera were collected . 
 culex species mainly selected chicken bait and 
 wyeomyia species selected rabbit bait . 
 ochlerotatus and psorophora species were 
 more abundant in rabbit - baited traps . 
 anopheles triannulatus , 
 coquillettidia nigricans , ochlerotatus 
 scapularis , mansonia titillans and 
 psorophora albigenu showed a strong attraction for human 
 bait . 
 the anopheles , coquillettidia , 
 culex and mansonia species were more 
 active between 05:00 pm-09:00 pm , while ochlerotatus , 
 psorophora , haemagogus and 
 wyeomyia were most active from 09:00 am-07:00 pm . 
 this 
 study provides additional information about the biology and ecology of arbovirus 
 vectors in chaco .