anthropic changes to the natural environment invariably impact biodiversity , and new habitats often become available after landscape alterations , particularly among culicids . according to forattini , newly established ecotopes promote the proliferation of mosquito species that become nuisances or disease vectors for humans . female mosquitoes of the family culicidae oviposit in several types and dimensions of reservoir water , where they cooccur with other species and are associated with plant matter . during immature stages , mosquitoes of the genera mansonia blanchard and coquillettidia dyar affix themselves to the roots of aquatic macrophytes , from which they derive oxygen accumulated in the aerenchyma of the plant floating organs . the eleven mansonia species listed for brazil [ 5 , 6 ] depend on macrophytes during larval and pupal stages . as with most culicids , mosquitoes from the genus mansonia are a nuisance to humans and animals in situations of high density and can become a public health concern due to their anthropophilic behavior . our group hypothesized that the damming of the paran river and construction of the engenheiro srgio motta hydroelectric plant , more commonly known as the porto primavera hydroelectric plant ( pphp ) , produced a favorable environment for mosquitoes of the tribe mansoniini owing to the propagation of macrophytes . the present study aimed to monitor the richness , diversity , and dominance of the ma . humeralis dyar and knab population in different phases of reservoir flooding and assess its possible consequences regarding human and animal contact . the present research was undertaken on the banks of the pphp reservoir , formed by the damming of the paran river , 28  km upstream from its confluence with the paranapanema river . although the reservoir impacts several municipalities in mato grosso do sul [ 8 , 9 ] and so paulo states , the study area was located in the presidente epitcio municipality in so paulo state , part of a larger project developed in this area . prior to the establishment of the pphp , the study region originally comprised a complex of flooded areas known as the  lagoa so paulo ecological reserve  , previously formed by the so paulo , bonita , comprida , tremendal , and jota lakes and consisting of a mosaic of rearing environments during rainy periods , with accumulated water . after construction of the dam , both permanently submerged and seasonally flooded areas were inundated by the reservoir . the original level of the paran river was 247  m above sea level . flooding was carried out in two stages : the initial phase in january 1999 raised the water level to 253  m , and in march 2001 , the second flooding stage elevated waters to the current level of 257  m. the area designated for mosquito capture , denominated site jb ( 520025w/213845s ) , is composed of flooded lowland , with the presence of floating macrophytes ( eichhornia crassipes ( mart . ) solms , pistia stratiotes linnaeus , salvinia sp . sguier , ricciocarpus natans ( l. ) corda , hidrocotyle umbellata linnaeus , cladium sp . linnaeus , egeria najas planch ) , in addition to rural plateau areas containing seven human settlements , with six aggregations of homes ( bairro campinal and rural villages of reassentamento lagoa so paulo ) . residents of these villages and rural landowners come into contact with the reservoir through leisure and/or fishing ( figure 1 ) . climate in the region is classified as aw - tropical , with a dry winter according to the kppen system . culicids were collected during each of the three flood stages : 247  m ( 07/1997 to 09/1998 ) , 253  m ( 07/1999 to 09/2000 ) , and 257  m ( 07/2001 to 09/2002 ) . adult mosquito collections were undertaken one day per month , using four capture methods : mechanical aspiration ( ma ) in one 15  min sampling effort per capture , in the morning period in riparian areas ; and shannon trap ( st ) , for 20  min of unit time in the evening at twilight , with intervals as follows : first and second precrepuscular , crepuscular , and first postcrepuscular . there were two individual collectors . in order to attract a greater number of mosquitoes for anthropophilic behavior , two collection methods were performed using humans : the human attractive technique ( hat 24  h ) , involving collections over a period of 24  h , with hourly separation of the material gathered by two individual collectors ; and the human attractive technique ( hatet ) , consisting of collections in the evening at twilight for 20  min of unit time , with increments divided into first and second precrepuscular ; crepuscular ; and first , second , third , and fourth postcrepuscular . the last two capture methods were not used during the 257  m stage because of operational and infrastructural difficulties . mosquitoes were identified in the entomology laboratory at the public health faculty of the university of so paulo . humeralis were pooled into the category  other species  since our aim was to specifically evaluate the population of this taxon . other species  at stages 247  m , 253  m , and 257  m. abbreviations used for species names were in accordance with reinert   and identifications were determined following forattini   and lane . monthly precipitation ( mm ) and air temperature ( c ) data were obtained from the so paulo energy company ( cesp ) and the integrated center of agro - meteorological information , of the campinas agronomy institute ( ciiagro - iac ) . statistical analyses were conducted on the mean monthly values of richness , diversity ( margalef ) , and dominance ( berger - parker ) ( exclusively for ma . humeralis ) . means between the periods before and after flooding were tested in order to evaluate frequency differences between ma . comparative analysis was performed using mann - whitney , anova , and post hoc ( tukey ) tests for indices of richness , diversity , and dominance and comparison of means , with spss computer software , version 10 . a total of 30,723 culicids were collected during the study , 22,181 were captured at flood stage 247  m ( preflooding ) , and of these , ma . humeralis accounted for 3.1% ( 695 ) . at the 253  m flooding stage ( first flooding ) , 7,982 mosquitoes were captured , 4,754 ( 59.6% ) of which were ma . a total of 560 specimens were collected during the second flooding stage ( 257  m ) , ma . humeralis corresponding to 53.8% ( 301 ) ( table 1 ) .   during preflooding , mean monthly richness and diversity values varied among the capture techniques , as did the dominance of ma . humeralis , the mean richness and diversity values of other culicids decreased after the first flooding stage ( 247  m253  m levels ) ( ma : richness p = 0.08 , diversity p = 0.04 , dominance absent ; st : richness p = 0.05 , diversity p = 0.06 , dominance p = 0.002 ; hat 24  h and hatet : richness and diversity : p < 0.001 , dominance p = 0.001 ) . humeralis was not collected using the ma technique during stage 247  m. following the second flooding stage ( 253  m257  m levels ) , these lower richness and diversity values were maintained ( ma : richness and diversity p = 0.01 , dominance p = 0.3 ; st : richness p = 0.01 , diversity p = 0.3 , dominance p = 0.04 ) . humeralis dominance remained high in ma captures , samples obtained with st were substantially reduced ( table 1 ) . monthly richness and diversity values with the ma capture method were significantly different in comparisons between flood stages , except for richness between flood stage 247  m and 253  m. means for st captures were also reduced between flood stages . richness and diversity values were statistically different in all comparisons , except for diversity between stages 247  m and 253  m , and 253  m and 257  m. captures using hat 24  h and hatet yielded significant declines in richness and diversity . although not statistically significant , dominance of this species was confirmed when the reservoir rose from 253  m to 257  m. dominance values for ma . humeralis between stages 247  m and 257  m were not significantly different with the st method ( p = 0.5 ) . when using hat 24  h and hatet , the mean dominance of ma . humeralis at stage 253  m increased significantly from 247  m.   monthly frequencies of other culicid species were correlated with the number of ma . humeralis in all capture methods during the three flooding stages . in relation to the ma technique , humeralis frequencies ( p = 0.3 ) during stages 253  m and 257  m and for  other species ( p = 0.2 ) during stages 247  m and 253  m.   no statistical difference was observed between mean temperature prior to flooding ( 23.3c ) and that following flooding stages 1 and 2 ( 24.7c ) when compared with ma . the same occurred for mean precipitation , which was higher ( 95.2  mm ) during the preflooding stage than subsequent periods ( 62.6 and 50.6  mm ) , but not statistically different . mansonia humeralis showed greater population density during winter and spring ( p > 0.1 ) . mean richness and diversity values changed based on evaluation at each of the three reservoir levels . immediately following initial flooding ( flood stage 253  m ) , a 64% reduction occurred in the number of adult culicids , suggesting that many rearing sites were destroyed and immature forms did not survive the rising water .   increased ma . humeralis abundance ( from 3.1% at 247  m to 59.6% at 253  m and 53.8% at 257  m ) suggests that this species benefitted from the flooding in relation to other culicids . this supports previous results following the flooding of the tucuru reservoir in amazonia , where high nuisance levels were recorded in humans and animals due to larger mansonia populations ( 97.1% ) . mansonia species were absent in forest fragments between the municipalities of presidente venceslau and caiu , near the study site sampled and in a similar ecological scenario . this contradicts our results in the preflooding stage , when an abundance value of 3.1% was recorded . the low frequency may be associated with the scarcity of macrophytes in the preflood water pools on the paran river floodplain .   with damming and the expansion of macrophyte assemblages , distribution of ma . differences in culicidae richness and diversity were substantial for flood stages 253  m and 257  m. diversity , evaluated by st , did not exhibit the same effect , possibly because this method was applied during a period of low mosquito activity . nevertheless , evening crepuscular captures with st and hatet produced similar results in relation to total mosquitoes captured , although they were used at different times . when analyzed in regard to richness and diversity prior to flooding , the capture method suggested variability between richness and diversity , and between diversity and dominance . the low capture rate of the ma method may be due to the random selection of shelters visited , while the higher rates observed with human presence are likely related to the anthropophilic behavior of ma . humeralis .   during immature collections along the so domingos river ( northern paran state ) , lopes and lozovei   concluded that culicids use forests adjacent to lakes as refuges . thus , increased nuisance levels are expected during periods of higher ma . humeralis activity . more recently , cruz et al .   found a predominance of mansonia near the madeira river hydroelectric plant in amazonia , emphasizing the importance of monitoring activities in areas with new reservoirs . a strong positive correlation was recorded in the present study between artificial flooding and population levels of ma . in addition to being an indicator of macrophytes , this species can become a nuisance in areas surrounding a reservoir owing to its highly anthropophilic behavior , as was the case near the tucuru revervoir . humeralis captured by ma at 253  m and 257  m. findings with ma may be explained by the fact that the species studied does not have continuous distribution , exhibited by few individuals during the 2nd and 3rd stages and absent in stage 1 . overall , diversity and richness of mosquito fauna were substantially affected by flooding . however , there was a notable increase in the ma . this species was present over the entire monitoring period , with peaks in winter and spring , a trend not observed for other culicids . surface waters drain into the lake during flooding and enrich the reservoir with nutrients , thereby stimulating the proliferation of macrophytes   and favoring mansonia . in addition , drainage channels may transport aquatic vegetation and disperse immature mosquitoes into other areas , making control measure a complex undertaking . other investigations have emphasized the vulnerability of areas near the dam in providing favorable conditions for the spread of arboviruses , a concern reinforced by our results ( wanderley et al . ) . humeralis was the primary focus of the present study due to the sharp increase in population dominance following flooding , which may generate a possible nuisance to the human population . however , a substantial amount of culicidae relevant to public health was recorded , also reported in other research , including aedes scapularis ( rondani ) and anopheles albitaris s.l . the authors suggest that during the operational phase of this hydroelectric plant , local authorities should monitor culicid activity using sustainable entomological surveillance .
the closure of two phases of the dam at the porto primavera hydroelectric plant on the paran river flooded a flawed system located in the municipality of presidente epitcio , so paulo state , favoring the proliferation of aquatic weeds . 
 this study aimed to observe the population of mansonia humeralis in the area , monitoring the richness , diversity , and dominance of this species both before and during different phases of reservoir flooding as well as evaluate its possible consequences concerning human and animal contact . 
 adult mosquitoes were collected monthly in the following periods : at the original level , after the first flood , and after the maximum level had been reached between 1997 and 2002 . 
 collection methods used were an aspirator , a shannon trap , and the human attractive technique . 
 a total of 30,723 mosquitoes were collected , ma . 
 humeralis accounting for 3.1% in the preflood phase , 59.6% in the intermediate , and 53.8% at maximum level . 
 this species is relevant to public health , since the prospect of continued contact between ma . 
 humeralis and the human population enhances the dam 's importance in the production of nuisance mosquitoes , possibly facilitating the transmission of arboviruses . 
 local authorities should continue to monitor culicid activity through sustainable entomological surveillance .