Synanthropy of mosquitoes and sand flies near the Aimorés hydroelectric power plant, Brazil
The environmental changes resulting from the construction of hydroelectric dams may affect the fauna of insect vectors and consequently the epidemiology of the diseases they transmit. This work examined the mosquito and sand fly fauna in the area of the Aimorés hydroelectric power plant, analyzing the seasonal distribution and the degree of species synanthropy in different ecotopes. Between November, 2008 and September, 2009, entomological captures were performed with the help of HP light traps in the rural, urban, and forest areas of Aimorés, Ituêta, Resplendor, and Baixo Guandu counties. The fauna proved to be quite diversified. Twenty-two species of mosquitoes and 11 species of sand flies were found. Culex quinquefasciatus was predominant among mosquitoes (76.7%), while Lutzomyia intermedia prevailed among sand flies (34.5%). Some of the captured species have medical interest. Supported by the high degree of synanthropy, those species reinforce the need for epidemiological surveillance.
Hydroelectric power plant installations have played an important role in electric power generation and consequently in Brazilian socioeconomic development. However, environmental changes caused by the building of dams, together with the increase in numbers of workers, usually affect outbreaks of diseases such as malaria, dengue, yellow fever, filariasis, and leishmaniasis (Kochtcheeva and Singh 1999). The installation of hydroelectric dams may affect the fauna of vector insects and, consequently, the epidemiology of the diseases they transmit, by interfering with their natural food sources, in their population density, and in the composition and dispersion of potential vector species (Ferreira et al. 2011, Figueiredo 2007, Guimarães et al. 1997, Paula and Gomes 2007, Rezende et al. 2009).
The vectors, including mosquitoes and sand flies, are sensitive to environmental changes. Thus, the knowledge of the adaptive responses induced by the damming of rivers and their impact on the composition and abundance in biological communities is required. The identification of vector insects and their relationship to the diseases they transmit are fundamental in determining mitigation measures to support the well-being and health of the local population.
This work aimed to identify the mosquito and sand fly fauna in the area of the Aimorés hydroelectric power plant, identifying the vector insects and analyzing the level of synanthropy of species captured in different ecotopes.
MATERIALS AND METHODS
The Aimorés hydroelectric power plant, installed by the Aimorés Hydroelectric Consortium, is located in the mesoregion of Rio Doce. Its main reservoir is 30.3 km2, 16.6 km2 of which corresponds to the flooded area occupying mainly the area of the Aimorés.
The predominant climate in the region of the dam is tropical with hot summer rains (average temperature around 24.6° C with average annual rainfall of 1,162 mm). The relief has altitudes ranging from 76 m to 1,118 m, with typical vegetation of the Atlantic Forest. With the installation of the hydroelectric plant, the Aimorés Hydroelectric Consortium reforested the area by planting native tree vegetation along the reservoir.
From November, 2008 to September, 2009, entomological captures were performed twice a month, in 22 sampling sites distributed in four municipalities located in the area of the project. The capturing sites were categorized in three ecotopes: a) urban area (ten sites), b) rural area (ten sites), and c) forest (two sites). Two HP light traps (Pugedo et al. 2005) were exposed from 16:00 to 08:00 for three consecutive nights in every month of capture. The collected insects were transported alive and then put into a –4° C freezer. After 50 min, a screening of the insects was carried out. Mosquitoes were placed in plastic pots containing fungicide and toilet paper and sand flies were placed in hemolysis tubes containing 70% alcohol.
Preparation and identification of specimens
The mosquitoes were assembled on entomological pins and cardstock triangle. The identification of specimens was performed using the classification key of Consoli and Oliveira (1994). The sand flies were prepared and assembled on slides in Berlese fluid, according to the technique of Langeron (1949). Subsequently, the identification of samples was performed using a compound microscope, according to the classification proposed by Young and Duncan (1994).
Analysis of the results
The collecting average per species was used in each ecotope (urban, rural, and forest) according to the variation in the number of points. The synanthropy index (SI) proposed by Nuorteva (1963) was calculated, according to the following formula:
Results and Discussion
From November, 2008 to September, 2009, a total of 3,099 specimens, belonging to ten genera and 22 species was captured. The species are listed in Table 1. Culex quinquefasciatus predominated, with 76.7% of the mosquito fauna captured. Mosquitoes developed in small collections of fresh water with traces of organic pollution, as a sign of human environments (Gomes and Forattini et al. 1990). They disturbed the sleep of residents, being very common inside homes and peridomicile areas (Natal et al. 1991). There are some concerns about both Culex quinquefasciatus and Aedes scapularis found in urban and rural areas of the studied cities, as they are considered vectors of lymphatic filariasis in some Brazilian states (Brasil 1997, Rachou et al. 1954), although there are no recorded cases of the disease in this region.
Table 1. Mosquitoes captured in HP light traps according to species in the area of the Aimorés hydroelectric power plant, from November, 2008 to September, 2009.
| Aedeomyia squamipennis ||0||12||3||2||5||49||71||2.3|
| Aedes scapularis ||0||4||0||11||0||7||22||0.7|
| Ae. albopictus ||0||16||2||0||0||0||18||0.6|
| Ae. fulvithorax ||0||3||0||0||0||0||3||<0.1|
| Aedes sp.||2||3||0||0||0||0||5||0.1|
| Anopheles albitarsis ||0||11||12||100||11||28||162||5.3|
| An. benarrochi ||0||0||1||7||0||0||8||0.2|
| An. braziliensis ||0||0||0||0||2||2||4||0.1|
| An. deaneorum ||0||4||0||0||1||0||5||0.1|
| An. darlingi ||5||0||0||0||0||0||5||0.1|
| An. evansae ||3||2||34||1||5||17||62||2.0|
| An. oswaldoi ||1||3||1||3||7||10||25||0.8|
| An. rangeli ||0||0||0||1||2||0||3||<0.1|
| An. triannulatus ||0||0||0||4||1||14||19||0.6|
| Anopheles sp.||23||0||0||0||0||0||23||0.7|
| Culex nigripalpus ||0||1||90||3||0||4||98||3.2|
| Cx. quinquefasciatus ||341||538||407||373||257||460||2,376||76.7|
| Culex sp.||9||0||0||0||0||0||9||0.3|
| Coquillettidia juxtamansonia ||0||15||0||2||0||1||18||0.6|
| Coquillettidia sp.||1||0||0||0||0||0||1||<0.1|
| Limatus durhami ||0||15||9||0||0||0||24||0.8|
| Limatus sp.||1||0||0||0||0||0||1||<0.1|
| Mansonia titillans ||13||9||23||9||2||36||92||3.0|
| M. wilsoni ||0||0||0||2||0||0||2||<0.1|
| Mansonia sp.||22||0||0||0||0||0||22||0.7|
| Phoniomyia sp.||0||11||0||0||0||0||11||0.3|
| Psorophora sp.||1||0||0||0||0||0||1||<0.1|
| Wyeomyia sp.||0||0||3||0||2||4||9||0.3|
The finding of Aedes albopictus is also relevant due to its potential in transmitting sylvatic yellow fever and dengue in the urban area, although unproven in Brazil (Gomes et al 2008, Degallier et al. 2003). In this case, the need for rigorous surveillance for cases of dengue in the urban area and large vaccination coverage against yellow fever in both urban and rural residents are emphasized. It was also observed that Aedes aegypti (Linnaeus, 1762), vector of dengue in urban areas (Gubler 1998), was not sampled in this study. The methodology used with the employment of light traps at night and not an active search for larvae or the utilization of more suitable traps for this species (Maciel-de-Freitas et al. 2006, Resende et al. 2010) may be an explanation for it. Thus, we strongly believe that dengue outbreaks that occurred in these places were due to the presence of Ae. aegypti in residences (Secretaria de Vigilância em Saúde 2008).
The presence of six species of the genus Anopheles deserves special attention. Anopheles darlingi, the main vector of Plasmodium sp. in Brazil (Rebêlo et al. 1997), was recorded in this study but in lower density. The other ones; An. albitarsis, An. oswaldoi, An. rangeli, An. triannulatus, and An. evansae have demonstrated the potential to transmit malaria because they have been found to be naturally infected with parasites in various regions (Póvoa et al. 2001). Therefore, it is necessary to be alert to the possibility of malaria outbreaks should a source of gametocytes be present in the studied area.
Mansonia titillans was a frequent species in our work. It is considered exophilic, but it was reported in the urban area probably due to the proximity of the breeding site to the place of capture. It was found to be carrying the agent of Venezuelan encephalitis and febrile diseases, also being able to transmit Dermatobia hominis eggs (Forattini 1965). Another captured species was Ae. squamipennis (2.3%). It is found only in an environment containing stagnant water with large amounts of aquatic vegetation. This mosquito could be adapted to anthropogenic environments but without characteristics of domiciliation due to the dietary requirements and breeding site conditions. It was captured in all three ecotypes, but so far the relationship between this species and the transmission of diseases that affect humans is unknown.
A total of 232 sand flies, belonging to two genera and 11 species, was captured (Table 2). The predominant species was L. intermedia with 34.5% of all sand flies collected (Table 2). Together with L. whitmani, L. intermedia is considered a vector of cutaneous leishmaniasis in southeastern Brazil (Peterson and Shaw 2003), while L. longipalpis is considered the main vector of visceral leishmaniasis in Brazil (Dedet 1993, Grimaldi-Jr et al. 1989). The existence of human cases of leishmaniasis in the municipalities of the influential area of the Aimorés hydroelectric power plant suggests the participation of these species in the transmission of Leishmania sp. in the region.
Table 2. Phlebotomine sand flies captured in HP light traps according to species in the area of the Aimorés hydroelectric power plant, from November, 2008 to September, 2009.
| Brumptomyia avellari ||0||6||1||5||2||2||16||6.9|
| Lutzomyia brasiliensis ||0||2||0||0||0||0||2||0.8|
| L. capixaba ||0||0||0||0||0||4||4||1.8|
| L. cortelezzii ||4||0||0||2||1||2||9||3.9|
| L. intermedia ||2||6||0||7||43||22||80||34.5|
| L. ischyracantha ||4||50||0||0||1||11||66||28.5|
| L. lenti ||1||0||0||0||0||0||1||0.4|
| L. longipalpis ||14||11||1||0||1||18||45||19.4|
| L. quinquefer ||0||0||0||2||0||0||2||0.8|
| L. termitophila ||0||2||0||0||0||0||2||0.8|
| L. whitmani ||2||0||0||0||0||2||4||1.8|
| Lutzomyia sp.||0||0||0||1||0||0||1||0.4|
Tables 3 and 4 show the synanthropy index by species of mosquitoes and sand flies. We noticed that some species of medical interest showed a high degree of synanthropy, with values close to +100. From the epidemiological point of view, this capacity of adaptation to the new conditions modified by humans reinforces the need for entomological surveillance in the studied area.
Table 3. Synanthropy index (SI) by species of mosquitoes captured in the area of the Aimorés hydroelectric power plant, from November, 2008 to September, 2009.
| Aedeomyia squamipennis ||25.3||62||12.7||7.9||43.6|
| Aedes scapularis ||27.3||72.7||0||2.2||66.3|
| Ae. albopictus ||88.9||11.1||0||1.8||94.4|
| Ae. fulvithorax ||66.7||33.3||0||0.3||83.3|
| Aedes sp.||22.2||22.2||55.6||0.9||–22.3|
| Anopheles albitarsis ||84||16||0||16.2||92|
| An. benarrochi ||87.5||12.5||0||0.8||93.7|
| An. braziliensis ||100||0||0||0.4||100|
| An. deaneorum ||40||60||0||0.5||70|
| An. darlingi ||60||40||0||0.5||80|
| An. evansae ||37||63||0||6.2||68.5|
| An. oswaldoi ||55.1||27.6||17.3||2.9||51.6|
| An. rangeli ||66.7||33.3||0||0.3||83.3|
| An. triannulatus ||57.9||42.1||0||1.9||78.9|
| Anopheles sp.||100||0||0||2.3||100|
| Culex nigripalpus ||1.9||93.1||5||10.2||43.4|
| Cx. quinquefasciatus ||47.5||45.7||6.8||251.2||63.5|
| Culex sp.||33.3||66.7||0||0.9||66.6|
| Coquillettidia juxtamansonia ||16.7||83.3||0||1.8||58.3|
| Coquillettidia sp.||0||0||100||0.5||–100|
| Limatus durhami ||6.2||62.5||31.3||3.2||6.1|
| Limatus sp.||100||0||0||1||100|
| Mansonia titillans ||25||75||0||9.2||62.5|
| M. wilsoni ||0||100||0||0.2||50|
| Mansonia sp.||68.2||31.8||0||2.2||84.1|
| Phoniomyia sp.||72.8||27.2||0||1.1||86.4|
| Psorophora sp.||0||0||100||0.5||–100|
| Wyeomyia sp.||5.9||35.3||58.8||1.7||–35|
Table 4. Synanthropy index (SI) by species of phlebotomine sand flies captured in the area of the Aimorés hydroelectric power plant, from November, 2008 to September, 2009.
| Brumptomyia avellari ||18.7||81.3||0||1.6||59.3|
| Lutzomyia brasiliensis ||50||50||0||0.2||75|
| L. capixaba ||0||100||0||0.4||50|
| L. cortelezzii ||55.6||44.4||0||0.9||77.8|
| L. intermedia ||7,5||92.5||0||8||53.7|
| L. ischyracantha ||4.5||95.5||0||6.6||52.2|
| L. lenti ||100||0||0||0.1||100|
| L. longipalpis ||77.8||22.2||0||4.5||88.9|
| L. quinquefer ||0||100||0||0.2||50|
| L. termitophila ||50||50||0||0.2||75|
| L. whitmani ||50||50||0||0.4||75|
| Lutzomyia sp.||100||0||0||0.1||100|
The occurrence of diseases such as dengue, malaria, filariasis, yellow fever, and leishmaniasis is related to the geographical distribution of the causative agent, vector, and of possible reservoirs, in addition to favorable environmental conditions. Thus, the concomitant presence of these links in the chain of each disease transmission in a particular area is fundamental to the existence of autochthonous cases. Cases of dengue, malaria, and visceral and cutaneous leishmaniasis seem to occur as expected, considering the proliferation of these diseases in Brazil. There is no evidence of increase in the incidence of these diseases after the implementation of the dam. However, the maintenance of fauna-monitoring programs for these insects in accordance with specific controlling actions for each disease is essential.