Bionomics of Culex quinquefasciatus within urban areas of Rio de Janeiro, Southeastern Brazil

Abstract

Bionomia de Culex quinquefasciatus em áreas urbanas no Rio de Janeiro, RJ ABSTRACT OBJECTIVE: To evaluate density, parity rates, daily survival and longevity of natural populations of Culex quinquefasciatus in three neighborhoods with distinct socio-economic and infrastructure profi les. METHODS:Mosquito collections of the Culex quinquefasciatus species were performed weekly during two four month periods, from August to November 2008 (spring) and March to June 2009 (fall), in a favela (slum), a suburban area and a middle class area of Rio de Janeiro, Southeastern Brazil. Collections were performed with backpack aspirators, in 20 randomly selected houses in each area per week, during 15-20 minutes per house. Ovaries were removed from captured females and classifi ed as initial, intermediary or fi nal stage. Furthermore, females were dissected for determination of parity based on the condition of the tracheal system. Mosquito survival rate and longevity were estimated on a per month basis for each neighborhood. RESULTS:We collected a total of 2,062 Culex quinquefasciatus, but monthly vector density was not correlated with temperature and rainfall. We dissected the ovaries of 625 Culex quinquefasciatus, and overall, there was a higher proportion of nulliparous females during the dryer months, while gravid females were more frequent in rainy months. In the middle class neighborhood, the parity rate reached up to 93.75% with survivorship of 0.979. Lower parity and survival rates were obtained in the suburban area (as low as 36.4% parity and 0.711 daily survival). Up to 84.7% of Culex quinquefasciatus females could survive the eight day period needed to complete West Nile Virus incubation. CONCLUSIONS:The survival rate of Culex quinquefasciatus varied signifi cantly between the neighborhoods. This suggests that vectorial capacity and disease transmission risk may vary greatly between different urban areas, which is potentially useful information for vector control programs. DESCRIPTORS:Culex. Parity. Survival. Longevity. 851Rev Saúde Pública 2012;46(5): Culex quinquefasciatus Say is a cosmopolitan mosquito with worldwide distribution, more frequent in tropical and subtropical areas in association with human dwellings. The adult females lay eggs preferentially in relatively large, permanent habitats with high concentrations of decomposing organic matter, such as sewage effl uents and septic tanks. However, immature stages of this species can be found in artifi cial containers often fi lled with polluted or organic-rich water, but rarely co-exist in the same container with the dengue vector Aedes aegypti.

The Abundance and Biting Patterns of Culex quinquefasciatus Say (Culicidae) in the Coastal Region of Nigeria

“…There was a preponderance of older mosquitoes during the dry season compared to the rainy season, as shown by the higher parity rates in the former than in the latter. This was contrary to the findings in Brazil where there were a higher proportion of nulliparous females during the dryer months, while gravid females were more frequent in rainy months [1]. This of course could not be due to a higher mortality during the rainy season because the higher humidity level during this season provides favorable conditions for survival as has been shown by higher survival of females kept for dissection in the rainy season than during the dry season.…”

“…quinquefasciatus is normally known to breed in open drains, open or cracked septic tanks, flooded pit latrines and drains, especially when polluted with organic matter [1,38]. Other breeding sites for C. quinquefasciatus in the area include natural containers of decaying Mbele fruits and broken suckaways.…”

“…The adult females lay eggs preferentially in relatively large, permanent aquatic habitats with high concentrations of decomposing organic matter, such as sewage effluents and septic tanks. However, immature stages of this species can be found in artificial containers often filled with polluted or organicrich water but rarely coexist in the same container with the dengue vector Aedes aegypti [1].…”

“…In addition to its public health importance, C. quinquefasciatus causes tremendous nocturnal discomfort and allergic responses due to its nuisance biting [1]. The nuisance biting usually affects a greater proportion of the population than the proportion habouring diseases transmitted by the mosquito species.…”

“…Since the ecological plasticity of C. quinquefasciatus may be useful in the determination of a costeffective control policy [1], the need for a comprehensive study to ascertain the biting characteristics of the mosquito species cannot be overemphasized. Furthermore, a study on the parity of the mosquitoes will provide a baseline data needed to measure effectiveness of control measures.…”