In addition to the change in behavior by adults, some culicid larvae can survive and develop in artificial breeding sites, indicating that these mosquitoes are carriers of a genetic adaptation. The use of artificial containers as breeding sites in anthropogenic areas demonstrates genetic plasticity, which directs the evolution of these culicids toward domiciliation1.
According to Martins and Barbeitos2, many insect physiological, morphological and behavioral adaptations are conditioned through the detection of signals produced by environmental changes occurring on a global and/or local scale (e.g., reduction of a particular resource). These changes could alter one or more biotic or abiotic variables that inform an insect or its offspring of a transition to a new environmental situation. Once the insect is in the new environment, the odds of survival and reproduction are effectively evaluated by the insect.
This study aimed to determine the culicid faunal composition in a landfill in Sapucaia, State of Rio de Janeiro, Brazil.
Sampling was conducted at the Sapucaia landfill located on the Mangueira da Boa Esperança farm, Highway BR 393, kilometer marker 124.4, at 21°57′37″S and 42°51′10″W at an altitude of 251 m above mean sea level (Figure 1A, 1B and 1C). Immature mosquitoes were collected from a percolation tank, which receives waste water manure generated by leaching from the Sapucaia City landfill in the State of Rio de Janeiro, over a two-day period during the third weeks of April, August and October 2011. During the collection period, daily temperature and pH readings were recorded. Specimens were collected by pouring water into a polyethylene tray and using a standard entomological ladle. After separation, the larvae and pupae were removed and placed in 250ml plastic bags (Whirl-Pak Bags®, San Diego, California, USA) for transport to the laboratory.
FIGURE 1 – Appearance of the container from which immature forms were collected: the percolation tank in the landfill of Sapucaia, State of Rio de Janeiro. A: Landfill of Sapucaia, B: Treatment tank and C: Transport to treatment plants.
The larvae and pupae were screened in the laboratory. A portion of the specimens was preserved in 70° GL ethanol for subsequent identification, while selected specimens were kept alive for the purpose of following their life cycles. The culicids were identified by direct observation of evident morphological characteristics under an optical microscope and based on the dichotomous keys described in the literature3–5.
In total, 1,135 immature Culicidae specimens were collected, including 1,100 (96.9%) specimens from Culex (Culex) usquatus Dyar, 20 (1.8%) specimens from Anopheles (Nyssorhynchus) argyritarsisRobineau-Desvoidy, 8 (0.7%) Lutzia (Lutzia) bigoti (Bellardi) specimens and 7 (0.6%) Limatus durhamiiTheobald specimens.
The water temperatures in the percolation tank where the immature mosquito forms were found ranged from 24°C to 34°C and varied among the collection periods. In comparison, the pH varied slightly and remained neutral to slightly basic.
Among the species found in this study, some epidemiological importance can be assigned to only two species. An. argyritaris was considered a possible vector of malaria, and further studies concluded that an absence of data supported this hypothesis. Some arboviruses have been isolated from Limatus spp., including Li. durhamii, which demonstrates the possibility of these mosquitoes being a vector for these viruses (Forattini5).
Although the collected species have already been found to colonize different types of artificial breeding sites, there has been no record of their colonization in breeding sites with physical characteristics similar to those of a strongly eutrophic landfill, as observed in this study.
Horsfall6 reported An. argyritarsis breeds in slightly flowing liquid accumulations within the soil of typical emergent vegetation. These requirements restrict the occurrence of this species in artificial breeding sites, which are normally located above ground, created with clean water and protected from excessive temperature elevations.
Forattini et al.7 discovered immature forms of An. argyritarsis, Aedes albopictus (Skuse) and Culex quinquefasciatus Say occupying the same water tank. Carreira-Alves8 collected An. argyritarsis from a disabled, uncovered water tank in the municipality of Maricá, State of Rio de Janeiro. This finding was in agreement with Silva et al.9, who revealed the presence of An. argyritarsis and Ae. albopictus sharing a water tank containing clean water. This natural behavior of An. argyritarsis to exploit artificial breeding sites containing clean water does not correspond with the findings of the present study.
According to Machado-Allison10, Lutzia bigoti larvae exhibit a predatory feeding activity, and these larvae are able to colonize artificial containers of small dimensions, such as tires, plastic containers, bamboo and tin cans1,11. In a study by Calado and Silva11 investigating artificial containers introduced in rural São José dos Pinhais, Paraná State, the majority (96.4%) of Lutzia bigoti specimens were collected in shaded areas located in the peridomicile. This result was not consistent with the finding of the present study, in which the samples of Lutzia bigoti were collected from open breeding sites exposed to direct sunlight.
Lopes1 reported that Li. durhamii predominantly colonized plastic containers. In a study conducted by Lourenço-de-Oliveira et al.12 in Granja Calábria, Jacarepaguá, State of Rio de Janeiro, Li. durhamii was not found to breed in natural standing water pools but instead was collected from artificial containers, such as abandoned utensils, and domestic water sources. The immature forms of this species have diversified behavior regarding breeding-site selection and can colonize natural breeding sites, such as fruit peels, leaves, palm spadices and hollow trees, as well as artificial containers, such as buckets and barrels13.
As shown by Forattini5, adaptation to artificial containers by some Anophelinae to artificial containers may expand their range of breeding site locations. Given the observations reported in this study, the discovery of An. argyritarsis, Li. durhamii and Lutzia bigoti in this type of breeding site may indicate a possible change in habit and/or adaptation to eutrophic environments.
