The sticky trap designed in the present work is a simple and cheap construction, which captures A. aegypti females. These characteristics allow its large scale usage as a complementary tool in the control of this mosquito species.
The larger number of traps in the field significantly improved AedesTrap performance in collecting A. aegypti. The increase in capture rates (0.8 to 2.6 mosquitoes/premise) due to the number of available AedesTraps is similar to results obtained by Wiliams et al. [21] in Australia. According to these authors, sites with 4, 6, and 8 sticky traps captured significantly more A. aegypti per site than sites with 1 and 2 traps. The results of the present study demonstrated that there is a strong relationship between the number of AedesTrap available and the capacity to detect mosquito infestation at sites. At all sites, ovitraps were concomitantly installed and shown to be more sensitive than AedesTraps in detecting the presence of A. aegypti, independent of the number of AedesTraps utilized. Studies of the performance of MosquiTrap in Belo Horizonte [10] and in Rio de Janeiro [4, 14] also indicated the superior capacity of ovitrap in detecting the presence of mosquitos. According to Honório et al. [14], although both traps are sought by females as an oviposition site, differences in their attractiveness may be one of the reasons for the low efficiency of MosquiTrap.
In previous works by this group (data not shown), utilizing AedesTraps and ovitraps with hay infusion in sites with high Aedes spp. infestation (>3,000 eggs/premise/month), a high positivity rate (98%) was registered for both traps, differing from what was observed here, where the positivity of ovitraps was always higher than that of AedesTraps. It is worth noting that besides differences in infestation levels between sites, the continuous presence of eggs in wood paddles, as well as volatiles originating from dead larvae and bacterial fermentation of water, may have influenced the attractiveness of the ovitrap. Other authors have also referred to the stimulating characteristic of Bti for Aedes spp. oviposition [17, 22].
Although the AedesTrap has been designed to collect adult A. aegypti, it also collected C. quinquefasciatus. The latter species is of great importance to public health in areas endemic for lymphatic filariasis, such as Recife in Brazil, as it is the vector of Wuchereria bancrofti, the etiologic agent of the disease [23]. The data presented here may serve as a starting point for further investigations on the use of AedesTrap to capture C. quinquefasciatus. This mosquito species has also been observed in other traps such as BGS-Trap [4] and Adultrap [24].
The higher positivity and capture rates of AedesTrap in outdoor areas confirmed the general consensus that this is the most appropriate location for the installation of traps, when the capture strategy is based on attracting A. aegypti females searching for oviposition sites [4, 25, 26]. In this study, about 30% of females were captured by AedesTrap exclusively outdoors relative to indoor. Similar behavior was also observed by Favaro and collaborators [27], in a study that utilized four MosquiTraps at each site and achieved 55% trap positivity per site.
Studies performed with other sticky trap models have revealed considerable variations with regard to their performance in the field, with low capture rates generally observed. Throughout the study, there was variation between traps containing A. aegypti and the average number of captured mosquitoes per trap. These observations were in accordance with most studies on the performance of sticky traps to monitor and control A. aegypti. Possible elements affecting this variance are environmental factors [24, 28] and the peculiar behavioral characteristics of A. aegypti, such as “skip oviposition” [4, 6, 9, 10, 29]. In contrast, Chadee and Ritchie [7] described a high rate of female capture in Trinidad, West Indies, using both standard and double sticky traps. The performance of the double sticky trap was significantly superior to that of the standard model, particularly in urban areas.
The “death stress oviposition” behavior described by Chadee and Ritchie [11] when females became stuck in glue, was also observed in the present study. According to the authors, the stress caused by imminent death stimulates females to release their eggs.
The AedesTrap capacity of detecting and capturing A. aegypti during the evaluation of its performance was similar within different precipitation patterns, a finding that was different for ovitraps, which increased egg collection according to rainfall levels. A longitudinal study performed by Regis et al. [19], in which ovitraps were distributed in eight neighborhoods of Recife, showed a low oviposition rate in the dry season, increasing to a peak number of eggs at the beginning of the rainy period, in most areas, other than Engenho do Meio, where the present study was performed. In this neighborhood, a large number of eggs was removed from the environment with the use of more than 4,000 ovitraps per km2. This fact was considered as the probable reason why high egg density figures were not observed in the rainy season.
Methodological differences between this and other studies of adult sticky trap, particularly the time of traps spent in the field and the absence of attractive features in the traps used in this study, make data comparison impractical. In the present study, positivity rates and adult capture by AedesTraps used tap water, and, being monitored every 28 days did not show significant differences over the period of performance evaluation.
Studies using MosquiTrap in Belo Horizonte, in the state of Minas Gerais, showed that in the dry season (May-June), 31.5% of the traps captured 0.11 females/week [10], while in Mirasol, in the state of São Paulo, 70% of MosquiTraps (September 2006 - Mach 2008) were positive, with an average of 1.3 females/week throughout the study, with no discrimination between the mean observed in dry and rainy periods [14]. The Adultrap captured 0.18 and 1.6 females/day/trap when utilized in field tests in Foz do Iguaçu, in the state of Paraná, and in Olaria, in the state of Rio de Janeiro, respectively [9, 24]. It is important to highlight that although daily or weekly observations offer more precise temporal information on infestation levels, they are logistically less viable in routine activities of entomological surveillance programs.
The use of reusable and low cost material to build traps stimulates the development of monitoring methods targeted at A. aegypti adults. In the present study, in which the disposable bottles were donated by restaurants, and traps were made by laboratory staff, the cost of the AedesTrap was less than U$3. This is particularly important considering the possibility of using a great number of AedesTraps in the endemic area, removing females from the environment. It is important to notice that until now there are no sensitive methods able to precisely estimate A. aegypti adult population density. In addition, the AedesTrap proved to be operationally viable and sustainable for monitoring A. aegypti adults within the conditions of health services in Brazil. Moreover, the presence of trapped mosquitoes attracted the attention of the community, a fact that could be used to enhance their effective participation in Aedes control programs.