Culex quinquefasciatus Say is a nocturnal mosquito that is involved in the transmission of vector-borne pathogens (e.g., West Nile virus, Wuchereria brancrofti) and is a nuisance in areas where it is not involved in pathogen transmission (Farajollahi et al. 2011; Turell 2012). This mosquito is distributed in tropical and subtropical areas of the world, particularly in urban areas (Mattingly 1962). Culex quinquefasciatus takes advantage of improper disposal of sewage water above or below ground in urban areas to oviposit and undergo immature development (Barrera et al. 2008; Burke et al. 2010; Chaves et al. 2009; Correia et al. 2012; Mackay et al. 2009). Culex quinquefasciatus and Aedes aegypti (L.) have widespread distribution in urban areas and some studies have shown that the abundance of these species is correlated (Barrera et al. 2019; Ng et al. 2018; Smith et al. 2009). Given the public health importance of these mosquitoes and the need to monitor their presence and abundance, it would be advantageous to use a same monitoring device that could efficiently track both species.

Commonly used traps to monitor females of Cx. quinquefasciatus are electromechanical, including Centers for Disease Control and Prevention (CDC) miniature light traps paired with CO₂, Biogent Sentinel (BG)-S traps with BG-lure or CO₂, and CDC gravid traps (e.g., McNamara et al. 2021; Medeiros et al. 2017; Muturi et al. 2007). Culex quinquefasciatus can also be collected using traps that do not use electricity (passive traps), such as ovitraps for the collection of egg rafts (Barbosa and Regis 2011) and sticky gravid traps for the collection of adult females like the CDC Autocidal Gravid Ovitraps (AGO traps; Acevedo et al. 2021; Mackay et al. 2013; Obregon et al. 2019; this study). Among these monitoring devices, dark BG-S baited with BG-lure (Barrera et al. 2013) and AGO traps (Barrera et al. 2021) have been used to monitor Cx. quinquefasciatus in Puerto Rico. Commonly, the control of immature Cx. quinquefasciatus is achieved by modifying or fixing urban structures that retain polluted water (Metzger et al. 2008) or by application of pesticides to control immature and adult stages (Nasci and Mutebi 2019). There are no previous studies addressing area-wide control of Cx. quinquefasciatus using mass trapping. Area-wide mosquito control with mass trapping involves the deployment of enough traps in the environment as to have a significant impact on the abundance of the mosquito population, and ideally also on vectorial capacity. A recent study using autodissemination devices to attract and contaminate adult mosquitos with an insect growth regulator (pyriproxyfen) for its transfer to additional oviposition sites, showed a significant reduction (55.5%) of the adult population of Cx. quinquefasciatus in Brazil (Garcia et al. 2020).

Given the importance of Ae. aegypti as the vector of dengue, chikungunya, and Zika viruses, we conducted a series of studies on the surveillance and control of this mosquito in various communities in southern Puerto Rico from 2011 to 2019 (Barrera et al. 2014 a, b). These studies showed that Autocidal Gravid Ovitraps (AGO traps) were effective tools for the surveillance and control of Ae. aegypti. Along with captures of Ae. aegypti, we captured numerous specimens of Cx. quinquefasciatus; a species that was previously found positive for the presence of West Nile virus in Puerto Rico (Barrera et al. 2010). Here, we report data collected on Cx. quinquefasciatus in the studied community where we conducted mass trapping using AGO traps (October 2011 – June 2014). The objectives were to report trap captures of Cx. quinquefasciatus and determine if AGO traps were useful to control female adults of this mosquito species.

We captured a mean (± SE) of 15.83 ± 0.35 females and 1.00 ± 0.03 males of Cx. quinquefasciatus per SAGO trap per week during the study. Thus, SAGO traps captured few male specimens. The results of the GLM analysis showed significant effects of the following variables on the numbers of Cx. quinquefasciatus: mass trapping (F_{1, 3597}= 20.77; P< 0.001), the week after trap servicing (F_{7, 3597}= 78.91; P< 0.001), accumulated rainfall (F_{1, 3597}= 15.92; P< 0.001), temperature (F_{1, 3597}= 3.98; P< 0.05), and relative humidity (F_{1, 3597}= 6.95; P< 0.01). The fixed coefficients showed a positive value for accumulated rainfall and negative values for temperature and relative humidity. Captures of female Cx. quinquefasciatus in SAGO traps were 19.05 ± 0.57 before the mosquito control intervention (October 2011 – February 2013) and 12.46 ± 0.36 during the intervention (March 2013 – June 2014). The coefficient for the effect of the intervention, keeping other factors constant, revealed a reduction of the relative abundance of Cx. quinquefasciatus by mass trapping of 31.2%.

The number of female Cx. quinquefasciatus increased following increases in accumulated rainfall (Fig. 1). It was also observed that the number of females oscillated in short cycles of approximately eight weeks (Fig. 1). These oscillations seemed to reflect significant changes in trap captures following scheduled servicing of the traps, which happened every eight weeks (Fig. 2). Peak captures occurred in AGO traps on the second week after setting up the trap with fresh water, hay packet, and sticky sheet, but decreased afterwards (Fig. 2). Sample autocorrelations of captured specimens revealed a periodicity of eight weeks as suspected from visual inspection of the temporal changes of trap captures between trap services (Figs. 1, 3). This result shows that the relative density of Cx. quinquefasciatus had recurrent increases every eight weeks throughout the study, coinciding with the schedule of trap servicing. The numbers of Cx. quinquefasciatus captured on the second week after servicing the traps should provide a more realistic representation of changes in the abundance of Cx. quinquefasciatus in time because the numbers of this species captured in AGO traps were lower during the other weeks between services (Figs. 1, 2). Mosquito counts every eight weeks showed a decrease in number of female Cx. quinquefasciatus after the initiation of mass trapping.

AGO traps were initially developed to monitor and control Ae. aegypti (Mackay et al. 2013). During field investigations to demonstrate their usefulness for Ae. aegypti, we noted and recorded the numbers and sex of other mosquito species, among which Cx. quinquefasciatus was the most abundant species (Acevedo et al. 2016; 2021). Data presented here for Cx. quinquefasciatus were concurrently collected during investigations in the same location, with the same mass trapping intervention that showed a 79% reduction in the population of Ae. aegypti (Barrera et al. 2014b; Lega et al. 2020). Data analyzed in this report showed that AGO traps can also be used, with some limitations, to monitor the relative abundance of female Cx. quinquefasciatus, and that mass trapping reduced this mosquito population by 31.2%, which was less than the reduction observed for Ae. aegypti (Barrera et al. 2014b). Thus, a targeted intervention against Ae. aegypti had some impact on the relative abundance of Cx. quinquefasciatus in the study area.

The results showed that the average number of female Cx. quinquefasciatus captured in AGO traps significantly changed in the ensuing weeks following trap set up or trap servicing, with the highest yields observed during the second week following trap set up. The AGO trap is set up with 8 l of water and a 30 g hay pack that decomposes over time, providing olfactory cues for gravid mosquitoes to lay eggs. Producing the infusion with the hay pack in situ or within the trap when it is already at the collection site has the advantage of not having to transport large quantities of liquid infusion that was fermented elsewhere to set up gravid traps (e.g., Popko and Walton 2016). Trap servicing occurs every eight weeks, which worked well for Ae. aegypti, because the decrease in trap captures during this time is not as apparent as what we observed here for Cx. quinquefasciatus (Barrera et al. 2014b). The availability of a trap that does not require frequent servicing is advantageous for programs that use mass trapping to control mosquitoes. This is because fewer human resources are needed the longer the period between trap servicing. The decline in trap yields of Cx. quinquefasciatus observed after the second week since trap servicing explains the modest reduction of mass trapping on the population of this mosquito. The rapid decline in attraction was likely the result of rapid decomposition of the hay pack, like what has been observed for fresh cuts of flowers added to flowerpots in cemeteries (Barrera et al. 1981). Thus, servicing the traps more frequently could increase the effectiveness of control on these mosquito species. Another factor that may limit the local control of Cx. quinquefasciatus by mass trapping is the species’ high dispersal capacity, which is in the range of kilometers (Medeiros et al. 2017). This dispersal capacity is far greater than what has been reported for the more sedentary mosquito species such as Ae. aegypti or Aedes albopictus (Skuse) (Medeiros et al. 2017). These results showed that AGO traps can be useful to monitor Cx. quinquefasciatus for two weeks after trap set up. To investigate if AGO traps could be used to monitor and control Cx. quinquefasciatus over extended periods of time without servicing, we suggest experimenting with increased initial or incremental amounts of hay per trap.

In conclusion, Cx. quinquefasciatus is attracted to AGO traps, possibly as a combination of their dark color, size, and volume of hay infusion. Maximal captures of this mosquito occurred on the second week after trap setting, likely related to the content of organic particles and microorganisms resulting from the decomposition of plant materials in the water (Barrera et al. 1981). Despite Cx. quinquefasciatus being attracted and captured by AGO traps, mass trapping resulted in a small reduction of the local population, possibly resulting from female mosquitoes flying in from outside the study area. This result contrasts with the observed higher, concurrent reduction of the population of Ae. aegypti (Barrera et al. 2014b). Because Ae. aegypti and Cx. quinquefasciatus are frequently associated in urban areas, mass trapping to control the former also has some limited control impact on Cx. quinquefasciatus. Control of the latter could be improved by frequently locating and treating its aquatic habitats within and around the community.