Roberto Barrera

Background: Aedes aegypti mosquitoes use diverse chemosensory cues to select an oviposition site. These cues are thought to provide information on factors such as food availability, predators, pathogens, and competitors. Most research on the stimuli attracting female Ae. aegypti to oviposit in natural or artificial containers has focused on the properties of the vessel and water, such as size, color, water quality, concentration of dissolved organic matter, and microorganisms. One understudied aspect of oviposition containers is periphyton, the complex community of microorganisms that can grow on the inner walls of containers where gravid Ae. aegypti females lay their eggs. Periphyton can potentially act as an indicator of the container’s suitability for females looking for an oviposition site, and as a source of food for future mosquito larvae. We were interested in understanding whether container periphyton attracts gravid Ae . aegypti females for oviposition and to assess the microbial composition of the periphyton community. Methods: To answer these questions, we collected periphyton from an artificial water-collecting container that had visible Ae. aegypti larvae and pupae. We propagated this periphyton in 36 plastic buckets with water, and once the periphyton was established, we conducted a series of attraction and oviposition choice experiments within a semi-field cage where gravid Ae. aegypti were released and presented with buckets with and without periphyton, periphyton-exposed water, or dechlorinated water. Additionally, we collected samples from the periphyton used in these assays for 16s rRNA microbial fingerprinting. Results: Across the 2 different experiments, encompassing 11 replicate trials, female Ae. aegypti consistently laid more eggs in buckets with periphyton compared to the controls, demonstrating that periphyton promotes Ae. aegypti oviposition. Results from 16s rRNA fingerprinting of periphyton specimens revealed that these communities are complex but predominantly composed of microbial taxa from the phyla Bacteroidetes, Cyanobacteria, and Pseudomonadota. Conclusions: Periphyton in artificial containers had attractive properties for Ae. aegypti oviposition and is composed by complex microbial communities. Understanding periphyton’s attractive properties could prompt the development and formulation of novel attractants useful in mosquito control.

Background: Aedes aegypti mosquitoes use diverse chemosensory cues to select an oviposition site. These cues are thought to provide information on factors such as food availability, predators, pathogens, and competitors. Most research on the stimuli attracting female Ae. aegypti to oviposit in natural or artificial containers has focused on the properties of the vessel and water, such as size, color, water quality, concentration of dissolved organic matter, and microorganisms. One understudied aspect of oviposition containers is periphyton, the complex community of microorganisms that can grow on the inner walls of containers where gravid Ae. aegypti females lay their eggs. Periphyton can potentially act as an indicator of the suitability of the container for females looking for an oviposition site, and as a source of food for future mosquito larvae. We were interested in understanding if container periphyton attracts gravid Ae. aegypti females for oviposition and to assess the microbial composition of the periphyton community. Methods: To answer these questions, we conducted a series of attraction and oviposition assays and collected samples from the periphyton used in these assays for 16s rRNA fingerprinting. Results: We demonstrated that periphyton promotes oviposition by Ae. aegypti. Results from 16s rRNA fingerprinting of periphyton specimens revealed that these communities exhibit high complexity and contain microbial taxa from several classes, including Cyanobacteria, Proteobacteria, Anaerolineae, and Cytophagia. Conclusions: Understanding the chemosensory interactions between mosquitoes and periphyton involved in egg laying could prompt the development and formulation of novel attractants useful in mosquito control.

Aedes aegypti is the primary urban vector for several important arboviruses, including dengue, chikungunya, yellow fever, and Zika viruses. Traditional dengue virus (DENV) surveillance relies on passive reporting of human cases, which often underestimates transmission due to asymptomatic or unreported infections. This study evaluated the utility of monitoring DENV in Ae. aegypti mosquitoes to improve detection of local dengue transmission and inform vector control strategies during the 2024 dengue epidemic in Puerto Rico. Mosquito surveillance was conducted in 15 neighborhoods within the San Juan metropolitan area where confirmed dengue cases had been recently reported. Adult female Ae. aegypti were collected weekly using Autocidal Gravid Ovitraps (AGO traps) placed within a 200 m radius of index cases. Pools of 1–20 mosquitoes were tested for DENV RNA and serotype using RT-PCR. Surveillance continued for up to 91 days in study areas, depending on virus detection. A total of 29,354 female Ae. aegypti were collected, of which 29,211 females were pooled (1–20 specimens per pool) into 3878 pools and analyzed. DENV was detected in 49 pools across 11 neighborhoods, with serotypes DENV-1, DENV-2, and DENV-3 identified. Multiple serotypes were sometimes detected in mosquitoes from the same neighborhood. Minimum infection rates and vector indices were higher during the epidemic than in previous inter-epidemic periods, and mosquito densities exceeded thresholds considered protective against outbreaks. Entomo-virological surveillance detected a greater variety and evenness of serotypes than passive human surveillance. These findings suggest that entomo-virological surveillance can complement passive case surveillance, providing a more comprehensive detection of DENV circulation. Integrating mosquito-based and human surveillance can improve outbreak detection, guide vector control, and aid in reducing dengue burden in affected communities.

We compared the number of Aedes aegypti females per trap and the number of detections of this mosquito species per week during 8 wk in 3 types of autocidal gravid traps, the Centers for Disease Control and Prevention (CDC) Autocidal Gravid Ovitrap (AGO), Biogents Gravid Aedes Trap (GAT), and Singapore Gravitrap (SGT), in central Puerto Rico. These traps use the same principles for attracting gravid Ae. aegypti females as traditional ovitraps, such as dark colors, standing water, and decomposing plant materials. The traps differ in size, AGO being the biggest and SGT the smallest. Average captures of female Ae. aegypti per trap per week were 11.1, 7.2, and 1.7 in AGO, GAT, and SGT traps, respectively, a pattern consistent with the sizes of the traps. These results indicated that GAT traps and SGT traps captured 35.5% and 84.7% fewer females of Ae. aegypti, respectively, than AGO traps. Although Ae. aegypti was present in all 20 sites during the 8 wk of observations, AGO, GAT, and SGT traps did not catch specimens in 1, 9, and 58 out of 160 observations per trap type (trap-wk), respectively. Trap failures were 1, 6, and 1 for the AGO, GAT, and SGT traps, respectively. Despite the absence of females of Ae. aegypti at some sites and weeks in each of the traps, all 3 traps were able to detect the presence of this mosquito at each of the 20 sites during the 8 wk of observations and could be used for Ae. aegypti surveillance.

: Dengue viruses (DENV) continue to cause large outbreaks in tropical countries, while chikungunya and Zika (ZIKV) viruses have added complexity to Aedes-borne disease prevention and control efforts. Because these viruses are transmitted by the same vectors in urban areas, it is useful to understand if sequential outbreaks caused by these viruses have commonalities, such as similar seasonal and spatial patterns, that would help anticipate and perhaps prevent future outbreaks. We explored and analyzed the heterogeneity of confirmed cases of DENV (2010–2014 and 2015–2022) and ZIKV (2016–2017) during outbreaks in the San Juan metropolitan area of Puerto Rico to explore their degree of overlap and prioritize areas for Aedes aegypti control. Deidentified, georeferenced case data were aggregated into grid cells (500 × 500 m) within a geographical information system of the study area and analyzed to calculate the degree of overlap between outbreaks. Spatial autocorrelations using local indicators of spatial associations were conducted to identify significant disease case hot spots and correlations between outbreaks. We found that 75% of cases during the three transmission periods were concentrated in 25% of the total number of grid cells covering the study area. We also found significant clustering of cases during each outbreak, enabling identification of consistent disease hot spots. Our results showed 85% spatial overlap between cases of ZIKV in 2015–2017 and DENV in 2010–2014 and 97% overlap between DENV cases in 2010–2014 and 2015–2022. These results reveal urban areas at greater risk of future arbovirus outbreaks that should be prioritized for vector control.

We investigated the effects of interannual El Niño Southern Oscillation (ENSO) events on local weather, Aedes aegypti populations, and combined cases of dengue (DENV), chikungunya (CHIKV), and Zika (ZIKV) viruses in 2 communities with mass mosquito trapping and 2 communities without mosquito control in southern Puerto Rico (2013–2019). Gravid adult Ae. aegypti populations were monitored weekly using Autocidal Gravid Ovitraps (AGO traps). Managing Ae. aegypti populations was done using 3 AGO traps per home in most homes. There were drought conditions in 2014–2015 concurrent with the emergence of a strong El Niño (2014–2016), wetter conditions during La Niña (2016–2018), a major hurricane (2017), and a weaker El Niño (2018–2019). The main factor explaining differences in Ae. aegypti abundance across sites was mass trapping. Populations of Ae. aegypti reached maximum seasonal values during the wetter and warmer months of the year when arbovirus epidemics occurred. El Niño was significantly associated with severe droughts that did not impact the populations of Ae. aegypti. Arbovirus cases at the municipality level were positively correlated with lagged values (5–12 mo.) of the Oceanic El Niño Index (ONI), droughts, and abundance of Ae. aegypti. The onset of strong El Niño conditions in Puerto Rico may be useful as an early warning signal for arboviral epidemics in areas where the abundance of Ae. aegypti exceeds the mosquito density threshold value.

We monitored trap captures of Culex quinquefasciatus using an interrupted time-series study to determine if autocidal gravid ovitraps (AGO traps) were useful to control the population of this mosquito species in a community in southern Puerto Rico. Data for this report came from a previous study in which we used mass trapping to control Aedes aegypti, resulting in a significant 79% reduction in numbers of this species. The AGO traps used to monitor and control Ae. aegypti also captured numerous Cx. quinquefasciatus. Culex quinquefasciatus was monitored in surveillance AGO traps from October 2011 to February 2013, followed by a mosquito control intervention from February 2013 to June 2014. Optimal captures of this mosquito occurred on the 2nd wk after the traps were set or serviced, which happened every 8 wk. Changes in collection numbers of Cx. quinquefasciatus were positively correlated with rainfall and showed oscillations every 8 wk, as revealed by sample autocorrelation analyses. Culex quinquefasciatus was attracted to and captured by AGO traps, so mass trapping caused a significant but moderate reduction of the local population (31.2%) in comparison with previous results for Ae. aegypti, possibly resulting from female mosquitoes flying in from outside of the study area and decreased attraction to the traps past the 2nd wk of trap servicing. Because Ae. aegypti and Cx. quinquefasciatus are frequently established in urban areas, mass trapping to control the former has some impact on Cx. quinquefasciatus. Control of the latter could be improved by locating and treating its aquatic habitats within and around the community.

Gravid traps that collect eggs or adult mosquitoes use color, size, or volume as well as water or plant infusions as attractants. Biorational larvicides have been used to prevent these devices from producing adult mosquitoes within the traps. Results from field assays on the use of several biorational larvicides for various mosquito species have provided mixed results in terms of increased, neutral, or reduced attraction. We investigated the use of Bacillus thuringiensis var. israelensis, spinosad, and novaluron in field assays in Puerto Rico to evaluate the behavioral response of Aedes aegypti and Culex spp. to autocidal gravid ovitraps (AGO traps). The purpose of the study was to increase the safety of these traps by preventing accidental release of adult mosquitoes when traps are opened or damaged. We also investigated whether trap color (blue, green, terracotta) that may be more amenable for use by residents in their properties induced a similar attraction response to the original black trap color. We found that the use of biorational larvicides did not significantly change the behavioral attraction of these mosquito species to AGO traps. For Ae. aegypti, green traps yielded the lowest captures while black, terracotta, and blue produced similar higher yields. Culex spp. in black traps showed significantly higher captures compared with other colors. These results suggest that black, terracotta, or blue AGO traps can be used for the surveillance and control of Ae. aegypti.