Dancing in the purple rain: color affinity and oviposition choices in Aedes sierrensis (Diptera: Culicidae)

The western tree hole mosquito, Aedes sierrensis (Ludlow) (Diptera: Clucidae), is a pestiferous mosquito with a range extending over the entire pacific seaboard and into portions of the intermountain west. As a peridomestic heartworm vector, it demands at least some level of surveillance to understand its abundance. However, the species is refractory to a majority of conventional vector surveillance approaches for tracking mosquitoes. To find more options for Aedes sierrensis surveillance, a variety of oviposition attractants were evaluated in arena-style choice assays using colony reared adults. A range of infusion treatments (e.g., alfalfa, oak, and beetroot) were examined and then combined with investigations of liquid color as well as ovicup color and entryway position. These studies revealed that Ae. sierrensis have an affinity for purple coloration, plain water, and larger entryway sizes for oviposition cups. A prototype ovicup was 3D-printed using purple filament and multiple types of entryways, and used to re-test infusion waters. No particular attraction differences were detected after normalizing for purple color. Comparisons to black 3D-printed cups yielded surprising observations that male mosquitoes also aggregated on purple cups while females sheltered, but not necessarily oviposited, in black cups. Although this was only a laboratory-based assessment, these studies provide useful information for future field trials of potential oviposition traps for surveillance of Ae. sierrensis.

Temperature Influence on Aedes aegypti Oviposition in the San Joaquin Valley of California

The establishment and oviposition of Aedes aegypti can vary from one location to another partially due to differing temperature and precipitation. In 2017, Ae. aegypti was first detected in Merced in the Central Valley of California. The objectives of this study were to examine the influence of temperature and precipitation on oviposition of Ae. aegypti, and to determine the beginning and end of the seasonal activity of Ae. aegypti in Merced. The study site consisted of a residential area in the north-east region of Merced where Ae. aegypti was first detected in Merced County. Fifty-four residences were randomly selected as ovitrap sites. Ovitraps were placed at field sites weekly for 12 months, from September 27, 2017, to September 27, 2018. Each week, ovitraps were inspected for the presence of mosquito eggs. Egg counts were used to calculate the following oviposition indices: the ovitrap index (OI) (percent of traps positive) and the egg density index (EDI) (eggs/positive traps). Oviposition occurred primarily from May through October, above a minimum temperature of 10°C, and when almost no rainfall occurred (0.5 mm total). During the year, the percent of positive traps per month ranged from approximately 1.2-67.3%, with highest values in June to October (43.9-67.3%). The highest mean monthly EDI was from July to October (34-44.6) and peaked in October at 44.6 eggs/trap. The EDI values are similar to other locations where Ae. aegypti transmits endemic vector-borne disease. These findings provide baseline data for Ae. aegypti control in Merced and the Central Valley of California.

Vertical Distribution of Oviposition and Temporal Segregation of Arbovirus Vector Mosquitoes (Diptera: Culicidae) in a Fragment of the Atlantic Forest, State of Rio de Janeiro, Brazil

Culicid species, which include potential vectors of yellow fever, are diverse and abundant, with species commonly co-occurring in certain sites. Studying these species can provide important insights into their vector potential and, consequently, epizootic cycles of arboviruses carried about by these vectors. Here, we evaluated the vertical distribution and temporal segregation of mosquito oviposition with emphasis on arbovirus vectors in a fragment of the Atlantic Forest in Casimiro de Abreu, Rio de Janeiro, Brazil. Two sampling points were selected: Fazenda Três Montes and the Reserva Natural de Propriedade Privada Morro Grande. Collections were carried out at two sites using 10 ovitraps installed on the vegetation cover at different heights (0, 2, 4, 6, and 8 m above ground level) and monitored monthly from July 2018 to December 2020. The hypotheses of temporal and vertical stratification were tested through a PERMANOVA, and the relationship of each species with the vertical distribution was evaluated individually through a correlation analysis. We collected a total of 3075 eggs, including four species of medical importance: Haemagogus leucocelaenus (n = 1513), Haemagogus janthinomys (n = 16), Aedes albopictus (n = 1097), and Aedes terrens (n = 449). We found that Hg. leucocelaenus had a positive relationship with height, exhibiting behavior that appears to benefit from higher heights. The abundance of Ae. terrens seemed to follow Hg. leucocelaenus, although we did not find a relationship with height for the former species. On the other hand, Ae. albopictus exhibited a negative relationship with height, becoming absent or outnumbered at higher strata. Our study site has already presented evidence of recent transmission of the wild yellow fever virus, supporting the need to carefully monitor the emergence of febrile diseases among residents in the surrounding areas and the local population.

Surveillance of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) as a Method for Prevention of Arbovirus Transmission in Urban and Seaport Areas of the Southern Coast of Brazil

Entomological surveillance is a traditional method to measure presence, distribution, and seasonal variation of vectors in urban areas, and is essential to targeted control activities to prevent arbovirus transmission. Ovitraps as one of the main components of surveillance programs, enable determination of female oviposition behavior, as well as identification of seasonal variations of the vector. The goals of this study were 1) to detect the mosquitos (Aedes aegypti Linnaeus) and (Aedes albopictus Skuse) (Diptera:Culicidae), in Paranaguá city, 2) to assess ovitrap positive index (OPI), egg density index (EDI), and their relationship with meteorological variables, and 3) to evaluate the vertical transmission of dengue, Zika, and chikungunya in Ae. aegypti and Ae. albopictus. The study was carried out in urban areas of Paranaguá city, an important port region of Brazil, from June 2017 to November 2018. The city was divided into 16 area-clusters. Three-hundred and thirty-one ovitraps were installed monthly, remaining for four days in selected places. Kernel density maps were done to compare the spatiotemporal distribution of collected eggs. Areas which maintained constant oviposition associated with vector activity were identified and were found to overlap the area-clusters with the highest EDI. As viral RNA was not detected, vertical transmission was likely not a maintenance mechanism of arbovirus circulation in Ae. aegypti and Ae. albopictus vectors. This study reiterates the importance, efficiency, and feasibility of ovitraps to monitor the presence and dynamics of Aedes spp. populations.

Assessment of Various Colors Combined with Insecticides in Devising Ovitraps as Attracting and Killing Tools for Mosquitoes

Dengue virus, transmitted by Aedes aegypti mosquitoes, is the most important emerging viral disease, infecting more than 50 million people annually. Currently used sticky traps are useful tools for monitoring and controlling Ae. aegypti. Therefore, this study was conducted to evaluate the attraction of Ae. aegypti mosquitoes using various colors, materials and insecticides. The laboratory and field assessed the four different colors of ovitraps (blue, green, black and transparent). Among the tested ovitraps, the black ovitraps showed the highest number of eggs (348.8) in the laboratory and maximum eggs (80.0) in field trials. In addition, six different materials (casein, urea, yeast, fish meal, chicken meal and water) were also used to evaluate mosquito's attraction. In our results, the highest number of eggs were collected with fish meal having 0.5% concentration in both laboratory (195.17) and the field (100.7). In laboratory trials, the Deltamethrin treated ovitraps (treated with Deltamethrin) significantly trapped and killed the highest percent of female Ae. aegypti (91.5%) compared to untreated (not-treated with Deltamethrin) ovitraps (3.3%). In field trials, the lethality was determined by installing 10 lethal ovitraps in one block and 10 untreated ovitraps in another block. The results indicate a significant reduction in eggs collected from the treated block (727 eggs) as compared to the untreated block (1865 eggs). The data also reveal that the ovitrap positive index (50) and egg density index (24.3) were also low in treated areas than in untreated areas, 83.3 and 37.3, respectively. It is concluded that the lethal ovitraps significantly reduced the Ae. aegypti population and thus could be considered an integral part of the integrated vector management (IVM) program.

Spatio-Temporal Modelling Informing Wolbachia Replacement Releases in a Low Rainfall Climate

Releases of Aedes aegypti carrying Wolbachia bacteria are known to suppress arbovirus transmission and reduce the incidence of vector-borne diseases. In planning for Wolbachia releases in the arid environment of Jeddah, Saudi Arabia, we collected entomological data with ovitraps across a 7-month period in four locations. Herein, we show that mosquito presence in basements does not differ from that of non-basement areas of buildings. In modelling mosquito presence across the study sites, we found the spatial structure to be statistically significant in one of the four sites, while a significant spatial structure was found for egg production data across three of the four sites. The length scales of the spatial covariance functions fitted to the egg production data ranged from 143 m to 574 m, indicating that high productivity regions can be extensive in size. Rank-correlation analyses indicated that mosquito presence tended to persist from the dry to wet season, but that egg production ranks at locations could reverse. The data suggest that, in Jeddah, the quality of the local environment for breeding can vary over time. The data support the feasibility of dry season releases but with release numbers needing to be flexible depending on local rates of invasion.

Larval Mortality and Ovipositional Preference in Aedes albopictus (Diptera: Culicidae) Induced by the Entomopathogenic Fungus Beauveria bassiana (Hypocreales: Cordycipitaceae)

Entomopathogenic fungi allow chemical-free and environmentally safe vector management. Beauveria bassiana (Balsamo-Crivelli) Vuillemin is a promising biological control agent and an important component of integrated vector management. We investigated the mortality of Aedes albopictus (Skuse) larvae exposed to five concentrations of B. bassiana using Mycotrol ESO and adult oviposition behavior to analyze the egg-laying preferences of wild Ae. albopictus in response to different fungal concentrations. We examined the mortality of mid-instars exposed to B. bassiana concentrations of 1 × 104, 1 × 105, 1 × 106, 1 × 107, and 1 × 108 conidia/ml every 24 h for 12 d. In the oviposition behavior study, the fungus was applied to wooden paddles at 1 × 105, 1 × 107, and 1 × 109 conidia/ml, and the paddles were individually placed into quad-ovitraps. Both experiments contained control groups without B. bassiana. Kaplan-Meier survival analysis revealed that larval mortality was concentration dependent. The median lethal concentration was 2.43 × 105 conidia/ml on d 12. The median lethal time was 3.68 d at 1 × 106 conidia/ml. Oviposition monitoring revealed no significant difference in egg count between the control and treatment paddles. We observed an inverse relationship between the concentration of B. bassiana and the percentage of paddles with eggs. We concluded that concentrations above 1 × 106 conidia/ml are larvicidal, and Ae. albopictus laid similar numbers of eggs on fungus-impregnated and control wooden substrates; however, they were more likely to oviposit on substrates without B. bassiana. With these findings, we suggest that B. bassiana-infused ovitraps can be used for mosquito population monitoring while also delivering mycopesticides to adult mosquitoes.

Risk-Based Mapping Tools for Surveillance and Control of the Invasive Mosquito Aedes albopictus in Switzerland

Background: In Switzerland, Aedes albopictus is well established in Ticino, south of the Alps, where surveillance and control are implemented. The mosquito has also been observed in Swiss cities north of the Alps. Decision-making tools are urgently needed by the local authorities in order to optimize surveillance and control. Methods: A regularized logistic regression was used to link the long-term dataset of Ae. albopictus occurrence in Ticino with socioenvironmental predictors. The probability of establishment of Ae. albopictus was extrapolated to Switzerland and more finely to the cities of Basel and Zurich. Results: The model performed well, with an AUC of 0.86. Ten socio-environmental predictors were selected as informative, including the road-based distance in minutes of travel by car from the nearest cell established in the previous year. The risk maps showed high suitability for Ae. albopictus establishment in the Central Plateau, the area of Basel, and the lower Rhone Valley in the Canton of Valais. Conclusions: The areas identified as suitable for Ae. albopictus establishment are consistent with the actual current findings of tiger mosquito. Our approach provides a useful tool to prompt authorities’ intervention in the areas where there is higher risk of introduction and establishment of Ae. albopictus.

Evaluation of the Diversity of Culicidae Vectors of the Sylvatic Yellow Fever Virus in Atlantic Forest Remnants with the Use of Ovitraps and Bamboo Traps

Mosquitoes transmit several pathogens in tropical regions, especially in forest areas. The diseases caused by these pathogens include malaria and several arboviruses such as yellow fever. Brazil has the largest endemic area in the world for yellow fever. Many factors can affect the sylvatic cycle of the disease, shifting it into human-inhabited areas. This study aims to examine the oviposition behavior of mosquito species that are effective or potential vectors of the yellow fever virus and which colonize bamboo traps and ovitraps installed at different heights. The positions of the traps in the strata were changed every 15 days. The collection of immature stages (eggs, larvae, and pupae) was performed every 2 weeks for 12 months from August 2018 to July 2019 in the city of Nova Iguaçu, state of Rio de Janeiro, Brazil, in an area near the Tinguá Biological Reserve (REBIO) in the districts of Adrianópolis and Rio D'ouro. Statistical tests were used to compare oviposition at each stratum, and correlation tests showed the relationship between the presence of eggs and immature mosquitoes (larvae and pupae) and temperature, precipitation, and trap type. The diversity was calculated for each trap type and height, as well as the dry and rainy seasons. During the sampling period, 3929 eggs and 4953 larvae and pupae were collected. The traps installed in the high strata remained empty when traps on the ground were installed at the same time, although not when they were installed on their own. The results obtained with this new proposed methodology suggest that diversity is greatest in the rainy season and in bamboo traps for either stratum. Furthermore, this study suggests that mosquitoes begin searching for breeding sites at ground level. Higher levels may be occupied due to the absence or impermanence of other breeding sites.

Rapidly Containing the First Indigenous Outbreak of Chikungunya in Taiwan-Lessons Learned

The first indigenous outbreak of chikungunya in Taiwan occurred in New Taipei City, northern Taiwan, from August to October 2019. This study identified important containment strategies for controlling the outbreak. The outbreak investigation and ovitrap data were collected from the Department of Health, New Taipei City Government. A geographic information system (GIS) was applied for spatial analysis, and descriptive statistics were used to compute the demographic features and medical visits of confirmed cases. There were 19 residents infected during the outbreak. The source of this outbreak was a mountain trail with abundant Aedes albopictus. The atypical symptoms and lack of a rapid test led to multiple clinical visits by the patients (mean: 2.79; standard deviation: 1.65). The clinical symptoms of chikungunya are very similar to those of dengue fever. We noted that only eight patients were polymerase chain reaction (PCR)-positive in their first blood collection, and an average of 3.13 days between illness onset and PCR-positive results. The improved laboratory panel test, targeted and rapid insecticide spraying at the households and their communities, strict closure of the mountain trail, and ovitrap surveillance for evaluating intervention were important approaches to rapidly contain the outbreak.

Ovitrap Preference in the Black Soldier Fly, Hermetia illucens (L.) (Diptera: Stratiomyidae)

<b>Background and Objective:</b> The adult female of the Black Soldier Fly (BSF) usually performs oviposition near decaying organic matter in cracks found in dry areas. In mass-rearing facilities or on a laboratory scale, females usually lay eggs on the provided ovitrap which is made of various types of materials. This study was aimed to observe the female preferential behaviour for ovitrap types during the oviposition period. <b>Materials and Methods:</b> The study was conducted in a semi-outdoor screen house with direct sunlight. The ovitrap materials used were: Dry leaves, wood, cardboard and plastic (infraboard). The parameters calculated in this study were ovitrap preference, oviposition duration, the number and weight of the eggs, fertility of eggs, development time and mortality of offspring. <b>Results:</b> The BSF females preferred the wood ovitrap to other ovitrap types. This was indicated by the high number of females visits, the number of egg-laying females and the total number of eggs on the wood ovitrap. Eggs found in the plastic ovitrap had the highest mortality compared to eggs found in the other ovitraps. <b>Conclusion:</b> The difference of ovitrap material affected female visitation preferences, the oviposition frequency and the duration of egg-laying of female BSF but did not affect offspring development time in any of the stages (egg-adults).

Oviposition of Aedes aegypti and Aedes albopictus on Ovitraps in Dry and Rainy Seasons in Southern Vietnam

Ovitraps were set inside and outside of 15 households in December 2012 (dry season) and August 2013 (rainy season) in 2 communes (An Thanh and Phu Hoa) of Binh Duong Province in southern Vietnam. Eggs laid in the ovitraps were collected after 4 days, dried, and soaked in water. Hatched larvae were transferred to cups and reared to adulthood to identify the species. The rate of positive ovitraps did not differ between December and August for Aedes aegypti, but it was lower in December for Ae. albopictus. The number of eggs laid per ovitrap by Ae. aegypti did not differ between December and August, while that for Ae. albopictus decreased significantly in December in both communes. Moreover, Ae. albopictus laid eggs in ovitraps placed outside the households. Therefore, it is necessary for future studies to investigate whether the major source containers for oviposition had dried in the dry season or Ae. albopictus entered diapause, leading to these observations.

Aedes albopictus (Diptera: Culicidae) Monitoring in the Lazio Region (Central Italy)

The Asian tiger mosquito Aedes albopictus (Skuse 1894) is assuming an ever-increasing importance as invasive species in Europe and consequently as human health and nuisance concern. In Central Italy, the species has been recently involved in a chikungunya outbreak. A 3 yr Ae. albopictus monitoring was carried out in 21 municipalities of the Lazio region (Central Italy), belonging to three provinces. Samplings were performed on a weekly basis using ovitraps, in order to investigate climatic and spatial variables driving egg abundance and Ae. albopictus period of activity. A temperature of 10.4°C was indicated as lower threshold for the onset of egg-laying activity, together with a photoperiod of 13:11 (L:D) h. The whole oviposition activity lasted 8 mo (May-December), with 95% of eggs laid between early June and mid-November and a peak at the end of August. Egg abundance was positively influenced by accumulated temperature (AT) of the 4 wk preceding sampling and negatively by precipitation during the week before. Egg-laying activity dropped with decreasing AT, increasing rainfall, and with a photoperiod below 10:14 (L:D) h. Our results pinpointed the importance of fine-scaled spatial features on egg abundance. Some of these fine-scaled characteristics have been highlighted, such as the presence of vegetation and human footprint index. Our model estimated an almost doubled maximum number of laid eggs for the maximum value of human footprint. Compelling evidence of the relevance of fine-scaled characteristics was reported, describing cases where human-made breeding sites driven the abundance of Ae. albopictus.

Effects of Color and Perforated Lid on Ovitrap Preference of Aedes aegypti and Aedes albopictus

The shape and color of an ovitrap affect the sampling efficiency of mosquitoes. We examined the effect of perforated lids of different colored cups on the preference of Aedes aegypti and Ae. albopictus for oviposition containers. The mosquito species were collected from Tuy Hoa City, Phu Yen Province, Vietnam in April 2016. Females of both species laid eggs in cups without a lid in the order of black, red, and green. However, the number of eggs laid by both species was not different between the black cups with a perforated lid and those without a lid. Aedes aegypti females laid more eggs in red cups with a perforated lid than cups without a lid. Green cups with a perforated lid were not preferred by Ae. aegypti and Ae. albopictus. Our results showed that the effect of perforated lids on oviposition preference was dependent on cup color and that it differed between the mosquito species. Out study provides valuable insights for the development of more effective ovitraps for Aedes mosquito surveillance and control.

Spatial analysis of dengue incidence and Aedes aegypti ovitrap surveillance in Belo Horizonte, Brazil

OBJECTIVES

Understanding the intra-urban spatial dynamics of Aedes aegypti and dengue transmission is important to effectively guide vector control. Ovitraps are a sensitive, cost-effective vector surveillance tool, yet few longitudinal studies have evaluated ovitrap indices and dengue occurrence. We aimed to assess the spatial patterns of dengue incidence and Ae. aegypti ovitrap positivity index (OPI) over time and to examine the spatial relationship between these two variables.

METHODS

This study used 12 years (2007-2018) of dengue case records and biweekly Ae. aegypti ovitrap data in Belo Horizonte, Brazil. We aggregated data by year and health centre catchment area (n = 152) and used both univariate and bivariate global Moran's I statistic and LISA to evaluate spatial clustering.

RESULTS

Annual dengue incidence ranged from 18 to 6262/100 000 residents and displayed spatial autocorrelation in 10/12 years, with shifting areas of high incidence. Annual OPI ranged from 35.7 to 47.6% and was clustered in all study years, but unlike dengue had consistent spatial patterns over time. Bivariate analysis found both positive (6/12 years) and negative (1/12 years) spatial associations between the two variables.

CONCLUSIONS

Low detected presence of Ae. aegypti was not a limiting factor in dengue transmission. However, stable spatial distribution of OPI suggests that certain areas may have persistent breeding sites. Future research should identify factors related to persistent Ae. aegypti hotspots to better guide vector management. Vector control efforts should be paired with additional data on population immunity, circulating serotypes and urban factors to better predict and control outbreaks.

[Effect of the combination of Metarhizium anisopliae and Gliocladium virens on the oviposition, hatching and emergency of Aedes aegypti]

OBJECTIVE

To evaluate the effect of the combination of Metarhizium anisopliae and Gliocladium virens, both with Aqua Reslin Super, on the oviposition, hatching and emergence of Aedes aegypti.

MATERIALS AND METHODS

Evaluations were carried out to determine the effect of treatments impregnated on filter paper and exposed within plastic containers on the oviposition, hatching and emergency of Aedes aegypti.

RESULTS

The results indicated that the fungus and insecticide combinations did not affect the oviposition behavior, but if the hatching of the eggs and the adult's emergency.

CONCLUSIONS

With the results it can be concluded that the combination of fungi + insecticide can be a good option to be applied in oviposition sites with a view to the development of a lethal ovitrap.

Ovitraps Provide a Reliable Estimate of Wolbachia Frequency during wMelBr Strain Deployment in a Geographically Isolated Aedes aegypti Population

Deployment of Aedes aegypti mosquitoes carrying the endosymbiont bacterium Wolbachia has been identified as a promising strategy to reduce dengue, chikungunya, and Zika transmission. We investigated whether sampling larvae from ovitraps can provide reliable estimates on Wolbachia frequency during releases, as compared to the expensive adult-based BG-Sentinel. We conducted pilot releases in a semi-field system (SFS) divided into six cages of 21 m², each with five ovitraps. Five treatments were chosen to represent different points of a hypothetical invasion curve: 10%, 25%, 50%, 75%, and 90% of Wolbachia frequency. Collected eggs were counted and hatched, and the individuals from a net sample of 27% of larvae per treatment were screened for Wolbachia presence by RT-qPCR. Ovitrap positioning had no effect on egg hatching rate. Treatment strongly affected the number of eggs collected and also the hatching rate, especially when Wolbachia was at a 10% frequency. A second observation was done during the release of Wolbachia in Rio under a population replacement approach when bacterium frequency was estimated using 30 BG-Sentinel traps and 45 ovitraps simultaneously. By individually screening 35% (N = 3904) of larvae collected by RT-qPCR, we were able to produce a similar invasion curve to the one observed when all adults were individually screened. If sampling is reduced to 20%, monitoring Wolbachia frequency with 45 ovitraps would be roughly half the cost of screening all adult mosquitoes captured by 30 BG-Sentinels. Our findings support the scale-up of Wolbachia releases, especially in areas with limited resources to afford massive trapping with BG-Sentinel traps.

First Detection of the Asian Tiger Mosquito, Aedes (Stegomyia) albopictus (Diptera: Culicidae), in Tunisia

Aedes albopictus (Skuse) is a widespread invasive mosquito vector species with a distribution including tropical and temperate climates; its range is still expanding. Aedes albopictus populations were recently detected in Morocco and Algeria, the countries neighboring Tunisia, but never in Tunisia. In 2018, we initiated an intensive field study using BG-Sentinel Traps, ovitraps, larval surveys, and citizens' reports to determine whether Ae. albopictus populations exist in Tunisia. In October 2018, we collected adults and larval stages of Ae. albopictus in Carthage, Amilcar, and La Marsa, less than 20 km, northeast of Tunis, the Tunisian capital. These Ae. albopictus larvae were primarily collected from Phoenician funeral urns at the archeological site of Carthage. This is, to our knowledge, the first detection of Ae. albopictus in Tunisia.

Association of dengue fever with Aedes spp. abundance and climatological effects

OBJECTIVE

To analyze the association of dengue fever incidence with Aedes mosquito's abundance, and the effect of climatological and geographical variables, in a region in Morelos State, Mexico.

MATERIALS AND METHODS

Weekly data during the period 2010 to 2014 was used. Mosquito abundance was determined using ovitraps. Confirmed dengue cases were obtained from the Epidemiological Surveillance System. Climatic variables were obtained from weather monitoringstations. The correlation between climate variables and ovitraps data was estimated using a multivariate regression model.

RESULTS

A correlation of mosquito abundance with dengue fever incidence, and a yearly pattern with seasonal variations were observed. The daily mean temperature, relative humidity and rainfall parameters were associated with mosquito egg abundance. Time lags of three and four weeks between egg counts and dengue fever incidence were observed.

CONCLUSION

Time lags between egg counts and dengue incidence could be useful for prevention and control interventions.

Influence of shading and pedestrian traffic on the preference of Aedes (Stegomyia) aegypti (Diptera: Culicidae) for oviposition microenvironments

Aedes aegypti mosquitoes are highly adaptable to abiotic stimuli. To evaluate the influence of shading and pedestrian traffic on the preference of Ae. aegypti for oviposition microenvironments, 20 sites were sampled weekly using ovitraps within the perimeter of Universidade Federal do Espírito Santo, located in São Mateus, Espírito Santo, Brazil. A spatial and statistical analysis was performed in order to assess the relationship between shading time, pedestrian traffic, and the presence of biological forms of Ae. aegypti. A temporal analysis of temperature and precipitation influence on oviposition was also made. Between June, 2013 and June, 2014, 7,362 Ae. aegypti eggs were collected. Over a 12-month period, we made weekly collections of Ae. aegypti eggs from ovitraps. Pedestrian traffic and shading time influenced the number of positive ovitraps; precipitation and temperature were correlated with the number of positive ovitraps (p <0.05). We conclude that the influence of temperature and precipitation was not significant for the oviposition index, and the frequency of oviposition was directly proportional to the number of individuals moving close to the traps during periods of greater shading.

Long-term spatio-temporal dynamics of the mosquito Aedes aegypti in temperate Argentina

Buenos Aires city is located near the southern limit of the distribution of Aedes aegypti (Diptera: Culicidae). This study aimed to assess long-term variations in the abundance of Ae. aegypti in Buenos Aires in relation to changes in climatic conditions. Ae. aegypti weekly oviposition activity was analyzed and compared through nine warm seasons from 1998 to 2014, with 200 ovitraps placed across the whole extension of the city. The temporal and spatial dynamics of abundances were compared among seasons, and their relation with climatic variables were analyzed. Results showed a trend to higher peak abundances, a higher number of infested sites, and longer duration of the oviposition season through subsequent years, consistent with a long-term colonization process. In contrast, thermal favorability and rainfall pattern did not show a consistent trend of changes. The long-term increase in abundance, and the recently documented expansion of Ae. aegypti to colder areas of Buenos Aires province suggest that local populations might be adapting to lower temperature conditions. The steadily increasing abundances may have implications on the risk of dengue transmission.

The State of the Art of Lethal Oviposition Trap-Based Mass Interventions for Arboviral Control

The intensifying expansion of arboviruses highlights the need for effective invasive Aedes control. While mass-trapping interventions have long been discredited as inefficient compared to insecticide applications, increasing levels of insecticide resistance, and the development of simple affordable traps that target and kill gravid female mosquitoes, show great promise. We summarize the methodologies and outcomes of recent lethal oviposition trap-based mass interventions for suppression of urban Aedes and their associated diseases. The evidence supports the recommendation of mass deployments of oviposition traps to suppress populations of invasive Aedes, although better measures of the effects on disease control are needed. Strategies associated with successful mass-trap deployments include: (1) high coverage (>80%) of the residential areas; (2) pre-intervention and/or parallel source reduction campaigns; (3) direct involvement of community members for economic long-term sustainability; and (4) use of new-generation larger traps (Autocidal Gravid Ovitrap, AGO; Gravid Aedes Trap, GAT) to outcompete remaining water-holding containers. While to the best of our knowledge all published studies so far have been on Ae. aegypti in resource-poor or tropical settings, we propose that mass deployment of lethal oviposition traps can be used for focused cost-effective control of temperate Ae. albopictus pre-empting arboviral epidemics and increasing participation of residents in urban mosquito control.

Biological and Chemical Characterization of a New Larvicide Ovitrap Made of Plastic With Pyriproxyfen Incorporated for Aedes aegypti (Diptera: Culicidae) Control

Aedes aegypti (L.) is a species of international concern because of its ability to transmit serious human arboviral diseases including yellow fever, dengue, and chikungunya, which have spread to all continents. Ovitraps are containers constructed to imitate Aedes' natural breeding sites and have been used for many decades as a sensitive and inexpensive surveillance tool for detecting the presence of container-inhabiting mosquitoes. In addition to their value for vector surveillance, various ovitrap devices have been evaluated as tools for suppressing Ae. aegypti populations. In this study, we performed a biological and chemical characterization of a new ovitrap prototype manufactured by injection molding of low-density polyethylene (LDPE) with the larvicide pyriproxyfen. Our research shows that pyriproxyfen was immediately released from the LDPE into the water of the ovitrap and led to an emergence inhibition of 100% for over 30 weeks. In addition, ovitraps continued to show a high larvicidal activity after over 20 washes. Pyriproxyfen was detectable in the water after 20 s and reached a peak after 24 h. Our results show that this ovitrap can be an effective, inexpensive, and low-maintenance tool for Ae. aegypti surveillance and control.

Field evaluation of baited traps for surveillance of Aedes japonicus japonicus in Switzerland

The efficacy of Centers for Disease Control (CDC) miniature light traps and ovitraps was tested in the outskirts of the city of Zurich in Switzerland for their use in the surveillance of Aedes (Hulecoeteomyia) japonicus japonicus (Theobald) (Diptera: Culicidae), the invasive Asian bush mosquito. Sets of single CDC traps were run overnight (n = 18) in three different environments (forest, suburban and urban) in 3 × 3 Latin square experimental designs. Traps were baited with: (a) carbon dioxide (CO2 ); (b) CO2 plus light, or (c) CO2 plus lure blend [Combi FRC 3003 (iGu® )]. At the same locations, mosquito eggs were collected weekly using standard ovitraps baited with different infusions (oak, hay or tap water) and equipped with different oviposition substrates (a block of extruded polystyrene, a germination paper strip or a wooden stick). Data were analysed using Poisson and negative binomial general linear models. The use of light (P < 0.001) or lure (P < 0.001) significantly increased the attractiveness of CDC traps baited with CO2 . Oak and hay infusions did not increase the attractiveness of ovitraps compared with standing tap water (P > 0.05), and extruded polystyrene blocks were preferred as an oviposition substrate over wooden sticks (P < 0.05) and seed germination paper (P < 0.05). Carbon dioxide-baited CDC miniature light traps complemented with light or iGu® lure and ovitraps containing standing tap water and polystyrene oviposition blocks can be considered as efficient and simple tools for use in Ae. j. japonicus surveillance programmes.

Evidence for Aedes aegypti (Diptera: Culicidae) Oviposition on Boats in the Peruvian Amazon

Dengue vector Aedes aegypti L. is invading peri-urban and rural areas throughout Latin America. Our previous research in the Peruvian Amazon has shown that river boats are heavily infested with immature and adult Ae. aegypti mosquitoes, likely playing a major role in their long-distance dispersal and successful invasion. However, the presence of immature mosquitoes provides no information about the timing of oviposition, and whether it took place in the boats. Here, we used baited ovitraps deployed on river boats to test the hypothesis that Ae. aegypti oviposition occurs during boat travel. We deployed 360 ovitraps on 60 different barges during August and October of 2013, and February 2014 (with 20 barges sampled during each month). We found that Ae. aegypti mosquitoes in 22 individual ovitraps from 15 of the 60 barges (premise index 25%) across all sampling dates. Further, the distribution of Ae. aegypti egg abundance was highly aggregated: 2.6% of traps (N=7) were responsible for 71.8% of eggs found, and 1.5% of traps (N=4) were responsible for all (100%) of the larvae found. Similarly, 5% of boats were responsible for the 71.47% of eggs. Our results provide strong evidence that Ae. aegypti oviposition commonly occurs during boat travel. Baited ovitraps could represent a cost-effective means of monitoring and controlling mosquito populations on boats.

High Resolution Spatial Analysis of Habitat Preference of Aedes Albopictus (Diptera: Culicidae) in an Urban Environment

Over the past decades, the Asian tiger mosquito (Aedes albopictus (Skuse, 1895)) has emerged in many countries, and it has colonized new environments, including urban areas. The species is a nuisance and a potential vector of several human pathogens, and a better understanding of the habitat preferences of the species is needed for help in successful prevention and control. So far, the habitat preference in urban environments has not been studied in Southern European cities. In this paper, spatial statistical models were used to evaluate the relationship between egg abundances and land cover types on the campus of Sapienza University in Rome, which is taken as an example of a European urban habitat. Predictor variables included land cover types, classified in detail on a high resolution image, as well as solar radiation and month of capture. The models account for repeated measures in the same trap and are adjusted for meteorological circumstances. Vegetation and solar radiation were found to be positively related to the number of eggs. More specifically, trees were positively related to the number of eggs and the relationship with grass was negative. These findings are consistent with the species' known preference for shaded areas. The unexpected positive relationship with solar radiation is amply discussed in the paper. This study represents a first step toward a better understanding of the spatial distribution of Ae. albopictus in urban environments.

Updated distribution of Aedes albopictus (Diptera: Culicidae) in Spain: new findings in the mainland Spanish Levante, 2013

In 2004, Aedes (Stegomyia) albopictus (Skuse, 1894) was observed for the first time in Catalonia, northeastern Spain. A decade later, it has spread throughout the eastern Mediterranean region of the country and the Balearic Islands. Framed within a national surveillance project, we present the results of monitoring in 2013 in the autonomous communities of the mainland Levante. The current study reveals a remarkable increase in the spread of the invasive mosquito in relation to results from 2012; the species was present and well-established in 48 municipalities, most of which were along the Mediterranean coastline from the Valencian Community to the Region of Murcia.

Invasion of Wolbachia at the residential block level is associated with local abundance of Stegomyia aegypti, yellow fever mosquito, populations and property attributes

Wolbachia can suppress dengue and control mosquito populations and this depends on the successful invasion of Wolbachia-infected mosquitoes into local populations. Ovitrap data collected during the recent invasion of wMel-infected Stegomyia aegypti (Diptera: Culicidae) (Linnaeus) into Gordonvale near Cairns, Australia, were used to identify variables that help predict the success of localized invasion. Based on the variance in Wolbachia frequencies across Gordonvale as well as at another release site at Yorkeys Knob in comparison to simulations, it was estimated that on average 2-4 females contributed eggs to an ovitrap. By collating ovitrap data from two collection periods at the start of the release from residential blocks, it was found that uninfected mosquitoes had a patchy distribution across the release site. Residential blocks with relatively high uninfected mosquito numbers were less easily invaded by Wolbachia than blocks with low numbers. The numbers of uninfected mosquitoes in ovitraps were negatively correlated with the proportion of brick houses in a residential block, whereas local Wolbachia frequencies were correlated positively with this variable as well as negatively with the amount of shading in a yard and availability of breeding sites. These findings point to proxy measures for predicting the ease of localized invasion of Wolbachia.

Prevalence and insecticide susceptibility of dengue vectors in the district of Batticaloa in eastern Sri Lanka

Unprecedented incidences of dengue have been reported in Sri Lanka in recent years. The district of Batticaloa, which was devastated by the 2004 Asian tsunami, is one of the districts affected by dengue. One option to curtail this disease is to implement appropriate vector control measures. A nine-month study was carried out within the Batticaloa Municipal Council limit from April to December 2008. Larval collections were conducted fortnightly using conventional ovitraps for nine months covering the dry and wet seasons. Ovitraps (indoor and outdoor) were placed in 15 randomly selected houses. The collected larvae were brought to the laboratory and reared under laboratory conditions. The larval forms and emerged adults were identified on the basis of reported morphological descriptions. The identified adults of 2-3 d old were exposed to common insecticides following the WHO protocol. During the study period, a total of 10,685 Aedes aegypti and Ae. albopictus mosquitoes were collected, with the former constituting 57% of the total sample. Both species were collected from indoor and outdoor ovitraps, and their prevalence was recorded throughout the study period. A seasonal shift was observed in the density, with Ae. aegypti predominating during the dry season and Ae. albopictus during the wet season. Both species were highly resistant to 4% DDT and susceptible to 0.25% permethrin. The continuous presence of potential dengue vectors may have contributed to the dengue prevalence in the district. Since both species can oviposit in indoor and outdoor ovitraps, public awareness and participation should be promoted in the vector control programme of the Ministry of Health along with continuous vector surveillance.

Culex mosquitoes (Diptera: Culicidae) egg laying in traps loaded with Bacillus thuringiensis variety israelensis and baited with skatole

The Southern house mosquito, Culex quinquefasciatus, is an important human health pest as a vector of several pathogens, including agents of lymphatic filariasis and arboviruses like West Nile virus. We conducted preliminary experiments in Recife, Brazil, to explore applications of Culex oviposition attractants in combination with Bacillus thuringiensis variety israelensis (Bti) in an attract-and-kill approach. Simple, cost-effective oviposition traps, BR-OVT, loaded with Bti and baited with or without attractant, were deployed in 10 homes for 30 d in 2 consecutive yr. Significantly higher numbers of egg rafts were deposited in traps baited with skatole or infusion than the control water traps. In the first year, 2006, significantly higher numbers of eggs were deposited in infusion-baited traps, particularly in the first 15 d of the experiment, than in skatole traps, but in the following year no significant difference was observed between synthetic and natural attractants. The tests strongly demonstrate that skatole or infusion can be used to enhance the number of egg rafts deposited on Bti-treated oviposition traps.