Applicability of the Mexican ovitrap system for Aedes vector surveillance in Colombia

Ovitraps can detect Aedes vectors at an early stage and can serve as an alarm indicator for outbreak prediction. This study aimed to summarize the available literature about the ovitrap system and to determine its feasibility, required resources and costs when installing and maintaining this vector surveillance system in the municipality of Los Patios, Colombia. A scoping review to assess the role of ovitraps as a tool for Aedes vector surveillance was conducted. The subsequent fieldwork consisted of mapping the municipality, manufacturing, and installing 40 ovitraps in 10 blocks, revising them weekly for 4 weeks by two half-time employed vector control technicians, and carrying out a cost analysis. A total of 38 studies were included in this review showing that ovitraps had a better performance than other entomological surveillance methods and a positive correlation with other entomological and disease variables. From the field results over 4 weeks, a high proportion of positive ovitraps (80%, 90%, 75%, 97.5%) and positive blocks (100%) as well as a good acceptance by house owners (76.9%), were identified. Operational indicators such as average installation time of the ovitraps (10h15 m), weekly reading and reinstallation (on average 7h27 m) and the cost of the intervention (COL$1,142,304.47/US$297) were calculated. Literature shows that ovitraps are sensitive to detect the presence of Aedes mosquitoes, providing data efficiently and timely for outbreak prediction. The field testing showed it is an affordable and feasible method in the context of a Colombian municipality and similar endemic areas.

From tissue engineering to mosquitoes: biopolymers as tools for developing a novel biomimetic approach to pest management/vector control

Background

Pest management has been facing the spread of invasive species, insecticide resistance phenomena, and concern for the impact of chemical pesticides on human health and the environment. It has tried to deal with them by developing technically efficient and economically sustainable solutions to complement/replace/improve traditional control methods. The renewal has been mainly directed towards less toxic pesticides or enhancing the precision of their delivery to reduce the volume employed and side effects through lure-and-kill approaches based on semiochemicals attractants. However, one of the main pest management problems is that efficacy depends on the effectiveness of the attractant system, limiting its successful employment to semiochemical stimuli-responsive insects. Biomaterial-based and bioinspired/biomimetic solutions that already guide other disciplines (e.g., medical sciences) in developing precision approaches could be a helpful tool to create attractive new strategies to liberate precision pest management from the need for semiochemical stimuli, simplify their integration with bioinsecticides, and foster the use of still underemployed solutions.

Approach proposed

We propose an innovative approach, called “biomimetic lure-and-kill”. It exploits biomimetic principles and biocompatible/biodegradable biopolymers (e.g., natural hydrogels) to develop new substrates that selectively attract insects by reproducing specific natural environmental conditions (biomimetic lure) and kill them by hosting and delivering a natural biopesticide or through mechanical action. Biomimetic lure-and-kill-designed substrates point to provide a new attractive system to develop/improve and make more cost-competitive new and conventional devices (e.g. traps). A first example application is proposed using the tiger mosquito Aedes albopictus as a model.

Conclusions

Biomaterials, particularly in the hydrogel form, can be a useful tool for developing the biomimetic lure-and-kill approach because they can satisfy multiple needs simultaneously (e.g., biomimetic lure, mechanical lethality, biocompatibility, and bioinsecticide growth). Such an approach might be cost-competitive, and with the potential for applicability to several pest species. Moreover, it is already technically feasible, since all the technologies necessary to design and configure materials with specific characteristics are already available on the market.

Graphical Abstract

Field evaluation of WALS truck-mounted A1 super duty mist sprayer® with VectoBac® WDG against Aedes aegypti (Diptera:Culicidae) populations in Manatee County, Florida

Aedes aegypti, the Dengue and Zika vector, is a domestic mosquito that is difficult to control. The challenge lies in the mosquito’s preference to lay its eggs in cryptic habitats such as fence post openings, buckets and bird baths, cups. Additionally, current methods of control are labor-intensive. We employed the WALS strategy to evaluate the operational efficacy of applying VectoBac WDG using a truck-mounted mister to control local populations of Ae. aegypti in urban settings with difficult-to-reach larval mosquito habitats. Our study was conducted in Cortez (Manatee County), Florida, USA (27° 27’ N, 82° 40’ W). We selected two study sites, one untreated control (21.9 ha) and one treatment site (23.1 ha) where historical data have shown high populations of Ae. aegypti based on weekly ovitrap surveillance. Weekly BGs and ovitraps (10–15 traps/site) were deployed to monitor adult population dynamics. A total of 50 bioassay jars were placed in the field each afternoon of the Bti application (8 application events) at fixed locations to collect droplets and gauge efficacy. We found significant reduction in female adults (P = 0.0002) and landing rate counts (P = 0.0058) as a result of treatment. Larval bioassays during the eight applications confirmed Bti deposit in a variety of coverage types regardless of placement in the yards. WALS applications with a truck-mounted mister can be effective at reducing disease carrying mosquito populations in residential areas and can be implemented in an integrated vector management program.

Influence of abiotic factors on the oviposition of Aedes (Stegomyia) aegypti (Diptera: Culicidae) in Northern Paraná, Brazil

Aedes aegypti is the main vector of dengue in the Americas and is also a transmitter of urban yellow fever arboviruses, Zika, and Chikungunya, all of which have substantial economic impacts on the affected countries. Through mathematical models, the influence of climatic factors on the oviposition of Ae. aegypti was determined. The data were collected in the city of Apucarana, Paraná State, using oviposition traps. Daily data were submitted to a negative binomial regression model (p < 0.05). The analyses were performed using the R statistical program to determine the climatic factors that most influenced oviposition. A Poisson regression showed that the variables temperature, atmospheric pressure, humidity, and precipitation significantly increased the number of eggs. However, using the semi-normal probability graph with a simulation envelope, it was determined that the Poisson regression model was not adequate to explain the relationships between the variables. Thus, a negative binomial regression model was used, which overcame the problem of overdispersion, and showed that only temperature affected the increase in the number of eggs, where an increase of 1 °C was expected to result in a 54.03% increase in the number of Ae. aegypti eggs.

Effectiveness of integrated Aedes albopictus management in southern Switzerland

BACKGROUND

The exotic invasive tiger mosquito, Aedes albopictus, appeared in southern Switzerland in 2003. The spread of the mosquito has been surveyed constantly since then, and an integrated vector management (IVM) has been implemented to control its numbers. The control measures focus on the aquatic phase of the mosquito with removal of breeding sites and applications of larvicides in public areas whereas private areas are reached through extensive public information campaigns. Here, we evaluated the efficacy of the IVM.

METHODS

Since all the municipalities with Ae. albopictus in southern Switzerland are currently implementing the IVM, Italian municipalities just across the Swiss-Italian border, where Ae. albopictus is present but no coordinated intervention programme is in place, served as control. Ovitraps and adult female traps were used to measure mosquito abundance in 2019. Generalised mixed-effects models were used to model the numbers of Ae. albopictus eggs and adult females collected. These numbers of Ae. albopictus eggs were compared to the numbers of eggs collected in 2012 and 2013 in a previous assessment of the IVM, using a hurdle model.

RESULTS

Mean numbers of Ae. albopictus eggs and adult females in 2019 were consistently higher in the municipalities not following an IVM programme. In these municipalities, there were about four times (3.8) more eggs than in the municipalities implementing an IVM programme. Also, the numbers of eggs and adult females increased steadily from the beginning of the Ae. albopictus reproductive season, reaching a peak in August. In contrast, the increase in numbers of Ae. albopictus was much more contained in the municipalities implementing an IVM programme, without reaching an evident peak. Comparison with data from 2012 and 2013 indicates that the gap between intervention and non-intervention areas may have almost doubled in the past 6 years.

CONCLUSIONS

The results of the survey strongly support the efficacy of the IVM programme implemented in southern Switzerland compared to municipalities without defined control measures. With the constant implementation of an IVM, it appears possible to contain the numbers of Ae. albopictus at a manageable level, reducing the nuisance for the human population and the risk of arbovirus epidemics.

Employing Different Traps for Collection of Mosquitoes and Detection of Dengue, Chikungunya and Zika Vector, Aedes albopictus, in Borderline of Iran and Pakistan

Background:

Southeastern Iran has been established as an area with the potential to harbor Asian tiger mosquito populations. In 2013, a few numbers of Aedes albopictus were detected in three sampling sites of this region. This field study was aimed to evaluate the efficacy of various traps on monitoring mosquitoes and status of this dengue vector, in five urban and 15 suburban/rural areas.

Methods:

For this purpose, four adult mosquito traps (BG-sentinel 2, bednet, Malaise, and resting box trap) were used and their efficacy compared. In addition, large numbers of CDC ovitraps were employed, within 12 months.

Results:

A total of 4878 adult samples including 22 species covering five genera were collected and identified from traps. It was not revealed any collection of Ae. albopictus. Statistical analysis showed no significant difference in meteorological variables between the two periods, the previous report and the current study. There were significant differences in the total number of mosquitoes collected by various traps in the region across different months.

Conclusion:

The resulting data collected here on the efficiency of the various trap types can be useful for monitoring the densities of mosquito populations, which is an important component of a vector surveillance system. While the presence of Ae. albopictus was determined in this potential risk area, there is no evidence for its establishment and further monitoring needs to be carried out.

A decade of arbovirus emergence in the temperate southern cone of South America: dengue, Aedes aegypti and climate dynamics in Córdoba, Argentina

BACKGROUND

Argentina is located at the southern temperate range of arboviral transmission by the mosquito Aedes aegypti and has experienced a rapid increase in disease transmission in recent years. Here we present findings from an entomological surveillance study that began in Córdoba, Argentina, following the emergence of dengue in 2009.

METHODS

From 2009 to 2017, larval surveys were conducted monthly, from November to May, in 600 randomly selected households distributed across the city. From 2009 to 2013, ovitraps (n = 177) were sampled weekly to monitor the oviposition activity of Ae. aegypti. We explored seasonal and interannual dynamics of entomological variables and dengue transmission. Cross correlation analysis was used to identify significant lag periods.

RESULTS

Aedes aegypti were detected over the entire study period, and abundance peaked during the summer months (January to March). We identified a considerable increase in the proportion of homes with juvenile Ae. aegypti over the study period (from 5.7% of homes in 2009-10 to 15.4% of homes in 2016-17). Aedes aegypti eggs per ovitrap and larval abundance were positively associated with temperature in the same month. Autochthonous dengue transmission peaked in April, following a peak in imported dengue cases in March; autochthonous dengue was not positively associated with vector or climate variables.

CONCLUSIONS

This longitudinal study provides insights into the complex dynamics of arbovirus transmission and vector populations in a temperate region of arbovirus emergence. Our findings suggest that Córdoba is well suited for arbovirus disease transmission, given the stable and abundant vector populations. Further studies are needed to better understand the role of regional human movement.

Field evaluation of Mosq-ovitrap, Ovitrap and a CO2-light trap for Aedes albopictus sampling in Shanghai, China

BACKGROUND

The Mosq-ovitrap (MOT) is currently used for routine surveillance of container-breeding Aedes in China. However, the effectiveness of monitoring Aedes albopictus using the MOT and other mosquito monitoring methods, such as the Ovitrap (OT) and the CO2-light trap (CLT), have not been extensively compared. Moreover, little is known about the spatial-temporal correlations of eggs with adult Ae. albopictus abundance among these three types of traps.

METHODS

Comparative field evaluation of MOT, OT and CLT for Ae. albopictus monitoring was conducted simultaneously at two city parks and three residential neighborhoods in downtown Shanghai for 8 months from April 21 to December 21, 2017.

RESULTS

Significantly more Ae. albopictus eggs were collected from both MOTs and OTs when traps remained in the field for 10 d or 7 d compared with 3 d (MOT: 50.16, 34.15 vs. 12.38 per trap, P < 0.001; OT: 3.98, 2.92 vs. 0.63 per trap, P < 0.001). Egg collections of MOTs were significantly greater than OTs for all three exposure durations (Percent positive: X 2 = 72.251, 52.420 and 51.429, P value all < 0.001; egg collections: t = 8.068, 8.517 and 10.021, P value all <0.001). Significant temporal correlations were observed between yields of MOT and CLT in all sampling locations and 3 different MOT exposure durations (correlation coefficient r ranged from 0.439 to 0.850, P values all < 0.05). However, great variation was found in the spatial distributions of Ae. albopictus density between MOT and CLT. MOT considerably underestimated Ae. albopictus abundances in areas with high Ae. albopictus density (>25.56 per day ⋅ trap by CLT).

CONCLUSION

The MOT was more efficient than the OT in percent positive scores and egg collections of Ae. albopictus. The minimum length of time that MOTs are deployed in the field should not be less than 7 d, as Ae. albopictus collections during this period were much greater than for 3 d of monitoring. MOT considerably underestimated Ae. albopictus abundance in areas with high Aedes albopictus density compared to CLT. In areas with moderate Aedes albopictus densities, MOT results were significantly correlated with CLT catches.

From eggs to bites: do ovitrap data provide reliable estimates of Aedes albopictus biting females?

BACKGROUND

Aedes albopictus is an aggressive invasive mosquito species that represents a serious health concern not only in tropical areas, but also in temperate regions due to its role as vector of arboviruses. Estimates of mosquito biting rates are essential to account for vector-human contact in models aimed to predict the risk of arbovirus autochthonous transmission and outbreaks, as well as nuisance thresholds useful for correct planning of mosquito control interventions. Methods targeting daytime and outdoor biting Ae. albopictus females (e.g., Human Landing Collection, HLC) are expensive and difficult to implement in large scale schemes. Instead, egg-collections by ovitraps are the most widely used routine approach for large-scale monitoring of the species. The aim of this work was to assess whether ovitrap data can be exploited to estimate numbers of adult biting Ae. albopictus females and whether the resulting relationship could be used to build risk models helpful for decision-makers in charge of planning of mosquito-control activities in infested areas.

METHOD

Ovitrap collections and HLCs were carried out in hot-spots of Ae. albopictus abundance in Rome (Italy) along a whole reproductive season. The relationship between the two sets of data was assessed by generalized least square analysis, taking into account meteorological parameters.

RESULT

The mean number of mosquito females/person collected by HLC in 15' (i.e., females/HLC) and the mean number of eggs/day were 18.9 ± 0.7 and 39.0 ± 2.0, respectively. The regression models found a significant positive relationship between the two sets of data and estimated an increase of one biting female/person every five additional eggs found in ovitraps. Both observed and fitted values indicated presence of adults in the absence of eggs in ovitraps. Notably, wide confidence intervals of estimates of biting females based on eggs were observed. The patterns of exotic arbovirus outbreak probability obtained by introducing these estimates in risk models were similar to those based on females/HLC (R0 > 1 in 86% and 40% of sampling dates for Chikungunya and Zika, respectively; R0 < 1 along the entire season for Dengue). Moreover, the model predicted that in this case-study scenario an R0 > 1 for Chikungunya is also to be expected when few/no eggs/day are collected by ovitraps.

DISCUSSION

This work provides the first evidence of the possibility to predict mean number of adult biting Ae. albopictus females based on mean number of eggs and to compute the threshold of eggs/ovitrap associated to epidemiological risk of arbovirus transmission in the study area. Overall, however, the large confidence intervals in the model predictions represent a caveat regarding the reliability of monitoring schemes based exclusively on ovitrap collections to estimate numbers of biting females and plan control interventions.

Oviposition ecology and species composition of Aedes spp. and Aedes aegypti dynamics in variously urbanized settings in arbovirus foci in southeastern Côte d'Ivoire

BACKGROUND

Aedes mosquito-transmitted outbreaks of dengue and yellow fever have been reported from rural and urban parts of Côte d'Ivoire. The present study aimed at assessing Aedes spp. oviposition ecology in variously urbanized settings within arbovirus foci in southeastern Côte d'Ivoire.

METHODS

Aedes spp. eggs were sampled using a standard ovitrap method from January 2013 to April 2014 in different ecosystems of rural, suburban and urban areas. Emerged larvae were reared until the adult stage for species identification.

RESULTS

Aedes spp. oviposition ecology significantly varied from rural-to-urban areas and according to the ecozones and the seasons. Species richness of Aedes spp. gradually decreased from rural (eight species) to suburban (three species) and urban (one species) areas. Conversely, emerged adult Aedes spp. mean numbers were higher in the urban (1.97 Aedes/ovitrap/week), followed by the suburban (1.44 Aedes/ovitrap/week) and rural (0.89 Aedes/ovitrap/week) areas. Aedes aegypti was the only species in the urban setting (100 %), and was also the predominant species in suburban (85.5 %) and rural (63.3 %) areas. The highest Ae. aegypti mean number was observed in the urban (1.97 Ae. aegypti/ovitrap/week), followed by the suburban (1.20 Ae. aegypti/ovitrap/week) and rural (0.57 Ae. aegypti/ovitrap/week) areas. Aedes africanus (9.4 %), Ae. dendrophilus (8.0 %), Ae. metallicus (1.3 %) in the rural, and Ae. vittatus (6.5 %) and Ae. metallicus (1.2 %) in the suburban areas each represented more than 1 % of the total Aedes fauna. In all areas, Aedes species richness and abundance were higher in the peridomestic zones and during the rainy season, with stronger variations in species richness in the rural and in abundance in the urban areas. Besides, the highest Culex quinquefasciatus abundance was found in the urban areas, while Eretmapodites chrysogaster was restricted to the rural areas.

CONCLUSIONS

Urbanization correlates with a substantially higher abundance in Aedes mosquitoes and a regression of the Aedes wild species towards a unique presence of Ae. aegypti in urban areas. Aedes wild species serve as bridge vectors of arboviruses in rural areas, while Ae. aegypti amplifies arbovirus transmission in urban areas. Our results have important ramifications for dengue and yellow fever vector control and surveillance strategies in arbovirus foci in southeastern Côte d'Ivoire.

Application of copper-based ovitraps in local houses in West Sumatra, Indonesia: a field test of a simple and affordable larvicide for mosquito control

Background

The application of oviposition traps (ovitraps) is one of the currently available rational methods used in mosquito control campaigns because it eliminates the larval stage. However, the use of current larvicides is hampered by their cost and applicability. Therefore, a more economical and practical alternative is urgently needed. We previously reported that copper in liquid form is a promising candidate due to its potent larvicide properties in a laboratory setting, affordability, and availability.

Methods

In the present study, a field test was performed by randomly placing copper-filled plastic pots with a concentration of 10 ppm in 21 local houses in Painan City, West Sumatra, Indonesia. Three of these pots including a control were placed inside, while another two were placed outside each of the houses.

Results

After 14 days, a large number of dead first and second instar larvae of Aedes spp. were observed in the copper-filled pots. Larvae in the control pots were all viable and thriving. Unhatched eggs and pupae were detected in several pots in the copper-treated group but were excluded from the analysis.

Conclusions

Our field data confirmed that copper is a potential larvicide for ovitraps, particularly in under-resourced areas.

Enhancement of Aedes albopictus collections by ovitrap and sticky adult trap

Background

In the last decades, Aedes albopictus has become an increasing public health threat in tropical as well as in more recently invaded temperate areas due to its capacity to transmit several human arboviruses, among which Dengue, Chikungunya and Zika. Enhancing the efficiency of currently used collection approaches, such as ovitraps and sticky traps, is desirable for optimal monitoring of the species abundance, for assessment of the risk of arbovirus transmission and for the optimisation of control activities.

Findings

Two sets of 4 × 4 Latin-square experiments were carried out in Tirana (Albania) to test whether modifications in ovitrap shape and size and in oviposition substrate would increase collections of Ae. albopictus eggs and whether hay-infusion would increase adult catches by sticky trap. Generalized Linear Mixed Models with negative binomial error distribution were carried out to analyse the data. Cylindrical ovitraps lined with germination paper yielded significantly higher egg catches than those exploiting either the (commonly used) wooden paddles or floating polystyrene blocks as oviposition substrates. No difference was observed between cylindrical and conical shaped ovitraps. Ovitraps and sticky traps baited with hay infusion yielded significantly higher egg and adult catches than un-baited ones. A significant relationship between ovitrap and sticky trap catches was observed both in the absence and in the presence of attractants, with ovitrap catches increasing more than sticky trap catches at increasing adult female densities.

Conclusions

This study provides grounds for optimisation of ovitraps and sticky traps as monitoring tools for Ae. albopictus by (i) supporting use of germination paper as most appropriate oviposition substrate; (ii) suggesting the possible use of stackable conical ovitraps for large scale monitoring; (iii) confirming the use of hay-infusion to increase egg catches in ovitraps, and showing that hay-infusion also significant increases adult catches by sticky traps.

Characterization of the spatial and temporal dynamics of the dengue vector population established in urban areas of Fernando de Noronha, a Brazilian oceanic island

Aedes aegypti has played a major role in the dramatic expansion of dengue worldwide. The failure of control programs in reducing the rhythm of global dengue expansion through vector control suggests the need for studies to support more appropriated control strategies. We report here the results of a longitudinal study on Ae. aegypti population dynamics through continuous egg sampling aiming to characterize the infestation of urban areas of a Brazilian oceanic island, Fernando de Noronha. The spatial and temporal distribution of the dengue vector population in urban areas of the island was described using a monitoring system (SMCP-Aedes) based on a 103-trap network for Aedes egg sampling, using GIS and spatial statistics analysis tools. Mean egg densities were estimated over a 29-month period starting in 2011 and producing monthly maps of mosquito abundance. The system detected continuous Ae. aegypti oviposition in most traps. The high global positive ovitrap index (POI=83.7% of 2815 events) indicated the frequent presence of blood-fed-egg laying females at every sampling station. Egg density (eggs/ovitrap/month) reached peak values of 297.3 (0 - 2020) in May and 295 (0 - 2140) in August 2012. The presence of a stable Ae. aegypti population established throughout the inhabited areas of the island was demonstrated. A strong association between egg abundance and rainfall with a 2-month lag was observed, which combined with a first-order autocorrelation observed in the series of egg counts can provide an important forecasting tool. This first description of the characteristics of the island infestation by the dengue vector provides baseline information to analyze relationships between the spatial distribution of the vector and dengue cases, and to the development of integrated vector control strategies.