A Low-Powered and Highly Selective Trap for Male Aedes (Diptera: Culicidae) Surveillance: The Male Aedes Sound Trap

Automated differentiation of mixed populations of free-flying female mosquitoes under semi-field conditions

Great advances in automated identification systems, or 'smart traps', that differentiate insect species have been made in recent years, yet demonstrations of field-ready devices under free-flight conditions remain rare. Here, we describe the results of mixed-species identification of female mosquitoes using an advanced optoacoustic smart trap design under free-flying conditions. Point-of-capture classification was assessed using mixed populations of congeneric (Aedes albopictus and Aedes aegypti) and non-congeneric (Ae. aegypti and Anopheles stephensi) container-inhabiting species of medical importance. Culex quinquefasciatus, also common in container habitats, was included as a third species in all assessments. At the aggregate level, mixed collections of non-congeneric species (Ae. aegypti, Cx. quinquefasciatus, and An. stephensi) could be classified at accuracies exceeding 90% (% error = 3.7-7.1%). Conversely, error rates increased when analysing individual replicates (mean % error = 48.6; 95% CI 8.1-68.6) representative of daily trap captures and at the aggregate level when Ae. albopictus was released in the presence of Ae. aegypti and Cx. quinquefasciatus (% error = 7.8-31.2%). These findings highlight the many challenges yet to be overcome but also the potential operational utility of optoacoustic surveillance in low diversity settings typical of urban environments.

The oral repellent - science fiction or common sense? Insects, vector-borne diseases, failing strategies, and a bold proposition

Over the last decades, unimaginable amounts of money have gone into research and development of vector control measures, repellents, treatment, and vaccines for vector borne diseases. Technological progress and scientific breakthroughs allowed for ever more sophisticated and futuristic strategies. Yet, each year, millions of people still die or suffer from potentially serious consequences of malaria or dengue to more recent infections, such as zika or chikungunya, or of debilitating consequences of neglected tropical diseases. This does not seem value for money. In addition, all current vector control strategies and personal protection methods have shortcomings, some serious, that are either destructive to non-target species or unsatisfactory in their effectiveness. On the other hand, the rapid decline in insect populations and their predators reflects decades-long aggressive and indiscriminate vector control. This major disruption of biodiversity has an impact on human life not anticipated by the well-meaning killing of invertebrates. The objective of this paper is to re-examine current control methods, their effectiveness, their impact on biodiversity, human and animal health, and to call for scientific courage in the pursuit of fresh ideas. This paper brings together topics that are usually presented in isolation, thereby missing important links that offer potential solutions to long-standing problems in global health. First, it serves as a reminder of the importance of insects to human life and discusses the few that play a role in transmitting disease. Next, it examines critically the many currently employed vector control strategies and personal protection methods. Finally, based on new insights into insect chemo-sensation and attractants, this perspective makes a case for revisiting a previously abandoned idea, the oral repellent, and its use via currently successful methods of mass-application. The call is out for focused research to provide a powerful tool for public health, tropical medicine, and travel medicine.

The MosHouse® Trap: Evaluation of the Efficiency in Trapping Sterile Aedes aegypti Males in Semi-Field Conditions

Arbovirus diseases, such as dengue, chikungunya, and Zika, are important public health problems. Controlling the major vector, Aedes aegypti, is the only approach to suppressing these diseases. The surveillance of this mosquito species needs effective collecting methods. In this study, a simple MosHouse sticky trap was evaluated in a semi-field condition. Our results demonstrated the efficiency of this trap in collecting Ae. aegypti males, and no significant difference (p > 0.05) in the numbers of males was detected when compared with the widely used BG- Sentinel trap. However, there were significantly lower numbers of females (p < 0.05) collected using the MosHouse trap when compared to the BG-Sentinel trap. We also found a significant difference (p < 0.05) in the collected numbers between irradiated and non-irradiated males. More irradiated males were collected in the MosHouse traps. The improvement of male collection was achieved with the addition of a sugar stick and sticky flags. Significantly higher numbers of males were collected in the MosHouse trap with sticky flags compared to the original one when they were released independently of females, but both were collected in higher numbers when they were released together (p < 0.05). In conclusion, our experiments demonstrated that the MosHouse trap could sample Ae. aegypti, especially males, as efficiently as the established BG-Sentinel trap, while the cost was more than 50 times lower, showing the potential of the MosHouse trap for improved Ae. aegypti male and female surveillance with very large numbers of traps at affordable costs. In addition, significantly (p < 0.001) increased male sampling was achieved by adding an external sticky flag on the MosHouse trap, providing an avenue for further development of the novel male-trapping strategy.

A literature review of dispersal pathways of Aedes albopictus across different spatial scales: implications for vector surveillance

BACKGROUND

Aedes albopictus is a highly invasive species and an important vector of dengue and chikungunya viruses. Indigenous to Southeast Asia, Ae. albopictus has successfully invaded every inhabited continent, except Antarctica, in the past 80 years. Vector surveillance and control at points of entry (PoE) is the most critical front line of defence against the introduction of Ae. albopictus to new areas. Identifying the pathways by which Ae. albopictus are introduced is the key to implementing effective vector surveillance to rapidly detect introductions and to eliminate them.

METHODS

A literature review was conducted to identify studies and data sources reporting the known and suspected dispersal pathways of human-mediated Ae. albopictus dispersal between 1940-2020. Studies and data sources reporting the first introduction of Ae. albopictus in a new country were selected for data extraction and analyses.

RESULTS

Between 1940-2020, Ae. albopictus was reported via various dispersal pathways into 86 new countries. Two main dispersal pathways were identified: (1) at global and continental spatial scales, maritime sea transport was the main dispersal pathway for Ae. albopictus into new countries in the middle to late 20th Century, with ships carrying used tyres of particular importance during the 1980s and 1990s, and (2) at continental and national spatial scales, the passive transportation of Ae. albopictus in ground vehicles and to a lesser extent the trade of used tyres and maritime sea transport appear to be the major drivers of Ae. albopictus dispersal into new countries, especially in Europe. Finally, the dispersal pathways for the introduction and spread of Ae. albopictus in numerous countries remains unknown, especially from the 1990s onwards.

CONCLUSIONS

This review identified the main known and suspected dispersal pathways of human-mediated Ae. albopictus dispersal leading to the first introduction of Ae. albopictus into new countries and highlighted gaps in our understanding of Ae. albopictus dispersal pathways. Relevant advances in vector surveillance and genomic tracking techniques are presented and discussed in the context of improving vector surveillance.

Evaluation of the New Modular Biogents BG-Pro Mosquito Trap in Comparison to CDC, EVS, BG-Sentinel, and BG-Mosquitaire Traps

Mosquito surveillance is an essential component of mosquito control and mosquito traps are a universally employed tool to monitor adult populations. The objective of this paper was to evaluate the new modular Biogents BG-Pro mosquito trap (BGP) and compare its performance to 4 widely used traps for adult mosquitoes: the BG-Sentinel (BGS), the BG Mosquitaire (BGM), the CDC miniature light trap (CDC), and the encephalitis vector survey trap (EVS). One semi-field and 9 field Latin square trials were performed in 7 countries. Results showed that the collection performance of the BGP was equivalent to or exceeded that of the BGS, BGM, CDC, and EVS traps in head-to-head comparisons. The BGP uses 35% less power than the CDC and 75% less than the BGS and BGM. This lower power consumption allows it to run at 5 V for 2 days using a small lightweight 10,000-mAh rechargeable power bank. The BG-Pro is an excellent alternative for the surveillance of mosquito species that are usually monitored with BG-Sentinel, CDC, or EVS traps.

Effect of BG-Lures on the Male Aedes (Diptera: Culicidae) Sound Trap Capture Rates

With global expansion of the two main vectors of dengue, Aedes aegypti (Linnaeus, Diptera: Culicidae) and Aedes albopictus (Skuse, Diptera: Culicidae), there is a need to further develop cost-effective and user-friendly surveillance tools to monitor the population dynamics of these species. The abundance of Ae. aegypti and Ae. Albopictus, and associated bycatch captured by Male Aedes Sound Traps (MASTs) and BG-Sentinel (BGS) traps that were unbaited or baited with BG-Lures were compared in Cairns, Australia and Madang, Papua New Guinea. Mean male Ae. aegypti and Ae. albopictus catch rates in MASTs did not significantly differ when deployed with BG-Lures. Similarly, males of both these species were not sampled at statistically different rates in BGS traps with or without BG-Lures. However, MASTs with BG-Lures caught significantly less male Ae. aegypti than BGS traps baited with BG-Lures in Cairns, and MASTs without BG-Lures caught significantly more male Ae. albopictus than BGS traps without BG-Lures in Madang. Additionally, BG-Lures significantly increased female Ae. aegypti catch rates in BGS traps in Cairns. Lastly, bycatch capture rates in BGS traps were not significantly influenced by the addition of the BG-Lures. While this study provides useful information regarding the surveillance of Ae. aegypti and Ae. albopictus in these locations, further development and investigation is required to successfully integrate an olfactory lure into the MAST system.

Designing Aedes (Diptera: Culicidae) Mosquito Traps: The Evolution of the Male Aedes Sound Trap by Iterative Evaluation

Effective surveillance of Aedes aegypti (Linnaeus, Diptera: Culicidae) is critical to monitoring the impact of vector control measures when mitigating disease transmission by this species. There are benefits to deploying male-specific traps, particularly when a high level of catch-specificity is desired. Here, the rationale behind the developmental process of an entirely new trap which uses a sound lure to capture male Ae. aegypti, the male Aedes sound trap (MAST), is presented as a target product profile with findings from developmental trials of key trap components and performance. Trial results suggest that the presence of a black base associated with the trap influenced male catches as did variations in size of this base, to a degree. Trap entrance shape didn't influence catch rates, but entrance size did. No significant differences in catch rates were found when sound lures were set to intermittent or continuous playbacks, at volumes between 63-74 dB or frequencies of 450 Hz compared to 500 Hz. Additionally, adult males aged 3 days post-eclosion, were less responsive to sound lures set to 500 Hz than those 4 or 6 days old. Lastly, almost no males were caught when the MAST directly faced continual winds of 1.5 ms^-1, but males were captured at low rates during intermittent winds, or if the trap faced away from the wind. The developmental process to optimising this trap is applicable to the development of alternate mosquito traps beyond Aedes sound traps and provides useful information towards the improved surveillance of these disease vectors.

The Effect of Sound Lure Frequency and Habitat Type on Male Aedes albopictus (Diptera: Culicidae) Capture Rates With the Male Aedes Sound Trap

The global distribution of Aedes albopictus (Skuse) is rapidly expanding which has contributed to the emergence and re-emergence of dengue and chikungunya outbreaks. Improvements in vector surveillance are necessary to facilitate optimized, evidence-based vector control operations. Current trapping technology used to target Ae. albopictus and other Aedes species for vector surveillance are limited in both scale and scope, thus novel tools are required. Here, we evaluated the Male Aedes Sound Trap (MAST) for its capacity to sample male Ae. albopictus. Aims of this study were twofold: 1) to determine the most effective frequency for capturing male Ae. albopictus and 2) to investigate fine-scale variations in male Ae. albopictus abundance. MASTs which produced sound lure frequencies between 500 and 650 Hz captured significantly more male Ae. albopictus than those with sound lure frequencies set to 450 Hz. Further, the higher sound lure frequency of 700 Hz significantly reduced catches relative to 650 Hz. MASTs placed in woodland habitats captured significantly more male Ae. albopictus than MASTs placed near houses. These results provide baseline information for optimizing sound lure frequencies and placement of the MAST to sample male Ae. albopictus in remote areas.

Outcomes from international field trials with Male Aedes Sound Traps: Frequency-dependent effectiveness in capturing target species in relation to bycatch abundance

Aedes aegypti and Aedes albopictus vector dengue, chikungunya and Zika viruses. With both species expanding their global distributions at alarming rates, developing effective surveillance equipment is a continuing priority for public health researchers. Sound traps have been shown, in limited testing, to be highly species-specific when emitting a frequency corresponding to a female mosquito wingbeat. Determining male mosquito capture rates in sound traps based on lure frequencies in endemic settings is the next step for informed deployment of these surveillance tools. We field-evaluated Male Aedes Sound Traps (MASTs) set to either 450 Hz, 500 Hz, 550 Hz or 600 Hz for sampling Aedes aegypti and/or Aedes albopictus and compared catch rates to BG-Sentinel traps within Pacific (Madang, Papua New Guinea) and Latin American (Molas, Mexico and Orange Walk Town, Belize) locations. MASTs set to 450-550 Hz consistently caught male Ae. aegypti at rates comparable to BG-Sentinel traps in all locations. A peak in male Ae. albopictus captures in MASTs set at 550 Hz was observed, with the lowest mean abundance recorded in MASTs set to 450 Hz. While significantly higher abundances of male Culex were sampled in MASTs emitting lower relative frequencies in Molas, overall male Culex were captured in significantly lower abundances in the MASTs, relative to BG-Sentinel traps within all locations. Finally, significant differences in rates at which male Aedes and Culex were positively detected in trap-types per weekly collections were broadly consistent with trends in abundance data per trap-type. MASTs at 550 Hz effectively captured both male Ae. aegypti and Ae. albopictus while greatly reducing bycatch, especially male Culex, in locations where dengue transmission has occurred. This high species-specificity of the MAST not only reduces staff-time required to sort samples, but can also be exploited to develop an accurate smart-trap system-both outcomes potentially reducing public health program expenses.

Detecting Aedes aegypti mosquitoes through audio classification with convolutional neural networks

The incidence of mosquito-borne diseases is significant in under-developed regions, mostly due to the lack of resources to implement aggressive control measurements against mosquito proliferation. A potential strategy to raise community awareness regarding mosquito proliferation is building a live map of mosquito incidences using smartphone apps and crowdsourcing. In this paper, we explore the possibility of identifying Aedes aegypti mosquitoes using machine learning techniques and audio analysis captured from commercially available smartphones. In summary, we downsampled Aedes aegypti wingbeat recordings and used them to train a convolutional neural network (CNN) through supervised learning. As a feature, we used the recording spectrogram to represent the mosquito wingbeat frequency over time visually. We trained and compared three classifiers: a binary, a multiclass, and an ensemble of binary classifiers. In our evaluation, the binary and ensemble models achieved accuracy of 97.65% (±0.55) and 94.56% (±0.77), respectively, whereas the multiclass had an accuracy of 78.12% (±2.09). The best sensitivity was observed in the ensemble approach (96.82% ± 1.62), followed by the multiclass for the particular case of Aedes aegypti (90.23% ± 3.83) and the binary (88.49% ± 6.68). The binary classifier and the multiclass classifier presented the best balance between precision and recall, with F1-measure close to 90%. Although the ensemble classifier achieved the lowest precision, thus impairing its F1-measure (79.95% ± 2.13), it was the most powerful classifier to detect Aedes aegypti in our dataset.