Biology and Behaviour of Aedes aegypti in the Human Environment: Opportunities for Vector Control of Arbovirus Transmission

Aedes aegypti is a ubiquitous vector of arboviruses mostly in urbanised areas throughout the tropics and subtropics and a growing threat beyond. Control of Ae. aegypti is difficult and costly, and no vaccines are available for most of the viruses it transmits. With practical control solutions our goal, ideally suitable for delivery by householders in affected communities, we reviewed the literature on adult Ae. aegypti biology and behaviour, within and close to the human home, the arena where such interventions must impact. We found that knowledge was vague or important details were missing for multiple events or activities in the mosquito life cycle, such as the duration or location of the many periods when females rest between blood feeding and oviposition. The existing body of literature, though substantial, is not wholly reliable, and evidence for commonly held “facts” range from untraceable to extensive. Source references of some basic information are poor or date back more than 60 years, while other information that today is accepted widely as “fact” is not supported by evidence in the literature. Many topics, e.g., sugar feeding, resting preferences (location and duration), and blood feeding, merit being revisited in new geographical regions and ecological contexts to identify vulnerabilities for exploitation in contro

Evaluation of a sticky trap for collecting Aedes (Stegomyia) adults in a dengue-endemic area in Thailand.

Development of new operational techniques for collection and monitoring of adult Stegomyia mosquitoes is considered a pressing need for surveillance and prevention of arboviruses. Here we report the results from a trial carried out in 2 dengue-endemic villages in Thailand to compare the ability to collect Aedes adults of a sticky trap versus a CDC backpack aspirator, which has been used routinely at the study area for entomological/epidemiological surveys.Our comparison was based on a comparable sampling effort required to carry out collections with 2 approaches. Over 19,000 specimens were collected, ∼90% of which were Culex spp. Sticky traps collected significantly more Aedes aegypti and Aedes albopictus females than did backpack aspirators when located outdoors. The percentage of positive sticky-trap catches was double for Ae. aegypti and almost 20 times higher for Ae. albopictus. Operational benefits of the sticky trap are discussed within the context of the results obtained

Mapping Aedes aegypti indoor resting behavior reveals a preference vulnerable to householder-led vector control

Many mosquito vectors rest inside human habitations, a behavioral trait that is exploited for vector control by indoor residual spraying (IRS) of interior walls with insecticide. Although IRS and its refined version targeted IRS are very effective against Aedes aegypti, they are expensive and logistically challenging to deliver in densely populated urban areas where outbreaks of dengue and other arboviruses are the greatest challenge. In experiments in Recife, Brazil, we set out to quantify the indoor resting behavior of Ae. aegypti at a level beyond that previously reported. We found that significantly more Ae. aegypti males, unfed and fed females visited the base of walls (height 0–20 cm, corresponding to 12.3% of the total wall surface) more frequently than upper wall areas, with the difference more pronounced at higher temperatures. When the lowest 20 cm of the walls was treated with an appropriate insecticide and colored black, we recorded up to 85% cumulative mortality after 24-h exposure in the experimental room. The findings are significant because feasibly, householders could treat this small and accessible target zone manually, without the need for visits by costly IRS teams or equipment, reducing insecticide use and enabling communities to actively protect their own indoor environment

Finding a Husband: Using Explainable AI to Define Male Mosquito Flight Differences

Mosquito-borne diseases account for around one million deaths annually. There is a constant need for novel intervention mechanisms to mitigate transmission, especially as current insecticidal methods become less effective with the rise of insecticide resistance among mosquito populations. Previously, we used a near infra-red tracking system to describe the behaviour of mosquitoes at a human-occupied bed net, work that eventually led to an entirely novel bed net design. Advancing that approach, here we report on the use of trajectory analysis of a mosquito flight, using machine learning methods. This largely unexplored application has significant potential for providing useful insights into the behaviour of mosquitoes and other insects. In this work, a novel methodology applies anomaly detection to distinguish male mosquito tracks from females and couples. The proposed pipeline uses new feature engineering techniques and splits each track into segments such that detailed flight behaviour differences influence the classifier rather than the experimental constraints such as the field of view of the tracking system. Each segment is individually classified and the outcomes are combined to classify whole tracks. By interpreting the model using SHAP values, the features of flight that contribute to the differences between sexes are found and are explained by expert opinion. This methodology was tested using 3D tracks generated from mosquito mating swarms in the field and obtained a balanced accuracy of 64.5% and an ROC AUC score of 68.4%. Such a system can be used in a wide variety of trajectory domains to detect and analyse the behaviours of different classes, e.g., sex, strain, and species. The results of this study can support genetic mosquito control interventions for which mating represents a key event for their success

Maintaining Quality of Candidate Strains of Transgenic Mosquitoes for Studies in Containment Facilities in Disease Endemic Countries

Transgenic mosquitoes are being developed as novel components of area-wide approaches to vector-borne disease control. Best practice is to develop these in phases, beginning with laboratory studies, before moving to field testing and inclusion in control programs, to ensure safety and prevent costly field testing of unsuitable strains. The process of identifying and developing good candidate strains requires maintenance of transgenic colonies over many generations in containment facilities. By working in disease endemic countries with target vector populations, laboratory strains may be developed and selected for properties that will enhance intended control efficacy in the next phase, while avoiding traits that introduce unnecessary risks. Candidate strains aiming toward field use must consistently achieve established performance criteria, throughout the process of scaling up from small study colonies to production of sufficient numbers for field testing and possible open release. Maintenance of a consistent quality can be demonstrated by a set of insect quality and insectary operating indicators, measured over time at predetermined intervals. These indicators: inform comparability of studies using various candidate strains at different times and locations; provide evidence of conformity relevant to compliance with terms of approval for regulated use; and can be used to validate some assumptions related to risk assessments covering the contained phase and for release into the environment

Containment Studies of Transgenic Mosquitoes in Disease Endemic Countries: The Broad Concept of Facilities Readiness

Genetic strategies for large scale pest or vector control using modified insects are not yet operational in Africa, and currently rely on import of the modified strains to begin preliminary, contained studies. Early involvement of research teams from participating countries is crucial to evaluate candidate field interventions. Following the recommended phased approach for novel strategies, evaluation should begin with studies in containment facilities. Experiences to prepare facilities and build international teams for research on transgenic mosquitoes revealed some important organizing themes underlying the concept of "facilities readiness," or the point at which studies in containment may proceed, in sub-Saharan African settings. First, "compliance" for research with novel or non-native living organisms was defined as the fulfillment of all legislative and regulatory requirements. This is not limited to regulations regarding use of transgenic organisms. Second, the concept of "colony utility" was related to the characteristics of laboratory colonies being produced so that results of studies may be validated across time, sites, and strains or technologies; so that the appropriate candidate strains are moved forward toward field studies. Third, the importance of achieving "defensible science" was recognized, including that study conclusions can be traced back to evidence, covering the concerns of various stakeholders over the long term. This, combined with good stewardship of resources and appropriate funding, covers a diverse set of criteria for declaring when "facilities readiness" has been attained. It is proposed that, despite the additional demands on time and resources, only with the balance of and rigorous achievement of each of these organizing themes can collaborative research into novel strategies in vector or pest control reliably progress past initial containment studies

Biology and Behaviour of Aedes aegypti in the Human Environment: Opportunities for Vector Control of Arbovirus Transmission

Aedes aegypti is a ubiquitous vector of arboviruses mostly in urbanised areas throughout the tropics and subtropics and a growing threat beyond. Control of Ae. aegypti is difficult and costly, and no vaccines are available for most of the viruses it transmits. With practical control solutions our goal, ideally suitable for delivery by householders in affected communities, we reviewed the literature on adult Ae. aegypti biology and behaviour, within and close to the human home, the arena where such interventions must impact. We found that knowledge was vague or important details were missing for multiple events or activities in the mosquito life cycle, such as the duration or location of the many periods when females rest between blood feeding and oviposition. The existing body of literature, though substantial, is not wholly reliable, and evidence for commonly held “facts” range from untraceable to extensive. Source references of some basic information are poor or date back more than 60 years, while other information that today is accepted widely as “fact” is not supported by evidence in the literature. Many topics, e.g., sugar feeding, resting preferences (location and duration), and blood feeding, merit being revisited in new geographical regions and ecological contexts to identify vulnerabilities for exploitation in control

Evaluation of a sticky trap for collecting Aedes (Stegomyia) adults in a dengue-endemic area in Thailand.

Development of new operational techniques for collection and monitoring of adult Stegomyia mosquitoes is considered a pressing need for surveillance and prevention of arboviruses. Here we report the results from a trial carried out in 2 dengue-endemic villages in Thailand to compare the ability to collect Aedes adults of a sticky trap versus a CDC backpack aspirator, which has been used routinely at the study area for entomological/epidemiological surveys. Our comparison was based on a comparable sampling effort required to carry out collections with 2 approaches. Over 19,000 specimens were collected, approximately 90% of which were Culex spp. Sticky traps collected significantly more Aedes aegypti and Aedes albopictus females than did backpack aspirators when located outdoors. The percentage of positive sticky-trap catches was double for Ae. aegypti and almost 20 times higher for Ae. albopictus. Operational benefits of the sticky trap are discussed within the context of the results obtained

Multivariate statistical and GIS-based approach to identify heavy metal sources in soils

The knowledge of the regional variability, the background values and the anthropic vs. natural origin for potentially harmful elements in soils is of critical importance to assess human impact and to fix guide values and quality standards. The present study was undertaken as a preliminary survey on soil contamination on a regional scale in Piemonte (NW Italy). The aims of the study were: (1) to determine average regional concentrations of some heavy metals (Cr, Co, Ni, Cu, Zn, Pb); (2) to find out their large-scale variability; (3) to define their natural or artificial origin; and (4) to identify possible non-point sources of contamination. Multivariate statistic approaches (Principal Component Analysis and Cluster Analysis) were adopted for data treatment, allowing the identification of three main factors controlling the heavy metal variability in cultivated soils. Geostatistics were used to construct regional distribution maps, to be compared with the geographical, geologic and land use regional database using GIS software. This approach, evidencing spatial relationships, proved very useful to the confirmation and refinement of geochemical interpretations of the statistical output. Cr, Cc and Ni were associated with and controlled by parent rocks, whereas Cu together with Zn, and Pb alone were controlled by anthropic activities. The study indicates that background values and realistic mandatory guidelines are impossible to fix without an extensive data collection and without a correct geochemical interpretation of the data