A novel video-tracking system to quantify the behaviour of nocturnal mosquitoes attacking human hosts in the field

Abstract

Many vectors of malaria and other infections spend most of their adult life within human homes, the environment where they bloodfeed and rest, and where control has been most successful. Yet, knowledge of peri-domestic mosquito behaviour is limited, particularly how mosquitoes find and attack human hosts or how insecticides impact on behaviour. This is partly because technology for tracking mosquitoes in their natural habitats, traditional dwellings in disease-endemic countries, has never been available. We describe a sensing device that enables observation and recording of nocturnal mosquitoes attacking humans with or without a bed net, in the laboratory and in rural Africa. The device addresses requirements for sub-millimetre resolution over a 2.0 × 1.2 × 2.0 m volume while using minimum irradiance. Data processing strategies to extract individual mosquito trajectories and algorithms to describe behaviour during host/net interactions are introduced. Results from UK laboratory and Tanzanian field tests showed that Culex quinquefasciatus activity was higher and focused on the bed net roof when a human host was present, in colonized and wild populations. Both C. quinquefasciatus and Anopheles gambiae exhibited similar behavioural modes, with average flight velocities varying by less than 10%. The system offers considerable potential for investigations in vector biology and many other fields.

Diffuse retro-reflective imaging for improved video tracking of mosquitoes at human baited bednets

“…The original approach to segmentation [5] used a difference image between consecutive frames and a single threshold value to identify movement. Whilst developing the RRS system, two issues were found.…”

“…Large field of view back lit imaging systems have been reported with two parallel imaging channels to give a measurement volume of 2 x 2 x 1.4 m in total with large aperture Fresnel lenses enabling collimated illumination and telecentric imaging [5]. As part of this study, algorithms were also reported that produced flight tracks of 25 mosquitoes over hour long recording periods.…”

“…Optical imaging techniques have been used for decades in entomological studies in diverse settings in the laboratory and field, and recently a tracking system was used to characterise in detail how Anopheles gambiae mosquitoes, the vectors of human malaria in sub-Saharan Africa, interact with human-occupied bednet [1,2,5]. Offering high spatial and temporal resolution, optical imaging has clear advantages for quantifying vector behaviour [6,7], but their application in typical sub-Saharan Africa dwellings present particular challenges.…”

“…As part of this study, algorithms were also reported that produced flight tracks of 25 mosquitoes over hour long recording periods. Four behavioural modes were identified: swooping, visiting (the bednet), bouncing and resting [5]. The data gave insight into mosquito host seeking behaviour and quantified an individual mosquito's contact with the bednet (and hence insecticide) with the information leading to the 'barrier bednet' concept [1,2,20].…”

“…Apart from the addition of a Gaussian filter for de-noising and classification of the region to determine the appropriate threshold, the mosquito segmentation algorithm is identical to the one described in [5]. Whilst more complex algorithms could be implemented, the requirement to control the computational overhead was important given the need for operation in the field and on data sets of approximately 2 TB per hour of recording from the two cameras.…”