1 Department of Entomology, Wageningen Agricultural University, The Netherlands
2 Noldus Information Technology b.v., Wageningen, The Netherlands
Mosquito behaviour is to a large extent mediated by olfactory cues, originating from mammalian hosts, plants and oviposition sites. Whereas the end result of such behaviour can be readily recorded (the mosquito has flown into an odour-baited trap from a distance), the manoeuvres through which this behaviour is accomplished may reveal the role of the various cues involved and provide possible avenues for the interruption of mosquito host-seeking behaviour. We have developed a system whereby the flight behaviour of nocturnal mosquitoes is recorded on video and analyzed off-line providing a reconstructed three-dimensional image of the flight behaviour and mathematical data on specific flight characteristics. Studies are conducted with Anopheles gambiae sensu stricto, a tropical mosquito which is only active nocturnally. Mosquitoes are released singly in a 60x60x180 cm windtunnel, where odours are released at the upwind end from a large glass funnel, with the wide opening facing the tunnel. The wind speed is 20 cm/sec and temperature and relative humidity are 27 °C and 60-70%, respectively. Mosquito behaviour is recorded with two CCD cameras, mounted under 30 degree angles approx. 50 cm above the tunnel. The behavioural arena videoed in this way is 60x60x60 cm and covers the upwind section of the tunnel. Light for behavioural guidance is provided by 4 units of 100 light emitting diodes (LEDs), each unit emitting 250 W of energy. The LED units are mounted behind the video cameras.
Video images are captured by a frame grabber which is linked to two video cassette recorders on which the signals of the two cameras are recorded. A computer program was developed to reconstruct the flight images in three dimensions, as well as to extract behavioural parameters for data analysis. Here we report the first, preliminary data from this study.
Images of the flight of An. gambiae in the absence and presence of odour were obtained and shown to provide insight in the flight behaviour of this mosquito when it approaches an artificial host. By adding a simulated plume to the reconstructed image, it was possible to pay special attention to the behaviour at the boundary layer of the odour plume, when the mosquito is leaving or entering odour and abrupt changes in behaviour modulated by odour are expected. Furthermore, it proved possible to obtain mathematical data on flight speed, angle of velocity and time spent in and out of the odour plume as well as accurate data on geographical location at any time during the test period. It is expected that this system will be used for detailed analysis of odour-mediated behaviour of nocturnal mosquitoes.