Fig. 1

a Prototype sensor (top) fitted to a BG-Mosquitaire trap (bottom). b Side view diagram of sensor and trap to illustrate operation. The exterior of the sensor unit (1) is formed by an inlet tube with a diameter of approximately 100 mm (2), sensor housing (3) and outlet tube (4). The housing contains an optical emitter (5), which projects collimated beams of light through the transparent flight tube (6) and onto an optical receiver (7) to create a sensing zone (8) within the flight tube. The trap (9) contains a suction fan (10), a removable catch bag (11) made of textile mesh and a perforated lid (12). The fan produces a flow of air downward through the inlet tube, flight tube and catch bag and upward through the perforated lid as indicated by the blue arrows. An insect (13) which flies close to the entrance of the inlet tube may then be sucked downwards through the sensing zone where it will be recorded and then trapped in the catch bag. As the mosquito passes through the sensing zone it casts a shadow upon the optical receiver according to the so-called optical extinction mode of operation. As the insect flaps its wings within the sensing zone, the light falling on the optical receiver is modulated, giving rise to changes in the amplitude in the recorded waveform