A BEHAVIORAL-TEST OF THE SENSITIVITY OF A NOCTURNAL MOSQUITO, ANOPHELES-GAMBIAE, TO DIM WHITE, RED AND INFRARED LIGHT

A behavioural test was used to determine the light sensitivity of the nocturnal mosquito Anopheles gambiae Giles s.s. to low intensities of 'white' light (tungsten filament), 'red' light (white light filtered by a darkroom safelight filter) and 'infra-red' light) of two types (white light filtered by a lambda>700 nm filter, and light-emitting diodes with lambda>900 nm). Mosquitoes were placed in a 20 cm diameter flight-tunnel and their 'optomotor' response to a pattern of stripes moving across their visual field (at 14.5 cm s(-1)) was recorded with infra-red-sensitive video. In free-flight, with ample light, the mosquitoes controlled their flight speed and direction in relation to the stripe movement, so that the stripes always appeared to move across their visual field from front to back. They did this by flying either with the moving stripes fast enough to overtake them (19.5 +/- 0.7 cm s(-1)), or against them more slowly (10.3 +/- 0.7 cm s(-1)). The net ground speed of the mosquitoes was thus c. 4-5 cm s(-1). This response was significant down to 10(-5) W m(-2) in 'white' light, and 10(-3) W m(-2) in 'red' light. At light intensities below threshold and in infra-red light, however, they appeared to fly at random with respect to the stripe movement. The assumption commonly made, that mosquitoes do not 'see' in red light, may thus have to be revised.