The Reactions of Culex Larvae and Pupae to Gravity, Light, and Mechanical Shock

Abstract

Mosquito larvae and pupae react to a change in light intensity or to a mechanical shock by dropping from the surface of the water. Two kinds of stimuli are combined to bring about the descent, one of them being kinetic and causing activity, and the other being directive and determining direction of movement. A kinetic stimulus is associated with time-rate of change of the stimulating agent, a directive stimulus with sustained action. Mechanical shock is kinetic; gravity is directive; light is both kinetic and directive. Larvae are either negative to gravity and positive to light or indifferent to these stimulating agents when at the surface. Mechanical shock or change in light intensity makes them positive to gravity and negative to light, and they descend. Soon there is a reversal of the reactions to these stimuli, and the animals return to the surface. Larvae react to a decrease in light intensity, less strongly if the light is below them than if it is above. They react less strongly to an increase of light from above, not at all with light below. The lesser efficiency of the light when it is below suggests that the effective rays are those which enter the eye from above. If so, with a light beneath the larvae, the effective rays are those that are reflected down from the surface.