Response of Some Night-Flying Insects to Polarized Light

Abstract

The possibility that night-flying insects may use naturally polarized light as a cue for flight, dispersal, migratory activities and for orientation during movements (at night) has rarely been considered. The reason for this neglect may well be the belief that the amounts of polarized light that are available to insects at night are too small to influence them. During recent investigations on the flight activity of the mosquito Culex pipiens australicus (Dobrotworsky and Drummond) and the moths Plutella xylostella (L.) and Epiphyas postvittana (Walk.), it was found that there are three peaks of flight activity during the lunar cycle (Danthanarayana 1976, this volume; Goodwin and Danthanarayana 1984). Two of these peaks correlated with the degree of polarization of moon light (which increases at the first and last quarters) and the third occurred at the time of full moon when moonlight is more intense, but less polarized. It is not known, however, whether the correlation between the degree of polarization of moonlight and the amount of flight activity is a cause-and-effect relationship. As a preliminary step towards resolving this problem, the response of night-flying insects to polarized light was examined with the aid of light traps, activity-meter studies and by histological determination of the pigment position of superposition eyes of moths. Moths were selected for laboratory experiments because there is much published work in the eyepigment movements of this group (see below); in previous studies more Lepidoptera have been trapped under polarized light than under nonpolarized light (Kovrov and Monchadskiy 1963) and observations on the light-brown apple moth, Epiphyas postvittana, suggested the existence of profound restlessness (Zugunruhe) during the above phases of the moon (unpublished information). Results obtained during these studies, as reported below, confirm that some night-flying insects respond to dimpolarized light to a greater extent than to nonpolarized light of the same intensity.