Light-Trap Catch of Turnip Moth (Agrotis segetum Denis et Schiffermüller, 1775) in Connection with the Night Sky Polarization Phenomena

Abstract

The study investigated the efficiency of the light-trap catch of Turnip Moth (Agrotis segetum Den. et Schiff.) in connection with the polarization of the night sky. The hourly catch data of drawing during three years were assigned to the data of the 41 environmental variables. First we made cluster analysis with the data pairs. Based on this, further calculations were made between the most important influencing factors and the catch data. The results were depicted together with the confidence intervals. We can conclude that the catch at night is determined mainly by the Humidity, Sun-Sky-Pol, Moon-Sky-Pol, Moon-Pol and Clock variables, slightly influenced by Wind and H-index variables. The high relative humidity of the air has a decisive influence on the catch, because the insect can see only the distorted sky polarization pattern, and according to our assumption its orientation is hampered. The Sun stays in the first and last collection hours above the horizon at most. At this time the Sun’s sky polarization is higher than the Moon’s one. The catch is also influenced mainly in these hours. In the majority of the night, the sky polarization originated from the Moon is much higher. In these hours the Moon's modifying effect is decisive. The Moon modifies the catch when he does not stay above the horizon. The azimuth angle of the moon is also a determining factor for the effectiveness of the catch. The Moon phase angle is high when azimuth is smaller than 91.7. Meanwhile, the polarization of the sky and the polarized moonlight are high. This situation increases the effectiveness of the catch. The effect of polarized moonlight on the catch is less significant than the sky polarization.