Diel flight behaviour and dispersal patterns of aquatic Coleoptera and Heteroptera species with special emphasis on the importance of seasons.

Dispersal flight is the most important and almost the only way for primary aquatic insects to find new water habitats. During a 30-week-long project, we monitored the flight dispersal behaviour of aquatic beetles and bugs with using highly and horizontally polarizing agricultural black plastic sheets laid onto the ground. Based on the flight data of more than 45,000 individuals and 92 species, we explored and described eight different diel flight activity patterns. We found that seven of eight dispersal patterns are consistent with the previous knowledge, while three conspicuous mass dispersal periods can be identified as in the mid morning and/or around noon and/or at nightfall. As an exception, we found a 'daytime' pattern occurred exclusively in spring, in which mass dispersal can be seen from mid morning to late afternoon. In contrast to previous studies, we emphasize here that the seasonality has to be considered in evaluation of the diurnal flight activity. According to the seasons, a 'three code sign' was proposed to indicate the diel dispersal flight behaviour of a species for a year. Most of the species utilize different diel activity patterns in different seasons. In spring, the daytime pattern was the preferred type, but in summer and autumn, the evening types were the most popular patterns. We stated that the seasonal change of air temperature has a crucial role in that a pattern could be manifested in a given season or not and brings a need to change the diel dispersal pattern among seasons.