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Currently, the distribution of diving beetles in Switzerland is poorly known making it difficult to determine conservation priorities for species with small and/or declining populations. In order to establish conservation priorities, in 2018, we surveyed diving beetles of the genusGraphoderusin the Grande Cariçaie reserves with special consideration for the Red ListedG.bilineatus. WhileG.bilineatusandG.cinereusshowed high habitat niche overlap, the distribution ofG.bilineatuswas limited to mainly one of the eight reserves. When comparing our results to available historical data, the habitat ofG.bilineatushas likely diminished during the last 40 years. Our study provides the first comprehensive documentation of the distribution ofGraphoderusspecies in the Grande Cariçaie. We further highlight the importance for improving the knowledge ofG.bilineatusdistribution in Switzerland to develop policy for conservation of this globally threatened species.

Despite mass movements of insects being documented for decades, whether dragonflies migrate in Europe has not yet been experimentally tested. Similarly, little is known about the influence of weather on the movement decisions and intensity of dragonflies. Taking advantage of large movements of dragonflies along the Baltic Sea coast of Latvia, we investigated whether European dragonflies showed directed movements indicative of migratory behaviour and how weather influences their movements. First, we performed orientation tests with individual dragonflies of two commonly captured species,AeshnamixtaandSympetrumvulgatum, to determine whether dragonflies showed directed flight and whether flight direction differed from wind direction. BothA.mixtaandS.vulgatumdisplayed a uniform mean southward orientation, which differed from the prevailing overhead wind direction, indicating migratory behaviour. Second, we investigated the influence of weather conditions on the abundance of dragonflies captured. Differences in flight behaviour in relation to weather conditions were observed betweenA.mixtaand the two smallerSympetrumspecies (S.vulgatumandS.sanguineum). Generally, temperature, cloud cover and wind direction were the most important predictors for dragonfly abundance, with temperature positively, and cloud cover negatively, influencing abundance.Aeshna mixtaappeared to select favourable tail winds (northerlies), whereas abundance ofSympetrumincreased with more easterly winds. Our results provide important information on the influence of local weather conditions on the flight behaviour of dragonflies, as well as evidence of dragonfly migration along the Baltic coast.

Despite mass movements of dragonflies being documented for decades, the influence of weather on the movement decisions and movement intensity of dragonflies has rarely been studied. Here, we investigate the influence of local weather conditions on flight behaviour of dragonflies in Europe, taking advantage of large movements of dragonflies occurring along the Baltic Sea coast of Latvia. Firstly, we performed orientation tests with individual dragonflies of two commonly captured species, Aeshna mixta and Sympetrum vulgatum, in order to determine if dragonflies showed directed flight and whether flight direction was independent from wind direction. Aeshna mixta displayed a uniform mean southward orientation (166.7°), independent from prevailing wind directions, whereas S. vulgatum did not show a uniform orientation. Secondly, we investigated the influence of weather conditions on the abundance of dragonflies captured. Behavioural differences in relation to weather conditions were observed between A. mixta and the two smaller Sympetrum species (S. vulgatum and S. sanguineum). Generally, temperature, cloud cover and wind direction were the most important predictors for migration intensity, with temperature positively influencing abundance and cloud cover negatively influencing abundance. Aeshna mixta appeared to select favourable tailwinds (northerlies), whereas hourly abundance of Sympetrum increased with more easterly winds. Our results provide important information on the influence of local weather conditions on the flight behaviour of dragonflies, as well as evidence of migration for A. mixta and most likely some Sympetrum species along the Baltic coast.

Despite mass movements of dragonflies being documented for decades, the influence of weather on the movement decisions and movement intensity of dragonflies has rarely been studied. Here, we investigate the influence of local weather conditions on flight behaviour of dragonflies in Europe, taking advantage of large movements of dragonflies occurring along the Baltic Sea coast of Latvia. Firstly, we performed orientation tests with individual dragonflies of two commonly captured species, Aeshna mixta and Sympetrum vulgatum, in order to determine if dragonflies showed directed flight and whether flight direction was independent from wind direction. Aeshna mixta displayed a uniform mean southward orientation (166.7°), independent from prevailing wind directions, whereas S. vulgatum did not show a uniform orientation. Secondly, we investigated the influence of weather conditions on the abundance of dragonflies captured. Behavioural differences in relation to weather conditions were observed between A. mixta and the two smaller Sympetrum species (S. vulgatum and S. sanguineum). Generally, temperature, cloud cover and wind direction were the most important predictors for migration intensity, with temperature positively influencing abundance and cloud cover negatively influencing abundance. Aeshna mixta appeared to select favourable tailwinds (northerlies), whereas hourly abundance of Sympetrum increased with more easterly winds. Our results provide important information on the influence of local weather conditions on the flight behaviour of dragonflies, as well as evidence of migration for A. mixta and most likely some Sympetrum species along the Baltic coast.