Strong diel variation in the activity of insect taxa sampled by Malaise traps

Abstract Malaise traps offer an efficient method for monitoring insect communities. Nonetheless, insect taxa may differ in diel activity, whereas longer‐term trap catches will integrate over such variation. Furthermore, fluctuations in weather may affect variation in taxon‐specific activity, thus affecting the relation between the community observed in trap catches and the total community present. In this study, we asked how diel‐ and weather‐related variation in insect activity influences Malaise trap catches. To this aim, we emptied 24 Malaise traps in a boreal forest in central Sweden with short time intervals across five consecutive days, while simultaneously recording the prevailing weather conditions. We found major differences in diel patterns across insect taxa. Significantly different communities were observed during different parts of the day, with the lowest abundances observed during mornings (6:00–12:00), lowest taxon richness during nights (22:00–06:00), and highest abundances and taxon richness during afternoons (12:00–18:00). Temperature affected both the occurrences and abundances of insect taxa in trap catches. Most taxa exhibited lower abundances with increased wind speed and cloud cover, and all taxa exhibited lower abundances with a rise in dew point. In conclusion, insect communities observed in Malaise trap samples vary substantially across the day in terms of both abundances and taxon richness. Before converting summary catches from longer‐term Malaise traps into metrics of insects available as, for example, prey or pollinators, we should thus consider what fraction of these communities are available for these ecosystem services during different parts of the day.