Detecting flying insects using mega-nets and meta-barcoding

Insect diversity and abundance are increasingly reported as being under pressure. However, monitoring insects across space and time is challenging, due to their vast taxonomic and functional diversity. This study demonstrates how nets mounted on rooftops of cars (car nets) and DNA metabarcoding can be applied to sample flying insect diversity across a large spatial scale within a limited time period. During June 2018, 365 car net samples were collected by 151 volunteers during two daily time intervals on 218 routes in Denmark. Insect bulk samples were processed with a DNA metabarcoding protocol to estimate taxonomic composition, and the results were compared to known flying insect diversity and occurrence data. We detected 15 out of 19 flying insect orders present in Denmark. Diptera. Psocoptera and Thysanoptera were overrepresented, while Hymenoptera, Coleoptera, Lepidoptera, Trichoptera, Odonata, Neuroptera and Plecoptera were underrepresented, compared to Danish estimates. We detected 319 species not known for Denmark. Our results indicate that this method can assess the flying insect fauna to a wide extent, but may be, like other methods, biased towards certain insect orders. Furthermore, car net sampling and DNA metabarcoding can update species records for Denmark while preserving specimens for natural history collections.