Detecting flying insects using car nets and DNA metabarcoding

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 richness and diversity across large
spatial scales 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 richness and occurrence data. Insect
and hoverfly richness and diversity were assessed across biogeographic
regions and dominant land cover types. We detected 15 out of 19 flying
insect orders present in Denmark, with high proportions of especially
Diptera compared to Danish estimates, and lower insect richness and
diversity in urbanised areas. We found 319 species not known for Denmark
and 174 species assessed in the Danish Red List. Our results indicate that
the methodology can assess the flying insect fauna at large spatial scales
to a wide extent, but may be, like other methods, biased towards certain
insect orders.