Optimizing sampling of flying insects using a modified window trap

Insect populations are globally declining but standardized long-term data to evaluate trends and consequences are largely missing. One difficulty among many is the rather narrow taxonomic cover of most conventional trap types, which makes the use of several complementary collection methods necessary to achieve comprehensive coverage. To avoid the effort associated with operating multiple traps, we demonstrate how to modify window traps in a simple and standardizable way to capture a wider range of flying insect taxa. While a typical window trap only has a collection unit below the windows, we added an additional collection unit on top of the windows. We tested this modified trap design in 135 study plots in a temperate forest over 5 months and compared trap catches between top and bottom collection units. The top collection unit captured considerably more individuals of Hymenoptera, Diptera, Lepidoptera, Neuroptera, Auchenorrhyncha and Thysanoptera than the bottom collection unit. In contrast, there were more individuals of Coleoptera, Heteroptera, Sternorrhyncha and Psocoptera in the bottom collection unit. Both collection units captured a highly distinct insect community and patterns were consistent throughout the season. These modified traps are suitable for collecting a broader range of flying insects compared to conventional window traps. The additional top unit is fast and easy to build and the traps require little maintenance while operating in the field. These characteristics make modified window traps with top and bottom collection units a promising tool for standardized and replicable biodiversity studies covering a broad range of insect taxa.