Sampling and mapping airborne arthropod eDNA using back-projection

Environmental DNA (eDNA) is a powerful tool for monitoring biodiversity, and recent advances have shown that arthropod eDNA can be sampled from air. Subsequent fingerprinting or meta-barcoding from airborne eDNA allows for species presence to be quantified. However, air samplers will only provide the sum of eDNA collected over the entirety of the sampling period (i.e., the eDNA signal is time integrated). Because of this limitation, a back-projection approach inspired by medical imaging must be applied to map where eDNA samples have been collected in space. Here we present initial proof-of-concept modeling studies that evaluate the feasibility of mapping arthropod eDNA from airborne samples, and we show data using native bee aggregations as model organisms. Specifically, we used custom built, highly portable air samplers to collect multiple sets of parallel transects, each set at a different angle, across a bee aggregation near the Virginia Tech campus. While running the transects, air was pumped over a glass fiber filter. We then extracted the eDNA from the filter, before we amplified it using bee specific primers. The quantities of eDNA from each transect were then back-projected to obtain a map of bee eDNA presence. We discuss the challenges and limitations of back-projection and the potential for this technique to be used for a variety of applications, including environmental monitoring, conservation, and pest management.