Detecting a Small Hive Beetle's eDNA in Honeybee Colonies

Early detection is important to limit the spread of invasive species. Molecular diagnosis using eDNA can be useful in this regard, but the sensitivity is often unknown. This holds true for small hive beetles (SHB), which are parasites of honeybee (HB) colonies and continue to spread globally. Here, we show that a single SHB can be detected in a HB colony using eDNA swab sampling, thereby suggesting a considerable potential for mitigation of this invasive species. Non-infested HB colonies were experimentally inoculated with 0 (controls), 1, 10 or 100 adult SHB. Then, swab samples were taken from different positions in and outside the hive. DNA analyses showed a strong positive correlation between Ct-values and time for all infestation levels. Ct-values varied between some time points and sampling positions, but post-infestation sampling of colonies with SHBs resulted in the detection of SHB eDNA at all levels of SHB infestation and for all exposure times, except for day 1. Even 1 SHB was successfully detected at all positions from the 2nd day of exposure onwards. It appears as if swab sampling constitutes a reliable diagnostic tool to even detect the very first SHB infesting a colony. Therefore, we recommend including this method for species monitoring and mitigation of this invasive species.