Ingestion of Varroa destructor by pseudoscorpions in honey bee hives confirmed by PCR analysis

The pseudoscorpions, Nesochernes gracilis and Chelifer cancroides, appear to have potential for control of varroa mites (Varroa destructor), but have not been observed to predate on varroa in honey bee hives. A molecular method was developed to determine, without the need for observation, whether a candidate predator was eating varroa in commercial hives. DNA extracted from pseudoscorpions, which had been observed to have fed on varroa, and DNA from those that had not come in contact with varroa were amplified by polymerase chain reaction (PCR) with primers that target the cytochrome oxidase subunit 1 gene specific to V. destructor. Varroa DNA was detected up to four weeks after a known varroa feeding event from extractions of pseudoscorpion DNA. No varroa DNA could be detected in the pseudoscorpions not exposed to varroa mites. Varroa DNA was reliably extracted and identified from pseudoscorpions known to have preyed upon varroa, including C. cancroides confined within a varroa-infested commercial honey bee hive. This molecular technique can therefore be used as an indicator of varroa predation by chelifers without requiring visual observation of predation.