Evaluation of the predatory mite Stratiolaelaps scimitus for the biological control of the honey bee ectoparasitic mite Varroa destructor

To date, studies exploring effective biocontrol agents of the honey bee (Apis mellifera) ectoparasitic mite Varroa destructor have either yielded mixed results or have been totally unsuccessful. In this study, we explored the efficacy of the predatory mite Stratiolaelaps scimitus (Mesostigmata: Laelapidae) as a biological control agent against V. destructor. We tested the ability of S. scimitus to prey on varroa in vitro using glass vials with two varroa mites each that were exposed (or not) to S. scimitus for 24 h. Additionally, in field tests conducted in Fall 2014 and Spring 2015, sets of honey bee colonies were either treated sequentially with 4-5 doses of 2,500 S. scimitus mites (experimental group), treated with the acaricide Apivar (R) (positive control group), or left untreated (negative control group). In vials containing varroa and S. scimitus mites, 97.10% of the 69 varroa mites tested died 24 h after exposure to S. scimitus. In contrast, in vials that were not treated with S. scimitus, only 6.85% of the 73 varroa mites tested died. We did not find a significant effect of S. scimitus treatment on lowering varroa numbers in field colonies compared to the untreated control group in either trial. Our results show that S. scimitus can predate on varroa in the laboratory, but not in the field settings we tested. More experiments should be performed to determine the ideal environmental conditions and correct dosage needed in apiary settings for the potential use of S. scimitus as a biocontrol agent against the varroa mite.