Predation behaviour of the pseudoscorpion, Chelifer cancroides, against Varroa destructor in the presence and absence of alternative prey and Apis mellifera

The potential efficacy of the polyphagous pseudoscorpion Chelifer cancroides (Chelifer) for biocontrol of the ectoparasite Varroa destructor (Varroa) in Apis mellifera (honey bee) hives was evaluated in laboratory experiments. Since Chelifer have a choice of prey in hives, their predation preferences were determined for Varroa and a common commensal in hives, Liposcelis entomophila (psocid). In arenas under ambient light, given a choice between the mite and psocids, the adult female Chelifer fed equally on both, whereas adult males and proto-, deuto- and trito-nymphs had a greater preference for psocid. The Chelifer cohorts killed 25%–80% of the 15 Varroa within 4 h. Individual female Chelifer regardless of hive experience killed a similar number of Varroa, and again 20-d later, when presented with new Varroa with or without bees present. Yet only hive-experienced males killed substantially more Varroa on both occasions than those without the hive experience, suggesting a preconditioning sex bias. However, Chelifer caged on brood comb with bees parasitised by Varroa did not affect mite fall, implying the Varroa needed to be removed first from bees for predation to occur. The Chelifer fed on more prey in the dark rather than light conditions, suggesting the predation on Varroa in bee hives would be greater than that observed in the lighted experiments. The time taken for Chelifer to kill another alternative prey species, Drosophila simulans, was influenced by the number of prey present. Extrapolating, a domiciled Chelifer in a hive could potentially kill at least one Varroa every week.