Laboratory trials were conducted to evaluate direct and indirect effects of three non-stinging species of adult worker ants (Hymenoptera: Formicidae) on mortality of adult female mites of Varroa destructor Anderson and Trueman, as a potentially natural source of Varroa control. Ant body length ranged from 1.3–3 times the width of Varroa, and by ascending size included Tapinoma sessile (Say) (Dolichoderinae), Formica (fusca L. group) and Lasius neoniger Emery (Formicinae), species commonly associated in or near hives of Apis mellifera on the Canadian prairies. Without a food supply, ten mites plus five ants of one species were sealed into polystyrene petri dishes that either allowed direct interaction or permitted only odours or other vapours from ants to pass. The Formicinae, especially Formica, attacked Varroa most harshly, killing practically all mites within 12-24 h, often amputating some legs. Ants were neither significantly sustained, nor harmed, by the mites. In the absence of ants, mites survived longest (median 96h) in the smaller, upper compartment of separation arenas than in contact arenas (48h). Varroa mortality was highest when confined above Formica, but mites did not succumb significantly sooner than control mites. However, at certain trial intervals (60–84h), mortality rates of mites above Formica were greater than in mites residing above either Lasius or Tapinoma. In the absence of ants, formic acid itself (18mg per trial dish) led to rapid mite death (5h).We conclude that these ant species, while capable of seizing and maiming the mites, did not perceive a threat from Varroa sufficient enough to warrant a high level of discharge of defensive products from their gasters toward the mites. Such chemical defence by ants might be utilized more commonly against Varroa mites intruding ant nests.
ant, Apis mellifera, formic acid, Formica (fusca group), Lasius neoniger, mite mortality, Tapinoma sessile, Varroa destructor