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  Integrated Pest Management - Compatible Biological Control of Varroa Mite of Honey Bee

David Boyle1

Partner: New Brunswick Beekeepers Association

Abstract: Varroa mites (Varroa destructor, Acari: Varroidae) are a serious problem for beekeepers, survival of hives with high mite populations being poor. The literature shows that entomopathogenic fungi (EF) have good potential as biocontrols for the mites. However, preliminary results showed that only a few strains of the many EF species (Beauveria bassiana, Metarhizium anisopliae, Hirsutella thompsonii or Lecanicillium sp.) tested could grow at 350C, this being a common temperature in the brood area of hives where the mites reproduce. Extensive screening led to selection of a thermo-tolerant sub-set of EF that could grow and sporulate in hives. Further in-vitro testing gave a smaller sub-set (five isolates) that killed mites on bees and brood, with minimal effect on immature or mature bees. Various potential spore-carrying materials were tested. An idea was that EF spores added to foundation beeswax might get into the brood cells. However, non-polar anti-fungal materials associated with the wax (and propolis) make this approach unlikely to work, since these compounds diffuse into waxes and oils. Inoculum should probably be introduced as dry spores or spores in aqueous (non-polar) carriers. Small scale (not-replicated) tests of the most promising EF were made in two mite-infested "mini-hives". These contained two frames of brood and approximately 500 bees each. They were maintained in an incubator while the brood developed, sugar water being provided to the bees through the top. A screen over the bottom retained the bees, provided ventilation, and allowed dislodged mites to drop onto a sticky board for counting. A mix of spores from the five promising EF isolates was sprayed on the frames and bees in one mini-hive, autoclaved (dead) EF preparation being sprayed into the other. Mite drop from both hives increased markedly following inoculation. Some mites from the EF-treated hive were infected with M. anisopliae, two morphologically distinct isolates being recovered. These EF are presumably hive tolerant and pathogenic to mites. Survival of adults and bee emergence from brood cells was similar in the two hives, the EF not having any dramatically detrimental effect. Although these limited mini-hive tests gave some information, replicated, longer term testing of the isolates under field conditions is needed to determine if these EF isolates can control Varroa in hives. Entomopathogenic fungal strains appropriate for use in these tests are available from MicroBiologicals's culture collection.

1Maritime MicroBiologicals, Inc. 24 Parker Street, Truro, Nova Scotia, B2N 3R1

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