|
||||||||||
| Department of Agriculture, Aquaculture and Fisheries |
||||||||||
|
||||||||||
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
Email: [email protected]