Sunday, December 11, 2011

Australia still Varroa free

      Of beekeeping nations Australia is the last country remaining free of the Varroa destructor mite.  The Varroa mite is a small mite (approximately 1mm in diameter) native to Asia and the Asian honey bee (Apis Cerana) which has developed a resistance to the mite enabling it to cope with it's presence.  In the early part of the twentieth century Russian beekeepers brought the European honey bee to the Korean Peninsula via the Trans Siberian Railroad where it became the first European honey bee (Apis Mellifera) infested with the Varroa.  There are two types of Varroa mite, Japanese and Korean of which the former Japanese has not as of yet spread to other parts of the world.  The Korean Varroa mite mutated and adapted to the European honey bee which has no defense to it's presence.  Over the last 50 plus years the Varroa has spread from country to country having reached North America about 30 years ago.  However, it did not establish a stronghold until the last decade when it's presence became a serious threat to the bees (both native and honey) in North America.  The Varroa displays vampire like behavior (blood sucking), is a carrier of so far 18 identified viruses (Including Sacbrood, Acute Bee Paralysis, Deformed Wing Virus and Israel Acute Paralysis) and is considered a major contributing factor in Colony Collapse Disorder.  New Zealand became infected with the Varroa mite in 2000 and it seems just a matter of time until Australia is populated by Varroa.  The method of entry into Australia will probably occur through Asian honey bees (very similar though slightly smaller than European) swarming undetected onto ships in Asia and entering the country along with their native Varroa through one of the many Australian ports.   At present Australian authorities are actively hunting down invasive Asian honey bee nests in Australia.  So far none of the Asian bees found in Australia have had Varroa.  Recently a second mite, the Jacobsonian Varroa mite was discovered in Papua New Guinea and although slightly smaller is similarly destructive. 

Varroa mites on bee larva

     We tested our bees at Cottonwood Community Garden in September and October and fortunately our Varroa numbers are manageable (less than 12 in a 24 hour period).  Our method of testing and probably the greatest defense to the Varroa is the use of a screened bottom board.  The board is simple to make and is simply a bottom board with one eigth inch hardware cloth under the hive instead of wood.  You can find construction plans for the screened bottom board in "Beekeeping Downloads" at the top of the page.  The idea is that the mites naturally fall off the bees (constant preening) and hive frames and with a traditional wooden bottom board they would simply crawl back on an adult bee.  With the screened bottom board they fall out of the hive and are unable to reenter.  A simple testing board, painted yellow for better visibility and covered in vaseline is slid through an opening in the back under the screened floor.  Left for 24 hours, using a magnifying glass we are able to get an approximate idea of the Varroa population in our hive.  Less than 50 is considered manageable.  The screened bottom board also helps to ventilate the hive keeping the heat down in the summer and reducing cold condensation in winter.  
Screened Bottom Board
     The Varroa reproduces in the bee larvae and in the fall when there is less pollen and nectar the queen lays less eggs so the Varroa population resides more in the adult bees.   This is the best time, if using natural methods (mineral oil or sugar dusting) to treat your hive for Varroa.  Freezing drone brood is a labor intensive but successful method of lowering mite population (Varroa Mite Controls).  Mites are now showing a resistance to the popular pesticides Apistan and Checkmite and evidence shows that the pesticides are absorbed into the wax comb and can have deadly effects on the long term health of the bees.  Formic and oxalic acid are also used though a little messy.  Recently an easier application of formic acid has been made available (Mite Away Quick Strips).  Antibiotics are used but the Varroa quickly adapts to antibiotics reducing the efficacy.  We sugar dusted in late September and October and got a significant mite drop each time.
Installing the mite test board
The numbers went from an average of 8 prior to dusting to 25 in the 24 hours following a sugar dusting.   Beekeepers should regularly check for mites ( Varroa Mite Detection) and treat accordingly.  Also watch for evidence of hygienic behavior in your bees.  Actually grooming off the mites, grasping them in their mandibles and biting them.  To test for biting use a magnifying glass when inspecting mite drop on your test board and look for mites with missing legs.  Guard bees displaying hygienic behavior may grab and shake infested bees trying to enter the hive, removing the mites and either killing them or chasing them away.  Group grooming has also been observed ( Bee Grooming).  It is believed by many that this behavior can be passed both genetically and by learning. 
     Here is a great movie which follows the efforts of Australian scientist Dr. Denis Anderson to keep the Varroa mite out of Australia.  


     Bees need our help now!  Neonicotinoid pesticides are killing bees now!(Insecticides and Bees)  Please make sure that the plants you buy do not contain neonicotinoid pesticides.  Most of the plants sold at Home Depot and other major distributors do.  


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