How the Varroa mite arrived in these countries is a mystery because it requires a living honeybee carrier to survive. The mite originated in Asia and started spreading. In 1955, it had infected USSR, in1961 China and India succumbed. In1974 it was South America, 1978 it was Africa, and during the 1980’s it spread to Europe. America discovered the mite in Florida late in 1987. In May 2000, New Zealand discovered serious bee pests. The only country free of the mite is Australia.
The bee mite, Varroa jacobsoni a.k.a. the Varoa destructor is an external parasite of the honeybee. It feeds on the haemolymph or the blood of the bee. The mites are about the size of a pinhead, deep in red brown color and oval in shape. The mite cannot survive without bees, dieing after two days. The critical time for a beehive to be infested by this killer mite is at the end of summer, which also coincides with the end of the honey flow.
At this time, the colony will be reduced in size in order to prepare for over winter. If the level of brood cannot sustain the hive the colony will disband, causing the hive to be robbed by other bees. The infestation will travel to other apiaries and eventually these hives will die. If the Varroa remains unchecked the honey and pollination industry will be severely affected.
Once inside the beehive, the female mite will lay brood cells. These cells will immerse themselves in the larval food at the base of the cell. Once the cell has been capped for the bee larvae to mature, the female mite moves onto the prepupa and begins to feed. The female lays eggs within 60 hours of the cell being capped and then every 30 hours after that. About 1 to 12 female and male eggs are laid. 5 days later, the male partner dies. Adult females mites then transfer to other bees within the hive through the close contact.
The best method of checking infestation, of course, is opening the hive and closely inspecting bees and brood. This could involve decapping some of the brood cells to check all stages of larval development; if the infestation is still in the early stages. But to quickly check a large number of hives one can:
-Observe the hive entrance (alighting board) and look for bees with crippled wings or bees that are having difficulty flying. Another indicator is a sudden decrease in the hive population, check in the late afternoon when the population is returning for the night.
-The quickest method is to slide a clean, white sheet of A3 paper in the hive entrance on top of the baseboard, fill the smoker with cardboard, get it to the point of smoking, and then add a handful of shredded tobacco. Generously smoke the entrance, pop the top a little, and then generously smoke the top. Smoke the entrance again.
Let it lie for 30 seconds, smoke again, and then slowly draw the sheet of paper out. The tobacco smoke irritates the mite enough to cause it to drop off the bee and fall to the paper. This is a quick method but not foolproof. If the hive is in the early stages of infestation there could only be one or two mites on the paper but will still prove infestation has occurred.
-A new method has been developed recently in the U.S. called the Powdered Sugar Shake. It needs a 2 liter preserving jar, the screw ring, mesh large enough to allow the mite to pass through, and fine mesh to allow the sugar to pass. Scoop about 300 bees (approx. the size of a baseball) and put them in the jar. Put in a tablespoon of icing sugar, seal the jar, and roll the jar.
Wait a couple of minutes and roll the jar gently again ensuring that the bees are all well coated. Replace the top with the coarse mesh and pour the sugar/mite mix into another container then put it through the fine mesh. If there are mites they will be visible. Replace the bees back in the hive where hive mates will groom the sugar from them.
It works because mites have a sticky pad that helps them stick to the bee. The icing sugar makes it difficult for them to adhere and the sugar stimulates the bees grooming. This method is very good as it is gentle on the bees and also provides 90% separation of the mite and bees.
There are two methods of control. The first is referred to as ‘biotechnical’ and involves the manual removal of the mite. The advantages to this method are that there are no chemicals introduced to the hive. It is also inexpensive. The disadvantages are one, it is time consuming, two, it is complicated, and three can cause the hive never to be mite free.
The second method involves chemical miticides. Different countries have licensed different chemicals for treatment but they are based on chemicals that will have a minimum residue in the hive and not have a detrimental effect on the hive population. In New Zealand we have just approved the use of Apistan in brood boxes only and after 2 years the data will be reviewed to determine the level of residue.
To date the best method of control has been a combination of both treatments though care has to be taken not to develop a miticide resistance among the mite.