Understanding the Varroa Destructor
Varroa mites are a threat to bees all over the world, and New Zealand is no exception. The tiny creatures spread disease, weaken colony health, and, left untreated, eventually kill the hive.
Although the mite has gained notoriety in recent years, it was actually identified over a century ago on the island of Java, Indonesia. It was discovered in colonies of the Asian honeybee, which had successfully adapted to live with the parasite without being affected.
Later, European settlers brought the Western Honey Bee to Asia, and the Varroa mite spread to these colonies as well. From there, it spread to colonies in Russia, Eastern Europe, and finally the rest of Europe. Now, the Varroa mite is found all over the world – with Australia being the only exception.
Unlike their Asian counterparts, Western Honey Bees have little to no defense against the Varroa mite. In Asia, the host/parasite relationship between bees and mites has evolved over thousands of years, but the western bees have not had time to develop a similar relationship.
Destructor by name and nature
The mite’s scientific name is the Varroa Destructor – for good reason. It weakens the immunity of honeybees, spreads disease, and can eventually lead to the destruction of the entire colony.
The Varroa mite travels from hive to hive on the bees themselves. Bees from different hives come into contact while out searching for food, and the mites simply jump from one bee to another.
When mites reach a hive, they head for the brood cells. When the cells are sealed, the mites will lay eggs on the larvae. The eggs generally hatch around the same time as the larvae, and the new mites will leave the cells and spread to other bees and larva cells. Sometimes, they will reproduce a second time while the larvae are developing, and the mites will feed on the larvae, causing diseases and defects such as deformed wings.
Mites feed on the ‘blood’ (haemolymph) of adult bees, leaving open wounds and making the bees more susceptible to infection and disease. Adult bees infected with the virus tend to have a lower life expectancy than unaffected bees. They are also less productive, as the mites can affect their ability to navigate and gather food efficiently.
Signs and symptoms
Identifying Varroa infestation can be tricky. When the mite population is low, your hive will show few symptoms. As it rises, however, more serious signs will appear.
Look out for a scattered brood pattern, damaged and weak bees, a low rate of return after feeding, shortened lifespan, and reduced weight in worker bees. You may also notice sunken, chewed-looking cappings and larvae slumped in their cells.
If you suspect a mite infestation, examining the hive may be enough to confirm your suspicions. If you’re unsure, there are a number of ways to check, including:
- Alcohol washing – this method uses rubbing alcohol to separate mites from a sample of bees so they can be seen more easily.
- Sugar shaking – this involves dusting bees with fine sugar, which helps loosen mites clinging to them. The sugar is then inspected for mites.
- Drone uncapping – using a scratcher, the beekeeper uncaps a number of drone cells and examines the larvae for mites and other symptoms of infestation.
- Sticky mat – a sticky mat placed at the bottom of the hive catches fallen mites, allowing the beekeeper to identify them.
Treatments and prevention
Because Varroa mites cause so much damage so quickly, they’re a huge threat to bee populations worldwide. There are treatment options and ongoing research into the issue, but a foolproof solution has yet to be developed.
Synthetic miticides can be used to eliminate mites in your hives, but it pays to be careful – mites can develop resistance to chemicals over time, making them harder to get rid of in future. It’s also important to be careful during application to avoid contaminating honey.
- Bayvarol Strips – 4 x plastic strips hook to the top of the frames of each brood box with 99% efficacy
- Apitraz – 2 x plastic strips hook to the top of the frames of each brood box with over 98% efficacy
Naturally-occurring chemicals can also be used to control mite infestations. These chemicals can contaminate honey, so must be used carefully.
- MAQS+ Strips – formic acid in these gel strips is released as a vapour, leading to the death of Varroa mites in the hive
- Oxalic Acid – this natural, plant-based compound is applied as a powder
- Thymovar Wafers – these wafers are impregnated with Thymol oil, which releases vapour into the hive at concentrations designed to kill mites without affecting bees
Some beekeepers choose to control Varroa through physical or behavioural methods, saving the chemical treatments for serious infestations. These methods generally help to keep the population of mites down, rather than eliminating them completely.
- Hive heating – this method involves heating the hive frames for several hours, which causes the mites to drop from the bees for easy removal.
- Perforated bottom board – this involves setting up a hive with a screened mesh floor. When mites drop from bees, they fall through and are unable to reenter the hive.
- Brood control methods – a range of more complex methods take advantage of the Varroa’s preference for drone brood. Some beekeepers will remove drone brood frames and freeze them to kill off the mites, while others will cut off drone brood comb at a certain stage of development. Because hives tend to produce an excess of drone brood, this can often be done without damage to the colony.
The Varroa Destructor continues to damage hives all over the world, endangering honey production and affecting crop pollination. Because it has such a wide-ranging impact, it is the focus of significant scientific research. As this research continues, beekeepers hope that an effective solution will be found.
One potential area is genetic interference. Some research has shown that it’s possible to knock out specific genes in the Varroa mite, while other efforts have focused on changing the genetic makeup of the honeybee itself.
In the meantime, it’s important to be vigilant about monitoring and treating your hives for Varroa infestation. Ignoring the issue isn’t an option.