Varroa: how to spot and report the pest

Varroa destructor is a parasitic mite of honey bee brood and is a reportable pest.

Clinical signs

Severe infestations of Varroa may lead to parasitic mite syndrome. The signs of this are:

• perforated cell cappings
• dead pupae
• chewed down or cannibalised larvae and pupae
• neglected brood
• deformed wings
• bees with shortened abdomens
• general weakening of the colony
• patchy or pepper-pot brood patterns
• sudden defensive behaviour
• colony loss

How Varroa is spread

Varroa mites are mobile and can readily move between bees and within the hive. However, to travel between colonies they rely on adult bees for transport - through the natural processes of drifting, robbing, and swarming. In this way mites can spread slowly over long distances.

The movement of infested colonies by beekeepers is the main way by which mites spread over long distances. To keep healthy and productive colonies, a consistent, ongoing program of monitoring and management of Varroa is needed.

Varroa treatments

Varroa can be controlled through the application of treatments that kill the mites, or through husbandry methods that rely on removal of infested brood or brood breaks to disrupt reproduction of the mites. To learn more about monitoring Varroa populations, please see the Varroa monitoring fact sheet on BeeBase. 

Husbandry methods exploit the fact that mites reproduce in bee brood. Generally, these methods are only used during the spring and summer months, but they can be a great benefit during a time when treatment options are limited. 

Drone brood removal

Varroa mites prefer parasitising drone brood, so a quick and easy way to reduce mite populations is with drone brood removal. See: fact sheet on using drone brood removal to control Varroa.

Other methods include queen trapping or performing an artificial swarm. 

How to control the pest

Varroacides are an important feature in control plans because they are effective at killing Varroa mites. There are two types of varroacide — synthetic pesticides and non-synthetic pesticides.

Synthetic pesticides

These have a single, specific mode of action. There is a high risk of pesticide resistance occurring in mites that are continuously exposed to these products, and there is documented evidence of resistance to these products in the UK and Europe. 

Non-synthetic pesticides

These act against mites in multiple ways, so there is a significantly reduced risk of resistance occurring. These products are based on the use of organic acids, or the essential oil, thymol, to control mite populations. Products based on these chemistries are recommended as the primary go-to treatments over synthetic pesticides, which should be reserved for emergency use only.

When using any treatments, it is important that you read and follow the label instructions and only use medicines that are approved under law. See: information about products authorised for use in the UK.

Further information is available to beekeepers on the Scottish Beekeepers Association website.

How to report Varroa

The Bee Diseases and Pest Control (Scotland) Amendment Order 2021 made Varroa reportable in Scotland. This legislation requires all beekeepers and officials in to report the presence of Varroa in any of the hives that they manage or inspect (in the case of bee inspectors).

All registered beekeepers in BeeBase were marked as having Varroa, so if you are registered and in an area with Varroa, you do not need to do anything. However:

• if you are not registered on BeeBase and wish to report Varroa, please do so by either registering for free on BeeBase or emailing our team at bees_mailbox@gov.scot
• if you do not have Varroa in your hives and are registered on BeeBase, please access your record, and change your status to Varroa not present

Varroa map

Our Honey Bee Health Team have produced a map which shows the current understanding of the distribution of Varroa across Scotland.

As movement of honey bees from infested areas is the most likely route of Varroa invasion into these areas, it is important that reasonable measures are taken to prevent the further spread of Varroa into these zones.

The map will be updated annually to take into account new reports.

Varroa learning package

As part of our Honey Bee Health Strategy, in partnership with SRUC and the Bee Health Improvement Partnership, we have produced a Varroa Learning Package for beekeepers in Scotland.