Although an unusual pest to encounter, pest managers should be vigilant in identifying the Varroa mite if they are dealing with a bee problem.
The Varroa mite is a major pest of honeybees globally. It is not established in Australia, but there is a current incursion in NSW that is of significant concern. Should the Varroa mite become established in Australia, not only will it impact honey production but will significantly impact the cost of crop pollination and indeed the ability to pollinate crops at the desired level, reducing agricultural output.
The current outbreak in NSW was detected in sentinel hives around the Port of Newcastle. These hives are positioned and inspected regularly, specifically as an early detection tool for potential Varroa mite incursions. Unfortunately, by the time the infestation was detected, it had already spread to other locations. Biosecurity placed restrictions on beehive movements and beekeepers are on high alert, so that any new infestations are detected as soon as possible, and the hives destroyed.
Although a number of Varroa mites infest Asian honeybees, only two species are parasites on the European honeybee: Varroa destructor and Varroa jacobsoni. They are very small, red/brown mites that live entirely on adult honeybees (as pictured above) and within the hive. They primarily feed on the bee larvae and pupae, although adult female mites will feed on adult bees. As they mainly feed on the larvae in brood cells, the early stages of the infestation are hard to detect.
Mites impact the health of individual bees, reducing body weight, foraging performance and longevity. Significant mite feeding can cause deformation. Mites can also transfer viruses, which further impact colony health. However, mite numbers increase slowly within the hive, and it is not until the third or fourth year of the infestation that the numbers become so significant that the colony declines and dies.
The mites are very mobile so can spread between adult bees and on beekeeping equipment. Mites can move from bees to flowers and so spread to other colonies. The risk of rapid and widespread movement of the mite can occur during the regular movement of commercial hives to fulfil pollination contracts, meaning a ban on hive movements is a key part of control measures.
What can pest managers do to help?
Firstly, it’s important to be able to recognise a Varroa mite on an infested bee. Although bees are not generally a focus for pest managers, if a worker bee is encountered and is behaving unusually, or if you are called in to deal with a bee swarm, get into the habit of having a closer look to see if you can see any mites present. Varroa mites are a notifiable pest, so collect a worker with mites for identification and contact the relevant state department.