There’s been a lot of attention given to European honey bees (Apis mellifera) recently. Even the Federal Parliament has got into the act, introducing bee hives to Parliament House in March and celebrating the first honey harvest this month. But why should we care about European honey bees? Do they really affect our lives in any meaningful way?
The answer, of course, is yes – and it’s mostly due to pollination. Honey is certainly an important and valuable product, but bees offer even greater utility through pollination. Many of the world’s food crops depend on pollination. Although pollen can be transferred by wind in some plants, many others rely on animals such as insects and birds to transfer the pollen. This includes insects such as European honey bees (Apis mellifera), which are therefore an important species in the global food supply. Crops dependent on pollination from bees and other insects include fruits like apples, nuts such as almonds, and high-value products that keep Australia running such as coffee and cocoa. Estimates of the value of pollination services from managed honey bees in Australia range up to $6 billion a year (p. 7).
Threats to honey bees
Worldwide, honey bee populations are subject to many threats. Two of the main problems are Varroa mites, which live on the bees, and the agricultural use of pesticides on plants. Pesticides such as neonicotinoids (the most frequently used class of pesticides globally) have been implicated in the decline of honey bees in Europe and North America. These pesticides are thought to affect honey bees even in sublethal doses that can be acquired, for example, by collecting pollen from plants not targeted with pesticides but which happen to grow near purposely-treated plants.
Scientific studies around the world have suggested that pesticides can affect the health of bees through immune suppression, increasing the possibility of suffering from viruses and parasite infections. In addition, pesticides can affect bee hive survival through other avenues. For example, worker bees exposed to neonicotinoids have a shorter life expectancy, worse hygiene and are more likely to lose their queen. Neonicotinoids can also affect the ability of honey bees to successfully forage for food: they can affect both the physical ability of bees to fly after one or two days of exposure and interfere with navigation back to the hive (believed to be due to memory problems). As well as the navigation problem, neonicotinoid ingestion can result in less communication of food sources to other bees, because affected bees perform fewer communicative ‘waggle dances’(video link), the method by which a bee tells its hive-mates where to find the best nectar and pollen. As a consequence of less food being successfully collected, the probability of hive survival is reduced.
A 2014 report from the Australian Pesticides and Veterinary Medicines Authority, however, concluded that there is a lack of consensus in the scientific literature on whether pesticides, especially neonicotinoids, are causing the honey bee declines in Europe or North America. Furthermore, ‘[I]nformation and advice … suggests that, in Australia, honey bee populations are not in decline and insecticides are not a highly significant issue, even though they are clearly toxic to bees if used incorrectly’. Pesticides are not entirely off the hook; if honey bee populations decline in the future, it is possible that restrictions such as those in Europe will be required. Varroa destructor mites, on the other hand, have been described as ‘the most serious threat to the viability of the Australian honey bee industry’.
The parasitic Varroa mites suck the hemolymph (similar to our blood) of honey bees, transmitting viruses and other pathogens. A virus transmitted to the bees is the major driver of colony loss, rather than the mite itself. The virus can devastate honey bee colonies, as without treatment, most honey bee colonies will die within a few years of incursion. Varroa mites have rapidly colonised much of the globe, spreading from north Asia to Europe, the USA, southeast Asia, South America, Africa and New Zealand. Although they are not yet established in Australia, experts believe that ‘it is a matter of when, not if,’ the Varroa mites become established.
Australian efforts to protect honey bees
Measures have been taken to protect Australia’s honey bee population from incursions by the Varroa mite and its relatives. As well as general programs to prevent the incursion of exotic pests into Australia such as the Northern Australia Quarantine Strategy (NAQS), there is the National Bee Biosecurity Program. As part of this program, the National Bee Pest Surveillance Program operates as ‘an early warning system to detect new incursions of exotic bee pests and pest bees’ through ‘a range of surveillance methods conducted at locations considered to be the most likely entry point of bee pests and pest bees throughout Australia’. Pest bees include invasive, non-native bees such as the Asian honey bee while bee pests include pests which can detrimentally affect bees such as mites.
Australia’s biosecurity and surveillance regime has successfully recognised and destroyed hives of Asian honey bees infested with Varroa jacobsoni in the Townsville area and Brisbane. Varroa jacobsoni is a relative of the Varroa mites discussed, but it lives on Asian, rather than European, honey bees. Although Varroa jacobsoni are not believed to move easily to European honey bees, there is still a risk they could change host and, like the Varroa mites, they carry transmissible diseases that affect bee health and chance of survival.
Encouragingly, some bees seem to be evolving a defence against the Varroa mites. Reports from Europe and the USA have stated that ‘in some instances bees were living with varroa [sic] mites and an associated virus’. Hopefully, we will understand the mechanism behind this defence in the future. Perhaps, if knowledge of that process grows, and our biosecurity and surveillance regimes continue, there is still hope that Australia will be able to avoid losing a large percentage of our honey bees to Varroa mite, thus retaining their valuable pollination services.