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Honey bees, crop pollination and Varroa mite
Frequently asked questions
What is Varroa mite, and why is it a threat to crop pollination?
Varroa mite, Varroa destructor, is a small mite, around 1 mm in diameter, that parasitises species of bees in the genus Apis, such as Apis cerana, the Asian honey bee, and Apis mellifera, the species that includes the European honey bee. In the 20th century two strains of V. destructor moved hosts from the natural host, the Asian honey bee, to the European honey bee. These two strains of Varroa destructor have spread world-wide and are regarded as the major challenge facing bee keeping internationally.
Untreated hives of European honey bees infested with Varroa are likely to die within 3 to 4 years. In other countries, populations of feral (wild) European honey bees that aren’t managed by bee keepers, have fallen by more than 90 per cent following the establishment of Varroa. The decrease in the populations of European honey bees reduces the amount of pollination services that are available to crops (Rosenkranz et al., 2010).
What is pollination and what types of pollination are there?
Pollination is the process in which pollen is transferred from the male part of the flower to the female part of the flower, thereby fertilising the ovule. The fertilised ovule grows into a seed which is contained in the fruiting part of the plant. Many of the grains, fruits and vegetables that we eat are the fruiting part of the plant which either contains or wholly comprises the seeds. Without pollination, the fruiting part of the plant does not form.
Flowers are pollinated in different ways. Wind is sufficient to transfer the pollen from the male to the female parts of the flower in some plants. These plants are said to be ‘wind pollinated’. In other plants, the pollen is transferred without the need for any transfer agent. These plants are said to be ‘passive self-pollinated’. In other plants an animal, often an insect, is required to transfer the pollen from the male to the female flower parts. These plants are said to be ‘animal pollinated’. Most plants are pollinated through a combination of the different mechanisms-i.e. some wind pollination and some animal pollination.
Are European honey bees better than other insects at pollinating crops?
Bees are better than any other group of animals at pollinating plants and have evolved with life cycles intimately connected with plants. European honey bees are the best known and most widely spread group of bees that have been domesticated to pollinate the crops eaten by humans. European honey bees can be reared and maintained domestically and deployed for large scale pollination, making them the most widely used pollinator of many crops. Although many other insects are more efficient pollinators of particular crops, because European honey bees are used at a high density they can pollinate a diverse range of crops.
Are all crops pollinated by insects?
No. The bulk of energy in our diets and feedstocks for animals comes from crops, such as wheat, corn and rice, that are exclusively wind or passively self pollinated and don’t require insect pollination (Table 1). However, insect pollination is essential for fruit set in other crops and these crops would have a yield reduction of more than 90 per cent without insect pollination. Insect pollination also contributes to the quality of produce, such as fruit size. Crops, such as broccoli or onions, don’t require insect pollination to form the part of the crop we eat, but insect pollination is important in generating seed to plant these crops. The range of dependence of crops to insect pollination is given in Table 1.
Essential = pollinators essential for most varieties (production reduction by 90 % or more comparing experiments with and without animal pollination)
Great = animal pollinators are strongly need (40-90 percent reduction)
Modest = animal pollinators are clearly beneficial (10-40 percentreduction)
Little = Some evidence suggests that animal pollinators are beneficial (0-10 percent reduction)
None = no production increase with animal mediated pollination
How much do feral (wild) European honey bees contribute to the pollination of Australian crops?
The European honey bee was introduced to Australia around 1822 and since then has spread widely across the country. It is not certain how much feral European honey bees contribute to the pollination of Australian crops and how much is contributed by native insects.
Which other countries have Varroa mite?
All countries with significant bee keeping industries have Varroa mite, except Australia. In addition to Australia, there are some countries in central Africa and some Pacific Island nations that don’t yet have Varroa mite-but these countries don’t have significant bee keeping industries.
What effect has Varroa had on the number of managed bee hives in other countries?
Since 1961 the reported global stock of commercial managed honey bee hives has increased by approximately 45 per cent (Figure 1). The number of bee hives in a particular country depends on a range of social and economic factors affecting the bee keeping industry in that country; Varroa is only one of these factors (vanEngelsdorp and Meixner, 2010).
Figure 1. The number of managed honey bee hives in the world from 1961-2008 (FAO Stat, 2011).
Varroa had no perceptible effect on the number of hives reported in Europe (Figure 2). The number of honey bee hives in Europe declined sharply in the early 1990s, coinciding with the end of communism, and the end of state support for beekeepers, in the previously communist bloc countries of Eastern Europe (Moritz et al., 2010). The number of hives reported Western European countries remained unchanged over the same period of time.
Figure 2. The number of managed hives in the whole of Europe, former Warsaw Pact countries and former EU 15 member countries from 1961-2008 (FAO Stat, 2011).
Rising incomes in rural areas, a declining rural workforce and the need to treat for Varroa has led hobby beekeeping to become less popular in some European countries (Potts et al., 2010).
In the United States the number of managed hives has declined steadily since the late 1940s, around 40 years before Varroa established there. This decline reflects declining terms of trade for United States beekeepers as the result of competition with lower-cost honey producing countries in South America. In contrast, due to their competitive advantage, the number of hives in South America has grown steadily since the mid-1970s, despite Varroa already being established there (Figure 3). However, the J strain of V. destructor in South America is less damaging than the K strain of V. destructor in the United States.
Figure 3. The number of managed honey bee hives in the Unites States and South American countries from 1961-2008 (FAO Stat, 2011).
What border biosecurity arrangements are in place to prevent Varroa getting into Australia?
The most likely entry pathway for Varroa into Australia is associated with its host, the European honey bee, on a vessel or conveyance of international origin or with bees brought into Australia illegally. The Department of Agriculture, Fisheries and Forestry (DAFF) management of bees from foreign countries is conducted on three fronts:
- vessels or conveyances arriving into the country
- cargo and containers on board those vessels
- surveillance of the movement of people, goods and vessels through the Torres Strait.
All vessels arriving in Australia must undergo quarantine clearance. Quarantine clearance may be in the form of assessment of documentation, physical inspection, targeted/random surveillance or a combination of these processes.
All vessels arriving into Australia are required to submit a Quarantine Pre Arrival Report (QPAR) to DAFF 96 to 12 hours prior to arrival. A question to which all masters must answer is “Have any insects, including bees, been discovered on board during this voyage?”, if so then a description of the insect and its location will be required.
Where bees have been reported or detected on a vessel prior to its arrival in port:
- an DAFF Entomologist is consulted for advice and directions on appropriate management of the bees on the incoming vessel and cargo, which can include meeting the vessel offshore
- DAFF advises the vessel of any special requirements on entry into the port by adding them to the Approval to Berth form DAFF provides to the vessel in response to the QPAR
- cargo is prohibited from being discharged from the vessel until the vessel has been cleared of the bee risk
- the vessel is inspected thoroughly with extra attention applied to locations where bees might inhabit.
DAFF conducts surveillance on vessels and port precincts if bee activity is reported or discovered by or on arriving vessels. An DAFF entomologist is contacted for treatment directions.
DAFF has also established appropriate communication material and contact information for stevedores and other port occupants to assist in timely reporting and management of bee activities.
If bees are discovered within cargo or on containers, they are ordered for treatment according to the requirements prescribed by an DAFF entomologist.
The Northern Australian Quarantine Strategy (NAQS) monitors the movement of all vessels, people and goods into Torres Strait islands. A major part of that program is the monitoring of the movement of traditional and non-traditional vessels between Papua New Guinea, the Torres Strait Protected Zone, the Special Quarantine Zones and the mainland across the Torres Strait. NAQS scientists also monitor the environs of these zones for evidence of incursions of exotic pests and disease.
What arrangements are in place to eradicate Varroa should it find its way into Australia?
A response to an incursion of Varroa (to contain and, if possible eradicate Varroa) is coordinated by the Office of the Chief Plant Protection Officer, of the Australian Government Department of Agriculture Fisheries and Forestry. Government authorities will follow the predetermined response plans laid out in Emergency Plant Pest Response Deed (EPPRD). The EPPRD is an agreement between governments and industries as to actions to occur in responding to pest of quarantine concern.
PLANTPLAN provides nationally consistent guidelines for response procedures, outlining the phases of an incursion (investigation, alert, operational and stand down), as well as the key roles and responsibilities of industry and government during each of these phases. It is updated regularly to incorporate new information or address gaps identified by the outcomes of pest of quarantine concern incident reviews.
What are the chances or eradicating Varroa mite if it’s found in Australia?
The chances of eradicating an incursion depend on the nature of the incursion, in particular how widespread it is when it is discovered. A widespread incursion is unlikely to be eradicable.
How will the honey bee and pollination continuity strategy be implemented?
Plant Health Australia (PHA), a non-profit company responsible for the administration of the EPPRD and for liaison between governments and industries with regards to plant pests of industry concern in Australia, has agreed to monitor implementation of the strategy. More information about PHA is available at: www.planthealthaustralia.com.au.
What is the Australian Government doing to prepare for Varroa should it establish here in the future?
The government coordinated preparation of the Honey bee industry and pollination continuity strategy should Varroa become established in Australia.
The Australian Government funds commodity focused Research and Development Corporations that allocate and manage these industry research and development funds. In recent years, Horticulture Australia Limited, which manages horticulture industry funding, and Rural Industries Research and Development Corporation (RIRDC), which manages honey bee industry funding, have worked together to jointly fund a Pollination Program. This program funds research on the pollination of Australia's horticultural and agricultural crops. Further information on this program can be found on the RIRDC website at: www.rirdc.gov.au.
Additional Australian Government resources are available through general scientific research and development agencies, such as the CSIRO, the University sector and research funding sources, such as the Australian Research Council. For example, Dr Denis Anderson, Principle Research Scientist with the CSIRO, has conducted extensive research on Varroa mite in South-East Asia and the Pacific. More information on Dr Anderson’s research can be found at: www.csiro.au/people/ps2dv.html.
Another example is the Australian Research Council linkage grant of $640,000 from 2010-2013 to the University of Western Australia for the “Better bees for tomorrow” project to better understand honey bee reproduction, diseases and immunity in more detail. More information on this, and related projects, can be found at: www.ciber.science.uwa.edu.au.
How does the recent establishment of Apis cerana (Asian honey bee) affect the ability of the Australian honey bee industry to manage the future establishment of Varroa?
In 2007, Asian honey bees were detected in Cairns, Queensland, with a national eradication program being undertaken. In 2011, a decision was made that it was no longer technically feasible to achieve eradication of the bees. On 20 May 2011 the Minister for Agriculture, Fisheries and Forestry, Senator the Hon Joe Ludwig, announced funding of $2 million to support a national pilot program aimed at transitioning to containment and management of Asian honey bees.
At this time it is not certain what effect the Asian honey bee will have on the Australian honey bee industry. However, the presence of A. cerana is not likely to have a direct impact on the spread of Varroa throughout Australia. The strains of Varroa destructor that exist on A. mellifera are not known to move from A. mellifera onto A. cerana- hence A. cerana will not act as a vector of this parasite- whereas feral A. mellifera will do so. Additionally the movement of strains V. jacobsoni from A. cerana onto A. mellifera is a rare occurrence—it appears that this occurs only when there has been long term exposure of both of the species of Apis as well as a strain of V.jacobsoni that has the characteristics of being able to survive on A. mellifera.
Now Australia has Asian honey bee, is the threat of Varroa mite more likely?
The Asian honey bee now in Australia is not carrying Varroa.
The greatest threat to the European honey bee are the strains of V. destructor that already parasitise the European honey bee, known as the J and the K strains. These strains have spread all over the world in the 20th century and are capable of parasitising the European honey bees in Australia.
FAO Stat 2011, Food and Agriculture Organisation of the United Nations http://faostat.fao.org/default.aspx
Klein A-M, Vaissiere BE, Cane JH, Steffan-Dewenter I, Cunningham SA, Kremen C and Tscharntke T 2007, ‘Importance of pollinators in changing landscapes for world crops’, Proceedings of the Royal Society B, vol. 274, pp. 303–313.
Moritz RFA, de Miranda J, Fries I, Le Conte Y, Neumann P and Paxton RJ 2010, ‘Research strategies to improve honey bee health in Europe’, Apidologie, vol. 41, pp. 227–242.
Potts SG, Roberts SPM, Dean R, Maris G, Brown MA, Jones R, Neumann P and Settele J 2010, ‘Declines of managed honey bees and beekeepers in Europe’, Journal of Apicultural Research, vol. 49, pp. 15-22.
Rosenkranz P, Aumeier P and Ziegelmann B 2010, ‘Biology and control of Varroa destructor’. Journal of Invertebrate Pathology 103, s96–s119.
vanEngelsdorp D and Meixner MD 2010, ‘A historical review of managed honey bee populations in Europe and the United States and factors that may affect them.’ Journal of Invertebrate Pathology. 103, s80–s95
14 Jul 2011