Tag Archives: bumblebee

UK Conservation Schemes to Boost Bee Diversity- Everything You Need to Know

All over the UK, farmers are paid to set aside fallow land for flowers to grow and even to sow mixes of wildflowers in their field margins, all in an effort to boost dwindling numbers of wild bees, as well as birds and biodiversity in general. These are much needed conservation measures to tackle the devastating problem of losing the most vital pollinator groups (bumblebees and solitary bees) that help sustain the food production of Britain. But how do these agri-environment schemes (aka environmental stewardships, ESSs) work, what are the problems with them, and how must they be improved?

Plight of the Bees

The pollinators- bumblebees, honeybees, solitary bees, butterflies (and many others) are arguably the most important animal group, and one we should be most bothered about. A third of all the fruit and veg you see in the supermarkets would not exist if it were not for the pollinating efforts of bees et al., and many of the flowers of plants and trees would not be able to reproduce, and would hence disappear. However, there is no one perfect species of beethat can pollinate anything (although honeybees are renowned generalists), so attention must be given to boosting general bee diversity, with perhaps a focus on the most efficient pollinators, and generalists that can access many flower structures (although generalists are typically short-tongued so can only access ‘open’ structures- however these species are usually quite common).

Bees have had it pretty rough during the last few hundred years of anthropogenic development. Although several land-use changes wrought by humans did them some good, such as clearing of forest to allow mid-successional habitat (e.g. wildflower meadows- perfect for bees!) to flourish and the growth of fields of fodder crop such as red clover (also brilliant for bees)- this was to be short lived! At the advent of the 2nd World War, our native biodiversity suffered the intensification of agriculture in Britain and in much of the rest of Europe (another evil that can be attributed to Hitler’s long list!). Since crop production needed to be maximised to feed a war-torn nation, small farms turned into monocultures with no semi-natural habitat or flowers; pesticides replaced other forms of pest management, and planting fodder crops to feed livestock (which also happen to be bumblebees’ preferred food plant) became a thing of the past.

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Nowadays, there are even more evils that are possibly killing off our bees. Stressors such as competition from non-native bee species, increased transmission of disease, climate change, and neonicotinoid pesticide misuse have all been implicated. Fortunately, the governments of the UK and EU recognised the threat to our native fauna and food production, and have a few schemes in place to help conserve the plighted pollinators…

Stewards of the Land

The idea of Environmental Stewardship Schemes (ESSs) is to encourage farmers and landowners to aid the conservation effort in England, in exchange for farming subsidies- aka cash- for either implementing a conservation measure, or by not using an intensive piece of management. Among the choices (graded on a points system) open to farmers are hedgerow planting, sowing mixes of wildflowers, planting fodder crops and leaving margins of fields without crops or pesticide sprays (so flowering weeds and rare plants can grow). So farmers and land-owners make up their minds on whether a cash subsidy (and the bonus to the ecosystem services they benefit from) will be more profitable than using the land for crops still.

Unfortunately, research has shown that even farms using the higher level of the stewardships (HLSs) were not seeing any increase in flowering plant diversity, and subsequently no increase in bee numbers or species. So what exactly is going wrong?

Why the Schemes Don’t Work (and How to Improve Them)

The “higher level” stewardship schemes (HLS) involve more hands on options such as the sowing of wildflowers and pollen/nectar plant seed mixes. However studies are reporting that whilst bees are visiting the flowers sown from these mixes, they strongly prefer wild occurring flowers which aren’t included in the schemes. This means that the so-called “entry level” stewardships (ELS) are having an equal to greater positive effect on the bee community as these schemes usually involve margins that are allowed a natural community of wildflowers to establish, which are those preferred by the majority of farmland bees.

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Whilst the pollen and nectar and wildflower seed mixes do a good job at increasing the numbers of a narrow suite of bumblebee species, there is little evidence of effects on species richness (diversity) or on solitary bee numbers (despite that group making up the majority of species present in farmland!). The solitary bees much prefer flowers in the families Asteraceae (such as Cat’s Ear and False Mayweed) and Apiaceae (like Cow Parsley), but these mostly grow wild on verges which explains the success of Entry-level Stewardships. To improve their effectiveness, these wildflower mixes used in ESSs should contain more of these flowers preferred by solitary bees, as they are dominated by Fabaceae flowers (beans, peas and clovers), which are only good for bumblebees. Wildflower communities also take a while to establish (over years in some cases), and different flowers can benefit different life stages of the same bumblebee species.

Unfortunately the troubles don’t simply lie at the scale of the methods of conservation. Farmers are offered around £30 per hectare in Entry-Level, which is often not an economical way of using arable land. Another issue is the farmers themselves can choose from the entire array of options on offer, which may seem like a rather blind approach to nature conservation if some ecosystem services are particularly lacking (e.g. natural insect pest control), and the bird or mammal nesting options are chosen. Infact 65% of the entry-level stewardships in 2009 included hedgerows with options for cutting, and whilst this is great for the natural enemy population (beetles, hoverfly larvae etc.) near the edge of the field, these options that don’t particularly favour pollinators.

Final Word

The future for these currently flawed, but potentially effective conservation schemes is uncertain. More research and development on the flower mixes used to benefit bees (and other important taxa, such as beetles) and a more systematic approach to the combinations of conservation measures offered is needed. And since these schemes are funded in part by the European Union (with £400 million paid to farmers annually), a vigilance from environmentally-savvy politicians is needed to ensure these subsidies carry on post-Brexit. The AES schemes cover an impressive 66% of agricultural land, which is therefore 46% of the entire land in the UK! Surely for nature to flourish, we must direct more attention to improving these schemes to best benefit our pollinators, crop pest natural enemies, farmland birds, mammals, and general biodiversity in the UK.

Further Reading

Carvell, C., Meek, W.R., Pywell, R.F., Goulson, D. and Nowakowski, M., (2007) Comparing the efficacy of agri‐environment schemes to enhance bumble bee abundance and diversity on arable field margins. Journal of applied ecology, 44(1), pp.29-40. [Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2006.01249.x/full%5D

Wood, T.J., Holland, J.M. and Goulson, D., (2015). Pollinator-friendly management does not increase the diversity of farmland bees and wasps. Biological Conservation, 187, pp.120-126. [Avaiable from: http://www.sciencedirect.com/science/article/pii/S0006320715001755%5D

http://www.gwct.org.uk/farming/advice/stewardship-schemes/countryside-stewardship/

http://www.conservationevidence.com/actions/700

Diseases in bumblebees and honeybees

All species of bumblebee and honeybee have associated diseases and parasites that impact on the health of populations. Emerging infectious diseases (EIDs) are those that pose a risk to human welfare (directly or indirectly) that affect ecosystem service production such as pollination of flowers or health of livestock. But what are these diseases and what are the factors that exacerbate them?

One commonly cited cause for colony collapse disorder (CCD) of the american honeybee (Apis mellifera) is the mite Varroa destructor. Varroa carries and transfers the viruses deformed wing virus (DWV) and acute bee paralysis virus (both implicated in CCD). Affliction with varroa mite also tends to weaken the immune system of honeybees. ‘Hygienic’ colonies of honeybees are able to remove the mites from brood cells and the workers groom themselves to remove the mite and disrupt it’s life cycle- this is a form of ‘resistance’ to the mite.

Other common parasites of honeybees include acarine tracheal mites, nosema spp (fungus that infest intestinal tracts), small hive beetle, wax moths and tropilaelaps (mites). Bacterial diseases include american foulbrood and european foulbrood and fungal diseases include chalkbrood and stonebrood. Honeybees are also susceptible to dysentery (inability to void faeces in flight) and viruses such as chronic and acute paralysis virus, kashmir bee virus, black queen cell virus, deformed wing virus and cloudy wing virus.

Researchers have found that two of these honeybee diseases (DWV and Nosema cerenae) are capable of infecting adult bumblebees. Further field work found that 11% of bumblebees were infected with DWV and 9% with N. cerenae, compared with honeybee infection rates of 35% and 7% respectively. The most likely explanation for the disease incidence in bumblebees is infection by honeybees, but bee-keepers can reduce the spread of disease by regular brood comb changes.  It is thought that ecological traits of these pollinating insects (e.g. overlapping geographic ranges, ecological niches and behaviours) promotes cross-species transmission of RNA viruses. Social behaviour and phylogenetic relatedness of social pollinators is thought to further facilitate transmission within and between hosts.

More recent evidence has suggested that commercial colonies bred for crop pollination and honey production can carry diseases (parasite infections and over 20 viruses) and be a threat to native species. Researchers found that 77% of imported bumblebee hives were contaminated with up to 5 different parasites. There is an urgent need for further research into the health of wild and imported bees and improvement in monitoring and management practices for honeybee and bumblebee colonies

Fürst, M. A., McMahon, D. P., Osborne, J. L., Paxton, R. J., & Brown, M. J. F. (2014). Disease associations between honeybees and bumblebees as a threat to wild pollinators. Nature, 506(7488), 364-366.

Manley, R., Boots, M., & Wilfert, L. (2015). Emerging viral disease risk to pollinating insects: ecological, evolutionary and anthropogenic factors. Journal of Applied Ecology.

How else do pollinators benefit from plants?

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Plants primarily attract pollinators by offering nectar rewards (as a source of sugar for energy) and pollen (as a protein source for developing young). In return, the pollinator will pass on the plant’s genetic material for sexual reproduction. Using this animal vector is much more efficient than relying on wind pollination, but how does the pollinator benefit from this interaction? Besides nectar and pollen, what other rewards can flowers offer? How can plants sometimes ‘deceive’ pollinators by providing a false reward?

Some neotropical plants, including orchids, produce scent which is collected by the males of Euglossine bees to use as pheromones for courtship. The bees secrete saliva full of lipids onto the floral surface, which absorbs the scent compounds and is then collected by the bee’s ‘corbicula’, a modified pollen basket. Whilst the bees are collecting these female-attracting scents, the orchid’s specialized anthers deposit a ‘pollonium’ onto the back of the bee.

Pollinators have also been found to consume floral tissues (the plant itself!) as a reward for assisting with reproduction. Beetle species often consume floral tissues but also act as pollinators. For example cycads are often pollinated by specialized weevils that eat the cycad ‘flowers’ called cones. To limit the damage done, the plants often produce low concentrations of secondary metabolite (toxins) that accumulate in the insect and this limits the amount of floral tissue the pollinator can eat.

Other specialized plant-pollinator mutualisms has the plant producing oils which are used by bees to build nests and feed larvae. In many cases these fatty acid secretions are made rather than nectar, which means a more specialized pollinator can co-evolve with the plant. This leads to more efficient pollination as the insect is limited to only travelling and distributing pollen between a few plant species.

Sometimes pollination occurs by deceit. The dead horse arum produces chemical compounds that mimic those produced by carcasses. This attracts carrion flies and traps them in the flower overnight, covering them with pollen. Orchids of the genus Ophrys emit compounds which mimic female wasp pheromones and have visual displays that look similar to female wasps. The male wasp visits and attempts to mate with the flower, but inadvertetly pollinates it if fooled twice! Neither of these plants reward the pollinator with food (or otherwise) for pollinating it- this one sided ecological interaction is known as ‘commensalism’.

Many different incentives to attract insect pollinators to specialise on a particular species (or genus) of plant exist. The bizarre strategy of the fig tree has a chalcid wasp insert its long ovipositor to lay its eggs inside the fig fruits. The fig tree grows it’s flowers inside the fig fruits so the wasp actually pollinates it in return for the plant providing a habitat and food source for the developing larvae. Other plants have been shown to ‘cheat’ and deceive their pollinators into accepting a non-existent reward (like the wild orchid wasp mimic). However recent research has found that bumblebees have a preference for plant scent compounds that give an honest indication of reward quality. Plant resources put towards reward quality is limiting however, so an equilibrium exists between the evolution of cheaters and ‘honest’ signallers.

 

Irwin, R. E., Adler, L. S., & Brody, A. K. (2004). The dual role of floral traits: pollinator attraction and plant defense. Ecology, 85(6), 1503-1511.

Knauer, A. C., Schiestl, F. P. (2014), Bees use honest floral signals as indicators of reward when visiting flowers. Ecology Letters. doi: 10.1111/ele.12386

Simpson, B. B., & Neff, J. L. (1981). Floral rewards: alternatives to pollen and nectar. Annals of the Missouri Botanical Garden, 301-322.