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.

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.

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

Miles From Home: How Ants can Navigate Long Distances (and back!) to Forage

Ants are well known for their extraordinary ability to find food, and bring back enough to feed their vast social organisations. Being able to form relationships with other organisms that digest food, carry objects 50 times their weight and achieve great feats of communication and learning all help them forage… but how exactly do they find their way? Recent research from the University of Edinburgh has concluded the fascinating story of how the Formicidae navigate.

Plot a Course! Direction of Travel

Ants can decide on a direction for walking by using the position of the Sun in their visual field, as specialised cells in their compound eyes can detect the UV polarised light emitted by the Sun. Ants can maintain the correct course, whilst decoupling information where their body is an which direction they are travelling in. They also make use of visual landmarks (such as leaf litter), olfactory and tactile cues, and some species use the Earth’s magnetic field for navigation. According to the researchers at the University of Edinburgh, the ants construct a more sophisticated representation than they thought possible from the small size of their ganglia (brains), and can integrate information from different modalities (and from different areas of the brain) into the representation of direction.

How Far? Keeping track of Distance

Day-foraging ants, such as those in the genus Cataglyphis, are able to navigate exceptionally long distance (up to 200 metres and back!) by recording the distance they have travelled as well as the direction. An internal pedometer helps the ant remember the number of steps taken and this information is integrated with the ‘optical flow’ of objects moving around their visual field (which is an illusion- of course it is actually the ant that moves). Rather than each ant randomly roving away from the hive in search of food, the successful ‘pioneer’ must communicate the location to her sisters so they can make a sortie to the high quality patch of forage en masse…

Follow the Leader: Scent Trails

The long line of ants that you are bound to see in tropical forests are formed from scent trails that allow them to navigate back home, even if it is 200 metres away and in the dark! The ability to find the shortest route back is a crucial adaptation for avoiding desiccation in hot and arid environments. However, in army ant species, a group of foragers who become separated from the main marching column can turn back and form a circular ant mill, and run round constantly until they die of exhaustion! Ants have also been recorded to carry each other along a route, if an older and more experience forager notices that an internal nest worker (which are less familiar with the outdoor environment) is off the trail.

Final Word

So ants are able to backtrack to the location of their nest using their memories and the Sun as a reference point, and the way they operate is very similar to a self-driving car. This new research gives a unique insight into how brains of ants (and other insects) operate, and will inspire the next developments in robot system building to mimic their functioning, which would especially be useful for robots that need to navigate in forested areas. Modelling the neural circuits in the ant brain will also be useful to simply understanding more about the complex behaviours of the fascinating family of insects.

Further Reading

http://www.cell.com/current-biology/fulltext/S0960-9822(16)31466-X

http://jeb.biologists.org/content/209/1/26

http://science.sciencemag.org/content/353/6304/1155

Bees: How do they Combat Disease?

A honeybee hive sick with disease can spell the end of a colony. Recent research has shown bees can use vaccinations and nurse one another to protect themselves from and prevent certain diseases. But how exactly do they do it?

Vaccinations

Honeybees live in huge colonies that co-operatively rear brood (developing eggs and larvae), so must find some way of protecting the next generation against disease. To do this, the workers actually naturally immunize their young against certain diseases which they might encounter. The findings of a recent paper, published in the journal PLOS Pathogens, finally reveal how the important immune-signal protein vitellogenin works to do this.

It was found foraging workers pick up and bring back contaminated pollen and nectar to the hive, and workers create royal jelly using it. The bacteria picked up from the environment persists in the jelly, and is then fed exclusively to the queen. The pathogens are digested in the queen’s gut and stored in the queen’s fat body (an organ similar to a liver). Fragments of the bacteria are then ‘carried’ by vitellogenin, taken via the blood to developing eggs inside the queen. These young are now immunized, all without taking a step outside their hexagonal brood cell.

Now that we know how bees immunize their young against infection, scientists can work on synthesizing a vaccine to prevent commercial bee colonies from becoming infected with disease- possibly aiding the fight against the crisis of colony collapse disorder (CCD).

But not all diseases in bees can be fought with immunity inherited from a parent. So how else do honeybees fight infection?

Nursing

Much like communist societies, honeybee hives divide up the hugely varied workload between different ‘castes’ of the colony (workers, drones and queen), and further divide workers into roles based on their size and age. Older, more experienced workers may be more likely to forage for the colony, and act as guard bees (they have actually been found to patrol the entrance the hive!). Younger, more naive workers however are usually more suited to nursing duties, which include feeding and tending to the queen and brood, as well as medical specialists which provide sick workers with anti-biotic laced honey.

A recent study, published in Behavioural Ecology and Sociobiology, gave nurse bees infected with a Nosema ceranae parasite a choice of honey from different plants. Bees with a higher level of infection tended to eat more sunflower honey, which contains the most antimicrobial activity. It also reduced the level of infection in the bees by 7%. A separate study suggests different honeys are effective against different diseases the bees may encounter. For example linden honey was better at fighter off a an infection of European foulbrood whereas sunflower honey was more effective against American foulbrood.

Nurse bees have other medical roles to reduce infection in a hive. For example, they can act as undertakers and remove the corpses of dead bees from the colony, dumping them far from the entrance. This behaviour is used to avoid spreading infections from pathogens and entomopathogenic fungi that proliferate on the bodies of dying insects,

In both of these incredible behaviours, bees can vaccinate and immunize their brood and sister workers by means of medicinal honey and food contaminated with bacteria. But where do these come from in the first place?

Natural Remedies

Floral nectar typically contains plant secondary compounds (those used for defence by the plant) which possess antimicrobial properties. This can be very useful to bees. Before the publishing of a recent study in PLoS One, we knew little more than the fact pollinators can reduce their parasite load by consuming nectar containing compounds such as nicotine.

This recent research has indicated parasitized bumblebees are taking advantage of these plant secondary metabolites in the wild, such as iridoid glycosides, and have a strong preference for visiting flowers that possess them. This quality of bees to self-medicate, by altering their foraging behaviour whilst parasitized, has massive implications for their ability to fight disease

Honeybees have other sources of medicine besides anti-microbial nectar. They have been found to collect resin from plants and incorporate it into their nests, which may help stop fungal parasities from colonizing their hive. (A study showed bees collect more of the resin when infected with fungal spores)

Final word

The fact that honeybees and bumblebees have evolved so many different ways in which to fight disease implies the risk that our wild pollinators face, as well as just how long they have been co-evolving alongside their assailing antagonists. Climate change and other drivers have recently made the problem of disease much worse, and research into this need to be rapid if we are to help our plighted pollinators.

Further Reading

Erler, S., Denner, A., Bobiş, O., Forsgren, E., & Moritz, R. F. (2014). Diversity of honey stores and their impact on pathogenic bacteria of the honeybee, Apis mellifera. Ecology and evolution, 4(20), 3960-3967.

Gherman, B. I., Denner, A., Bobiş, O., Dezmirean, D. S., Mărghitaş, L. A., Schlüns, H., … & Erler, S. (2014). Pathogen-associated self-medication behavior in the honeybee Apis mellifera. Behavioral Ecology and Sociobiology, 68(11), 1777-1784.

Richardson, L. L., Bowers, M. D., & Irwin, R. E. (2015). Nectar chemistry mediates the behavior of parasitized bees: consequences for plant fitness.Ecology.

Salmela, H., Amdam, G. V., & Freitak, D. (2015). Transfer of immunity from mother to offspring is mediated via egg-yolk protein vitellogenin. PLoS Pathog, 11(7), e1005015.

Simone-Finstrom, M. D., & Spivak, M. (2012). Increased resin collection after parasite challenge: a case of self-medication in honey bees. PLoS One,7(3), e34601.

5 Fascinating Facts about Ladybirds.

Ladybirds are members of the beetle family Coccinellidae, and are predatory insects that control populations of aphids in gardens and in fields. Ladybirds, or ladybeetles/ladybugs, are well recognizable insects that are adored for their beautifully spotted bodies, but there are several things about ladybirds that one should know…

1. Ladybirds practice cannibalism

When food is scarce, ladybirds may resort to eating whatever soft-bodied organism is nearby, including other adults, pupa, larvae and even eggs of other ladybirds. Even the ladybird larvae which are the first to emerge eat their future siblings (unhatched eggs), but some of these have not even been fertilised by the adult, presumable for the purpose of giving the first hatching young more of a chance of survival.

2. Ladybirds bleed from their knees when threatened.

Ladybirds signal their toxicity using aposematic coloration (black spots upon red, white spots upon orange…), but they have another defence. When startled, ladybirds will seep toxic and foul-smelling hemolymph (rich in alkaloids) from its leg joints, leaving yellow stains on the surface below it. Predators are deterred by the prospect of eating such a rank smelling and bad looking prey item, and are repulsed enough to search elsewhere.

3. Ladybirds are highly promiscuous

Ladybirds are so promiscuous that in 2-spot ladybirds clutches often contain eggs fertilised by more than 3 different males. Because of this, ladybirds can transmit mites that feed on blood below the elytra to one another during mating- an STD! A mite-infested ladybird can reduce the size and viability of clutches. And as expected the higher the number of mating partners, the more mites a female ladybird will catch- sometimes up to 81 mites!

4. Ladybirds aggregate in the winter to hibernate

When temperatures fall and days become shorter, ladybirds seek shelter in protected locations- under leaves, behind bark and even in houses. Thousands of ladybirds may gather in one location to take advantage of the collective heat for energy conservation.

5. A ladybird may eat as many as 5000 aphids in its lifetime

Aphids are beneficial predators that control populations of pest aphids, whitefly, scale insects and mealybugs. An extremely hungry ladybird can consume 50 aphids per day. To ensure that ladybird larvae have access to plenty of aphid prey, their eggs are laid among a young aphid colony.

MYTHS:

“You can tell a ladybird’s age by the number of spots” Spots actually indicate species. (Two-spotted ladybird, 10-spotted ladybird..)

“Those big white spots are the ladybird’s eyes”. Those white spots are there to scare predators.

Further Reading:

Majerus, M. E. (1994). Ladybirds. HarperCollins Academic.

Roy, H., Brown, P., Frost, R., & Poland, R. (2011). Ladybirds (Coccinellidae) of Britain and Ireland. Natural Environment Research Council (NERC).

Featured image from www.alexanderwild.com.

What is Climate Change doing to our Bees?

Insect pollinators ensure transfer of genetic material between plants (sexual reproduction) and maximisation of fruit sets and yields. However these beneficial insects are in decline worldwide, owing to the intensification in crop production of the 20^th century (giving less diverse forage), misuse of pesticides and proliferation of various diseases. A driver of decline still under contention is global warming (more accurately climate change) as the effects are hard to predict and will be different for specific groups of pollination- an optimum foraging temperature for bees may be not be so good for pollinating moths, butterflies, hoverflies or birds.

Temperature too high?

Many insects are ectotherms, meaning they do no generate their own heat and need to bask in the sun to become warm enough. Pollinator groups such as butterflies have their distributions limited by low temperatures at high latitudes, so when the climate warms in these areas the generalist species (those that may feed on a wide breadth of flowers) are expected to expand their distribution northwards, but a colder winter temperature will cause their range to recede southwards. For bumblebees the relationship is not as clear- some species have retreated northwards (Bombus distinguendus) and others have retreated southwards (B. sylvarum). Other problems may arise for bumblebee queens that overwinter and emerge from dormancy to find their newly-found colonies is out of sync with their forage plants- this is known as a phenological mismatch or phenotypic asynchrony.

Out-of-sync with host plants?

Climate change is causing phenological advances (a delay) of flowering in plants which means insects have a shorter foraging season to feed and raise their young (either by feeding larvae or provisioning resources to eggs). Non-Apis bees (bees other than honeybees) in particular are shifting in relation to their host plants, with their queens even emerging from overwintering to find very few nectar plants have flowered yet, suggesting no clear pattern for phenological mis-matching. But some researchers argue that in robust pollinator networks there is an assemblage of multiple plant species for early emerging or late emerging pollinators to feed on, and vice versa. For specialist pollinators there is also a risk of spatial mismatches, where plants offering nectar and pollen shift their range and distribution much to the chagrin of specialist pollinators that must ‘track’ their host plant by migration (but this depends on dispersal ability, commonness of preferred nesting habitat). Generalists, however, will be able to take advantage of biodiversity of forage plants and will be affected less. In response to pressures to alter their diet, some bee species have even been rapidly evolving shorter tongues in order to feed from plants with shallower corollas. In 40 years, 2 alpine species of bumblebee (Bombus balteatus and B. sylvicola) have reduced their tongue length by 3 millimetres in response to a 60% decline in flower production.

Exacerbating other drivers of decline?

Climate change may interact synergistically with other causes of declines, for instance increased temperatures may speed up pathogen growth rates and lead to increased proliferation of bee parasites, such as varroa mite. Climate warming is speculated to increase the competition for resources between native bees and invasive ‘super-generalists’, possibly leading to extinction by competitive exclusion. Climate change may also cause development of agricultural methods that have an adverse effect on bees, such as devoting more land to growing crop monocultures (reducing florally diverse habitats) or increased use of pesticides.

What can be done?

Efforts are being made to help sustain pollinator diversity in agricultural landscapes, such as the compulsory planting of wildflowers through environmental stewardship schemes. However some researchers argue the existing biodiversity of food plants will ensure plant-pollinator phenological synchrony against climate change, and only very specialist feeders will be at risk. The rapid evolution of some at-risk bee species (such as those with shorter tongues) will also play a key role in recovery of pollinator populations. Efforts to mitigate the effects of climate change (such as reduction of emissions and geo-engineering solutions) would also reduce the subsequent effects on pollinator decline.

Further Reading:

Bartomeus, I., Ascher, J. S., Wagner, D., Danforth, B. N., Colla, S., Kornbluth, S., & Winfree, R. (2011). Climate-associated phenological advances in bee pollinators and bee-pollinated plants. Proceedings of the National Academy of Sciences, 108(51), 20645-20649.

Burkle, L. A., Marlin, J. C., & Knight, T. M. (2013). Plant-pollinator interactions over 120 years: loss of species, co-occurrence, and function. Science,339(6127), 1611-1615.

Garibaldi, L. A., Steffan-Dewenter, I., Winfree, R., Aizen, M. A., Bommarco, R., Cunningham, S. A., … & Klein, A. M. (2013). Wild pollinators enhance fruit set of crops regardless of honey bee abundance. Science, 339(6127), 1608-1611.

Miller-Struttmann, N. E., Geib, J. C., Franklin, J. D., Kevan, P. G., Holdo, R. M., Ebert-May, D., … & Galen, C. (2015). Functional mismatch in a bumble bee pollination mutualism under climate change. Science, 349(6255), 1541-1544.

News Roundup: Autumn 2015.

Disease eradications, Bee vaccinations and Entomophagy- catch up on all the latest entomological news stories you might have missed!

Risks of Eating Insects

The European Food Safety Authority (EFSA) have recently published a report on using insects as a protein source for animal feed and human consumption. It found that edible insects could contain biological and chemical contaminants, depending on how the large scale insect farms were managed.

With an estimated global population of 9 billion by 2050, using insects as a high quality source of protein as feed (for chickens, for example) could give a much needed food conversion rate (lower levels of initial energy and water required). Insect meat is also a quality source of fat, fibre, minerals and vitamins.

It is estimated that insects such as flies, moths, mealworms and crickets/locust already form the diet of at least 2 billion people. There is still clearly a way to go until western cultures can adopt new foodstuffs and a better understanding of the hazards of eating insects is required for the next step.

GM Mosquitoes trial reduced Dengue by 95%

A trial where scientists released thousands of ‘friendly’ Aedes aegypti mosquitoes infected with a bacteria that will intended to suppress dengue fever has yielded positive results. The theory was that the genetically modified yellow fever carrying mosquitos breed with the existing population and become the dominant type, thus eliminating the disease spreading variants.

The results of the Oxitec trial in Brazil found that the disease carrying mosquito number were reduced by 95%, well below the disease transmission threshold. The control was species-specific, and the Oxitec male mosquitoes mate with the naturally occurring females of the population and their offspring die before they can transmit the disease.

New methods of pest control like this are crucial as Aedes aegypti is developing resistance to insecticides and removal of breeding sites leads to them re invading the following year from neighbouring habitats that are inaccessible to us. There is also no vaccine or specific medication currently for dengue, chikungunya or zika virus (3 debilitating mosquito-borne diseases) so the development of new methods is crucial.

Honeybees give each other Vaccinations

Once a disease takes hold of a hive, the workers of a honeybee colony become disorientated and fail to forage to feed their sisters and brood. Luckily bees naturally immunize their young against certain diseases found in their environment, and scientists have recently discovered how exactly they do this.

The latest research suggests that the queen is fed on royal jelly from pollen infected with bacteria, and these are digested in the gut and stored in the queen’s fat body. Pieces of the bacteria are then bound to vitellogenin (a blood protein) and this is carried via blood to supply developing eggs with immunity.

The industries relying on honeybees colonies and the pollination service could benefit if a similar vaccine was produced for other bee diseases- like american foul brood. The discovery of vitellogenin, the carrier of immune-priming signals, could have implications for other animals that pass on immunity to their young.

Wasps are an indicator for environmental decline

A decline in wasps is thought to be a reaction to the increased harm of pesticides on wasps, and their food resource. Wasps play a key role in ecosystems (a ‘keystone species’), and taking them out would cause many systems in an ecosystem to collapse- for example dead insects and detritus would accumulate, with pestilent flies possibly taking advantage of this and proliferating.

A possible decline in wasps that might go unnoticed is what’s called a ‘shifting baseline syndrome’, meaning that small declines in number each year might go unnoticed, despite a reduction in 50% of population over 20 years (for example).

For the 2 most recognizable species of social wasp, Vespula germanica and Vespula vulgaris, there have been reported losses in number and this has been attributed to a reduction in their food resources- wasps are carnivorous during colony development (eating dead insects, aphids, etc.) and take advantage of sugar foods (such as fermenting fruit) late in the season. The decline of wasps could therefore be a signal that insects lower in the food chain are vanishing too and endangering whole systems. Environmental decline should be indicated by more than just a decline in wasps, though!

Further Reading:

Entomophagy http://www.bbc.co.uk/news/science-environment-34476742

Dengue Mosquitos http://entomologytoday.org/2015/07/03/genetically-engineered-mosquitoes-reduce-population-by-95-percent/

Honeybee Immunization http://entomologytoday.org/2015/08/03/researchers-discover-key-to-bee-vaccination/

Wasps and Ecosystems http://www.independent.co.uk/voices/nature-studies-fewer-wasps-to-swat-is-a-sign-of-an-ecosystem-in-serious-trouble-a6680881.html

Bank Holiday Special – Why insects are so colourful: The complex business of survival

Mastering Entomology

In the desperate struggle to evade predators, many insects have evolved toxic or bad-tasting skin, a camouflaged body (‘crypsis’), or a startle response to scare away predators. In this “evolutionary arms race”, adaptations on one side call forth counter adaptations on the other side. One such defensive adaptation is to appear toxic using brightly coloured (‘conspicuous’) body coloration- this is known as ‘aposematism’ (“Ay-PO-Sematism”). This idea that signals are sent by prey to predators to indicate toxicity was first suggested by Wallace to Darwin in 1861- they theorised that this evolved to stop predators attacking toxic prey to benefit both sides.

Aposematic warning coloration is a widely utilised form of defence used in all the animal kingdom (not just insects) and has evolved separately from many different evolutionary lines (convergent evolution). It can warn predators of defences such as a painful sting, repellent spray (such as a Bombardier beetle’s noxious…

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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.

Social Wasp Hierarchy: Who becomes Queen?

Social wasps have a caste system which separates individuals into reproductive males, infertile female ‘workers’ and a single reproductive queen. Towards the end of the summer, the existing queen runs out of stored sperm to fertilise eggs with so produces eggs that will eventually develop into fertile females. As each juvenile stage (egg, larva and pupa) is spent in a brood cell, the young queens that emerge must therefore compete to become the ultimate reproductive queen. But what factors determine which young queen dominates the hierarchy?

Eusocial species of wasps usually have their hierarchy determined by morphology of individuals. In the european wasp, Vespula vulgaris, the larvae that have been fed the most nutrients (which eventually becomes the largest reproductive adult female) will become the queen. The location of each cell is directly related to the amount of food a larva can receive, so the queen cells are usually located at the bottom of the nest which encounters most of the foragers. Several candidates of queens arise, which then compete to create a hierarchy of queens for an ultimate queen to be selected. The precise reasons behind the variations in queens is unknown, but it is thought to be related to fat stores which elevate a queen’s quality.

However not all social wasps have castes with such a variation in size and structure of individuals. In polistine paper wasps and stenogastrines (hover wasps), the hierarchy of females is determined behaviourally through dominance interactions. These hover wasps do not have predetermined or rigid castes, and young females need to constantly assert dominance to climb a strict age-based inheritance queue to become the reproductive (queen). Paper wasp colonies are founded by multiple reproductive females, and one of these foundresses will acquire dominance over the others and become the sole reproducer, with the others becoming ‘helper females’.

All female wasps are potentially capable of becoming the colony’s queen, which is usually achieved by a wasp laying eggs first and constructing the nest. Multiple young females usually compete with each other by eating the eggs of rival females. The queen may simply be the female that eats the largest number of eggs whilst safeguarding her own (and laying the most). Once the eggs have hatched, the subordinate females stop laying eggs and instead forage for the new queen and feed her young. If the dominant female dies, a new hierarchy may be established with a former worker acting as the replacement queen.

Different genera of wasps have different strategies for deciding which female becomes the egg laying queen that will give rise to a new progeny. However all strategies end up with the strongest and most reproductively capable female becoming queen. One or a multitude of factors may influence how competitive a young queen is, which include morphology (size and structure), nutrition (fat stores) and behaviour (e.g. aggression). Paper wasps have been found to recognise individual faces, so more complex forms of communication (using facial cues) may be used in the competition to become queen.

How else do pollinators benefit from plants?

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.