Tag Archives: insects

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…

neivamyrmex_army_ants_raiding_trail.jpg

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

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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.

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.

How else do pollinators benefit from plants?

bees

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.