Apocalypse by mosquito?

As part of our molecular tools lecture, expertly executed by Joe Roberts, we discussed the recent advancements of gene editing and its use in the eradication of malaria in Africa. Crispr is the cutting-edge gene editing tool that has garnered a lot of attention since it’s discovery in 2007. Further developments have led to it being the simplest method for editing the nucleotides on a DNA strand altering the original gene which can result in resistance to diseases, alleviate genetic disorders or treat blood diseases.

Despite its multitude of uses genetic engineering has been faced with large amounts of controversy. Gene drive, which is the promotion of specific genes in a population that cause infertility or death through release of carriers into the wild, has faced mass criticism due to the uncontrollable nature of the concept. Once these genetically engineered individuals are released, there is little that can be done to prevent the spread of the unwanted gene across species through natural hybridisation. There are also concerns over the potential impacts of eradicating an entire species from an ecosystem, which could result in a collapse if the eradicated species is an important food source-as in the case of mosquitos.

Malaria-carrying mosquitoes of the Anopheles family are one of the prime candidates for gene drive control. The infected females spread malaria through their bites, which release the parasite into the bloodstream of the unlucky animal. Malaria is life threatening, killing half a million people annually so control of the vectors (mosquitoes) is of particular importance. Many studies have been done into the prospect of gene drive control of these insects, with the most recent being the release of genetically engineered males into Burkina Faso that you may have seen on the news in the last couple of weeks, treated as the new apocalypse.

The release of these mosquitoes is being controlled by the non-profit research organisation “target Malaria” as a test for the potential release of gene drive organisms. The mosquitoes being released in their experiment are all sterile, thus are unable to pass on their edited genes. They are simply being released to gather data on their dispersal and won’t last more than a few weeks in the ecosystem. So, no, we haven’t reached the point of using gene drive in the control of malaria quite yet, but the organisation is hoping to eventually use their mosquitoes to eradicate Anopheles in sub Saharan Africa, albeit with more work needing to be done.

Whilst gene drive systems have been highly effective in population control for lab studies, the issues around potential hybridisation needs to be considered and it’s been discovered that these mosquitoes are capable of developing resistance to the edited genes through random mutations. Lab work is limited and simply can’t match the population size found in the wild-thus the rate of mutation faced by their gene drive experiments is much lower as they have fewer individuals to experience a random mutation. Therefore, actual field results may be hampered by development of resistance.

We are faced, then, with the final dilemma. Does the risk befit the reward? Do we risk the transfer of these genes through hybridisation to save the lives of half a million people a year? Is the rate of mutation high enough to negate the entire gene drive system in the wild populations? All that can be done is further research, taking the necessary precautions before leaping into a potentially disastrous situation. Which is exactly what the Burkina Faso release is for.

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The collection conundrum: How useful are Museum collections?

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Hope the whale suspended over Hintze hall

Visiting a museum for the first time can be a magical experience. Wandering through the vast halls, awing at the exhibits and looking at all the various artefacts within the museum walls can inspire wonder and intrigue into pretty much anyone.For me, the Natural History Museum is one of the greatest museums I have ever visited; with its breath-taking architecture, plethora of exhibitions and host of scientific specimens within the main halls and the Darwin centre cocoon. However, just walking around and taking in all of this doesn’t even scratch the surface of the treasures held within.

The NHM (like most museums) isn’t just a place to visit, but also a cornucopia of scientific research and constant study which the museum wants to share with as many people as possible. They do this by hosting talks in the Darwin centre, ‘Lates’ evenings – where you can go to talk with curators and participate in backstage tours of the collection areas – and even through sleepovers at the museum. On some occasions, however, the museum will have stalls erected during visiting hours to engage the public about the collections.

I have been fortunate enough to help talk to the public about the Entomological collections held within the museum, the most prevalent questions being – “How many insects do you have?”, “Where do you keep them all?” and even, “How do you keep that many insects alive?”. Most people respond to the answers by enthusing about how amazing it is that so much has been collected and how the museum can manage to keep it in such good condition. However, there are equally many people condemning this fact; believing that it is cruel to have pinned so many specimens instead of simply recording their whereabouts. This got me thinking; why is there an aversion – in some people – to Museum collections? Do we really need hundreds of a single species pinned in boxes? And do they all just sit there gathering dust?

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A collection box from the NHM containing moths collected in South Africa

In short, the answer is as follows; these questions arise from a lack of understanding on museum collections and the data they hold which can be used for scientific study, particularly that of entomology. The collection data held within museums is invaluable and help progress our understanding of a variety of topics surrounding the specimens. Entomology benefits heavily from the use of museum data in studies, many published papers use the date, life stage (adult, pupa, larva) and site in which a specimen was collected in order to discuss how Lepidoptera may have been affected by climate change. One paper even looks at how the phenology (life cycle) of British butterflies has changed since the 19th century. It talks of how the rates of phenological change in butterflies (as a response to changes in host plant flowering periods) is slowing down and should these changes continue, it could cause greater problems for many species.

Furthermore, some papers even use genetic data extracted from museum specimens in order to help determine how some species of insect have evolved, and look at the changes in biodiversity within a given habitat. One such paper used tissue samples from both dry and ethanol preserved specimens of sack-bearer moth (Mimallonidae) to construct a phylogeny for the moth family. The results of that study will greatly contribute to further studies concerning the biogeography, evolution and host plant relations of Mimallonids.

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The caterpillar of a Mimallonid moth which will later go on to build a “sack” of silk (from which it’s common name is derived).

Recently, the Natural History Museum has embarked on a large scale digitisation of their collections, starting with the Lepidoptera in a project called iCollections. The digitisation of the collections held within the museum are available to the public through the NHM data portal. This provides a wealth of data on the digitised specimens (including year, location, species, holotypes, paratypes etc.) which lends itself to further use of their data in many studies concerning conservation, biogeography, taxonomy and genetics. The large sample sizes of the collections and range of locality and year of collection add to this possibility of further study, helping to increase our overall understanding of the many insect species held within museums.

Overall, Museums are fantastic places filled with the potential of further study, and those like the NHM have an unending potential to help develop our understanding of insects through time. On the 6th February the Harper Entomology students will be visiting the NHM where we hope to learn even more about the wondrous Entomological collections held within their walls.

 

Understanding the Impacts of the Beekeeping Buzz

As part of my campaign to promote pollinator friendly gardening, in my hometown Neilston, I got chatting with a lot of people.

My Plants for Pollinators stall at the Neilston Cattle Show

The reception I received was greater than I could ever have hoped for, with so many schools and nurseries already running projects to help raise awareness of the decline in bees. What amazed me the most, though, was the sheer number of people who had taken an interest in beekeeping. Many had already become certified beekeepers with their first hive. Hearing local people so passionate about the life of an insect made me so proud of my community.

It’s not just my community that has taken its hand to apiculture (beekeeping). Beekeeping has been on the rise for the past decade, particularly in the cities. Most people become beekeepers as a hobby, interested in reconnecting with nature within an urban environment. Recently, there has been a rise in people raising bees out of concern for the environment, as I found in my home town.

The issue, though, is that there are very few studies out there regarding the positive or negative impacts these introduced honeybee colonies can have on the environment.

One study has found that the introduction of honeybees has negatively impacted the survival rates of bumblebees, whilst another showed that honeybees had no significant effect on local flora or fauna. It’s difficult to assess the truth amidst conflicting reports – but there have been concerns raised that need definitive answers.

Wildflower populations have been shown to increase due to honeybees increasing pollination of the plants, however, pollination is not as simple as a single bee going from one flower to the other. Each species is better suited for the pollination of certain plants and are inefficient pollinators of others. When honeybees are the primary source of pollination in an environment, the plants that they prefer or are capable of pollinating are fertilised more often. This can result in alterations to floral diversity, which in turn may lead to a decline in the preferential food plant of other bee species.

Honeybees have also been shown to they can deplete a plant’s nectar source without providing any pollination. The competition for nectar in these plants has resulted in changes to the behaviour of fellow pollinators. In Australia, the honeybees out-compete the New Holland Honeyeater, resulting in the birds increasing their territories.

New Holland Honeyeater, Image by Louise Docker

This could result in them running out of resources, and ultimately, a decline in their population – though no significant declines have been documented so far. A recent study has emerged trying to measure the impact apiaries can have, but their result was highly variable and merely highlighted the need for further research on the impacts honeybees have on wild bee populations and other native fauna. It’s surprising that no study has focused on the impact apiaries can have on other insect pollinators such as hoverflies.

I find this topic particularly concerning, in part to the lack of research, but mostly due to the skewed opinion of the well-meaning public. Apiculture is an excellent hobby to get into, with many benefits for yourself and particularly for agricultural crops. It is irresponsible, however, to take up apiculture to benefit the bees, especially when there is so little evidence available. That’s why more research needs to be done into this topic so that we can have a clearer picture of the true impact beekeeping can have and so those who only wish to help aren’t mislead into doing the exact opposite.

Shropshire Entomology Day – 04/02/2018

Yesterday, me (@EntoAqib) and three fellow entomologists (@pseudoliam, @ento_the_wild and @Apis_linzi) began our journey to the Shropshire Entomology Day at the Field Studies Council centre at Preston Montford, bright and early *shudders*. Upon arrival we were greeted with tea and biscuits, alas, we felt alive once more. After signing in and a warm welcome from Sue Townsend (the FSC chair) we saddled up and waited patiently for the talks to begin.

Starting off was Peter Boardman, a dipterist with a particular fondness for craneflies. He gave us an overview of his past year working for Natural England. He began with tales of traversing the country, sampling at stunning SSSI’s (Sites of Special Scientific Interest); accompanied with pictures of beautiful critters. However, it’s not always sunny days spent sweep netting, there’s also an immense amount of post-fieldwork time and effort that goes into sorting, identifying and then recording specimens!

Next up, was Mike Shurmer, a micromoth super-fan and recorder. Turns out micromoths aren’t just boring brown things, they come in a bunch of different colours and patterns. They are the most diverse of UK Lepidoptera, trumping the substantially more popular butterflies and macro-moths, highlighting their importance and need for attention. Some notable records were mentioned, one of which was Crambus ulliginosellus:

Crambus uliginosellus

Crambus ulliginosellus © Jens Christian Schou

 

,this funky looking moth, with an equally funky name, was recorded in Shropshire recently for the first time in 50 years! The presentation ended with a challenge, so I’m going to re-present you guys with the same challenge:

Look out for these two micromoths:-

Twenty-plume moth

  • Keep a look out indoors, in wood stores, garden sheds and in garages.

Twenty-plume moth ©RodBaker

Ectodemia septembrella (slightly trickier)

  • Has leaf mining larvae (the larvae feed within the leaves).
  • Look out for feeding signs on Hypericum spp., commonly known as St. Johns Wort.

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    Feeding signs of the leaf mining larvae of Ectodemia septembrella ©BarryDickerson

If you do find them (or any other micromoth) remember to submit a record on iRecord!

Third on the agenda was a short presentation by Keiron Brown about BioLinks, a project being ran by the FSC which aims to train individuals of varying expertise in the identification and recording of several invertebrate groups, including relatively overlooked ones.

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Focus species groups of the BioLinks project ©HeatherCampbell

Following suit was a talk by Godfrey Blunt on the problems associated with mapping invertebrates. He began by highlighting the problems with current record mapping. Firstly, just because an organism was once there it doesn’t mean it’s still there now. Current mapping uses the botanists approach, but unlike plants, inverts can move. So, if something was found in a spot away from it’s range it doesn’t mean it’s expanding its natural range, it’s very likely that it’s just a chance recording. Therefore, it is important to note that record maps depict static resident population not mobile ones. He also stated that it shouldn’t just be about simply putting a blob on a map, we should be selective in the data we input (especially with old records), as too many inputs may make a map difficult to interpret. The other side of this problem coin is that not having enough records, which is just as bad. He offered an adequate manner (he stressed that this isn’t a solution) of addressing this problem by adopting the mapping approach used by ornithologists; using different sizes of dots and different shapes depending on the record. This provides a visual source of information which is clearer and substantially easier to interpret. Richard Burkmar gave a demonstration on how to use nifty QGIS to produce a base map with the necessary information and then overlaid the records onto it, followed by a resounding “ooooo” from the audience at the pretty result.

Lawrence Bee followed up with a presentation on what went into the making of the British Spiders Field Guide which he co-authored. It’s a handy dandy book jam-packed with lots of info and tons of gorgeous photographs of spiders. I just couldn’t resist grabbing myself a copy!

 

Lunch break!

With our stomachs full, we were ready for another round of talks. It was time for a talk which I was really looking forward to- rearing bushcrickets in captivity! Jon Delf talked through several aspects of rearing: starting a culture, suitable housing, feeding requirements, mating and how to treat their eggs. Everything you need to know to rear bushcrickets in the comfort of your own home.

Next up was fellow entomologist and @EntoMasters student, Liam Andrews. His talk was titled: “Pseudoscorpions of Shropshire”. He started off by informing the crowd about this understudied group with an overview. There’s only 27 species in the UK, but about 3500 worldwide (probably substantially more). He then went on to talk about their physiology and behaviour. Pseudoscorpions display phoretic behaviour- they hitch a ride on other organisms such as flies and beetles to disperse. Their physiology is pretty awesome, these little predators are armed with venomous pedipalps (but some don’t have any venom) and chelicerae which they use to subdue their prey. The chelicerae are also tipped with silk producing structures called the galea. The audience was also informed on how to sample for them. A Tullgren funnel can be used, however these aren’t readily accessible, but you can make your own (pic below)! Sieving compost heaps and leaf litter may also expose these elusive critters, as well as scouring under rocks and logs. The informative presentation came to a close with a run through all the species recorded within Shropshire.

 

Viv Marsh then delivered a talk on siting and managing artificial bee hotels, with a focus on Osmia bicornis, a stingless bee species which is an effective pollinator. The last presentation of the day was by dipterist Nigel Jones, on the insects which he found sweep netting a single ash tree in his back garden. His finds were very interesting to say the least, including a potentially new species to science! It’s incredible how a single tree can boast such diversity.

Aaaaand that’s a wrap! I’d like to thank the organisers and the speakers for such a fantastic day! Hopefully I can make it next year for another day full of ento-goodness.

Follow these folks on twitter:

FSC Centre Preston Montford: @PrestonMontford

FSC Preston Montford chair: @SueTownsend3

Peter Boardman: @pebo22 who runs the cranefly recording scheme @CRStipula

Keiron Brown: @KeironDBrown and the official BioLinks twitter account @FSCBioLinks

Mike Shurmer: @mike_shurmer

Liam Andrews: @pseudoliam who also runs @PseudoscorpUK

Lawrence Bee: @LawrenceBee

Richard Burkmar: @burkmarr

 

By Aqib Ali  (Twitter:@EntoAqib, Email: Aqib1996@hotmail.co.uk, Linkedin: Aqib Ali)

MSc Entomology Twitter: @EntoMasters

How Insects Survive in Extreme Cold Winters

Insects survive in many different environmental conditions, across the world. But, when winter hits temperatures can be extreme in places, reaching  -60℃, and colder! So how do insects survive this extreme fluctuation in temperature? Some insects migrate to avoid these temperatures, but some species stay put, and have physiological adaptations to survive the winter months. Thousands of species spanning several orders, including Lepidoptera, Coleoptera and Mecoptera, use two techniques to survive: freeze tolerance and freeze avoidance, which have evolved independently for many species (Dennis, et al, 2015; Duman, et al, 2004; Li, 2016).

1) Freeze Tolerance:

As temperatures start falling in autumn, insects begin to synthesise 3 components key to their winter survival, these are: antifreeze proteins (AFPs), polyols and ice-nucleating agents (INA proteins).

Freeze tolerant species survive by encouraging ice formation in extracellular spaces, using INA proteins. Through osmosis, water is drawn through the cell membrane creating an equilibrium, through these two methods ice is prevented from forming within the insect’s’ cells, which can lead to severe damage and could become lethal (Bale, 2002).

However, the insect is still susceptible to injury from the ice, this is where the polyols come in. These are used to prevent mechanical damage to the insect and have various uses to do this, such as reducing the fluctuation of water across the cell membrane (Bale, 2002).

The insect has one final hurdle to overcome to ensure its survival over winter. As the winter months draw to an end the temperature begins to rise, and water may attach to the ice crystals, within the extracellular spaces, and cause secondary recrystallisation. This is where it gets complicated. Using AFPs, insects can prevent the growth of ice crystals as they preferentially grow from surfaces with a small radius.  AFPs prevent this by adsorbing onto these low radius surfaces of the ice crystal meaning that that they do not grow, unless the temperature reaches the colligative melting point – the Kelvin effect. Essentially the ice crystal will not grow unless the temperature reaches the hysteretic freezing point. Due to the AFPs the water becomes supercooled, and the freezing point is much lower than usual, termed the hysteretic freezing point (Duman, et al, 2004; Zachariassen and Kristiansen, 2000).

2) Freeze Avoidance:

Freeze avoidance is a completely different strategy, using the same materials. Freeze avoidance works by keeping the insects bodily fluids liquid, throughout the entire winter, as opposed to letting the extracellular spaces freeze (Dennis, et al, 2015).

First things first, the insect has its last meal and finds a nice spot to overwinter. Then it begins the process of removing any ice nucleating substances from its body: it’s water content becomes reduced whilst its fat content increases and the digestive system is emptied (Bale, 2002). The insect then synthesises AFPs and polyols which results in the insect having a very low supercooling capacity and thus preventing any bodily fluids from being able to freeze, as long as the temperature remains above their supercooling point (Overgaard and MacMillan, 2017).

To summarise some insects have complex systems allowing them to survive the extreme cold, and it’s pretty cool!

By Linzi Thompson (Email: thompsonlinzi@gmail.com, Twitter: @Apis_linzi )

Harper Adams MSc Entomology Twitter: @EntoMasters

 

References:

Bale, JS. 2002. Insects and Low Temperatures: from Molecular Biology to Distributions and Abundance. Philosophical Transactions of the Royal Society B: Biological Sciences. 357, pp.849-862.

Dennis, AB, Dunning, LT, Sinclair, BJ, and Buckley, TR. 2015. Parallel molecular routes to cold adaptation in eight genera of New Zealand stick insects. Scientific Reports. Nature. 5

Duman, JG, Bennett, V, Sformo, T, Hochstrasser, R, and Barnes, BM. 2004. Antifreeze Proteins in Alaskan Insects and Spiders. Journal of Insect Physiology. 50, pp.259-266.

Li, NG. 2016. Strong Tolerance to Freezing is a Major Survival Strategy in Insects Inhabiting Central Yakutia (Sakha Republic, Russia), the Coldest Region on Earth. Cryobiology. 73, pp.221-225.

Overgaard, J, and MacMillan, HA. 2017. The Integrative Physiology of Insect Chill Tolerance. Annual Review of Physiology. 79, pp.187-208.

Zachariassen KE, and Kristiansen, E. 2000. Ice nucleation and Antinucleation in Nature. Cryobiology. 41, pp.257-279.

The marvels of chocolate

Have you ever wondered where chocolate comes from and if it is possible that there will be a chocolate shortage in the future? Have you ever wondered if chocolate has anything to do with entomology? According to the Telegraph newspaper the average person In the UK spends a minimum of £57 on chocolate per year. It is therefore no surprise that the Theobroma cacao tree, from which we get most of our chocolate, is the second most important tropical cash crop, being worth $5 billion, providing employment for approximately 40-50 million farmers in Africa and Asia. (Schawe et al. 2013). Chocolate is processed from cocoa beans which grow on the 5-8 metre tall T. cacao tree (Young, 1982). As well as chocolate the cocoa beans are also processed into many well-known products such as cocoa powder and cosmetics (Schawe et al. 2013). Chocolate is not only delicious, but it has actually played a major role in human society by representing power and celebration and was even historically used as a currency.

The red/ brown egg shaped cocoa pods containing the cocoa beans are only produced if the flower is successfully pollinated by a particular insect. For once we are not talking about bees. Although you probably will not believe me, the pollinator is actually a fly, well, two species of the biting midge. Their Latin names are Forcipomyia quasiingrami and Lasiohela nana and they both belong to the Ceratopogonidae family (Young,1982). Can you believe it! Chocolate production is solely reliant on a biting midge!

The biting midge is 2-3mm long, about the size of a grain of rice (Young, 1982). Considering how important the midge is it lives quite a secretive life, the larvae (maggot) feed on dead organic matter and fungus and the adults require pollen and blood for egg production (Leston, 1970). The midge larvae click and jump so maybe that has made you rethink your opinion of maggots (Frimpong, 2009). Well when you think of flies you may automatically think of their larvae the maggot. I am writing this to show you wonder of chocolate, I certainly don’t want to put you off it. But without the midge larvae there would be no chocolate! Therefore if we destroy this annoying midge we would have no chocolate. Which would be worse?

So when you think of chocolate what do you imagine the flowers would be like? Well actually they are 5 pink sepals, holding 5 pouch like yellow petals. The petals conceal a ring of 5 staminodes, infertile stamens which enclose a central ring of 5 stamens covered in pollen. The flower’s ovaries are in the centre. The midges hover and weave around the aromatic flowers before crawling into the petal. The red nectar lines guide the midge towards the central narrow nectaries, where it feeds on nectar. The pollen from the previous flower visited is transferred to the ovary, fertilising the seed. When the midge crawls out of the flower it consumes some of the stamens pollen, but a large majority of pollen sticks to the midges long caudal hairs (Young, 1985). The midge then flies up to 6m away or is blown 100m-3km away from the flower, to another flower (Frimpong, 2009; Klein et al. 2008; Groneveld, 2010) and so it continues.

So far so good, but what if I was to tell you this midge is becoming rare, then what would you say? And what should we do about this? What if I was also to tell you that these midges also depend on rotting bananas and fungus growth on them for larvae growth (Leston, 1970) would you change your mind about fungus? The main reason for the midges decline appears to be loss of its microhabitat of dead leaves and discarded cocoa pods. The farmers are keeping their plantations too clean, banana peel may be the answer.

There is an additional problem. This particular tree (T. cacao ) is inefficient at producing fruit. Flowers must be pollinated on their first day of bloom. Otherwise, after 2 days, the flowers drop to the ground. As a result less than 5% of the 10% of flowers that are successfully pollinated develop into fruit (Groneveld, 2010). So next time you open a 100g chocolate bar remember it took 1 pod with 30-40 seeds to produce it. In a year alone the cocoa industry uses about 35 trillion cocoa pods. And so perhaps it is no wonder chocolate can be loosely translated to “the food of the gods”. So, next when you hear someone talking about the importance of bees just stop for a minute and consider the midges and how without them there would be no chocolate. And, next time a midge bites you think of their cousins the insect pollinators.

By Ruth Carter


References

Encyclopedia of Life. 2015. Theobroma cacao. [On-line]. Encyclopedia of Life. Available from: http://eol.org/pages/484592/overview [01/11/2015].

Frimponga, E., Gordona, I., Kwaponga, P. and Gemmill-Herrena, B. 2009. Dynamics of cocoa pollination: Tools and applications for surveying and monitoring cocoa pollinators. International Journal of Tropical Insect Science, 29 (2), pp. 62-69.

Groeneveld, J., Tscharntke, T., Moser, G. and Clough, Y. 2010. Experimental evidence for stronger cacao yield limitation by pollination than by plant resources. Perspectives in Plant Ecology, Evolution and Systematics, 12 pp. 183-191.

Kew. 2015. Theobroma cacao (cocoa tree). [On-line]. Home Science & Conservation, Discover plants and fungi. Available from: http://www.kew.org/science-conservation/plants-fungi/theobroma-cacao-cocoa-tree[01/11/2015].

Klein, A., Cunningham, S., Bos, M. and , S., I. 2008. Advances in pollination ecology from tropical plantation crops. Ecological Society of America, 89 (4), pp. 935-943.

Schawe, C., Durka, W., Tscharntke, T., Hensen, I. and Kessler, M. 2013. Gene flow and genetic diversity in cultivated and wild cacao (Theobroma cacao) in Bolivia1. American Journal of Botany, 100 (11), pp. 2271-2279.

Young, A. 1985. Studies of cecidomyiid midges (Diptera: Cecidomyiidae) as cocoa pollinators (Theobroma cacao L.) in Central America. Proceedings of the Entomological Society of Washington, 87 (1), pp. 49-79.

Young, A. 1982. Effects of shade cover and availability of midge breeding sites on pollinating midge populations and fruit set in two cocoa farms. Journal of Applied Ecology, 19 (1), pp. 47-63.

Young, A., Severson D. 1994. Comparative analysis of steam distilled floral oils of cacao cultivars (Theobroma cacao L., sterculiaceae) and attraction of flying insects: Implications for a Theobroma pollination syndrome. Journal of Chemical Ecology, 20 (10), pp. 2687-2703.

 

 

 

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

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 chemical spray) or a toxic (or unpalatable) taste. Entomological examples of these bright colours include the malevolent yellow and black of wasps, the familiar black-spotted red body of ladybirds and the monarch butterfly’s bright stripes of orange and black with white dots. Even honeybees and bumblebees are striped to warn birds of their painful sting, although the vile taste of their sting must be learned by the predator through repeated encounters.

But why are toxic insects usually conspicuous and not cryptic? A brightly coloured “lone mutant” in a population of cryptic prey would be more easily spotted by predators, seemingly making the genes coding for bright colour less advantageous. However, bright coloration does give a survival advantage- predators will generally only consume similar-looking items and be wary of prey that are novel or conspicuous. For example naïve birds that have not yet encountered toxic prey may have innate colour biases to stop them eating brightly coloured insects. More experienced birds will be able to remember that eating a particular colour pattern will lead to a bad feeling- that is unless some insects cheat however…

Insects that have evolved to mimic another insect’s body pattern, sound or behaviour, usually resemble a dangerous, aposematic species. This is known as batesian mimicry, and can fool predators into thinking it has defences or a bitter taste, when actually it is harmless (this is not to be confused with Müllerian mimicry, where several toxic species resemble each other). These ‘cheats’ gain a survival advantage without having to produce metabolically costly toxins or evolve a ‘weapon’. An example of this is the hornet moth, a mimic of the yellowjacket wasp- it resembles the wasp’s striking body pattern, which deters predators, but it is not capable of stinging. However more mature predators may be able to detect a fake through experience or social learning. So a scarcity of mimics is actually advantageous for both the mimic and the model insect- too many mimics and the predators will stop responding to the warning signals.

Aposematic colouration as an anti-predator strategy is simply an evolutionary alternative to other forms of protective coloration. Other ‘options’ for predator defence include background matching (a form of crypsis) and disruptive coloration, where bold and contrasting colours on an animal’s periphery act to break up its outline and confuse predators. Another intriguing form of protective coloration is known as ‘masquerade’, where the animal resembles an inanimate object (like a leaf) so the predator sees the prey, but mis-classifies it as something inedible. An extreme form of masquerade can be found in the devious pink orchid mantis, which also utilises this technique for hunting- it will wait until an unsuspecting fly lands on it to drink nectar, and instead be grasped and eaten!

AposematismAbove are examples of the different anti-predator defences that insects can achieve using body colour and pattern. (Clockwise from top left: bombardier beetle, green bush cricket, buff-tipped moth and hawk moth.)

Despite the successes of these other forms of defensive coloration, aposematism remains a widespread and successful alternative anti-predator strategy to being camouflaged, which has evolved to protect prey from predators. Predators’ sensory and cognitive abilities have been important in the evolution of warning coloration, and there are ‘cheats’ that take advantage of these otherwise reliable signals of danger.

Author – Chris Mackin (@EntoChris

Further Reading:

Allen, J. A., & Cooper, J. M. (1985). Crypsis and masquerade. Journal of Biological Education, 19(4), 268-270.

Endler, J. A. (2006). Disruptive and cryptic coloration. Proceedings of the Royal Society B: Biological Sciences, 273(1600), 2425-2426.

Endler, J. A., & Greenwood, J. J. D. (1988). Frequency-dependent predation, crypsis and aposematic coloration [and discussion]. Philosophical Transactions of the Royal Society B: Biological Sciences, 319(1196), 505-523.

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