Prunella – mistress of plasticity

Now that I have your attention, this is not an article about soft porn or fetishes, but rather a paean for that humble ‘weed’ Prunella vulgaris – Self-heal, Heal all, Woundwort, Heart of the Earth and many other names, depending on where in the World you come from.   Prunella vulgaris is in the family Lamiaceae, so related to mints and dead-nettles.  It is an edible weed, the young leaves can be used in salads and it can also be used in soups, stews, or used whole and boiled as a pot herb.

The instantly (to me at any rate) recognisable flower of Prunella vulgaris

Prunella as I will now familiarly call her, has a very wide geographical native range and has also been introduced into South America where she does very well indeed (Godoy et al., 2011).

Distribution of Prunella vulgaris, blue native, brown introduced. http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:455176-1

 The name Prunella is derived from ‘Brunella’, a word which is itself a derivative, coming from the German name for quinsy, (a type of throat inflammation), die Braüne, which it was historically used to cure.  That is the other aspect of this glorious plant, it has many medicinal properties, hence the many common names refer to its healing powers, almost as many as Athelas of Lord of the Rings fame 😊  It was traditionally used in European herbal medicine for sore throats, fever reduction and like Athelas, for accelerating the healing of wounds (Matthiolus, 1626).  More recently it has become of interest as a possible cure for conditions associated with the herpes simplex virus (Psotováa et al., 2003) and inhibiting anaphylactic shock and other immediate type allergic reactions (Shin et al., 2001).  So truly a wonder drug, and again proving that “Old Wives Tales” are in many cases based on more than just superstition.

My interest in Prunella vulgaris, is however, based on its wondrous plasticity, as the three photographs below show nicely.  Depending on grazing (or mowing) pressure, Prunella can grow to reproductive maturity at heights  ranging from just over 2 cm to just under 30 cm. Truly remarkable.

I am of course, not the first person to be fascinated by this plasticity and the taxonomic and evolutionary ins and outs of this lovely plant (Nelson, 1965; Warwick & Briggs, 1979) but I still find it fascinating, and who knows, perhaps one day I might do some work on it myself 😊

The other thing that I like about Prunella is that she is also provides a living for aphids.  She has her own rare and specific one, Aphis brunellae, but is also kind enough to let a few other species make a living on her, Aphis gossypii, Aphis nasturtiiAulacorthum solani,  Macrosiphum euphorbiae, the ubiquitous Myzus persicae, M. ornatus and Ovatomyzus chamaedrys (Blackman & Eastop, 2006).

Aphis brunellae, rare in the UK – with thanks to the two Bobs for permission to use the photograph. http://influentialpoints.com/Images/Aphis_brunellae_colony_on_Prunella_vulgaris_c2015-08-21_15-37-27ew.jpg

 

Finally, you will have noticed that the Prunella aphid is A. brunellae, which is derived from the original name of Prunella (I guess Prunella Scales is happy, she could have been Brunella Scales).  Interestingly, her alter-ego was not removed until fairly recently, her tombstone is shown below.

References

Blackman, R.L. & Eastop, V.F. (2006) Aphids on the World’s Herbaceous Plants and Shrubs Volume 1 Host Lists and Keys.  Wiley, Oxford.

Godoy, O., Saldaña, A., Fuentes, N., Valladares, F. & Gianoli, E. (2011)  Forests are not immune to plant invasions: phenotypic plasticity and local adaptation allow Prunella vulgaris to colonize a temperate evergreen rainforest. Biological Invasions, 13, 1615-1625.

Matthiolus, P.A. (1626) Kräuterbuch.  Noringberg.

Nelson, A.P. (1965) Taxonomic and evolutionary implications of lawn races in Prunella vulgaris (Labiatae). Brittonia, 17, 160-174.

Psotová, J., Kolá, M., Sousek, J., Ívagera, Z., Vicar, J. &Ulrichová, J. (2003) Biological activities of Prunella vulgaris extract. Phytotherapy Research, 17, 1082-1087.

Shin, T.Y., Kim, Y.K. & Kim, H.M. (2001) inhibition of immediate-type allergic reactions by Prunella vulgaris in a murine model.  Immunopharmacology & Immunotoxicology, 23, 423–435.

Warwick, S.I. & Briggs, D. (1979) The genecology of lawn weeds III. Cultivation experiments with Achillea millefolium L., Bellis perennis L., Plantago lanceolata L., Plantago major L. and Prunella vulgaris L. collected from lawns and contrasting grassland habitats.  New Phytologist, 83, 509-536.

 

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Pick and mix 11 – Another ten links to look at

I’m still on holiday in France so just a series of links this week.


Links to things I thought interesting (picture is the room door of the Ibis Style hotel we stayed at in Paris)

 

Is “novelty” holding science back?

Using radio tagging to improve the conservation of stag beetles

How ‘Nature’ keeps us healthy, from potted plants to hiking

How scientists at Rothamsted Research and the University of North Texas have engineered a relative of cabbage to produce fish oil

Agricultural efficiency will feed the world, not dogma

A really interesting article about migration and movement of people

Dave Goulson’s work on pesticide residues in garden plants summarised by plant ecologist Ken Thompson

Using a field journal to strengthen learning

At the risk of seeming big-headed an interesting episode of Entocast

I don’t normally post about birds but after this golden oriole

committed suicide against our patio doors thought that this deserved a mention

 

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The Natural World in Haiku form

Traditionally in the world of journalism, August is regarded as lacking any news of note, and is, in the UK at any rate, dubbed the “Silly Season”.  In homage to that view-point, and instead of doing one of of my usual blog posts, I searched for all the haikus I have tweeted over the last three years and present them here for light relief.

 

Thirsty snails

Short of water, snails

Circle and swirl on the rocks,

Waiting for a storm.

All the stones of any consequence were encrusted with snails.  Then the rain came and they were gone.

Italy 25 July 2014

 

Evening lift-off

Italian evening;

Bats swoop as stag beetles lift

Into lurching flight

Note the hole in the left elytrum, the resident kitten at our Italian holiday villa really enjoyed herslf snatching the poor lumbering beasties (in this case a Rhinoceros beetle) out of the air ☹

Italy 27 July 2014

 

Breakfast?

Italian morning;

Lizards scurry on the stairs

as cicadas sing

Admittedly not on the stairs, but close enough 😊

28 July 2014

 

Seasons

 

Spring has sprung

 White, pink fluttering,

the gentle breeze scattering;

cherry blossom falls

Outside my office – 24 May 2016

 

Summer?

Blue sky, sun shining

Ducklings following mother

Winged aphids – summer?

4 May 2016

 

Summer?

Dull, damp, cold drizzle.

Clouds glowering down on me.

Flaming June my foot 😦

29 June 2017

 

St Martin

September sunshine;

Eating lunch sitting outside.

What could be better?

10 September 2014

 

On the way

 September morning,

Sunlit, moist mist-laden trees;

Autumn is coming

8 September 2014

Autumn

Crickle, crackle; leaves,

underneath my slipping feet.

Autumn is with us.

20 October 2015

 

I used to camp here as a lad!

Sodden tent, wet feet.

Rolling hills and drystone walls.

English Lake District

8 October 2014

 

Damp

How I hate mizzle;

as wet as real rain, but no

comforting refrain

26 November 2015

 

Satisfaction

Shuffling through brown leaves

On a sunny autumn day;

So satisfying.

2 November 2016

 

Wet Pavements in Lille

Desert boots are great

except when soles are holey.

Then rain means wet feet

10 December 2014

 

Transience

Icing sugar snow,

Gently being washed away;

Grey drizzle falling

29 January 2015

Miscellanea

 

Job downside

Academics hate

marking student assignments

on a sunny day

7 December 2016

 

Sunday lunch

 Butterflied mint lamb

roast potatoes and carrots;

apple and pear tart.

11 December 2016

 

Dedicated to @IMcMillan who spends a lot of time at stations

Cardboard coffee cups

tentatively raised to lips;

Morning commuters

7 July 2016

 

Definition

Searching for the why

and how things are like they are;

Entomology

20 December 2015

 

Blood Moon

Lustrous, silver orb

Bloody, awe-inspiring moon

Night-time amazement

28 September 2015

 

Evening entertainment

Bats, swiftly looping

Snatching insects from the sky

Feeding on the wing

26 July 2017

 

Regular readers, rest assured, normal service will be returned in the next post 🙂

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Pick and mix 10 – ten more links to look at

Links to things I thought interesting

 

Why conservation needs to work around people’s values

If you ever wondered why so many plants have wort in their name.

The academic work-life balance is so wrong.  Errant Science takes a humourous look at a very serious subject.

Learn about the biology of peaches and how to cook them

Interesting commentary on a  paper about how walnuts have invaded forest ecosystems

Continuing with the food theme, how a Swedish countess introduced potatoes to the European diet

Have you ever heard a hawk moth squeak?  Now you can and they use their genitals to make the sound 🙂

If you ever wondered how beetles fold their wings, then here is the answer.  Full details about a complex subject.

Polish scientists are looking at ways of making eating insects more appetizing

Finally, William Playfair the Scottish scoundrel who invented all the graphs we love to hate

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CROPSS – Inspiring biology students to consider careers in crop protection

A couple of years ago, the BBSRC decided to scrap one of their most successful and inclusive PhD training awards, the iCASE.    In their own words, BBSRC will no longer operate an annual competition for industrial CASE (iCASE) studentships, instead allocating the majority of these studentships to the BBSRC Doctoral Training Partnerships (DTP) for awarding alongside their standard studentships.    At one fell stroke the BBSRC reduced the diversity of their PhD portfolio by a significant amount and also dealt a huge blow to those of us working in crop protection, at a time when food security and the need to feed the world is of paramount importance.  Later that year the BBSRC, possibly in response to those of us who kicked up a public fuss about the loss of the iCASE scheme came up with a very inadequately funded scheme called STARS aimed at getting undergraduates interested in some of the vulnerable skill sets that the BBSRC by their actions had made even more vulnerable.  Despite the paltry amount of money available I felt that I had to apply, if only because having complained about lack of funding it would show lack of commitment to the cause 🙂  I duly applied putting forward an application to run a one week crop protection summer school for fifteen students a year for three years.  I was successful and last week we ran our first CROPSS Summer School here at Harper Adams University.  We particularly targeted first and second year undergraduates doing biology and ecology courses at other universities with little or no agricultural content in their degrees.  Our participants came from the universities of Bath, Birmingham, Bristol, Cambridge, Liverpool and Swansea, and apart from one student who came from a farming family, they had no previous experience of agriculture, let alone crop protection.

The Summer School started on Sunday afternoon, with an introduction from me about why crop protection was important and how Integrated Pest Management is all about ecology, NOT spraying and eradication, something I have been banging on about for many years 🙂  This needs to be reiterated again and again and as loudly as possible. We then had an excellent dinner and I took them all to the bar where I cruelly subjected them to a Pub Quiz, all picture rounds.  The first round was all about charismatic megafauna (almost all answered correctly), then dog breeds (about 75% correct), then common British wild flowers (about 60% correct), common British trees (40% correct), common British insects (30% correct), I think you can see where I am going with this  🙂

The week was divided up between agronomy, entomology, nematology, plant pathology, weed science and spray technology, with a mixture of lectures, field work and laboratory work.  In the evening we had guest speakers from the different crop protection sectors, from the agrichemical industry through to government, our last speaker being the Chief Plant Health Officer, Nicola Spence.  The external speakers had been asked to explain how they had ended up in their current positions and to talk about careers in those areas.  I was very impressed with the willingness of the students to engage with the speakers and the questions they asked were extremely discerning.

We were very lucky to be blessed with excellent weather and the harper Adams University Catering Department came in for very high praise indeed J  apparently our catering is much better than at the universities represented by our delegates.

As the old adage goes, a picture is worth a thousand words…..

Catching insects in the Natural England plots

Sorting pitfall traps catches

Plant pathology in the brand new labs

Heading off with John Reade to sample weeds

Enjoying the sun and spotting weeds

Simon Woods from the Engineering Department explaining the fine points of knap sack sprayers

Andy Cherrill extolling the joys of motorised suction sampling

Enjoying the bar with one of the guest speakers, Neal Ward

All in all, we all had a good time, and if you don’t believe me here are some of the responses from the student feedback

The students were great, enthusiastic, engaged and we really enjoyed the course and are very much looking forward to seeing a new CROPSS cohort next year.

Finally, for those of you interested, here is the timetable of the week:

 

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Pick and mix 9 – a few links to click

Links to things I thought might grab your fancy

Interested in plants?  Find the latest State of the World’s Plants report here

Butterfly lovers?  Special issue of Journal of Insect Conservation devoted to butterfly conservation

Communicating entomology through video

Speaking of which, I did one on aphids once upon a time 🙂

How bees see may help us develop better cameras

How bumblebee flight may help us develop better drones

The Sixth Mass Extinction of vertebrates on the way but what about all the invertebrates that keep the world functioning?

Interesting article on insect symbolism in 19th Century British art

Weirdly interesting art based on the “natural world” by Katie McCann

This account of sexism in academia shocked and horrified m

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My Bête Noire – The Journal of Vertebrate (oops sorry, Animal) Ecology

Back in 2014 I took the Journal of Animal Ecology to task for pretty much ignoring most of the animal world and publishing almost exclusively vertebrate papers.  Ken Wilson their Editor-in-Chief decided to check up on this claim and to his chagrin, found that I was right in my assertion 🙂

As a loyal subscriber to the print copy of the journal I am very aware of the front cover photograph and have had two occasions this year to publicly praise the journal for their invertebrate-themed covers.  Then I received the July issue which despite having an invertebrate themed In Focus article, featured a leopard as their poster animal.   Although I love cats, I feel that the mega-cats, and the other so-called large charismatic mega-fauna do ecology as a whole, and entomology in particular, a great deal of harm. They suck away much-needed funds and bright capable students into an area that is vastly over-supplied with resources that could be much more profitably used elsewhere, i.e. the study of our planet’s dominant animal inhabitants, the invertebrates.

Journal of Animal Ecology cover images 2017

 My first reaction to the leopard picture was to go through my shelves and look at all the front covers of the journal since they adopted the new size and format, to see how biased (I automatically assumed that they would be) they were towards vertebrates.   I was not surprised, there was indeed a very strong vertebrate bias.

Journal of Animal Ecology front covers, 2009-2016

Just over 80% of the covers had a vertebrate subject; taxonomically they break down to 50% mammals, 20% birds and 11% fish.   Considering the true species composition of the known number of vertebrates, mammals (less than 0.5% of described animal life, about 5 500 species) are vastly over-represented to say the least.  Fish people should be particularly incensed 🙂

Relative proportions of described animal life.  Fish as the most speciose vertebrate group get a picture 🙂  I apologise to any nematologists who might be reading this post 🙂

So what about the journal content, has editorial policy change since 2014 and how are the invertebrates doing?  Ken stated in his blog that taxonomically speaking the papers published in Journal of Animal Ecology were approximately, 30% bird, 26% mammal, 12% fish and 20% insect related. I did a quick count of the papers published in 2015 and 2016.  Things are changing, birds and mammals are down (24% and 22% respectively) and fish are on the up (17%), but vertebrates still account for 67% of papers published in the last two years. Although the journal is still very vertebrate biased that is a definite improvement, but still not back to the glory days of the 1970s,  Nevertheless, well done Ken and colleagues.  Progress is being made (whether deliberately or not) to redress the balance, but still much more is needed to put invertebrates in the lead where they deserve to be.   More insect front covers would surely be easy enough to implement and help reinforce the message that insects and other invertebrates are where most of real world ecology is to be found.  Over to you Ken 🙂

 

Post script

I always feel a bit guilty about taking the Journal of Animal Ecology to task, because when compared with the Journal of Zoology,  JAE are paragons of virtue in regard to publishing invertebrate papers but I guess that as a long-standing member of the British Ecological Society I feel a somewhat more proprietorial interest 🙂

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Pick and mix 8 – another pick from the mix

Links to some interesting stuff – well I thought so anyway

 

An interesting idea of how scientists might reach politicians using Twitter

Similarly, Trump, Brexit and a crisis of participation in universities

For those of you interested in the press coverage of the UK General Election, an analysis of the newspaper coverage.  I guarantee that you will be surprised as to which were the two most impartial papers.

Once upon a time we had the milk lake and the butter mountain, but now a butter shortage means bad news for croissant lovers in France

According to the Financial Times, a lot of companies are interested in starting companies to produce and market insects as food

A post by one of my former students @annaplatoni, about her bee work

On why you shouldn’t be dismissive of the “dead grandmother” excuse

Inspiring young Victorians to enjoy entomology through sport

Seven visions of London as a National Park City

I very seldom recommend anything about birds this article about the shape of bird eggs is worth reading just for the graphics

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Not all aphid galls are the same

A galling experience – what on earth is an aphid-induced phytotoxemia?

Scientists, actually let me correct that, all members of specialist groups, be they plumbers or astrophysicists, love their jargon.  Insect-induced phytotoxemias is a great example. What entomologists and plant physiologists mean by this term is plant damage caused by an insect.  The visible damage that insects can cause to plants ranges from discolouration, lesions, and malformation of stems and leaves. As the title of this post suggests I am going to discuss galls.  Many insects produce galls, some of which can be spectacular such as Robin’s pin cushion gall caused by the wasp, Diplolepis rosae, but being a staunch aphidologist I am going to concentrate on various leaf deformities caused by aphids.

Robin’s pin cushion gall, caused by Diplolepis rosae.

https://upload.wikimedia.org/wikipedia/commons/9/93/Diplolepis-rosae.jpg

Aphids are true bugs, they are characterised by the possession of piercing and sucking mouthparts, the stylets, think of a hypodermic needle, being the piercing part of the mouthparts.

Aphid mouthparts, showing the passage of the stylets to the phloem (Dixon, 1973).

It was originally thought that the various leaf deformities resulting from aphid feeding was a direct result of the mechanical damage caused by the stylet entering the leaf and rupturing cell walls or possibly by the transmission of a disease. A series of elegant experiments by Kenneth Smith in the 1920s showed however, that insect salivary gland extracts were needed to cause the damage (Smith, 1920, 1926).  Puncturing leaves with needles did not produce the same symptoms.  The leaf rolls, leaf curls and pseudo-galls caused by aphids vary between species even when the aphids are closely related or their host plants are.  As an example of the latter, the bird cherry-oat aphid, Rhopalosiphum padi, causes what I would describe as a leaf roll, i.e. the leaves curl in from the edges towards the mid-rib, to make something that resembles a sausage.

Leaf roll pseudo-galls on bird cherry, Prunus padus, caused by the bird cherry oat aphid, Rhopalosiphum padi.

On the other hand, the cherry blackfly, Myzus cerasi, that has Prunus avium as its primary host, causes what I describe as leaf curls (think ringlets and curls in human hair terms), in that the leaf rolls up from the tip down towards the stalk (petiole).

Leaf curl on Prunus avium caused by the Chery black fly, Myzus cerasi

Similarly, there are two closely related aphid species, Dysaphis devecta and D. plantaginea, both feed on apple leaves, but D. devecta prefers to feed on the smaller veins while D. plantaginea prefers to feed on the mid-rib. The former causes a leaf-roll, the latter a leaf curl.

Dysaphis galls http://influentialpoints.com/Gallery/Dysaphis_devecta_species_group_rosy_leaf-curling_apple_aphids.htm

As well as leaf rolls and leaf curls, some aphids are able to induce leaf folds.  The poplar-buttercup gall aphid, Thecabius affinis being a good example.

Leaf fold on poplar caused by Thecabius affinis Poplar-buttercup gall aphid. Photo from the excellent Influential Points web site. http://influentialpoints.com/Gallery/Thecabius_affinis_Poplar-buttercup_gall_aphid.htm

You might think that it is the aphid feeding site that causes the characteristic roll, curl or fold, but if groups of D. devecta or D. plantaginea are caged on the stem of an apple seedling, young leaves several centimetres away will develop leaf rolls characteristic of each species suggesting that they are caused by specific substances in the saliva of each aphid (Forrest & Dixon, 1975).  Aphid saliva is known to contain a huge range of proteins from amino acids to digestive enzymes (Miles, 1999) so it is highly likely that different aphid species have evolved different suites of enzymes that enable them exploit their respective host plants more efficiently.  Entomologists who work on plant galls suspect that there is something in the saliva that makes the plant’s hormones trigger the gall formation, but they freely admit that they are still just guessing.  Leaf rolls and curls are pretty tame when you come to look at the galls some aphids can induce.  Aphids from the family Pemphigidae cause structural deformations that totally enclose them and their offspring.

Petiole galls caused by (left) Pemphigus spyrothecae (photo Graham Calow, http://warehouse1.indicia.org.uk/upload/med-p1771un6n510nt146ugosslt1hip5.jpg) and (right) Pemhigus bursarius gall (Photo Graham Calow http://www.naturespot.org.uk/species/pemphigus-bursarius)

Pemphigus populitransversus, the Cabbage root aphid or poplar petiole aphid (Photo Ryan Gott Ryan Gott‏ @Entemnein)

Not all enclosed galls are on petioles, the witch-hazel cone gall aphid (Hormaphis hamamelidis causes very distinctive galls on the leaves of its host plant.

Cone galls on witch hazel caused by Hormapahis hamamelidis http://www.inaturalist.org/photos/377819

So what is it with insect galls?  Are they of any use?  Peter Price and colleagues (Price et al., 1987) very succinctly summarised the four hypotheses that address the adaptive value of insect galls; a) No adaptive value (Bequaert, 1924), b) adaptive value for the plant (Mani, 1964), c) adaptive value for plant and herbivore (mutual benefit) (Cockerell, 1890) and d) adaptive value for the insect.  This last hypothesis is further subdivided into nutritional improvements, micro-environmental improvements and natural enemy protection (Price et al., 1987).

Becquaert’s non-adaptive hypothesis is and was easily and quickly dismissed (Price et al., 1987), so I will move swiftly on to the plant-protection hypothesis which Price et al., dismiss almost as swiftly.  In essence if galls are not associated with enhanced growth and survival of the galled plant then there is no protection offered.  In fact, galling insects have been used as biological control agents against weeds (e.g. Holloway & Huffaker, 1953; Gayton & Miller, 2012) which to put it mildly, does not suggest any benefits accruing from being galled.  That said, you could argue (weakly) and assuming that the plant is in control of producing the gall, that by confining the insect to a particular part of the plant it is “contained” and can be dealt with if it is causing too much damage by for example premature leaf abscission (Williams & Whitham, 1986).

The mutual benefit hypothesis is also easily dismissed as there is no evidence that galls improve the fitness of a plant as galling insects are parasites of the plant.  You might argue that fig wasps and figs mutually benefit each other, but in this case I think we are looking at special case pleading as the fig wasp are pollinators (Janzen, 1979).

So that takes us on to the adaptive value for insects hypothesis which makes a lot more sense as it is the insect (in this case the aphid), that has made the investment in what you might justifiably term, mutagenic saliva (Miles, 1999).

There is overwhelming evidence so support the nutrition hypothesis that galled leaves and galls are nutritionally superior to ungalled leaves (Llewellyn, 1982); e.g. acting as nitrogen sinks (Paclt & Hässler, 1967; Koyama et al., 2004), enhancing development and fecundity for succeeding generations of aphids (e.g. Leather & Dixon, 1981) and providing better nutrition for non-galling aphids and other insects (e.g. Forrest, 1971; Koyama et al., 2004; Diamond et al., 2008).   I also found a description of an aphid, Aphis commensalis, the waxy buckthorn aphid, which lives in the vacated galls of the psyllid Trichochermes walker, but whether this is for protection or nutritional reasons is not clear (Stroyan, 1952). 

The microenvironment hypothesis which suggests that the galls provide protection from extremes in temperature and humidity was hard to support with published data when Price et al. (1987) reviewed the topic. They mainly relied on personal observations that suggested that this might be true.  I found only two references in my search (Miller et al, 2009) that supported this hypothesis, albeit one of which is for gall wasps.  I have so far only been able to find one reference that suggest galls benefit aphids, in this case protecting them from very high temperatures (Martinez, 2009).

The natural enemy protection hypothesis has been tested almost as much as the nutrition hypothesis and in general terms seems to be a non-starter as gall forming insects seem to be especially attractive to parasitoids; see Price et al., (1987) for a host of references.  Aphids, however, may be a different case, free-living aphids have many parasitoid species attacking them, but those aphids that induce closed galls are singularly parasitoid free, at least in North America (Price et al., 1987). Although this may have been from lack of looking, as parasitoids have been identified from galls of the aphid Pemphigus matsumarai in Japan (Takada et al., 2010).  Closed galls are not always entirely closed as some need holes to allow honeydew to escape and migrants to leave (Stone & Schonrogge, 2003) which can act as entry points for natural enemies, but cleverly, the aphids have soldier aphids to guard against such insect invaders.

Sometimes the potential predator can be a vertebrate.  The aphid Slavum wertheimae forms closed galls on wild pistachio trees, and are, as with many other closed gall formers, not attacked by parasitoids (Inbar et al., 2004).  Wild pistachios are, however, attractive food sources to mammalian herbivores and gall aphids being confined to a leaf, unlike free living aphids could be inadvertently eaten. The galls however, contain higher levels of terpenes than surrounding leaves and fruits and emit high levels of volatiles that deter feeding by goats and other generalist herbivores thus protecting their inhabitants (Rostás et al., 2013). Not only that, but to make sure that any likely vertebrate herbivores avoid their gall homes, they make them brightly coloured (Inbar et al., 2010).   Aphids really are great at manipulating plants.

Cauliflower gall on wild pistachio, caused by Slavum wertheimae (Rostás et al., 2013).

Leaf rolls and curls on the other hand are more open structures, and in my experience, aphids that form leaf rolls or curls, are very vulnerable once a predator finds them crowded together in huge numbers.  Gall-dwelling aphids, including those that live in rolls and curls, tend, however, to be very waxy, and this may deter the less voracious predators.  I tend to support the nutritional benefit hypothesis in that with host alternating aphids, the enhanced nutrition enables rapid growth and development and is a way of building up numbers quickly, and hopefully the aphids are able to migrate to a new host, before the natural enemies find them.

Real life drama, Rhopalosiphum padi on Prunus padus at Harper Adams University May-June 2017.  In this instance the aphids won, and the plant was covered in hungry ladybird larvae eating mainly each other and the few aphids that had not managed to reach adulthood.

One thing that struck me while researching this article was that all the aphids producing galls, rolls or curls were host-alternating species. A fairly easily tested hypothesis for someone with the time to review the biology of about 5000 aphids, is that only host alternating aphids go in for galls.  This could be a retirement job J.

There are, depending on which estimate you agree with, somewhere between 8 000 000 to 30 000 000 insect species (Erwin, 1982; Stork, 1993; Mora et al., 2011), but even the highest estimate suggests that only 211 000 of these are galling species (Espirito-Santos & Fernandes, 2007).  And a final thought, if galls are so great why don’t all aphids and other phloem and xylem feeding insects go in for them?

References

Becquaert, J. (1924) Galls that secret honeydew.  A contribution to the problem as to whether galls are altruistic adaptations.  Bulletin of the Brooklyn Entomological Society, 19, 101-124.

Cockerell, T.D.A. (1890) Galls. Nature, 41, 344.

Diamond, S.E., Blair, C.P. & Abrahamson, W.G. (2008) Testing the nutrition hypothesis for the adaptive nature of insect galls: does a non-adapted herbivore perform better in galls?  Ecological Entomology, 33, 385-393.

Dixon, A.F.G. (1973) Biology of Aphids, Edward Arnold, London

Erwin, T.L. (1982) Tropical forests: their richness in Coleoptera and other arthropod species. The Coleopterists Bulletin, 36, 74-75.

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Pick and mix 7 – more eclectic links from the past week

Links to stuff I have read with interest; quite a lot about bees this week 😊

Interesting reflections on a life in science by Rich Lenski when he gave an address to newly graduated PhD students

A nice summary of what conservation biocontrol is all about, incidentally by a former PhD student of mine 🙂

An interesting opinion piece on how conservation efforts should move away from a species focus and use functional traits instead

Green walls – are they good for wildlife? – coincidentally written by another former student of mine 🙂

I totally agree – ecologists need to get outside more often

A blistering tale – what makes Blister beetles cause blisters

Saving the honeybee from the Varroa mite using a fungal biological control agent?

If you like bees and/or are a beekeeper, this interesting article by Norman Carreck, Science Director of the International Bee Research Association is a must read

Worrying evidence that it is not just insecticides that are killing bees – fungicides may also be a major culprit

On being a sustainable entomologist and helping to save the planet

 

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