Monthly Archives: May 2015

Mellow Yellow – Not all aphids live on green leaves

I have written before about aphids and how their quest for the ideal food plant may explain the evolution of host alternation; we find that most aphid species tend to be associated with rapidly growing meristems, or newly flushing leaves (Dixon, 2005). Some aphids are so keen on young plant tissue that they ‘engineer’ youth in their host plants, injecting salivary compounds and forming leaf–rolls, pseudo-galls and galls, all of which act as nutrient sinks and lengthen the time that the modified leaves stay green and nutrient-rich

leaf roll Rhopalosiphum

 Leaf-roll caused by Rhopalosiphum padi on bird cherry, Prunus padus.

Leaf roll Myzus cerasi

Pronounced leaf roll pseudo-gall caused by Myzus cerasi on Prunus avium.

Non host-alternating (autoecious) aphids, such as the sycamore aphid Drepanosiphum platanoidis, the maple aphid, Periphyllus testudinaceus, or the birch aphid, Euceraphis punctipennis, have no such escape route; they are confined to their tree host for the year, albeit, they can, if they ‘wish’, fly to another tree of the same species, but essentially they are held hostage by the their host plant. As the season progresses, leaf nutritional and physical properties change; going from young tender green leaves, with high nitrogen and water contents, to mature, tough leaves, low in nitrogen and water to yellow senescing leaves with again, higher nitrogen levels (Awmack & Leather, 2002) and finally of course, dead brown leaves of no nutritional value.

Seasonal changes

Sycamore and maple aphids, enter a state of suspended animation ‘summer aestivation’ (Essig, 1952; Dixon, 1963), whilst birch and poplar aphids, whose hosts plants often produce new growth during the year, ‘track’ these new leaves (Wratten, 1974; Gould et al., 2007). As far as these aphids are concerned young tissue is their best food source, with senescent tissue being second best and mature leaves being least favoured. During the summer they will, however, take advantage of mature leaves that are prematurely senescing, such as those attacked by leaf diseases such as tar spot. I have often found sycamore aphids feeding and reproducing on these infected leaves whilst those aphids on neighbouring mature leaves remain in aestivation.

Tar spot 2

Effects of tar spot on sycamore leaves

Host-alternating (heteroecious) aphids on the other hand are somewhat different. As their life cycle includes a programmed migration back to their primary tree host in autumn, those autumn morphs (oviparae) are adapted to senescent tissue (Leather & Dixon, 1982, Kundu & Dixon, 1993, 1994). Similarly, the spring morphs (fundatrices and fundatrigeniae) are adapted to young leaves and find it difficult or impossible, to make a living on senescent leaves.
Morphs and host age

There are yet other aphids, such as the green spruce aphid Elatobium abietinum, the pine aphid, Eulachnus agilis and the black pecan aphid, Melanocallis caryaefoliae, that are senescence specialists. In contrast to the flush specialists, these aphids engineer senescence, also using salivary compounds,  and are unable to survive on young foliage (Bliss, 1973; Fisher, 1987; Cottrell et al., 2009).

Elatobium in action

Elatobium abietinum ‘engineering’ senescence on spruce needles and avoiding young flushing tissue.

It is interesting to speculate that perhaps these tree-dwelling non host-alternating aphids are secondarily derived from the autumn part of the life-cycle of host-alternating aphids. After all, if non host-alternating aphids on herbaceous host plants are off-shoots of the summer part of the host-alternating life-cycle why not the other way round. There is just so much more to learn about aphids. Yet another reason why I love aphids so much 😉


Awmack, C.S. & Leather, S.R. (2002) Host plant quality and fecundity in herbivorous insects. Annual Review of Entomology, 47, 817-844.

Bliss, M., Yendol, W.G., & Kearby, W.H. (1973) Probing behaviour of Eulachnus agilis and injury to Scotch pine. Journal of Economic Entomology, 66, 651-655.

Cottrell, T.E., Wood, B.W. & Ni, X. (2009) Chlorotic feeding injury by the Black Pecan Aphid (Hemiptera: Aphididae) to pecan foliage promotes aphid settling and nymphal development. Environmental Entomology, 38, 411-416.

Dixon, A.F.G. (1963) Reproductive activity of the sycamore aphid, Drepanosiphum platanoides (Schr) (Hemiptera, Aphididae). Journal of Animal Ecology, 32, 33-48.

Dixon, A.F.G. (2005) Insect Herbivore-Host Dynamics. Cambridge University Press, Cambridge.

Fisher, M. (1987) The effect of previously infested spruce needles on the growth of the green spruce aphid, Elatobium abietinum. Annals of Applied Biology, 111, 33-41.

Gould, G.G., Jones, C.G., Rifleman, P., Perez, A., & Coelman, J.S. (2007) Variation in Eastern cottonwood (Populus deltoides Bartr.) phloem sap content caused by leaf development may affect feeding site selection behaviour of the aphid, Chaitophorous populicola Thomas (Homoptera: Aphididae). Environmental Entomology, 36, 1212-1225.

Kundu, R. & Dixon, A.F.G. (1993) Do host alternating aphids know which plant they are on? Ecological Entomology, 18, 61-66.

Kundu, R. & Dixon, A.F.G. (1994) Feeding on their primary host by return migrants of the host alternating aphid, Cavariella aegopodii. Ecological Entomology, 19, 83-86.

Leather, S.R. & Dixon, A.F.G. (1981) Growth, survival and reproduction of the bird-cherry aphid, Rhopalosiphum padi, on it’s primary host. Annals of applied Biology, 99, 115-118.

Wratten, S.D. (1974) Aggregation in the birch aphid, Euceraphis punctipennis (Zett.) in relation to food quality. Journal of Animal Ecology, 43, 191-198.


Post script

A lot of what I describe comes from a talk I gave in 2009 at a workshop in Oxford on autumn colours (the output of which was Archetti, M., Döring, T.F., Hagen, S.B., Hughes, N.M., Leather, S.R., Lee, D.W., Lev-Yadun, S., Manetas, Y., Ougham, H.J., Schaberg, P.G., & Thomas, H. (2009) Unravelling the evolution of autumn colours: an interdisciplinary approach. Trends in Ecology & Evolution, 24, 166-173. I always meant to write the talk up as an Opinion piece but procrastination set in badly. I was somewhat annoyed with myself when earlier this year this excellent piece by the legendary ecologist and entomologist, Tom White, appeared; I have only myself to blame, six years is a very long bit of procrastination 😉

White, T.C.R. (2015) Senescence-feeders: a new trophic sub-guild of insect herbivores Journal of Applied Entomology, 139, 11-22.


Post post script

This post is dedicated to my eldest son, Sam, who died quietly in his sleep, at a tragically young age, December 23rd 2010.   It would have been his birthday on the 21st May.  Despite being a molecular biologist, (he worked at the Sanger Institute), he was as green as you can get, a great naturalist and conservationist, with an incredibly gentle soul. He strongly believed in conserving the World’s natural resources and amused colleagues by sticking up signs in the toilets at the Sanger, which read “If its yellow let it mellow, if its brown flush it down”.



He is sorely missed by us all. He also had more Nature papers than me 😉

Parkhill, J., Achtman, M., James, K.D. et al., (2000) Complete DNA sequence of a serogroup A strain of Neisseria meningitides. Nature, 404, 502-506

Parkhill, J., Dougan, G. , James, K.D. (2001) Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18. Nature, 413, 848-852.

Parkhill, J., Wren, B.W., Thomson, N.R. et al., (2001) Genome sequence of Yersinia pestis, the causative agent of plague. Nature, 413, 523-527.

Parkhill, J., Sebaihia, M., Preston, A. et al., (2003) Comparative analysis of the genome sequences of Bordetella pertussis,   Bordetella parapertussis and Bordetella bronchiseptica. Nature Genetics, 35, 32-40

Wood, V., Gwilliam, R. Rajandream, M.A. et al., (2002) The genome sequence of Schizosaccharomyces pombe . Nature, 415, 871-880




Filed under Aphidology, Aphids

Distant Elephants and Low-Hanging Fruit – confessions of a procrastinator


verb; procrastinate – delay or postpone action; put off doing something

I hate writing full-blown grant applications. The thought of sitting down with a blank page in front of me, and justifying why I want to do the research, saying how well it fits the remit of the research council, demonstrating how great I am (track record of applicant), articulating my hypotheses, outlining the work packages, writing an impact statement, getting costings to draw up a budget, justifying the resources requested, and so on and so on, and all with the knowledge that there is an about 1 in 5 chance of getting funded, does not fill me with any great enthusiasm. It also takes up a huge amount of my time and to do it properly you really do need to sit down and exclude all other activities.

I also find it difficult to start writing a paper from scratch, or get to work on a new presentation;  I should, for example, be getting my plenary lecture for ENTO15 ready, but as it only May 11th and I am not speaking until September 2nd I am finding it difficult to get started on that. This is despite the fact that it was only by a superhuman effort before Christmas I got the written version submitted to Ecological Entomology on the required day (now available on Early View if you are interested).  Of course I am steadfastly ignoring the fact that I will be on holiday from July 24th until August 17th and that on my return I will be marking several MSc project reports!


I have several delaying (apparently according to Microsoft Word, procrastinatory doesn’t exist) tactics, or low-hanging fruits, that I can pick

Low-hanging fruit

when faced with things I don’t really like doing; I can tidy my desk,


I can go to check my aphid cultures (a very useful 800 m walk to the glasshouses), I can walk to the Postgraduate Office to check applications (450 m from my office), do a sweep round the PhD offices (also 450 m away from my office) to see how my students are doing, check my email (again and again), accept a request to review a paper, although this then necessitates writing a report 😉 , and as an Editor, I have the very useful excuse that I need to log on to the journal site to check what is happening; the list is long and can certainly fill my day.


In our defence, procrastinators are actually very useful for the academic community; we are the people who agree to review papers, agree to be external examiners, sit on internal and external committees, do a lot of teaching and generally act as good citizens, although perhaps not as altruistically as our colleagues might think, after all we do have an ulterior motive.

Is there a cure?

There are things that we can do; a colleague of mine, does not open her emails on a Monday, I don’t have the will power to do this, I find it difficult enough to ignore my email for two-hour periods, which is my attempt at giving myself a chance to get really into doing some writing. Some people (those who are sociable and find it hard not to go to coffee or chat with colleagues) work from home; again this does not work for me as I then find household chores to distract me. I once went on a time management course in which the use of a daily To Do List was suggested. I dutifully began one of these but found that because of reactive tasks my proactive list just carried on to the next day and never seemed to get completed so that didn’t work for me either, but perhaps I should have said no to the reactive tasks or been less ambitions with the number of things on my To Do List? If anyone has further suggestions please let me know.

So how is that I complete anything substantial? For external tasks this is easy, I promise to deliver, and because I take my solemn promises to other people very seriously indeed, the task gets done, no matter how much I would rather not do it. Unfortunately, promises to myself I find much easier to break, so things that I regard as non-life or career-threatening, do tend to fall by the wayside.



All in all, I’m very lucky as my procrastinatory (it does exist Microsoft – see here) habits are relatively mild and surmountable, and I have managed to get this far in life without any serious failures.

There are, however, some people who procrastinate because of fear of failure, they set themselves the impossible goal of perfection (unless of course you are a gymnast or diver). This can lead to some very serious failures; for example, students who don’t answer any questions in an exam because they are afraid that their answers will be wrong and hand in a blank answer book, despite having it pointed out to them that if they don’t write anything they will definitely fail. I have also known students who find it almost impossible to hand in written work because they are afraid that it won’t be good enough, despite being told that unless I can see something I can’t help them improve it. To a non-sufferer the solution seems incredibly simple, just get out there and do something, how difficult can it be? It is, however, not simple at all, it can actually be a serious psychological problem that needs very sympathetic and supportive handling, ranging from sharing the task with a friend, colleague or even a suitably sympathetic supervisor, to professional counselling. It is not something to be dismissed lightly as an exasperating foible. Please, please remember this the next time you come across a colleague or student who persistently fails to complete tasks on time. They are not doing it on purpose.  Talk to them about the problem and address the issues sympathetically and with compassion and recommend them to seek psychological help if you feel it is necessary.
Post script

Apropos my latest attempt at writing a major grant proposal, the closing date is 17th May and given that I am writing this on the 11th May and I have, so far only written the opening paragraph of a ten page proposal, I fear that the elephant is about to arrive and trample me 😉


Post post script

It amazes me how many times you hear or see, people using the word prevaricate when they mean procrastinate; they are very different in meaning and not something you would want to own up to in public. Prevaricate means to act or speak in an evasive way (for great examples listen to a politician being interviewed), which to me at least, implies dishonesty.




Filed under Bugbears, The Bloggy Blog, Uncategorized

The UK needs more forest health specialists

Last week (April 22nd and 23rd 2015) I had the pleasure of attending the Institute of Chartered Foresters’  National Conference in Cardiff.  The theme of the conference was Tree health, resilience and sustainability.

ICF conference

 The PowerPoint versions of the presentations are available here.

It was very well attended with over 150 delegates and divided into six sessions; Setting the Scene, Overseas Experience, Perspectives on Risk, Searching for Resilience and Sustainability, Practical Responses in the Field and finally Messages for Government and the Profession.  The speakers came from a range of backgrounds; universities, research institutes, the forest industry and others.  Dr John Gibbs, a former colleague of mine from Forest Research opened the formal talks with a masterly review of how forest health problems were tackled in the last century, using Dutch Elm Disease as his focal organism. He was followed by Professor James Brown from the John Innes Institute discussing how lessons from agriculture could be used to develop strategies to combat tree diseases.  Both these speakers pointed out that there was a grave shortage of forest pathologists and entomologists in the UK, particularly in the university sector.   James Brown commented that he had been shocked to discover he had only been able to count seven people in the sector working on tree diseases and added that this did not make them forest pathologists.  We had talks from overseas speakers such as Professor Mike Wingfield from South Africa on global forest health threats, Jim Zwack from the USA speaking on the Emerald Ash Borer as an urban pest problem and Catherine St-Marie highlighting the fact that climate change was aiding and abetting the spread of the Mountain Pine Beetle in Canada.

There was a surprisingly interesting talk on the problems of insuring forests against pests and disease form Phil Cottle of Pardus Underwriting Limited and an enlightening presentation from Professor David Ball from Middlesex University talking about uncertainty and decision-making.  Again both these speakers highlighted the need for further information about pests and diseases.

Day 2 had us searching for resilience and sustainability within the UK forestry sector with a very entertaining talk from Jo O’Hara, Head of Forestry Commission Scotland.  Her talk really drove home to me how much UK forestry has changed over the last 30 years; when I joined the Forestry Commission in 1982 they had only just appointed their first woman District Officer, and now a woman runs FC Scotland – a very welcome sign of change.  Tariq Butt from Swansea University spoke about the use of entomopahogenic fungi as biological control agents in forestry, something increasingly moving higher on the agenda as we face the loss of even more conventional pesticides in the next few years and Martin Ward, the Director-General of EPPO asked us to consider how global plant health arrangements could be improved to protect trees more effectively.  Again the message was that we need more forest health specialist, and not just in the UK.   After the morning coffee break, Joan Webber, the Principal Pathologist for Forest Research UK, spoke about detection and precautionary measures to combat biosecurity threats and yet again highlighted the need for further research and eyes on the ground; in other words more specialist staff are required.  Neil Strong from Network Rail drew our attention to the problems caused by trees to our railway system and then Bill Mason extolled the virtues of increasing species and structural diversity when planting new forests and managing older ones, to improve resilience.

The afternoon session kicked off with Clive Potter from Imperial College talking about understanding what the public’s concerns about tree health are and how certain events can amplify risk perception among the public.  The public outcry about Chalara and Ash Dieback being a particularly good example of the phenomenon.  I followed with a talk about the needs for professional education which gave me the opportunity to point out what subject areas should be covered in an aspiring forester’s education.

Essential skills

I was also able to remind my audience that the number of UK universities providing specific forestry training at undergraduate level had dwindled to less than a handful and that despite offering modules purporting to cover forest health problems, only two employ specialist staff in those areas.  At postgraduate level there is only one course that deals specifically with forest health issues in the UK, the MSc in Conservation & Forest Protection that I run at Harper Adams University.

My take-home messages to a very receptive audience was that students need more emphasis on identification skills and much more practical experience, that current forestry professionals need to keep their eyes open and practice looking for pests and diseases as well as taking any opportunity to refresh their training and that UK universities offering forestry related courses need to employ more forest entomologists and forest pathologists.  Even more importantly, the UK government need to make sure that there are financial incentives to encourage universities to employ more forest entomologists and forest pathologists by increasing targeted research funding in those areas and once increased, maintain those levels of funding.  There also needs to be a clear signposting of career opportunities for the next generation of forest health scientists and if we as a country are serious about safeguarding our native woodlands and forest estate, then more jobs need to be created.

As I have written elsewhere, we cannot afford to sit back and hope that things will get better on their own.  Versions of this slide appeared on the screen several times during the course of the conference.  We are under attack and we need more suitably qualified people to help repel and contain the invaders.

Forest pests


Additional reading

Leather, S.R. (2014) Current and future threats to UK forestry. Outlooks on Pest Management, 25, 22-24.

Leather, S.R. (2014) How prepared is the UK to combat future and current threats to forests? Commonwealth Forestry Association Newsletter, 64, 10-11.


Post script

I am very grateful indeed to the Institute of Chartered Foresters for giving me the opportunity to speak at the conference and for providing generous hospitality.  It was one of the most engaging and interesting conferences that I have been to for a very long time.  Well done ICF.


Post post script

It was also good to see Twitter being used very successfully with the #Treehealth hashtag.  We even had participants from the Canadian Forestry Service!

ICF tweets


Filed under EntoNotes, Uncategorized