Tag Archives: bird cherry ermine moth

Satiable curiosity – side projects are they worthwhile?

I’ve been meaning to write this one for quite a while.  It was stimulated by two posts, one from the incredibly prolific Steve Heard, the other by the not quite so prolific, but equally interesting,  Manu Saunders.  First off, what is a side project?  To me, a side project is one that is not directly funded by a research council or other funding agency or, in some cases, one that you do in your spare time, or to the horror of some line-managers, is not strictly in your job description 🙂 The tyranny of modern research funding dictates that projects must have specific research questions and be accompanied by hypotheses and very specific predictions; most proposals I referee, even contain graphs with predicted results and almost all have ‘preliminary data’ to support their applications.   This is not necessarily a bad thing but to directly quote Manu Saunders from her blog post

“Whittaker’s (1952) study of ‘summer foliage insect communities in the Great Smoky Mountains’ is considered one of the pioneer studies of modern community ecology methods. The very short Introduction starts with the sentence “The study was designed to sample foliage insects in a series of natural communities and to obtain results of ecological significance from the samples.” No “specific research questions” and the hypotheses and predictions don’t appear until the Discussion” Sounds like bliss.

The central ethos of my research career which began in 1977, can be summed up by this quotation uttered by the character ‘Doc’ in John Steinbeck’s novel Sweet Thursday “I want take everything I’ve seen and thought and learned and reduce them and relate them and refine them until I have something of meaning, something of use” (Steinbeck, 1954).* The other thing that has driven me for as long as I can remember, and why I ended up where I am,  is something I share with Rudyard Kipling’s Elephant Child, and that is a “satiable curiosity”:-) Something that has always frustrated me, is that, in the UK at least, most funded research tends to be of a very short duration, usually three years, often less than that**, and if you are very lucky, maybe five years.  If you work on real life field populations, even if you work on aphids, these short term projects are not really very useful; laboratory work is of course a different matter.

I got my first ‘permanent’ job in 1982 working for UK Forestry Commission Research based at their Northern Research Station (NRS) just outside Edinburgh.  My remit initially was to work on the pine beauty moth, Panolis flammea and finally, on the large pine weevil, Hylobius abietis.  As a committed aphidophile, I was determined, job description or not, to carry on working with aphids. I decided that the easiest and most useful thing to do was to set up a long-term field study and follow aphid populations throughout the year.  My PhD was on the bird cherry-oat aphid, Rhopalosiphum padi, a host alternating aphid, the primary host of which is the bird cherry, Prunus padus, with which  Scotland is very well supplied, and fortuitously, just down the road from NRS was Roslin Glen Nature Reserve with a nice healthy population of bird  cherry trees.  I chose ten suitable trees and started what was to become a ten-year once a week, lunch time counting and recording marathon.  I also decided to repeat a study that my PhD supervisor, Tony Dixon had done, record the populations of the sycamore aphid, Drepanosiphum platanoidis.  In the grounds of NRS were five adjacent sycamore tree, Acer pseudoplatanus, and these became my early morning study subjects, also once a week. I had no articulated hypotheses, my only aim was to count and record numbers and life stages and anything else I might see. Anathema to research councils but exactly what Darwin did 🙂

Although it was a ‘permanent’ job, after ten years I moved to Imperial College at Silwood Park and immediately set up a new, improved version of my sycamore study, this time a once weekly early morning*** walk of 52 trees in three transects and with much more data collection involved, not just the aphids, their natural enemies and anything else I found and on top of all that, the trees themselves came in for scrutiny, phenology, growth, flowering and fruiting, all went into my data sheets.  I also set up a bird cherry plot, this time with some hypotheses articulated 🙂

As a result of my weekly walk along my sycamore transects, a few years later I set up yet another side project, this time an experimental cum observational study looking at tree seedling survival and colonisation underneath different tree canopies. At about the same time, initially designed as a pedagogical exercise, I started my study of the biodiversity of Bracknell roundabouts.

One might argue that most undergraduate and MSc research projects could also come under the heading of side projects, but I think that unless they were part of a long term study they aren’t quite the same thing, even though some of them were published.  So, the burning question, apart from the benefits of regular exercise, was the investment of my time and that of my student helpers and co-researchers worth it scientifically?

Side project 1.  Sycamore aphids at the Northern Research Station, 1982-1992

I collected a lot of aphid data, most of which remains, along with the data from Side project 2, in these two notebooks, waiting to be entered into a spreadsheet.  I also collected some limited natural enemy data, presence of aphid mummies and numbers killed by entomopathogenic fungi.  Tree phenological data is limited to bud burst and leaf fall and as I only sampled five trees I’m not sure that this will ever amount to much, apart from perhaps appearing in my blog or as part of a book.  Nothing has as yet made it into print, so a nil return on investment.

Raw data – anyone wanting to help input into a spreadsheet, let me know 🙂 Also includes the data for Side project 2

 

Side project 2.  Rhopalosiphum padi on Prunus padus at Roslin Glen Nature Reserve 1982-1992

I was a lot more ambitious with this project, collecting lots of aphid and natural enemy data and also a lot more tree phenology data, plus noting the presence and counting the numbers of other herbivores.  I have got some of this, peak populations and egg counts in a spreadsheet and some of it has made it to the outside world (Leather, 1986, 1993: Ward et al., 1998).  According to Google Scholar, Ward et al., is my 6th most cited output with, at the time of writing, 127 citations, Leather (1993) is also doing quite well with 56 citations, while Leather (1986) is much further down the list with a mere 38 citations.  I have still not given up hope of publishing some of the other aphid data.  I mentioned that I also recorded the other herbivores I found, one was a new record for bird cherry (Leather, 1989), the other, the result of a nice student project on the bird cherry ermine moth (Leather & MacKenzie, 1994).  I would, I think, be justified in counting this side project as being worthwhile, despite the fact that I started it with no clear hypotheses and the only aim to count what was there.

 

Side project 3.  Everything you wanted to know about sycamores but were afraid to ask 1992-2012

As side projects go this was pretty massive.  Once a week for twenty years, me and on some occasions, an undergraduate research intern, walked along three transects of 52 sycamore trees, recording everything that we could see and count and record, aphids, other herbivores, natural enemies and tree data, including leaf size, phenology, height, fruiting success and sex expression.  My aim was pretty similar to that of Whittaker’s i.e.   “…to sample foliage insects in a series of natural communities and to obtain results of ecological significance from the samples”  truly a mega-project.  I once calculated that there are counts from over 2 000 000 leaves which scales up to something like 10 000 000 pieces of data, if you conservatively estimate five data observations per leaf. Quite a lot of the data are now computerized thanks to a series of student helpers and Vicki Senior, currently finishing her PhD at Sheffield University, but certainly not all of it. In terms of output, only two papers so far (Wade & Leather, 2002; Leather et al., 2005), but papers on the winter moth, sycamore and maple aphids and orange ladybird are soon to be submitted.  On balance, I think that this was also worthwhile and gave me plenty of early morning thinking time in pleasant surroundings and a chance to enjoy Nature.

The sycamore project – most of the raw data, some of which still needs to be computerised 🙂

 

Side project 5. Sixty bird cherry trees 1993-2012

This project has already featured in my blog in my Data I am never going to publish series and also in a post about autumn colours and aphid overwintering site selection.  Suffice to say that so far, thanks to my collaborator Marco Archetti, two excellent papers have appeared (Archetti & Leather, 2005; Archetti et al., 2009), the latter of which is my third most cited paper with 101 cites to date and the former is placed at a very respectable 21st place.  I don’t really see any more papers coming out from this project, but I might get round to writing something about the study as a whole in a natural history journal. On balance, even though only two papers have appeared from this project, I count this as having been a very worthwhile investment of my time.

All now in a spreadsheet and possibly still worthwhile delving into the data

 

Side project 5.  Urban ecology – Bracknell roundabouts 2002-2012

This started as a pedagogical exercise, which will be the subject of a blog post in the not too distant future. The majority of the field work was done by undergraduate and MSc students and in the latter years spawned a PhD student, so a side project that became a funded project 🙂 To date, we have published seven papers from the project (Helden & Leather, 2004, 2005; Leather & Helden, 2005ab; Helden et al., 2012; Jones & Leather, 2012; Goodwin et al., 2017) and there are probably two more to come.  Definitely a success and a very worthwhile investment of my time.  The story of the project is my most requested outreach talk so also gives me the opportunity to spread the importance of urban ecology to a wider audience.

The famous roundabouts – probably the most talked and read about roundabouts in the world 🙂 Sadly Roundabout 1 i n o longer with us; it was converted into a four-way traffic light junction last year 😦

 

Side project 6.  Testing the Janzen-Connell Hypothesis – Silwood Park, 2005-2012

I mentioned this project fairly recently so will just link you to it here.  So far only one paper has come out of this project (Pigot & Leather, 2008) and I don’t really see me getting round to doing much more than producing another Data I am never going to publish article, although it does get a passing mention in the book that I am writing with former colleagues Tilly Collins and Patricia Reader.  It also gave undergraduate and MSc project students something to do.  Overall, this just about counts as a worthwhile use of my time.

Most of this is safely in a spreadsheet but the data in the notebooks still needs inputting

According to my data base I have published 282 papers since 1980 which given that I have supervised 52 PhD students, had 5 post-docs, and, at a rough estimate, supervised 150 MSc student projects and probably 200 undergraduate student projects doesn’t seem to be very productive 😦 Of the 282 papers, 125 are from my own projects, which leaves 139 papers for the post-docs and PhD students and 17 from the side projects.  Three of the papers published from the side projects were by PhD students, so if I remove them from the side projects that gives an average of 2.3 papers per side project and 2.4 papers per post-doc and PhD student.   So, in my opinion, yes, side projects are definitely worth the investment.

 

References

Archetti, M. & Leather, S.R. (2005) A test of the coevolution theory of autumn colours: colour preference of Rhopalosiphum padi on Prunus padus. Oikos, 110, 339-343.

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.

Goodwin, C., Keep, B., & Leather, S.R. (2017) Habitat selection and tree species richness of roundabouts: effects on site selection and the prevalence of arboreal caterpillars. Urban Ecosystems, 19, 889-895.

Helden, A.J. & Leather, S.R. (2004) Biodiversity on urban roundabouts – Hemiptera, management and the species-area relationship. Basic and Applied Ecology, 5, 367-377.

Helden, A.J. & Leather, S.R. (2005) The Hemiptera of Bracknell as an example of biodiversity within an urban environment. British Journal of Entomology & Natural History, 18, 233-252.

Helden, A.J., Stamp, G.C., & Leather, S.R. (2012) Urban biodiversity: comparison of insect assemblages on native and non-native trees.  Urban Ecosystems, 15, 611-624.

Jones, E.L. & Leather, S.R. (2012) Invertebrates in urban areas: a review. European Journal of Entomology, 109, 463-478.

Leather, S.R. (1986) Host monitoring by aphid migrants: do gynoparae maximise offspring fitness? Oecologia, 68, 367-369.

Leather, S.R. (1989) Phytodecta pallida (L.) (Col., Chrysomelidae) – a new insect record for bird cherry (Prunus padus). Entomologist’s Monthly Magazine, 125, 17-18.

Leather, S.R. (1993) Overwintering in six arable aphid pests: a review with particular relevance to pest management. Journal of Applied Entomology, 116, 217-233.

Leather, S.R. & Helden, A.J. (2005) Magic roundabouts?  Teaching conservation in schools and universities. Journal of Biological Education, 39, 102-107.

Leather, S.R. & Helden, A.J. (2005) Roundabouts: our neglected nature reserves? Biologist, 52, 102-106.

Leather, S.R. & Mackenzie, G.A. (1994) Factors affecting the population development of the bird cherry ermine moth, Yponomeuta evonymella L. The Entomologist, 113, 86-105.

Leather, S.R., Wade, F.A., & Godfray, H.C.J. (2005) Plant quality, progeny sequence, and the sex ratio of the sycamore aphid, Drepanoisphum platanoidis. Entomologia experimentalis et applicata, 115, 311-321.

Pigot, A.L. & Leather, S.R. (2008) Invertebrate predators drive distance-dependent patterns of seedling mortality in a temperate tree Acer pseudoplatanus. Oikos, 117, 521-530.

Steinbeck, J. (1954) Sweet Thursday, Viking Press, New York, USA.

Wade, F.A. & Leather, S.R. (2002) Overwintering of the sycamore aphid, Drepanosiphum platanoidis. Entomologia experimentalis et applicata, 104, 241-253.

Ward, S.A., Leather, S.R., Pickup, J., & Harrington, R. (1998) Mortality during dispersal and the cost of host-specificity in parasites: how many aphids find hosts? Journal of Animal Ecology, 67, 763-773.

Whittaker, R.H. (1952) A Study of summer foliage insect communities in the Great Smoky Mountains. Ecological Monographs, 22, 1-44.

 

*

I was so impressed by this piece of philosophy that it is quoted in the front of my PhD thesis 🙂

**

My second post-doc was only for two years.

***

You may wonder why I keep emphasising early morning in relation to surveying sycamore aphids.  Sycamore aphids are very easy to disturb so it is best to try and count them in the early morning before they have a chance to warm up and become flight active.

 

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Data I am never going to publish – A tale of sixty trees

In 1981 I spent a lot of time trudging through snow, cross-country skiing and snow-shoeing my way across the snowy wastes of Finland to snip twigs off bird cherry trees.  This was part of my post-doc which was to develop a forecasting system for the bird cherry-oat aphid, Rhopalosiphum padi.  On returning to the lab I then spent many a happy hour counting how many aphid eggs were nestled in between the buds and the stem on each twig.  It was while doing this that I noticed that some of the twigs were infested with the overwintering larval shields of the bird cherry ermine moth, Yponomeuta evonymellus.  Of course I then started counting them as well 🙂  I noticed that trees with lots of aphid eggs didn’t have very many larval shields and I wondered why. Some later observations from marked trees in Scotland appeared to provide evidence that the aphids and the moths tended to either prefer different trees or perhaps excluded each other.

Negative correlation between moths and aphids – more moths equals fewer aphids and vice versa

Based on these data I hypothesised that the two insects were indirectly competing for resources by altering plant chemistry and/or architecture thus making the trees less or more suitable for egg laying in the autumn (Leather, 1988).  I tested this experimentally when I was working for the Forestry Commission in Scotland using potted bird cherry trees that I defoliated to a lesser or greater extent to see if I could induce changes in foliar quality and tree growth rates that might influence subsequent colonisation by the aphids and moths. As predicted, those trees that had been defoliated, albeit by me and not by moth larvae, were less attractive to aphids in the autumn (Leather, 1993).  These effects were still apparent five years after the beginning of the experiment (Leather, 1995) when I had to desert my trees as I moved to a new position at Imperial College’s Silwood Park campus.

Given that apart from the location, the SE of England, this was my idea of a dream job for life (colleagues at the time included John Lawton, Mike Hassell, Bob May, Stuart McNeill, Mike Way, Brad Hawkins, Shahid Naeem, Mike Hochberg, Chris Thomas to name but a few), I decided to start up two long-term projects to see me through the next 30 years, one observational (my 52 sycamore tree project), the other experimental, a follow up to my bird cherry defoliation experiment.

I went for a simplified design of my earlier experiments, just two defoliation regimes, one to mimic aphid infestation (50%), the other to mimic bird cherry ermine moth defoliation (100%) and of course a non-defoliated control.  I also planted the trees in the ground to better simulate reality.  Using potted plants is always a little suspect and I figured that I would need to do rather a lot of re-potting over the next 30 years 🙂

The grand plan!

I sourced my trees from a Forestry Commission nursery thinking that as the national organisation responsible for tree planting in the UK I could trust the provenance of the trees.  Things didn’t go well from the start.  Having planted my trees in autumn 1992 and established the treatments in the spring of 1993 I discovered that my bird cherry, rather than being from a native provenance (seed origin) were originally from Serbia! Hmm 🙂  It was too late to start again, so I decided to carry on.  After all, bird cherry although widely planted in the SE, has a native distribution somewhat further north and west, which meant I was already operating close to the edge of ‘real life’, so what did an extra 1600 kilometres matter?

The mainly ‘natural’ distribution of bird cherry (left, Leather, 1996) and the current distribution including ‘introduced’ trees https://www.brc.ac.uk/plantatlas/index.php?q=plant/prunus-padus

Next, I discovered that my fence was neither rabbit nor deer proof.  I almost gave up at this point, but having invested a lot of time and energy in setting up the plot I once again decided to carry on. On the plus side, the trees most heavily defoliated and bitten back were mainly from the 100% defoliation treatment, but did give me some negative growth rates in that year.

My original plan was to record height (annually), bird cherry egg numbers (every December), bird cherry ermine moth larval shields (annually), bud burst and leaf expansion once a week, leaf-fall (annually), and once a month, defoliation rates in two ways, number of damaged leaves and an overall estimation of percentage defoliation.  This was a personal project, so no grant funding and no funding for field assistants.  It soon became clear, especially when my teaching load grew, as Imperial started replacing whole organism biologists with theoretical and molecular biologists, and I was drafted in to take on more and more of the whole organism lecturing, that I would not be able to keep both of my long term projects going with the same intensity.  Given the ‘problems’, associated with the bird cherry project, I decided  that I would ditch some of my sampling, bud burst was scored on 21st March every year and defoliation only measured once, in late summer and egg sampling and height recording came to a halt once the trees grew above me (2005)!  This allowed me to carry on the sycamore project as originally intended*.

I kept an eye on the trees until I left Silwood Park in 2012, but by 2006 I was only monitoring bud burst and leaf fall feeling that this might be useful for showing changes in phenology in our ever-warming world.  One regret as I wandered between the then sizeable trees in the autumn of 2012 was that I had not taken a before and after photograph of the plots.  All I have are two poor quality photos, one from 2006, the other from 2012.

The Sixty Tree site April 2006.

The Sixty Tree site April 2010 with a very obvious browse line

 

So, after all the investment in time, and I guess to a certain extent money (the trees and the failed fencing, which both came out of my meagre start-up funding**), did anything worthwhile come out of the study?

The mean number of Rhopalosiphum padi eggs per 100 buds in relation to defoliation treatment

As a long-time fan of aphid overwintering it was pleasing to see that there was a significant difference not only between years (F= 8.9, d.f. = 9/29, P <0.001), but also between treatments with the trees in the control treatment having significantly more eggs laid on them than the 100% defoliation treatment (F= 9.9, d.f. = 2/ 29, P <0.001 with overall means of 1.62, 1.22 and 0.65 eggs/100 buds).  This also fitted in with the hypothesis that trees that are defoliated by chewing herbivores become less suitable for aphids (Leather, 1988).  I must admit that this was a huge surprise to me as I had thought that as all the trees were attacked by deer the year after the experimental treatments they would all respond similarly, which is why I almost gave up the experiment back in 1994.

Bud burst stage of Prunus padus at Silwood Park on March 21st 1996-2012; by treatment and combined

When it came to budburst there was no treatment effect, but there was a significant trend to earlier budburst as the trees became older which was strongly correlated with warmer springs, although as far as spring temperatures were concerned there was no significant increase with year.

Mean spring temperature (Silwood Park) 1993-2012 and relationship between mean spring temperature and bud bust stage on 21st March.

Mean date of final leaf fall of Prunus padus at Silwood Park 1995-2012; by treatment and combined

At the other end of the year, there was a significant difference between date of final leaf fall between years but no significant difference between treatments.  In retrospect I should have adopted another criterion.  My date for final leaf fall was when the last leaf fell from the tree.  Those of you who have watched leaves falling from trees will know that there are always a few who are reluctant to make that drop to the ground to become part of the recycling process.  Even though they are very obviously dead, they hang there until finally dislodged by the wind.   I should really have used a measure such as last leaf with any pigment remaining.  I am sure that if I could be bothered to hunt down the wind speed data I would find that some sort of correlation.

Mean height (cm) of Prunus padus trees at Silwood Park 1993-2005 and Diameter at Breast Height (DBH) (cm) at the end of 2012

Except for the year after the deer attack, the trees, as expected, grew taller year by year.  There was however, no significant difference between heights reached by 2005 or in DBH at the end of 2012 despite what looked like a widening gap between treatments.

Defoliation scores of Prunus padus at Silwood Park 1993-2004; % leaves damaged and overall defoliation estimates

My original hypothesis that trees that were heavily defoliated at the start of their life would be more susceptible to chewing insects in later life, was not supported.  There was no significant difference between treatments, although, not surprisingly, there was a significant difference between years.  Average defoliation as has been reported for other locations was about 10% (Kozlov et al., 2015; Lim et al., 2015).

Number of Prunus padus trees with severe deer damage

That said, when I looked at the severity of deer attack, there was no effect of year but there was a significant effect of treatment, those trees that had been 100% defoliated in 1993 being most attractive to deer.   In addition, 20% of those trees were dead by 2012 whereas no tree deaths occurred for the control and less severely defoliated treatments.

I confess to being somewhat surprised to find as many significant results as I did from this simple analysis and was momentarily tempted to do a more formal analysis and submit it to a journal.  Given, however, the number of confounding factors, I am pretty certain that I would be looking at an amateur natural history journal with very limited visibility.  Publishing it on my blog will almost certainly get it seen by many more people, and who knows may inspire someone to do something similar but better.

The other reason that I can’t be bothered to do a more formal analysis is that my earlier work on which this experiment was based has not really hit the big time, the four papers in question only accruing 30 cites between them.  Hardly earth shattering despite me thinking that it was a pretty cool idea;  insects from different feeding guilds competing by changing the architecture and or chemsitry of their host plant.  Oh well.  Did anything come out of my confounded experiment or was it a total waste of time?  The only thing published from the Sixty Trees was a result of a totally fortuitous encounter with Marco Archetti and his fascination with autumn colours (Archetti & Leather, 2005), the story of which I have related in a previous post, and which has, in marked contrast to the other papers, had much greater success in the citation stakes 🙂

And finally, if anyone does want to play with the data, I am very happy to give you access to the files.

References

Archetti, M. & Leather, S.R. (2005) A test of the coevolution theory of autumn colours: colour preference of Rhopalosiphum padi on Prunus padus. Oikos, 110, 339-343. 50 cites

Kozlov, M.V., Lanta, V., Zverev, V., & Zvereva, E.L. (2015) Global patterns in background losses of woody plant foliage to insects. Global Ecology & Biogeography, 24, 1126-1135.

Leather, S.R. (1985) Does the bird cherry have its ‘fair share’ of insect pests ? An appraisal of the species-area relationships of the phytophagous insects associated with British Prunus species. Ecological Entomology, 10, 43-56.  14 cites

Leather, S.R. (1988) Consumers and plant fitness: coevolution or competition ? Oikos, 53, 285-288. 10 cites

Leather, S.R. (1993) Early season defoliation of bird cherry influences autumn colonization by the bird cherry aphid, Rhopalosiphum padi. Oikos, 66, 43-47. 11 cites

Leather, S.R. (1995) Medium term effects of early season defoliation on the colonisation of bird cherry (Prunus padus L.). European Journal of Entomology, 92, 623-631. 4 cites

Leather, S.R. (1996) Biological flora of the British Isles Prunus padus L. Journal of Ecology, 84, 125-132.  14 cites

Lim, J.Y., Fine, P.V.A., & Mittelbach, G.G. (2015) Assessing the latitudinal gradient in herbivory. Global Ecology & Biogeography, 24, 1106-1112.

 

 

*which you will be pleased to know, is being analysed as part of Vicki Senior’s PhD project, based at the University of Sheffield.

**£10 000 which even in 1992 was not overly-generous.

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