Tag Archives: Forestry Commission

Ideas I had and never followed up

“When I was younger, so much younger than before” I never needed any help to come up with ideas for research topics or papers.   When I was doing my PhD and later as a post-doc, I used to keep a note pad next to my bed so that when I woke up in the middle of night with an idea (which I often did) I could scribble it down and go back to sleep.  (These days sadly, it is my bladder and not ideas that wake me up in the wee small hours 🙂*)

On waking up properly, these ideas, if they still seemed sensible, would  move onto Stage 2, the literature search.  In those days, this was much more difficult than it is now, no Google Scholar or Web of Science then, instead you had to wade though the many hard-copy Abstract series and then get hard copies of the papers of interest.  Once in my hands, either via Inter-library loans or direct from the author, or even photocopied from the journal issue (we did have photocopiers in those days), the papers would be shoved into a handy see-through plastic folder (Stage 3).  Depending on how enthusiastic I was about the idea, I would then either mock-up a paper title page or put the folder in the ‘to deal with later’ pile (Stage 4).   Many of these eventually led on to Stage 5, experiments and published papers.  Others have languished in their folders for twenty or thirty years.

As part of my phased run up to retirement (2021), I have started farming out my long-term publishable (hopefully) data-sets to younger, more statistically astute colleagues and ‘publishing’ less robust, but possibly useful data on my blog site.  I have also, somewhat halfheartedly since the task is monumental, started to go through my old field and lab books that

monumental-data

A monumental collection of data.  The top right picture is my 20-year sycamore data set.  I estimate that there are about 7 million data points in it; of which to date only 1.6 million, give or take a million, are computerised.  I also have a ten-year bird cherry aphid data set from Scotland, waiting to go on the computer, any volunteers?

are not yet computerised.  Whilst doing this I came across some Stage 3 folders, which as you can see from the colour of the paper have languished for some time.

the-forgotten-nine

The Forgotten Nine

 

There were nine forgotten/dismissed proto-papers, the oldest of which, judging by the browning of the paper and my corresponding address, dates from the early 1980s, and is simply titled “What are the costs of reproduction?”.  This appears to have been inspired by a talk given by Graham Bell at a British Ecological Society, Mathematical Ecology Group meeting in 1983.  In case you are wondering, this was one of those meetings supposed to bring theorists and empiricists together.   It didn’t work, neither group felt able to talk to each other 🙂  The idea, inevitably based on aphid data, didn’t bear any fruit, although I do have this graph as a souvenir.  If anyone wants

graph

In those days we used graph paper 🙂

 the data, do let me know.

Slightly later, we find the grandly titled, “Size and phylogeny – factors affecting covariation in the life history traits of aphids”.  This had apparently been worked up from an earlier version of a paper, less grandly, but no less ponderously, titled, “Size and weight: factors affecting the level of reproductive investment in aphids”.  This is based on some basic dissection data from eight aphid species and presents the relationships, or lack of, between adult weight (or surrogate measure), ovariole number, potential fecundity and the number of pigmented embryos.  As far as I can remember these are data that Paul Wellings** and I collected as a follow-up to work we had published from a side project when we were doing our PhDs at the University of East Anglia (Wellings et al., 1980).  The second title was inspired by a paper by Stephen Stearns (Stearns, 1984), who was something of a hero of mine at the time, and was, I guess, an attempt to publish pretty simple data somewhere classier than it deserved 🙂  So this one seems to be a Stage 4, almost Stage 5 idea, and may, if I have time or someone volunteers, actually get published, although I suspect it may only make it to a very minor journal under its original title.

Then we have a real oddity, “Aphids, elephants and oaks: life history strategies re-examined”.  This one as far as I remember, is based on an idea that I had about r- and k-selection being looked at from a human point of view and not the organism’s point of view.  My thesis was that an oak tree was actually r-selected as over its life-time it was more fecund than an aphid 🙂  I suspect this was going to be aimed at the Forum section of Oikos.

The next one, dates from the late-1980s, “Protandry versus protogyny: patterns of occurrence within the Lepidoptera”, and reflects the fact that females of the pine beauty moth, Panolis flammea, on which I was then working, emerge before the males (Leather & Barbour, 1983; Leather, 1984), something not often reported in Lepidoptera.  I wondered what advantage (if any) this gave P. flammea.  I planned this one as a review or forum type paper but never got beyond the title and collecting two references (Robertson, 1987; Zonneveld & Metz, 1991).  I still think this is an interesting idea, but do feel free to have a go yourselves, as again, I suspect that I won’t actually get round to it.

Finishing off my time in Scotland, is a paper simply entitled, “Egg hatch in the bird cherry aphid, Rhopalosiphum padi.” I have ten years of egg hatch data from eight trees waiting to be analysed.  This is almost certainly not worth more than a short note unless I (or a willing volunteer) tie it in with the ten years data on spring and autumn populations on the same trees 🙂 Aphid egg data although not very abundant, is probably not in great demand.  My first published paper (Leather, 1980) was about egg mortality in the bird cherry aphid and 36 years later has only managed to accrue 32 citations, so I guess not an area where one is likely to become famous 🙂

I then have four papers dating from my time as an Associate Member of the NERC Centre for Population Biology at Silwood Park.   The first is titled, “The suitability of British Prunus species as insect host plants” and was definitely inspired by my foray into counting host plant dots as exemplified by the late great Richard Southwood (Leather, 1985, 1986).  I think I was going to look at palatability measures of some sort.

The next is called ‘Realising their full potential: is it important and how many insects achieve it?”  I’m guessing that this was a sort of follow-up to my second most-cited paper ever (Leather, 1988), the story of which you can read here, if at all interested.  Most insects, even those that are pests, die before achieving anywhere near their full reproductive potential, but then so do we humans, and our population continues to grow.  So in answer to the question, I guess not and no it doesn’t matter 🙂

Also linked to insect reproduction is the next paper, which I have followed up with the help of a PhD student, and do hope to submit in the near future, “Queue positions, do they matter”.  As this one may actually see the light of day, I won’t say anything further about it.

And finally, another one about aphid eggs, “Bud burst and egg hatch synchrony in aphids”.  This one was going to be based on my then ten-year sycamore aphid data but is now based on my twenty-year data set and is now in the very capable hands of a PhD student and hopefully will see the light of day next year.

There are also a number of other folders with no titles that are just full of collections of reprints.  I can only guess at what these ideas were so won’t burden you with them.

I mentioned at the beginning of this piece that I don’t wake up in the middle of the night with ideas any more.  As we get older I think there is a tendency to worry that we might run out of ideas, especially when, as we do in the UK, suffer from ludicrously underfunded research councils with very high rejection rates that don’t allow you to resubmit failed grant applications.  It was thus reassuring to see this recent paper that suggests that all is not lost after you hit the grand old age of 30.  That said, I do believe that as you move away from the bench or field, the opportunity to be struck by what you see, does inevitably reduce.  As a PhD student and post-doc you are busy doing whatever it is you do, in my case as an ecological entomologist, counting things, and inevitably you see other things going on within and around your study system, that spark off other ideas.  It was the fear of losing these opportunities as I moved up the academic ladder, which inevitably means, less field and bench time and more time writing grant applications and sitting on committees, that I specifically set aside Monday mornings (very early mornings) to my bird cherry plots and even earlier Thursday mornings to survey my sycamore trees.   Without those sacrosanct mornings I am pretty certain I would have totally lost sight of what is humanly possible to do as a PhD student or post-doc.  This, thankfully for my research group, means that I had, and have, realistic expectations of what their output should be, thus reducing stress levels all round.   As a side benefit I got to go out in the fresh air at least twice a week and do some exercise and at the same time see the wonderful things that were going on around and about my study areas and as a bonus had the chance to get some new ideas.

 

References

Leather, S.R. (1984) Factors affecting pupal survival and eclosion in the pine beauty moth, Panolis flammea (D&S). Oecologia, 63, 75-79.

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.

Leather, S.R. (1986) Insect species richness of the British Rosaceae: the importance of host range, plant architecture, age of establishment, taxonomic isolation and species-area relationships. Journal of Animal Ecology, 55, 841-860.

Leather, S.R. (1988) Size, reproductive potential and fecundity in insects: Things aren’t as simple as they seem. Oikos, 51, 386-389.

Leather, S.R. & Barbour, D.A. (1983) The effect of temperature on the emergence of pine beauty moth, Panolis flammea Schiff. Zeitschrift fur Angewandte Entomologie, 96, 445-448.

Robertson, H.G. (1987) Oviposition and site selection in Cactoblastis cactorum (Lepidoptera): constraints and compromises. Oecologia, 73, 601-608.

Stearns, S.C. (1984) The effects of size and phylogeny on patterns of covariation inthe life history traits of lizards and snakes. American Naturalist, 123, 56-72.

Wellings, P.W., Leather , S.R., & Dixon, A.F.G. (1980) Seasonal variation in reproductive potential: a programmed feature of aphid life cycles. Journal of Animal Ecology, 49, 975-985.

Zonneveld, C. & Metz, J.A.J. (1991) Models on butterfly protandry – virgin females are at risk to die. Theoretical  Population Biology, 40, 308-321.

 

*I hasten to add that I do still have new ideas, they just don’t seem to wake me up any more 🙂

**Now Vice-Chancellor of the University of Wollongong

 

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It isn’t easy being an applied ecologist – working on crops limits publication venues

“This is Simon Leather, he’s an ecologist, albeit an applied one” Thus was I introduced to a group of visiting ecologists by my then head of department at the Silwood Park campus of Imperial College. As you can imagine I was somewhat taken aback at this public display of the bias that ‘pure’ scientists have against those that they regard as ‘applied’.  I was (and still am), used to this attitude, as even as an undergraduate doing Agricultural Zoology when we shared modules with the ‘pure’ zoologists, we were regarded as a slightly lower life form J  Working in Finland as a post-doc in the early 1980s it was also obvious that there was a certain degree of friction between the pure and applied entomologists, so it was not a phenomenon confined entirely to the UK.  To this day, convincing ecology undergraduates that integrated pest management is a suitable career for them is almost impossible.

I was an ecologically minded entomologist from early childhood, pinning and collecting did not interest me anywhere near as much as insect behaviour and ecology, but I knew that I wanted to do something “useful” when I grew up. Having seen my father in action as a plant pathologist and crop protection officer, it seemed to me that combining entomology with agriculture would be an ideal way to achieve this ambition.  A degree in Agricultural Zoology at Leeds and a PhD in cereal aphid ecology at the University of East Anglia (Norwich) was the ideal foundation for my chosen career as an applied ecologist/entomologist.

I started my professional life as agricultural entomologist working both in the laboratory and in the field (cereal fields to be exact), which were easily accessible, generally flat, weed free and easy to manipulate and sample.  In the UK even the largest fields tend to be visible from end to end and side to side when you stand in the middle or edge (even more so now than when I started as wheat varieties are now so much shorter, less than half the height they were in 1977).

applied-fig-1

 

Having fun as a PhD student – aphid ‘sampling’ in Norfolk 1978

applied-fig-2

I haven’t grown since I did my PhD so wheat must have shrunk 🙂

See the post script to see what wheat used to look like.

Laboratory experiments, even when working on mature plants were totally do-able in walk-in growth rooms, and at a push you could even fit whole earing wheat plants into a growth cabinet.

I then spent ten years working as a forest entomologist, where field sites were the exact opposite, and extreme measures were sometimes required to reach my study animals, including going on an official Forestry Commission tree climbing course.

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Pole pruners – (of only limited use) and tree climbing (great fun but laborious)

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Scaffold towers for really high work, but expensive (and scary on sloping hillsides).

And as for lab work, not a chance of using mature plants or even plants more than two to three years old.  Excised branches and/or foliage (rightly or wrongly) were the norm*.

Doing field work was, despite the sometimes very physically challenging aspects, a lot of fun, and in my case, some very scenic locations.  My two main field sites were The Spey Valley and

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Sutherland and Caithness, both of which provided magnificent views and of course, a plethora of whisky distilleries

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where I discovered what is now my favourite single malt 🙂

The real fun came when it was time to submit papers.  Journal choice was (and is) very important.  As Stephen Heard points out, journals have a ‘culture’ and it is very important to pick a journal that has the right editorial board and ethos. The laboratory work never seemed to be a huge problem, referees (perhaps wrongly) very rarely criticised the use of young plants or excised foliage. I was able to publish the output from what was a very applied project, in a range of journals from the very specialised to the more ecological. This selection for example, from 1985-1987 (Leather, 1985, 1986; Leather & Burnand, 1987; Leather et al., 1985), appeared in Ecological Entomology, Oecologia, Functional Ecology and Bulletin of Entomological Research respectively.

Papers reporting field-based work were a little bit harder to place in journals outside the mainstream forestry ones, particularly when it came to experimental work.  One of the problems was that ecological referees unused to working in forests tended not to have a grasp of what was involved in setting up and servicing an experiment in a forest plantation or stand.  A farmer has no great objection to an entomologist removing 100 wheat tillers a week from his 2 ha field (at 90 stems per metre2, even a 16 week field season would only remove a tiny fraction of his crop).  A forest manager on the other hand with a stocking density of 3000 stems per hectare would look askance at a proposal to remove even 100 trees a month from a hectare plot, especially if this was repeated for seven years.  Sample size was thus a problem, even when using partial sampling of trees, e.g. by removing say only one branch.  When it came to field scale replication, to compare for example, three treatments and a control on two different soil types, where each treatment plot is a hectare, things get a bit difficult. The most that we could service, even with help (since we did not have huge financial resources), was three replicates of each treatment.  In agricultural terms this seems incredibly low, where 10m2 plots or even smaller, are very often used (e.g. Staley et al., 2009; Garratt et al., 2011).

We thus ended up with our experimental papers in the really specialised forestry journals (e.g.  Leather, 1993; Hicks et al., 2007).  On the other hand, those papers based on observational, long-term data were easier to place in more general ecological journals (e.g. Watt et al., 1989), although that was not always enough to guarantee success (e.g. Walsh et al., 1993; Watt et al., 1991).  Another bias that I came across (perhaps unconscious) was that referees appeared, and still do, think that work from production forests is not as valid as that coming from ‘natural’ forests, especially if they are tropical. We came across this when submitting a paper about the effects of prescribed burning on carabid populations in two sites in Portugal (Nunes et al., 2006).  We originally sent this to a well-known ecological journal who rejected it on the grounds of low replication, although we had also replicated it temporarily as well as geographically.  I was not impressed to see a paper published in this journal shortly after they had rejected our manuscript in which the authors had reported changes in insect communities after a one-off fire event in a tropical forest, without even the benefits of pre-fire baseline data.  We had in the meantime, given up on general ecology journals and submitted our paper to a local forestry journal.  Such is life.

I originally started this essay with the idea of bemoaning the fact that publishing studies based in production forests in more general journals was more difficult than publishing agriculturally based papers, but got diverted into writing about the way applied ecologists feel discriminated against by journals and pure ecologists.  I may or may not have convinced you about that.  To return to my original idea of it being more difficult for forestry–based ecologists to break out of the forestry journal ghetto than it is for agro-ecologists to reach a broader audience, I present the following data based on my own publication record, which very convincingly demonstrates that my original feeling is based on fact, albeit based on an n of one 🙂

applied-fig-7

Numbers of agricultural and forestry based papers published by me in different journal categories.

I might also add that being an entomologist also limits where you can publish, so being an applied entomologist is something of a double whammy, and when it comes to getting research council funding, don’t get me started!

References

 Garratt, M.P.D., Wright, D.J., & Leather, S.R. (2010) The effects of organic and conventional fertilizers on cereal aphids and their natural enemies. Agricultural and Forest Entomology, 12, 307-318.

Hicks, B.J., Aegerter, J.N., Leather, S.R., & Watt, A.D. (2007) Differential rates of parasitism of the pine beauty moth (Panolis flammea) depends on host tree species. Scottish Forestry, 61, 5-10.

Leather, S.R. (1985) Oviposition preferences in relation to larval growth rates and survival in the pine beauty moth, Panolis flammea. Ecological Entomology, 10, 213-217.

Leather, S.R. (1986) The effect of neonatal starvation on the growth, development and survival of larvae of the pine beauty moth Panolis flammea. Oecologia, 71, 90-93.

Leather, S.R. (1993) Influence of site factor modification on the population development of the pine beauty moth (Panolis flammea) in a Scottish lodgepole pine (Pinus contorta) plantation. Forest Ecology & Management, 59, 207-223.

Leather, S.R. & Burnand, A.C. (1987) Factors affecting life-history parameters of the pine beauty moth, Panolis flammea (D&S): the hidden costs of reproduction. Functional Ecology, 1, 331-338.

Leather, S.R., Watt , A.D., & Barbour, D.A. (1985) The effect of host plant and delayed mating on the fecundity and lifespanof the pine beauty moth,  Panolis flammea (Denis & Schiffermuller) (Lepidoptera: Noctuidae): their influence on population dynamics and relevance to pest management. Bulletin of entomological Research, 75, 641-651.

Nunes, L.F., Silva, I., Pité, M., Rego, F.C., Leather, S.R., & Serrano, A. (2006) Carabid (Coleoptera) community change following prescribed burning and the potential use of carabids as indicator species to evaluate the effects of fire management in Mediterranean regions. Silva Lusitania, 14, 85-100.

Staley, J.T., Stewart-Jones, A., Pope, T.W., Wright, D.J., Leather, S.R., Hadley, P., Rossiter, J.T., Van Emden, H.F., & Poppy, G.M. (2010) Varying responses of insect herbivores to altered plant chemistry under organic and conventional treatments. Proceedings of the Royal Society of London B, 277, 779-786.

Walsh, P.J., Day, K.R., Leather, S.R., & Smith, A.J. (1993) The influence of soil type and pine species on the carabid community of a plantation forest with a history of pine beauty moth infestation. Forestry, 66, 135-146.

Watt, A.D., Leather, S.R., & Stoakley, J.T. (1989) Site susceptibility, population development and dispersal of the pine beauty moth in a lodgepole pine forest in northern Scotland. Journal of Applied Ecology, 26, 147-157.

Watt, A.D., Leather, S.R., & Evans, H.F. (1991) Outbreaks of the pine beauty moth on pine in Scotland: the influence of host plant species and site factors. Forest Ecology and Management, 39, 211-221.

 

Post script

The height of mature wheat and other cereals has decreased hugely over the last two hundred years.  Cereals were originally a multi-purpose crop, not just providing grain for humans, but bedding straw for stock and humans, winter fodder for animals, straw for thatching and if really desperate, you could make winter fuel out of discarded straw**.

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John Linnell  – Wheat 1860  You wouldn’t have been able to see Poldark’s (Aidan Turner) manly chest whilst he was scything in this field!

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Pieter Breugel the Elder – Die Kornernter – The Harvesters  (1565) – Head-high wheat crops and not just because the average height was lower in those days.

 

*As I was writing this article I came across this paper (Friberg & Wiklund, 2016) which suggests that using excised plants may be justifiable.  Friberg, M. & Wiklund, C. (2016)  Butterflies and plants: preference/performance studies in relation to plant size and the use of intact plants vs. cuttings.  Entomologia experimentalis et applicata, 160, 201-208

**My source for this is Laura Ingalls Wilder – Little House on the Prairie, to be exact 🙂

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When frustration becomes serendipitous – My second most cited paper

For most of the 1980s and the early 1990s I worked for the UK Forestry Commission as a research and advisory entomologist. As a civil servant I was subjected to a lot more rules than I am now as a university academic. The most frustrating set of rules in my mind, were those associated with publishing papers. The initial consultation with a statistician before your experiment was planned and any subsequent collaboration with the analysis was very sensible, and I had no problems with that part of the process at all. Our statisticians were very good in that they helped you decide the analysis but expected you to learn GenStat (the Forestry Commission standard statistics programme) and do it yourself unless you were really stuck.

The next bit was the frustrating part. When it came to writing papers you first submitted your paper to your line manager. They then read your paper, very frustrating indeed for me, as my immediate boss considered papers a very low priority and it could be several months before he got around to passing it back with comments and suggestions. Then it was passed to a member of one of the other department such as silviculture, tree breeding or pathology for them to read and make comments. The idea behind this being that it helped make the paper accessible to a wide audience, again a good idea. The problem at this stage was that once again your paper was likely to be a low priority, so yet more delay. Once that was done you then had to submit your paper to the Chief Research Office for him to read and comment on, so once again yet more delay. This meant that quite often it was a year before you actually were able to submit your paper to a journal, which could be deeply frustrating to say the least.

Frustrated

In 1986 a new journal to be published by the British Ecological Society was announced, Functional Ecology. In those days, the dreaded Impact Factors had not yet raised their ugly heads, and one tended to publish in journals relevant to your discipline, or, as in this case, the fancy took you.  I thought it would be cool to publish in the first issue of the first volume of this new journal.  I therefore set to work, with the help of one of our statisticians to produce a paper about life history parameters of the pine beauty moth, from a more ecological point of view and not from the more applied view-point of it as a forest pest (my job remit). I was very proud of the paper and confess to having got somewhat carried away in the discussion, so much so, that it was suggested by all who read it in the very lengthy internal appraisal process, that most of the discussion should be cut as being too far away from the main story. As the process had taken so long already I decided to go with the flow and eventually submitted my paper about a year after first writing it, incidentally giving my statistician a co-authorship. It was accepted and did indeed appear in the first volume of Functional Ecology, albeit the last of the year (Leather & Burnand, 1987)! It has to date (14th October 2015) being cited 53 times, by no means a disgrace, but certainly not my second-most cited paper.

I mentioned earlier that I was really proud of my discussion and I decided that I was going to publish it regardless. I reworked it slightly and submitted it to Oikos as a Forum piece, taking the calculated risk of not submitting it through the official Forestry Commission system. My reasoning was, that a), it was unlikely to be read by anyone in the Forestry Commission, being a very ecological journal, and b), if challenged I would say that it had already been seen by the powers that be, albeit not officially. To my relief it was accepted as is (Leather, 1988) and my immediate boss never mentioned it. To my surprise and delight this is now my second-most cited paper, having so far acquired 207 citations and still picks up a reasonable number of cites every year. I guess that I should actually be grateful to all those internal referees who insisted that I cut my discussion down so drastically.

References

Leather, S.R. (1988) Size, reproductive potential and fecundity in insects: Things aren’t as simple as they seem. Oikos, 51, 386-389.

Leather, S.R. & Burnand, A.C. (1987) Factors affecting life-history parameters of the pine beauty moth, Panolis flammea (D&S): the hidden costs of reproduction. Functional Ecology, 1, 331-338.

 

Post script

In case you wondered, my most cited paper is an Annual Review paper, written with one of my former PhD students, Caroline Awmack, and now has almost a thousand citations (994 as of today).

Reference

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

 

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Midwinter Madness – The Snow flea

Between 1982 and 1992 I worked as a research and advisory entomologist for the UK Forestry Commission based at their Northern Research Station just outside Edinburgh. For the first five years of my time there I worked almost exclusively on the pine beauty moth, Panolis flammea. The pine beauty moth is

snowflea 1

a native insect that became a pest of a non-native tree, Pinus contorta, then a tree that was widely planted over northern Britain. The majority of planting in Scotland was in the north and this meant that my study sites were in Sutherland and Caithness and Aberdeenshire. My main experimental forest was west of Aberdeen in the Spey valley (very handy for the whisky trail) in the Elchies block of Criagellalchie Forest.

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My experimental forest with nearby distillery marked 😉

In Mid-January 1984, I headed north to do some maintenance on my head capsule collecting funnel traps.

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In those days, snow was a perennial hazard, even in the south of Scotland and as I progressed northwards the drifts at the side of the road became increasingly higher. When I reached the forest gates, it was obvious that I was not going to be able to drive to my site. The sun was shining, the sky was blue and the snow glistened. A perfect day for a walk, albeit one of 10 km. Luckily, the weather had been sunny for the last couple of days so the snow was mostly hard enough to walk on. Only in a few places did I break the surface and find that I was standing on about a metre depth of snow. Two hours later as I was approaching my field site, squinting against the sun bouncing off the white untouched snow, I saw black spots moving on the surface. My immediate thought was that I was suffering the first stages of snow-blindness, but as I got nearer I saw that the black dots were actually insects. At first sight I thought I was hallucinating, was this some strange bizarre form of life perhaps an aphid-fly hybridization experiment gone wrong? On closer examination I realised that I was looking at wingless Mecopterans.

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Male snow flea, Boreus hyemalis http://mecoptera.free.fr/Boreus-hyemalis.html

 

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Female Boreus hyemalis, note the sting-like ovipositor. http://www.wbrc.org.uk/WORCRECD/32/Bingham–John–Snow_Flea_Boreus_hyemalis.html

Although I was familiar with Scorpion-flies, I had never seen these critters before.

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The aptly named Scorpion fly Panorpa communis : https://commons.wikimedia.org/wiki/File:Scorpion_Fly._Panorpa_communis._Mecoptera_(7837166610).jpg

I collected a few to send off for identification and confirmation and carried on into the depths of the forest to check on my funnels. On returning to civilization a day or so later I sent my specimens off to the Natural History Museum and shortly after was informed that I had they were the snow flea, Boreus hyemalis and that I had extended the recorded range of this particular species, albeit only by a few miles.

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My record – it lasted 10 years as the furthest north before M.S.C. Elliott recorded it in February 1994 in Easter Fearn in the north-west Highlands.

Boreus my record

Distribution of Boreus hyemalis in 1994; my record, then the furthest North.

 

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Current recorded distribution of Boreus hyemalis – obviously widespread – just lacking people willing to go and look for it in the winter 🙂

So what is a snow flea. It is of course, not a flea, being a Mecopteran or Scorpion fly, albeit non-winged.  In Britain there are three species with wings (in the genus Panorpa), the larvae and adults both being predatory on other insects. The adult snow flea is about 5mm long, and lives among moss on which it feeds as both a larva and adult (Withycombe, 1922, 1926). Interestingly, the BugLife site states that they are predatory in both the larval and adult stage. I am not sure where they got this information as they do not cite a reference and all the published literature I have seen indicates that they are moss feeders (Withycombe, 1922, 1926; Fraser, 1943; Hågvar, 2010). Indeed, Wthycombe (1922) conducted a series of experiments on the larvae and conclusively demonstrated that they were unable to complete their development unless fed on moss, although the adults will apparently also feed on dead insects.

These are true winter-active insects, adults emerging in October and November when they mate and lay their eggs the eggs at the base of moss plants), Polytrichium commune being the preferred host (Fraser, 1943). The eggs start to hatch in November and the larvae forage within the moss clumps, pupating towards the end of the summer, emerging as adults after 6-8 weeks.  The adults, which are wingless, thus come out in the coldest months of the year, usually between October and April.  They are most easily seen when walking or jumping on the snow surface. Considering that the adults are winter-active they have a surprisingly high super-cooling point (-6.5oC) (Sömme & Östbye, 1969), especially when compared with the cereal aphid, Sitobion avenae, which has a super-cooling point of -24oC but rarely survives English winters (Knight & Bale, 1986). The BugLife site wonders “how they (snow fleas) manage to jump up to 5 cm without muscular hind legs” but Burrows (2011) found that their jumping prowess is by virtue of large depressor muscles within the thorax which enables them to jump distances of up to 10 cm with a take-off velocity of 1 m s-1, indicating a force of about 16 times their body weight.  So aptly named in this respect too.

The Snow flea is not found (or at least has not been recorded) in the mild south-west of Britain, seeming to prefer areas with a harsher winter. Climate warming may thus pose a threat for this intriguing and little studied insect. Perhaps it is time for us all to venture out in mid-winter and start scanning the surface of snow drifts in heathland areas for these elusive creatures before it is too late.

 

References

Burrows, M (2011) Jumping mechanism and performance of snow fleas (Mecoptera, Boreidae). Journal of Experimental Biology, 214, 2362-2374.

Fraser, F.C. (1943) Ecological and biological notes on Boreus hyemalis (L.) (Mecopt., Boreidae). Journal of the Society for British Entomology, 2, 125-129

Knight, J. D. & Bale, J. S. (1986). Cold hardiness and overwintering of the grain aphid Sitobion avenae. Ecological Entomology 11, 189-197.

Sömme, L. & Östbye, O. (1969) Cold-hardiness in some winter active isnects. Norsk Entomologisk Tidsskrift, 16, 45-48

Withycombe, C. L. (1922). On the life history of Boreus hyemalis L. Transactions of the Entomological Society of London, 1921, 312-318.

Withycombe, C. L. (1926). Additional remarks upon Boreus hyemalis L. Entomologist’s Monthly Magazine, 62, 81-83.

 

Useful link

For more images and observations see http://www.wbrc.org.uk/WORCRECD/32/Bingham–John–Snow_Flea_Boreus_hyemalis.html

 

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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

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How ready is the UK to combat current and future threats to our forests and woodlands?

Almost exactly two years ago (February 2012) a consignment of ash trees sent from a nursery in the Netherlands to one in Buckinghamshire, were confirmed to be infected by the fungus causing ash dieback, Chalara fraxinea.  By October of that year, it had been confirmed by Food & Environment Research Agency (FERA) scientists to be present in a number of woodland sites within the natural environment.  The story was quickly picked up by the national press http://www.telegraph.co.uk/earth/earthnews/9660538/Ash-dieback-now-beyond-containment.html and other media http://www.bbc.co.uk/news/science-environment-20079657 and articles about the severity of the disease and our inability to control it spread proliferated at  a fantastic rate.  Partly as a result of this, the Tree Health and Plant Biosecurity Expert Taskforce was convened by the Government’s Chief Scientific Advisor in November 2012.  I was invited to be a member of the Taskforce which was an independent, multi-disciplinary group of members of the academic community, https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/200428/tree-taskforce-tor.pdf and very willingly, agreed to serve on it.   Our remit was to “provide advice on the current threats to tree health and plant biosecurity in the UK and make recommendations about how those threats could be mitigated”.   What surprised me and other members of the Task Force was the interest and emotional responses that ash dieback generated among the general public.  After all, a few years earlier another one of our iconic tree species, oak, was under threat by another fungal disease, Phytopthora ramorum, somewhat misleadingly known as Sudden Oak Death, which despite its potential threat to cause landscape level changes comparable with those caused by Dutch Elm Disease (Potter et al., 2011) failed to cause the same  level of media hysteria.  Our best guess for why there was such an outburst of press and media coverage and subsequent public concern about ash dieback, was that the Chalara outbreak was the straw that broke the camel’s back.  People, had perhaps become sensitised to forestry due to what seemed to be a constant stream of stories of threats, both man-made, such as the proposed sell-off of parts of the Forestry Commission’s estate by the UK government in 2010 http://www.telegraph.co.uk/earth/countryside/8082756/Ministers-plan-huge-sell-off-of-Britains-forests.html and natural, such as Sudden Oak Death and other pests and diseases.

For the record, although Chalara  fraxinea is now being treated as a quarantine pest under national emergency measures and is widespread across the  United Kingdom and Northern Ireland, it no longer makes the front pages of our national newspapers.

Ash dieback distribution

http://www.forestry.gov.uk/chalara

We in the Tree Health Taskforce did not just consider ash dieback; we reviewed the whole range of biotic threats, both current and future, and highlighted a number of reasons that we felt had contributed to the problems and made recommendations about how these could be rectified.  In essence, how could we stop yet another ash dieback scenario occurring. Our joint report was published in May 2013 https://www.gov.uk/government/publications/tree-health-and-plant-biosecurity-expert-taskforce-final-report.  One of our major findings was that the UK as a whole lacked, or would shortly lack, enough trained personnel able to recognise and respond to threats to our forests and woodlands from native and alien pests and diseases.  One of the more immediate outcomes of our report was the rapid commissioning of some research to determine just how serious the situation actually was.

The results of this report were published by Defra on February 5 of this year,  TH0115 Strategic Analysis of Capability and Capacity to undertake Tree Health Research and Evidence Activity in the UK.  The report highlighted research and evidence themes identified by key policy stakeholders and forest researchers from the university sector, research institutes and forest industry.

Ten themes were identified – Horizon scanning, Pathways and trade, Pest and pathogen biology and epidemiology, Detection and surveillance, Ecological patterns, Control and Management, Adaptation and resilience in forests and forestry, Governance and contingency planning, Economic evaluation and analysis and finally Public engagement, communication and citizen science.

Three of the themes – Pest and pathogen biology and epidemiology, Control and management and Adaptation and resilience in forests and forestry, were identified as areas where existing research providers lack current capability and/or capacity in one or more types of expertise.

The report also highlighted that there are serious skills shortages in the UK in mycology, plant pathology and entomology, especially in relation to forest health. Even in those disciplines where universities still run undergraduate degree courses, tree specific expertise such as silviculture, the care and cultivation of forest trees, was also noted as being in short supply.

So how did we get into this mess?  Why are we seeing what appears to be an unprecedented assault on the UK by invasive forest pests and diseases (Defra 2013).  Exotic and invasive insects are not a new phenomenon in the UK; the European spruce sawfly, Gilpinia hercyniae was first recorded in 1906, the Douglas fir woolly aphid Gilleteela (Adelges) cooleyi) in 1913, the web spinning larch sawfly Cephalcia lariciphila in 1953, Megastigmus spermotrophus, the Douglas fir seed wasp since at least the late 1940s,  Ips cembrae, the large larch bark beetle, since at least 1955

Ips cembrae

Ips cembrae  http://www.padil.gov.au/pests-and-diseases/Pest/Main/135614

and the great spruce bark beetle, Dendroctonus micans since at least 1973 (Crooke & Bevan, 1957; Bevan 1987).  Apart from Dendroctonus, none of these insects has however, had landscape level effects or for that matter, made the headlines to the same extent that ash dieback did.   Since the beginning of the current century the situation has changed dramatically, the influx of tree pathogens has continued to rise at an almost exponential rate and the number of potentially landscape changing insect pests has also seen an increase e.g. the horse chestnut leaf miner, Cameraria ohridella, first seen in London in 2002  (Straw & Williams,  2013) is now found as far north as Liverpool in the West and North Yorkshire in the East (personal observation); the pine tree lappet moth Dendrolimus pini, established in Scotland since 2004.  The oak processionary moth, Thaumetopoea processionea, has been firmly established in London since at least 2006 and looks set to spread further north and west (Townsend, 2013); it is probably only the bizarre weather we have had the last couple of years that has slowed it down slightly.  The Asian longhorn beetle, Anoplophora glabripennis, caused some concern when an outbreak was found in 2012 in Kent; the eradication of which resulted in the felling of several hundred healthy trees.

Anapolophora

Anopolophora glabripennis  (source USDA)

A related species, the Citrus longhorn beetle A. chinensis, is often intercepted but so far is not known to have established in the UK (Nigel Straw personal communication.)

Given the time that it takes for an exotic insect to reach noticeable population levels, all these insects may have actually established four or five years earlier and it could already be too late to eradicate these pests.  Attempts to eradicate the Oak processionary moth from London have, for example, now ended and been replaced by a policy of containment and eradication is only attempted in the case of new outbreaks outside London (Forestry Commission 2013).  Another species which has often been intercepted since the 1970s, is Ips typographus, a severe pest of spruce.  Other possible invaders include the pine processionary moth Thaumetopoea pityocampa, other Ips species attacking pine and spruce, and of great, and increasing concern, the emerald ash borer, Agrilus planipennis, a native of Asia which is now spreading rapidly outwards from Moscow (Straw et al., 2013).

Agrilus_planipennis_001

Agrilus planipennis  (source Pennsylvania Department of Conservation and Natural Resources – Forestry Archive)

So what may have caused this flood of new forestry pests in the UK?  The most obvious change to forestry practice in the UK which undoubtedly influenced the rise of the exotic conifer pests of the first half of the 20th Century was the large-scale afforestation programmes of many non-native tree species, brought about by the formation of the Forestry Commission in 1919.  This rapid afforestation of sites, many of which had not had trees on them for centuries,  provided new hosts for native pests and pathogens and inadvertently allowed the introduction of non-native insects.  The other major change over the last 50 years or so is in global trade patterns; the world is a much smaller place, goods travel extremely quickly, come from much further afield and in greater volumes.  The ability to transport living plant material has also much improved.  In pre-container and pre-bulk air transport days, goods that were packed with unprocessed or poorly processed timber (pathways exploited by many bark beetles) took many weeks to make the long sea voyages and the insect pests often did not survive to make it to land and a new host plant.  Long sea-voyages also meant that the transport of living plant material and their accidental insect passengers also had less chance of surviving to reach the UK.  Another major change to our trade habits is the “instant tree/garden syndrome” where developers and the general public are no longer willing to wait several years for their trees to grow; rather they plant semi-mature trees, many of which come from outside the UK and which come with very large root-balls.  It is impossible for the Plant Health and Seed Inspectorate (PHSI) service to check the huge volume of soil associated with these roots and many organisms must be entering the UK unbeknownst to the very over-stretched PHSI.

An often overlooked change that I am certain has contributed to the large-scale invasion of tree pests and diseases, is a result of re-organisation of the Forestry Commission.  Prior to 1990, the Forestry Commission had a localised approach to forest management.  Most forest blocks or amalgamations of them had a Chief Forester or Head Forester in charge of them.  He (very rarely she), lived in the near vicinity and much like the old village Bobby, walked his beat regularly.  Changes in forest health were thus much more likely to be spotted early and a forest pathologist or entomologist from either The Northern Research Station (NRS) or Alice Holt called in to make an assessment as to the cause of the problem.  I worked at NRS during the 1980s and early 1990s so have had personal experience of the effectiveness of this system.  By 1990, the Forestry Commission had amalgamated many forests and the number of District Offices was much reduced with a consequent reduction in the number of foresters living in near to individual forest blocks.  Forest health problems were thus much less likely to be noticed at an early stage.

The other major change was the decision to shift research to amenity forestry and away from commercial production forestry leading to a reduction in the number of entomologists and pathologists employed by the Forestry Commission as budgets were redirected.  There are now no longer enough key personnel in these disciplines to cope adequately with current problems, let alone those likely to arise.  At the same time within the university sector, the way in which government-funded universities was changed  to a system based on the outcome of the notorious publication metric based Research Assessment Exercise.  This disadvantaged academics specialising in niche applied disciplines such as entomology and plant pathology whose research output rarely, if ever, made it into the hallowed pages of Nature and Science.  Recruitment of staff in these areas in the research intensive universities was severely curtailed and retirees replaced by molecular biologists or vertebrate ecologists publishing in so-called ‘high-impact’ journals (Leather, 2009).  Universities have also replaced many specialist niche degrees with more broadly based subjects perceived to be more attractive to students.  As a result, teaching in these areas has also suffered and very few biology undergraduates in the UK today have any experience with whole organismal biology or the field and taxonomic skills needed be able to recognise forest health problems outside in the real world (Leather & Quicke, 2010).  The situation is now very critical, with, as far as I know only two forest entomologists (if you count me) and one forest pathologist teaching in UK universities today.  This is not a healthy situation for the country and we in the Tree health and Plant Biosecurity Expert Taskforce highlighted the need to address key skills shortages in this area as an urgent priority (Defra, 2013).

Worryingly, the problems do not just lie with exotic and invasive pests.  There are a number of long-established native pest species that still need research into their control and management.  The large pine weevil Hylobius abietis, which in the words of the

hylobius2

Hylobius abietis adults

first Forestry Commission entomologist J W Munro writing just ten years after the formation of the Forestry Commission stated “The pine weevil (Hylobius abietis) problem still occupies the attention of the Forestry Commissioners” (Munro, 1929).  The same statement is still as pertinent today although control measures for this insect have evolved greatly from the early use of DDT and organophosphates to more sophisticated, but possibly no more effective, biological control options (Torr et al., 2007).  The pine beauty moth, once a harmless indigenous moth species, rose to become a notorious pest of the introduced Lodgepole pine during the 1970s and still continues to pose a threat to Scottish plantations today (Hicks et al., 2008).   The often over-looked pine looper moth, Bupalus piniarius, may yet cause problems to our native Scots pine (Straw et al., 2002a). The green spruce aphid, Elatobium abietinum  has never gone away (Straw et al., 2002b) and may, if climate change predictions  are correct, make Sitka spruce a non-viable crop in the UK (Straw et al., 2009).

This is a problem we ignore at our peril.  Action needs to be taken, sooner, rather than later. As conventional chemicals are withdrawn and fewer chemicals approved for use in forestry, the emphasis must inevitably shift to biological control methods using classical natural enemies or biopesticide approaches with entomopathogenic fungi or nematodes or microbially derived pesticides such as Bt which was used against the Oak processionary moth in Berkshire in 2013.  We may even be able to develop even more specific methods such as pheromone disruption combined with improved tree resistance (Leather & Knight, 1997).   We need to improve quarantine measures, develop better detection methods and urgently provide more funding to enable the employment and maintenance of an expanded Plant Health Inspectorate as recommended by the Tree Health and Plant Biosecurity Expert Taskforce (Defra, 2013) and by TH0115.  The latter report highlighted the widespread concerns about the lack of undergraduate and even more critically, the lack of MSc and PhD opportunities in forestry and tree health in particular.

A key recommendation of the report is that funding needs to be put in place to support postgraduate level teaching and training support. This is to make sure a new generation of people capable of working in the tree health area, assisting a smoother and more efficient transition from broad-based undergraduate biology degrees to PhD level research.

To staff the proposed new inspectorate and to make sure we have a new cohort of well-trained forest health experts, we need to encourage newly qualified undergraduates to take up the existing training opportunities at post-graduate level, such as the MSc courses run in Entomology, Integrated Pest Management and Conservation & Forest Protection at Harper Adams University by offering government bursaries.  We are planning to launch new MSc courses in Plant Pathology, Plant Nematology and Forestry Management from September 2014.  We also offer undergraduate degrees in Countryside and Environmental Management and Wildlife Conservation and Natural Resource Management, both of which have significant woodland and forest-related elements

In addition, we need to persuade UK universities to employ forest entomologists and pathologists in academic posts by increasing the amount of appropriate whole organism research funding in these areas.  The Forestry Commission’s Forest Research arm also needs to be able to expand its staff in entomology and pathology to enable it to cope with existing and future threats to our forest estate.  Without such capacity building the future of forestry in the UK is uncertain to say the least.

Post Script

At the risk of seeming to blow our own trumpet still louder, another recommendation from the recent Defra report is that a virtual Centre for Tree Health Science should be created. This would be created by linking together those organisations currently active in the field and with appropriate training provision available.  A number of recent key appointments and the newly launched multidisciplinary Centre for Integrated Pest Management (CIPM) mean that we at Harper Adams University are also in an excellent position to undertake research in this area.  We are, as I write, involved in projects on Oak Processionary Moth and Acute Oak Decline.

References

Bevan, D (1987) Forest Insects.  Forestry Commission Handbook 1, HMSO, London.

Crooke, M & Bevan, D (1957) Notes on the first occurrence of Ips cembrae (Heer) (Col., Scolytidae). Forestry 30, 21-28

Defra (2013) Tree Health and plant Biosecurity Expert Taskforce Final Report.  https://www.gov.uk/government/publications/tree-health-and-plant-biosecurity-expert-taskforce-final-report

Forestry Commission (2013) The Oak Processionary Moth http://www.forestry.gov.uk/opm#description accessed 23 October 2013

Hicks, BJ, Leather, SR & Watt, AD (2008) Changing dynamics of the pine beauty moth (Panolis flammea) in Britain: the loss of enemy free space? Agricultural and Forest Entomology, 10, 263-271.

Leather, S.R. (2009) Institutional vertebratism threatens UK food security. Trends in Ecology & Evolution, 24, 413-414.

Leather, SR & Knight, JD (1997) Pines, pheromones and parasites:a modelling approach to the integrated control of the pine beauty moth. Scottish Forestry 51, 76-83.

Leather, S.R. & Quicke, D.L.J. (2010) Do shifting baselines in natural history knowledge threaten the environment? Environmentalist, 30, 1-2.

Munro, JW (1929) The biology and control of Hylobius abietis L. Part 2. Forestry 3, 61-65.

Potter, C., Harwood, T., Knight, J.D. & Tomlinson, I. (2011) Learning from history, predicting the future: the UK Dutch elm disease outbreak in relation to contemporary tree disease threats. Philosophical Transactions of the Royal Society B, 366, 1966-1974. http://rstb.royalsocietypublishing.org/content/366/1573/1966.short

Straw, NA. & Williams, DT (2013) Impact of the leaf miner Cameraria ohridella (Lepidoptera: Gracillariidae) and bleeding canker disease on horse-chestnut direct effects and interaction. Agricultural and Forest Entomology 15, 321-333.

Straw, NA, Armour, H & Day, KR (2002a) The financial costs of defoliation of Scots pine (Pinus sylvestris) by pine looper moth (Bupalus piniaria). Forestry, 75, 525-536.

Straw, N.A., Timms, J.E.L., & Leather, S.R. (2009) Variation in the abundance of invertebrate predators of the green spruce aphid Elatobium abietinum (Walker) (Homoptera: Aphididae) along an altitudinal transect. Forest Ecology & Management, 258, 1-10.

Straw, NA., Fielding, NJ, Green, G & Price, J (2002b) The impact of green spruce aphid, Elatobium abietinum (Walker), on the growth of young Sitka spruce in Hafren Forest, Wales: delayed effects on needle size limit wood production. Forest Ecology and Management  157, 267-283.

Straw NA, Williams, DT, Kulinich O & Gninenko, YI (2013) Distibution, impact and rate of spread of emerald ash borer Agrilus planipennis (Coleoptera: Buprestidae) in the Moscow region of Russia.  Forestry 86, 515-522

Torr, P, Heritage, S, & Wilson, MJ (2007) Steinernema kraussei, an indigenous nematode found in coniferous forests: efficacy and field persistence against Hylobius abietis. Agricultural and Forest Entomology 9, 181-188.

Townsend, M (2013) Oak processionary moth in the United Kingdom. Outlooks on Pest Management 24, 32-38.

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