Tag Archives: defoliation

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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Ten Papers that Shook My World – Haukioja & Niemelä (1976) – the plant “immune response”

To me this is a landmark paper, both personally and for ecology in general.   I first came across it in the second year of my PhD at the University of East Anglia (1978) and given where it was published, would probably never have seen it if my supervisor, Tony Dixon, hadn’t had a collaborative link with Erkki Haukioja of Turku University (Finland).

That individual plants of the same species are more or less susceptible (constitutive or innate resistance) to pests and diseases has been known for a very long time (e.g. Painter, 1958; Beck, 1965) and has been exploited by plant breeders as part of many pest management programmes.  Despite the stunning footage of the questing bramble in David Attenborough’s classic documentary The Private Life of Plants, plants are often thought of as passive organisms.  The idea that plants might actually respond directly and quickly to insect attack was more in the realms of science fiction than science fact, but this all changed in the 1970s. In 1972 a short paper in Science (Green & Ryan, 1972) suggested that plants might not be as passive as previously thought. Green & Ryan working in the laboratory with the Colorado Potato Beetle, Leptinotarsus decemlineata, showed that when tomato leaves were damaged by beetle feeding the levels of a proteinase inhibitor were raised not just in the wounded leaves but in nearby leaves as well. As proteinase inhibitors were well-known to be part of the plant defence system, they hypothesised that this was a direct response of the plant to repel attack by pests and that it might be a useful tool in developing new pest management approaches. So what does this have to do with two Finnish entomologists?

Erkki Haukioja and his long-term collaborator, Pekka Niemelä were working on an important lepidopteran defoliator of birch, in the far north of Finland, at the Kevo Subarctic Research Station.Kevo

http://www.eu-interact.org/field-sites/finland-4/kevo/

The defoliator that they were working on was the autumnal moth, now Epirrita autumnata, but then Oporinia autumnata.

Epirrita

http://ukmoths.org.uk/show.php?bf=1797

The autumnal moth, as with many tree-feeding Lepidoptera, has a 7-10 year population cycle (Ruohmäki et al., 2000).

Population cycles

Natural enemies are often cited as the causes of these cycles (Turchin et al., 1999) although other factors such as weather (Myers, 1998) or even sunspot activity (Ruohmäki et al., 2000)

Sunspot

have also been suggested. It had also been suggested that the marked population cycles of the larch bud moth, Zeiraphere diniana were caused by changes in the susceptibility of their host trees after defoliation (Benz, 1974). In 1975, Haukioja and his colleague Hakala, attempting to explain the cyclical nature of the E. autumnata population cycles wondered if they were being driven by the insects themselves causing changes in the levels of chemical defence in the trees. To test this Erkki and Pekka did two neat field experiments, remember Green & Ryan’s work was laboratory based and did not test the effects seen on the insects. They first fed Epirrita larvae on foliage from previously defoliated and undefoliated birch trees and found that the pupae that developed from those larvae fed on previously defoliated trees were lighter than those that had fed on previously undefoliated trees (Hauikioja & Niemelä, 1976). At the same time they also did an experiment where they damaged leaves but then rather than feeding the larvae on those leaves, fed them on nearby adjacent undamaged leaves and compared them with larvae feeding on leaves from trees where no damage had occurred. Those larvae feeding on undamaged leaves adjacent to damaged leaves grew significantly more slowly than those feeding on leaves that came from totally undamaged trees (Haukioja & Niemelä, 1977). So pretty convincing evidence that the trees were responding directly to insect damage and altering their chemistry to become more resistant, i.e. an induced defence and not a constitutive one.

Their results had a major impact on the field. The great and the good from around the world found it a fascinating subject area and a plethora of papers investigating the effects of insect feeding on induced defences in birch and willow trees soon followed (e.g. Fowler & Lawton, 1984a; Rhoades, 1985; Hartley & Lawton, 1987) and not forgetting the original researchers (e.g. Haukioja & Hahnimäki, 1984). I, with the aid of colleagues, also added my ‘two pennorth’ (I did say the idea shook my world) by extending the concept to conifers (Leather et al., 1987; Trewhella et al., 1997). The terms rapid induced resistance and delayed induced resistance soon entered the language, the first to describe those changes that occurred within minutes of feeding damage and the second, those that did not take effect until the following year (Haukioja & Hahnmäki, 1984; Ruohmäki et al., 1992) Such was the interest generated by the topic that by 1989 there were enough studies for a major review to be published (Karban & Myers, 1989).

Controversy reared its ugly head early on when Doug Rhoades suggested that not only did plants resist insect attack actively but that they could talk to each other and warn their neighbours that the ‘bad guys’ were in the neighbourhood (Rhoades, 1983, 1985). This sparked a brief but lively debate (e.g. Fowler & Lawton, 1984b, 1985). Ironically it is now taken as axiomatic that plants talk to each other using a range of chemical signals (van Hulten et al., 2006; Heil & Ton, 2008) as well as informing the natural enemies of the pests that a suitable food source is available (e.g. Edwards & Wratten, 1983; Amo et al., 2013; Michereff et al., 2013).

Ton cartoon

A great cartoon from Jurriaan Ton at Sheffield University. https://www.shef.ac.uk/aps/staff-and-students/acadstaff/ton-jurriaan

We now have a greatly increased understanding of the various metabolic pathways that induce these defences against different insect pests (e.g. Smith & Boyko, 2007) and can, by genetically manipulating levels of compounds such as jasmonic and salicyclic acids or even applying them directly to plants affect herbivorous insect communities and their natural enemies thus improving crop protection (e.g. Thaler, 1999; Cao et al., 2014; Mäntyllä, 2014). No wonder this was an idea that shook my world, and yours.

 

Post script

The study of induced plant defences or resistance is now dominated by molecular biologists and current practice is to use the term priming and not induced defence. The increased understanding that this new generation has brought to the field is undeniable but I always feel it is a great shame that they seem to have forgotten those early pioneers in the field.

 

References

Amo, L., Jansen, J.J., Van Dam, N.M., Dicke, M., & Visser, M.E. (2013) Birds exploit herbivore-induced plant volatiles to locate herbivorous prey. Ecology Letters, 16: 1348-1355.

Baldwin, I.T. & Schultz, J.C. (1983) Rapid changes in tree leaf chemistry, induced by damage: evidence for communication between plants. Science, 221, 277-279.

Beck, S.D. (1965) Resistance of plants to insects. Annual Review of Entomology, 10, 207-232.

Benz, G. (1974). Negative Ruckkoppelung durch Raum-und Nahrungskonkurrenz sowie zyklische Veranderung. Zeitschrift für Angewandte Enomologie, 76: 196-228.

Cao, H.H., Wang, S.H., & Liu, T.X. (2014) Jasomante- and salicylate-induced defenses in wheat affect host preference and probing behavior but not performance of the grain aphid, Sitobion avenae. Insect Science, 21, 47-55.

Edwards, P.J. & Wratten, S.D. (1983) Wound induced defences in plants and their consequences for patterns of insect grazing. Oecologia, 59: 88-93.

Fowler, S.V. & Lawton, J.H. (1984a) Foliage preferences of birch herbivores: a field manipulation experiment. Oikos, 42: 239-248.

Fowler, S.V. & Lawton, J.H. (1984b) Trees don’t talk : do they even murmur? Antenna, 8: 69-71.

Fowler, S.V. & Lawton, J.H. (1985) Rapidly induced defences and talking trees: the devils’ advocate position. American Naturalist, 126: 181-195.

Green, T.R. & Ryan, C.A. (1972) Wound induced proteinase inhibitor in plant leaves: a possible defense mechanism against insects. Science: 175: 776-777.

Hartley, S.E. & Lawton, J.H. (1987) Effects of different types of damage on the chemistry of birch foliage and the responses of birch feeding insects. Oecologia, 74: 432-437.

Haukioja, E. & Hakala, T. (1975) Herbivore cycles and periodic outbreaks. Report of the Kevo Subarctic Research Station, 12: 1-9

Haukioja, E. & Hanhimäki, S. (1984) Rapid wound induced resistance in white birch (Betula pubescens) foliage to the geometrid Epirrita autumnata: a comparison of trees and moths within and outside the outbreak range of the moth. Oecologia, 65, 223-228.

Haukioja, E. & Niemelä, P. (1976). Does birch defend itself actively against herbivores? Report of the Kevo Subarctic Research Station 13: 44-47.

Haukioja, E. & Niemelä, P. (1977). Retarded growth of a geometrid larva after mechanical damage to leaves of its host tree. Annales Zoologici Fennici 14: 48-52.

Heil, M. & Ton, J. (2008) Long-distance signalling in plant defence. Trends in Plant Science, 13: 264-272.

Karban, R. & Myers, J.H. (1989) Induced plant responses to herbivory. Annual Review of Ecology & Systematics, 20: 331-348.

Leather, S.R., D., W.A., & Forrest, G.I. (1987) Insect-induced chemical changes in young lodgepole pine (Pinus contorta): the effect of previous defoliation on oviposition, growth and survival of the pine beauty moth, Panolis flammea. Ecological Entomology, 12: 275-281.

Mäntyllä, E., Blande, J.D., & Klemola, T. (2014) Does application of methyl jasmonate to birch mimic herbivory and attract insectivorous birds in nature? Arthropod-Plant Interactions, 8, 143-153.

Michereff, M.F.F., Borges, M., Laumann, R.A., Dinitz, I.R., & Blassioli-Moraes, M.C. (2013) Influence of volatile compounds from herbivore-damaged soybean plants on searching behavior of the egg parasitoid Telonomus podisi. Entomologia experimentalis et applicata, 147: 9-17.

Trewhella, K.E., Leather, S.R., & Day, K.R. (1997) Insect induced resistance in lodgepole pine: effects on two pine feeding insects. Journal of Applied Entomology, 121: 129-136.

Myers, J. H. (1998). Synchrony in outbreaks of forest lepidoptera: a possible example of the Moran effect. Ecology 79: 1111-1117.

Painter, R.H. (1958) Resistance of plants to insects. Annual Review of Entomology, 3: 267-290.

Rhoades, D.F. (1983) Responses of alder and willow to attack by tent caterpillar and webworms: evidence for pheromonal sensitivity of willows. American Chemical Society Symposium Series, 208: 55-68.

Rhoades, D.F. (1985) Offensive-defensive interactions between herbivores and plants: their relevance in herbivore population dynamics and ecological theory. American Naturalist, 125: 205-238.

Ruohomäki, K., Hanhimäki, S., Haukioja, E., Iso-iivari, L., & Neuvonen, S. (1992) Variability in the efficiency of delayed inducible resistanec in mountain birch. Entomologia experimentalis et applicata, 62: 107-116.

Ruohmäki, K., Tanhuanpää, M., Ayres, M.P., Kaitaniemi, P., Tammaru, T. & Haukioja, E. (2000) Causes of cyclicity of Epirrita autumnata (Lepidoptera, Geometridae): grandiose theory and tedious practice. Population Ecology, 42: 211-223

Smith, C.M. & Boyko, E.V. (2007) The molecular basis of plant resistance and defence responses to aphid feeding: current status. Entomologia experimentalis et applicata, 122: 1-16.

Thaler, J. (1999) Induced resistance in agricultural crops: effects of Jasmonic acid on herbivory and yield in tomato plants. Environmental Entomology, 28, 30-37.

Turchin, P., Taylor, A. D. &Reeve, J. D. (1999). Dynamical role of predators in population cycles of a forest insect: an experimental test. Science 285: 1068-1071.

Van Hulten, M., Pelser, M., van Loon, L.C., Pieterse, C.M.J. & Ton, J. (2006) Costs and benefits of priming for defense in Arabidopsis. Proceedings of the National Academy of Sciences USA, 103: 5602-5607.

 

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Silk- not just a spider thing

Mention silk and most people will, I guess, immediately think of spiders and cobwebs.

Pressed a bit further, some may mention silkworms, and some might even know the word sericulture and that the common silkworm feeds on mulberry bushes.   What they may not know, is that the silk worm is the larvae of the moth Bombyx mori and that there are actually four species of lepidopteran larvae commonly used in silk production.  These are pictured below in the lovely illustration from Meyers Konversations-Lexikon; next to the picture are some B. mori larvae.

Silkworm larvae Silkworms

Meyers Konversations-Lexikon, 4th Auflage, Band 14, Seite 826a (4th ed., Vol. 14, p.826a)

Four of the most important domesticated silk moths. Top to bottom: Bombyx mori, Hyalophora cecropia, Antheraea pernyi, Samia cynthia. From Meyers Konversations-Lexikon (1885-1892

Silk production is of course not just a feature of spiders and lepidoptera.  It is a widespread feature of insect life, being used for pupal cases, as a mode of transport (ballooning) as shown by larvae of the gypsy moth and other species of Lepidoptera,

ballooning gypsy moth            ballooning gypsy moth drawing

protective cases as in larval caddis flies or also, by some caddis fly larvae, as fishing equipment.

 caddisfly_larva  Caddis fly net

But in my opinion, the most dramatic use of silk is that seen in a genus of micro-moths, belonging to the Yponomeutidae, the small ermine moths, Yponomeuta.  They and their relatives, are silk-producers extraordinaire.  Collectively, they are known as small ermine moths; so called because of their adult colouration which resembles the ermine worn by nobility and small, because of the existence of several larger moths with ermine in their names.

Yponomeuta_evonymellus

http://commons.wikimedia.org/wiki/File:Yponomeuta_evonymella-02_(xndr).jpg#file

The larvae are less attractive and are the web/silk producers.

Yponomeuta_evonymella_caterpillars

http://commons.wikimedia.org/wiki/File:Yponomeuta.evonymella.caterpillars.jpg

My particular favourite is the bird cherry ermine moth, and not just because the bird cherry is my favourite tree.  (My eldest son’s middle name is bird cherry, albeit in Finnish). The adult moths lay their eggs in August, in clusters of up to 100 or so on young twigs of the bird cherry Prunus padus, cover them with an egg shield and then die (Leather, 1986).  The eggs hatch shortly afterwards and the larvae spend the winter under the egg shield until the following spring.  When the buds begin to burst in spring, the larvae emerge from beneath the shield and begin to feed gregariously on the newly emerging leaves, spinning a web that protects them from natural enemies  and may also help in thermoregulation and as a trail indicator (Kalkowski, 1958)  http://edepot.wur.nl/201846 .  It is possible to have great fun by selecting a lead larvae to act as a trail blazer and watch the rest of the colony follow them to a destination you have chosen.

Every three to four years or so, populations of the moths get so high that they exhaust their food supplies, defoliating entire trees and covering  them with a tough coating of silky white webbing (Leather, 1986; Leather & Mackenzie, 1994).  In fact, in Finland, I once saw three neighbouring trees totally enveloped in a silken tent caused by the bird cherry ermine moth, Yponomeuta evonymellus, that you could enter and shelter inside from the rain.  Once they really get going as spring progresses, the landscape, particularly if in an area where bird cherry is common, begins to take on a somewhat wintry look, which for May is a little odd.  Those of who you, who have travelled north of Perth in Scotland, on the A9, will be familiar with this phenomenon.  It frequently makes the Scottish newspapers and generates headlines such as “winter wonderland” or “ghostly landscape”. As they run out of trees, the larvae begin to migrate in a desperate search for trees with leaves still on them, and by now, have become less fussy about what they eat.  It is at this wandering stage of their life that the true extent

Yponomeuta webbing  bird cherry emrine moth webbing

of their singlemindedness (I have seen a trail of thousands of larvae marching along a railway line; they didn’t survive the passing of the 0850 from Helsinki) and their ability to produce silk becomes startlingly apparent.

Ermine moths on car    Ermine_moth_larva_on_a_Swedish_army_bike

http://commons.wikimedia.org/wiki/File:Ermine_moth_larva_on_a_Swedish_army_bike.jpg

Truly, silk is not just a spider thing.

Kalkowski, W. (1958). Investigations on territorial orientation during ontogenic development in Hyponomeuta. Folia Biol Krakow 6: 79-102.

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. (1986). Insects on bird cherry I The bird cherry ermine moth, Yponomeuta evonymellus(L.). Entomologist’s Gazette 37: 209-213.

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