Tag Archives: phenology

Data I’m never going to publish – factors affecting sycamore flowering and fruiting patterns

As a teenager I used to have a favourite thinking place, underneath a large beech tree half-way down the school drive.  I used to watch the activities of my school mates, while contemplatively chewing beech nuts (my school friends found this mildly disgusting).

Some years beech nuts were much easier to find than others; although I didn’t realise it at the time, this was my introduction to the phenomenon of masting.  At this point I had better fill you in on the basics of tree reproduction. Like most plants, trees reproduce by producing flowers that are pollinated, depending on the species, by vertebrates, insects or the wind. The fertilised flowers then produce seeds that are housed in what we term fruit or cones, and which in many cases aid their dispersal. Reproduction is energetically a costly process, reserves channelled to reproduction cannot be use for growth and defence.  Trees have evolved three different approaches to this problem. Some trees produce a moderate number of seeds in most years, others have an Irregular fruiting pattern and some, such as beech and oak, have strongly periodic fruiting patterns, “mast” years.  Interestingly (my wife hates me starting sentences off like this), trees that mast are wind pollinated.

Beech (Fagus sylvatica) mast production over a sixteen year period in England. Data from Hilton & Packham (1997

You might wonder why, if reproduction is costly, that some trees are ‘willing’ to expend so much energy in one go.  There are two schools of thought regarding this. One, which I find fairly convincing, is the “predator satiation” hypothesis (Janzen, 1971).  This basically says that the trees, by having on and off years, starve their specialist seed predators in the off years, thus reducing predator pressure by killing lots of them off. In the mast years, there are enough seeds to feed the surviving predators and produce another crop of trees.  A more recent, and less exciting suggestion (to me anyway), is that if the trees have a mass synchronised flowering effort, i.e. a mast year, then the chances of being pollinated are greatly increased (Moreira et al., 2014).

People tend to associate masting with trees that produce heavy fruit, acorns, hazel nuts and beech nuts for example, and I was no exception, so it wasn’t until a couple of years (1995) after I started my mega-sycamore study at Silwood Park that I had a bit of a revelation. I realised that not all of the trees flowered and that there seemed to be a lot fewer seeds that year than I remembered there being the year before. Sycamore seeds come equipped with two little wings (they are wing dispersed) and occur in little bunches (infructescences) so are quite noticeable.

Winged sycamore seed and ‘bunch’ of sycamore fruit

My sycamore study was one of my many side projects set up to satisfy my’ satiable curiosity’ and I had, at the time thought that I had made sure I was measuring everything that could possibly interact with the aphids feeding on the trees. I had, however, somehow overlooked sycamore flower production 🙂 I had taken into account that in some years the sycamore aphid can be present in huge numbers and and I was well aware from the work of my PhD supervisor

Sycamore aphids emerging in spring – some years you can see even more on the newly flushing buds

Tony Dixon, that the aphids can cause substantial losses to tree growth (Dixon, 1971), so had included tree girth and height measurements into my massive data collection list. Strangely, however, despite knowing from my work with

The effect of the sycamore aphid, Drepanosiphum platanoidis, on leaf area of two sycamore, Acer pseudoplatanus, trees over an eight year period (Dixon 1971).

the bird cherry-oat aphid Rhopalosiphum padi, that even quite low numbers of aphids could have substantial negative effects on cherry production (Leather, 1988), I had totally overlooked sycamore flowering and seed production. I am just thankful, that I only missed three years of flowering data 🙂

The effects of bird cherry aphid infestation on reproductive success of the bird cherry, Prunus padus (Leather, 1988)

Unlike the rest of my sycamore data set, the flowering data collection was actually set up to test a hypothesis; i.e. that aphid numbers affected flowering and seed set. Sycamore is in some ways similar to the well-known masting species such as oak and beech in that it is (jargon coming up) heterodichogamous. All flowers are functionally unisexual and appear sequentially on a single inflorescence. The inflorescences can however be either protandrous, i.e. male anthesis takes place before the stigmas become receptive, or protogynous where the reverse sequence takes place. Where it differs from the typical masting species is that is produces wind dispersed seeds and is wind and insect pollinated; oak, beech and hazel are entirely wind pollinated.  Pierre Binggelli, then based at the Unibersity of Ulster, hypothesised that protandrous trees may suffer less herbivore damage than protogynous trees (Binggeli, 1992). He suggested that protogynous trees, having less energy available to invest in defensive chemistry, are more attractive to insect herbivores, particularly chewers. On the other hand, sycamore trees that have been subject to previous insect infestation have fewer resources available to produce female flowers, become protandrous and avoid infestation by herbivores the following year. Presumably the next year, having escaped insect attack by being protandrous they should become protogynous again. So, if I wanted to test this hypothesis, I needed to learn how to sex sycamore flowers. Despite a handy guide that I came across (Binggeli, 1990), ) I found it almost impossible, to do, so

A. Protogynous inflorescence (female II flowers of Mode G are male II in Mode B). B. Protogynous infructescence, Mode B. C. Protogynous infructescence, Mode G. D. Protandrous inflorescence.
E. Protandrous infructescence. F. Vegetative shoot, G. Flowering shoot (Mode E).
H. Fruiting shoot (Flowering Modes B,C,D & G). (From Binggeli, 1990)

contacted Pierre, who very kindly agreed to check some of my ‘guesses’ for me.  Despite this help, I still found it very difficult so opted (very unwisely as it turned out) to collect fruit samples from each tree, put them in paper bags, and bring them back to the lab for sexing at a later date.  As you have probably guessed, I ended up with lots of paper bags which I then, not very cleverly, stored in plastic bin bags.  This went on for several years as I kept putting off the day when I would have to sit down and sex several thousand bunches of sycamore fruit. Then came the happy disastrous day when I came back from holiday to find out that the cleaners had disposed of my bin bags. To tell the truth I was not that upset as it gave me an excuse to stop collecting the fruit samples and reduced my feelings of guilt about having huge piles of unsexed sycamore fruit bunches cluttering up the lab 🙂 I did, of course, carry on counting the number of flowers on the trees, which was much easier data to collect and analyse.

I reluctantly ended my study in 2012 when I left Silwood Park for pastures new, but despite this I still haven’t analysed all my sycamore data, although I was very happy a couple of years ago when a PhD student from the University of Sheffield (Vicki Senior) volunteered to analyse some of my sycamore aphid data which was published last year (Senior et al., 2020). The winter moth data and orange ladybird data are also being analysed by a couple of my former students and hopefully will also be published by next year.

So what does the sycamore fruiting data show? Well, first, despite sycamore being reproductively somewhat atypical of other masting trees species, I would contend that my 17-year data set of sycamore fruit production looks remarkably similar to the Hilton and Packham beech masting data set. I am thus confident in stating that sycamore is a masting species.

Mean sycamore fruit production at Silwood Park, averaged from 52 trees 1996-2012,

Am I able to link sycamore seed production with aphid abundance, is the fruiting pattern a result of herbivory?  I can’t test Pierre Binggeli’s hypothesis about sex changing trees, because I lost the data, but I can try and see if aphid infestation affects fruit production. The two most common aphid species on the Silwood Park sycamore trees are the sycamore aphid Drepanosphum platanoidis and the maple aphid, Periphyllus acericola.  

Mean sycamore aphid and mean maple aphid loads (average annual counts per 40 leaves from all trees) 1996-2012.

They can both occur in high numbers, but in general, the average numbers of P. acericola are much higher than D. platanoidis. The reason why P. acericola has much higher numbers is a result of its over-summering strategy.

Over-summering morphs of the sycamore and maple aphid. Images from https://influentialpoints.com/Gallery/Drepanosiphum_platanoidis_common_sycamore_aphids.htmhttps://influentialpoints.com/Gallery/Periphyllus_acericola_Sycamore_Periphyllus_Aphid.htm#other

While the sycamore aphid spends the summer aestivating (basically a summer version of hibernation in that metabolism is reduced and reproduction ceases), the maple aphid produces a huge number of nymphs, known as dimorphs, which over-summer in dense, immobile aestivating colonies.  The sycamore aphid can escape predators by flying off the leaves if disturbed, the maple aphid dimorphs on the other hand, rely on their huge numbers to ensure survival of some of them over the summer to resume development and reproduce as autumn approaches, a form of predator satiation. They thus suffer a huge reduction in numbers compared with the sycamore aphid. (I must publish that one day). This makes drawing conclusions about the of herbivory (aphid feeding) on the trees a bit difficult.

Mean combined aphid load, showing how the number of dimorphs of the maple aphid skew the perceived aphid load.

Given that Tony Dixon showed that sycamore aphids cause a significant reduction in tree growth (Dixon, 1971), I

Relationship between mean combined aphid load (sycamore and maple aphid) and mean sycamore fruit production.

expected to see a negative relationship between aphid numbers and fruit production. What I did find was that there was a significant positive relationship between sycamore aphid numbers and fruit production, i.e. the more sycamore aphids, the more fruit produced, whereas with the maple aphid it was the other way round, more maple aphids, fewer fruit. If I combined the aphid loads, then the relationship becomes significantly positive, the more aphids you get the

Relationship between mean combined aphid load and the number of sycamore fruit produced the following year.

significantly negative relationship between aphid numbers and sycamore fruit production, but as I pointed out earlier this is driven by the preponderance of maple aphid dimorphs in the summer. You might also argue, that rather than looking at aphid numbers and sycamore fruit production in the same year, I should be comparing aphid numbers with fruit production the following year, i.e. a lag effect. I did indeed think of this, and found that there was, for both aphid species, no significant relationship between aphid numbers the previous year and fruit produced the following year. In fact, if I was an undergraduate student I would point out that there was a positive trend between aphid numbers and fruit production 🙂  If I do the same analysis using the combined aphid load, then the relationship becomes significantly positive, the more aphids you get the more sycamore fruit you get the following year which although counter-intuitive fits with the idea that stressed trees tend to produce more offspring (seeds) (Burt & Bell, 1991) and given that we know from Tony Dixon that the sycamore aphid causes a significant reduction in growth (Dixon, 1971) which is an indication of plant stress (Grime, 1979) makes perfect sense. 

Relationship between mean combined aphid load and the number of sycamore fruit produced the following year.

Instead of mean aphid load, perhaps we ought to be thinking about aphid occurrence at crucial times of the year for the tree, for example budburst. If you go back to the top of the page and look at the photograph of the infested buds you can see that there can be a huge number of aphids present at this time of year just when the trees are starting to wake up and put on new growth. Any interference to the uptake of nutrients at this phase of their life cycle could be detrimental to fruit production.  One way to measure this is by looking at the date the first aphids appear on the buds in the expectation that the earlier the aphids start to feed, the bigger their impact on the trees. Sure enough, the earlier the aphids start feeding, the lower the number of fruit produced.

Significant negative relationship between date of first appearance of aphids on the buds and number of fruit produced in spring.

Although all the relationships I have discussed and shown are significant, the amount of variation is explained is pretty low (over 20% but less than 30%). The relationship that explains most of the variation in any one year is the size of the tree, the bigger the tree the more fruit it produces.

Relationship between size of sycamore tree and number of fruit produced (2009).

As a rule of thumb, the bigger a tree the older it is and older trees have more resources and can afford to produce more offspring than younger smaller trees.

In conclusion, what I can say with confidence is that there is significant variability in sycamore fruit production between years and this is, in my opinion, evidence of masting events, and may be linked to the size and timing of aphid load but is moderated by the size and age of the trees. If you have any other suggestions please feel free to add them in the comments.

If anyone is interested in delving into the data in more depth I will be very happy to share the raw data and also the local weather data for the site.

References

Binggeli P. (1990) Detection of protandry and protogyny in sycamore (Acer pseudoplatanus L.) from infructescences. Watsonia,18, 17-20.

Binggeli P. (1992) Patterns of invasion of sycamore (Acer pseudoplatanus L.) in relation to species and ecosystem attributes. D.Phil. Thesis, The University of Ulster.

Burt, A. & Bell, G. (1991) Seed production is associated with a transient escape from parasite damage in American beech.  Oikos, 61,145–148.

Dixon, A.F.G. (1971) The role of aphids in wood formation. 1. The effect of the sycamore aphid, Drepanosiphum platanoides (Schr.) (Aphididae) on the growth of sycamore. Journal of Applied Ecology, 8, 165-179.

Hilton, G.M. & Packham, J.R. (1997) A sixteen-year record of regional and temporal variation in the fruiting of beech (Fagus sylvatica L.) in England (1980-1995). Forestry, 70, 7-16.

Hilton, G.M. & Packam, J.R. (2003) Variation in the masting of common beech (Fagus sylvatica L.) in northern Europe over two centuries (1800-2001). Forestry, 76, 319-328.

Janzen, D. H. (1971) Seed predation by animals. Annual Review of Ecology and Systematics, 2,465–492.

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

Leather, S.R. (2000) Herbivory, phenology, morphology and the expression of sex in trees: who is in the driver’s seat? Oikos, 90, 194-196.

Moreira, X., L. Abdala-Roberts, Y. B. Linhart, and K. A. Mooney. (2014_. Masting promotes individual- and population-level reproduction by increasing pollination efficiency.Ecology, 95, 801–807.

Grime ., J.P. (1979) Primary strategies in plants, Transactions of the Botanical Society of Edinburgh, 43,2, 151-160.

Senior, V.L., Evans, L.C., Leather, S.R., Oliver, T.H. & Evans, K.L. (2020) Phenological responses in a sycamore-aphid-parasitoid system and consequences for aphid population dynamics; A 20 year case study. Global Change Biology, 26, 2814-2828.

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Filed under Aphidology, EntoNotes

Opening and closing windows for herbivorous insects – Ten more papers that shook my world (Feeny, 1970)

For an insect, be it an herbivore, a predator or a parasite,  phenological coincidence is a matter of life or death   As autumn approaches and the days shorten, or depending on your physiology, the nights lengthen, the senescence feeders (White, 2015) come into their own, and aphids look forward to the increased flow of nitrogen in the phloem (Dixon, 1977). The flush feeders have long since passed their peak and readied themselves for winter, waiting as pupae, or hibernating larvae and adults, for the return of spring (Leather et al., 1993). Enough of the lyricism, on with the story. It is all about timing, or more technically, phenology.

As with many great concepts, the idea of a phenological window was based on good solid natural history.  Back in 1970 Paul Feeny, chemist* turned entomologist, published a landmark paper (Feeny, 1970) based on observations he had made during his PhD at the University of Oxford. Whilst wandering round Wytham Woods he had noticed that there were marked seasonal patterns in the number of lepidopteran species feeding on the oak trees, with more than half feeding in the spring (Feeny, 1966).

Most species of oak feeding Lepidoptera are spring feeders (from Feeny 1970).

Feeny wondered what was driving this very marked seasonal feeding pattern. Despite working closely with Varley and Gradwell, both very much in the natural enemy and weather drive insect population cycles camp (Varley, 1963; Varley & Gradwell, 1970), he suggested some alternative explanations, among them leaf toughness, which he measured using a ‘penetrometer’. He

Following in the great entomological tradition of homemade equipment – Feeny’s penetrometer (feeny, 1970).

also measured leaf water content, leaf nitrogen content, sugar and leaf tannins, all of which are characteristics of the host plant, i.e. bottom-up factors.  All his measurements showed that young leaves were much more suitable for winter moth larval growth and survival than the older leaves, in that nitrogen and leaf water content were higher in young leaves than

Mean larval and pupal weights of groups of 25 fourth-instar winter moth larvae reared on young and more mature oak leaves (data from Feeny, 1970).

old leaves, and young leaves were more tender than the older leaves.  He did not, however, consider leaf toughness to be the driving force selecting spring feeding, instead homing in, on what we know term host quality (Awmack & Leather, 2002), high nitrogen and leaf water content, coupled with lower levels of leaf tannins.  Although he did not use the term phenological coincidence in the paper it is clear from this paragraph that this is what he meant  “A high nitrogen content in young growing leaf tissue is, of course, expected and has been shown for many plants (e.g., Long 1961). Its coincidence in oak leaves with the main period of larval feeding is striking and supports the view that nitrogen content may be one of the most important factors governing early feeding”.

Influential though it was, two things struck me about Feeny’s paper, first, although the whole thrust of his argument is that oak plant chemistry is more suitable for lepidopteran larvae in the spring than later in the year, he makes no mention of the variation in timing of bud-burst that is, in oaks and many other trees, very obvious. Second, he appears to have overlooked the seminal paper by Paul Ehrlich and Peter Raven about the coevolution of secondary plant chemistry and host use by butterflies (Ehrlich & Raven 1964), now termed the coevolutionary arms race (Kareiva, 1999).

More recently, people have realised that coevolution of plant defences and herbivore utilisation is not just to do with plant chemistry, but also with the timing of budburst. Local populations of trees and the insects that feed on them ‘try’ to second guess egg hatch and budburst respectively, in the case of the tree to disrupt synchrony of herbivore egg hatch with peak budburst and vice versa in the case of the larvae (e.g. Tikkanen & Julkunen-Tiitto, 2003; Senior et al., 2020). The whole idea of phenological coincidence has now been renamed the phenological match hypothesis (Pearse et al., 2015).

The phenological match hypothesis can be summarised as follows:

  1. Phenological coincidence – folivores and leaves emerge synchronously, thus, those leaves emerging at the population mean will experience the highest herbivore damage.
  2. Folivores emerge first before the population mean of leaf set, so leaves that develop earlier will suffer more damage by folivores than those that emerge later.
  3. Buds break before folivore egg hatch – early-season folivores emerge after the population mean of leaf set, by which time leaf defences are in place and the folivores can’t cope as shown by Feeny (1970).

Diagrammatic representation of the phenological match hypothesis (Pearse et al., 2015).

So now for the shaking my world bit. Despite being an academic grandchild of George Varley (he was my PhD supervisor’s supervisor) so coming from two generations of top-downers, I was, for many years an ardent advocate of the bottom-up school of insect population regulation.  I am now a little less biased against top-down effects, although as someone who works in crop protection and largely with herbivorous insects, I am more likely to look for solutions from the bottom-up :-).  Of course, my ideal solution is to use biological control coupled with plant resistance, thus marrying the two in perfect harmony as all good integrated pest managers aim to do**.

Oddly, even though as a PhD student, I photocopied most of Feeny’s papers, including conference proceedings and book chapters, I failed to cite a single one of them in my thesis.  When you consider that my whole thesis was pretty much based around the idea of phenological coincidence, (although like Feeny I did not use the term), this was a major omission on my part. Instead, influenced by Evelyn Pielou and her concept of seasonality, I invented a new word, seasonability*** to describe the concept (Leather, 1980).

Seasonality has been defined as being synonymous with environmental variability (Pielou, 1975). In much the same way seasonability in aphids can be defined as the pre-programmed responses to predictable environmental changes, in other words, the aphid anticipates the trend in conditions

If you work on aphids, the plant and its growth stage is pretty much everything that matters (Leather & Dixon, 1981) and if you work on an host-alternating aphid, this becomes even more important perhaps being one of, if not the major factor, driving the adoption of the host alternating life-cycle (Dixon, 1971).  My PhD work and most of what I have done since, is firmly based on the timing of events in insect life histories and their host plants,

The opening and closing of the phenological window for tree dwelling aphids (Dixon 1971).

be it programmed phenotypic response to changes in predictable changes in host nutritional quality in aphids (Wellings et al., 1980), to explaining why insects are pests in some environments and not others (Leather et al., 1989; Hicks et al., 2007). Despite the fact that the papers published from my

From my thesis (Leather, 1980) demonstrating a phenological window in wild grass host suitability for the bird cherry aphid when it needs to move from its woody host. Note my pretentious attempt to add yet more jargon to the aphid world – influx, reflux, what was I thinking! That said, note how it fills the gap on the graph above.

thesis were almost entirely based onthe effects of  host plant phenology on the growth and survival of aphids (e.g. Leather & Dixon, 1981, 1982) the word phenology is strikingly absent. I also note with some amusement, that over the years I seem to have been reluctant to use the term in the titles of papers.  Of the 218 papers that the Web of Science tells me I have authored, only five contain the word in their title (Leather, 2000; Bishop et al., 2013; Rowley et al., 2017, 2017; Senior et al., 2020). Of those I am senior author of only one, which leads me to wonder if have an unconscious bias against the word?

References

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

Bishop, T.R., Botham, M.S., Fox, R., Leather, S.R., Chapman, D.S. & Oliver, T.H. (2013) The utility of distribution data in predicting phenology. Methods in Ecology & Evolution, 4, 1024-1032.

Dixon, A.F.G. (1971) The life cycle and host preferences of the bird cherry-oat aphid, Rhopalosiphum padi (L) and its bearing on the theory of host alternation in aphids. Annals of Applied Biology, 68, 135-147.

Dixon, A.F.G. (1977) Aphid Ecology: Life cycles, polymorphism, and population regulation. Annual Review of Ecology & Systematics, 8, 329-353.

Ehrlich, P.R. & Raven, P.H. (1964) Butterflies and plants a study in coevolution. Evolution, 18, 586-608.

Feeny, P. P. 1966. Some effects on oak-feeding insects of seasonal changes in the nature of their food. Oxford D. Phil. thesis. Radcliffe Science Library, Oxford.

Feeny, P. (1970). Seasonal changes in oak leaf tannins and nutrients as a cause of spring feeding by winter moth caterpillars.Ecology, 51, 565–581

Hicks, B.J., Aegerter, J.N., Leather, S.R. & Watt, A.D. (2007) Asynchrony in larval development of the pine beauty moth, Panolis flammea, on an introduced host plant may affect parasitoid efficacy. Arthropod-Plant Interactions, 1, 213-220.

Kareiva, P. (1999) Coevolutionary arms races: Is victory possible? Proceedings of the National Academy of Sciences USA, 96, 8-10.

Leather, S.R. (1980) Aspects of the Ecology of the Bird Cherry-Oat Aphid, Rhopalosiphum padi L.  PhD Thesis University of East Anglia, Norwich.

Leather, S.R. & Dixon, A.F.G. (1981) The effect of cereal growth stage and feeding site on the reproductive activity of the bird cherry aphid Rhopalosiphum padi. Annals of Applied  Biology, 97, 135-141.

Leather, S.R. & Dixon, A.F.G. (1982) Secondary host preferences and reproductive activity of the bird cherry-oat aphid, Rhopalosiphum padi. Annals of Applied Biology, 101, 219-228.

Leather, S.R. (2000) Herbivory, phenology, morphology and the expression of sex in trees: who is in the driver’s seat? Oikos, 90, 194-196.

Leather, S.R. & Dixon, A.F.G. (1982) Secondary host preferences and reproductive activity of the bird cherry-oat aphid, Rhopalosiphum padi. Annals of Applied Biology, 101, 219-228.

Leather, S.R., Walters, K.F.A. & Dixon, A.F.G. (1989) Factors determining the pest status of the bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), in Europe: a study and review. Bulletin of Entomological Research, 79, 345-360.

Pearse, I.S., Funk, K.A., Kraft, T.S. & Koenig, W.D. (2015) Lagged effects of early-season herbivores on valley oak fecundity. Oecologia, 178, 361-368.

Pielou, E.C. (1975) Ecological Diversity, John Wiley & Sons Inc., New York.

Rowley, C., Cherrill, A., Leather, S.R. & Pope, T.W. (2017) Degree-day base phenological forecasting model of saddle gall midge (Halodiplosis marginata) (Diptera: Cecidomyiidae) emergence. Crop Protection, 102, 154-160.

Rowley, C., Cherrill, A., Leather, S.R., Nicholls, C., Ellis, S. & Pope, T. (2016) A review of the biology, ecology and control of saddle gall midge, Haplodiplosis marginata (Diptera: Cecidomyiidae) with a focus on phenological forecasting. Annals of Applied Biology, 169, 167-179.

Senior, V.L., Evans, L.C., Leather, S.R., Oliver, T.H. & Evans, K.L. (2020) Phenological responses in a sycamore-aphid-parasitoid system and consequences for aphid population dynamics; A 20 year case study. Global Change Biology, 26, 2814-2828.

Thompson, J.N. (1988) Coevolution and alternative hypotheses on insect/plant interactions. Ecology, 69, 893-895.

Tikkanen O-P. & Julkunen-Tiitto, R. (2003) Phenological variation as protection against defoliating insects: the case of Quercus robur and Operophtera brumata. Oecologia, 136, 244–251.

Varley, G.C. (1963) The interpretation of change and stability in insect populations. Proceedings of the Royal Society of Entomology Series C, 27, 52-57.

Varley, G.C. & Gradwell, G.R. (1970) Recent advances in insect population dynamics. Annual Review of Entomology, 15, 1-24.

Watt, A.D. & McFarlane, A. (1991) Winter moth on Sitka spruce: synchrony of egg hatch and budburst, and its effect on larval survival. Ecological Entomology, 16, 387-390.

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.

White, T.C.R. (2015) Senescence-feesders: a new trophic subguild of insect herbivore. Journal of Applied Entomology, 139, 11-22.

*Not many people realise that Paul Feeny’s first two degrees were in chemistry.

**unfortunately, the UK research councils don’t agree with me and despite several grant applications have bounced me every time. 😦

***it never caught on 😦

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Filed under Ten Papers That Shook My World

Journals of Irreproducible Research – downgrading reproducibility and fact checking

As far as I am concerned, good science is about communication and reproducibility, or, as Stephen Heard argues, at least being able to believe that it is reproducible.  I would argue a bit more strongly than Stephen, in that I think you should, at the very least, be able to be confident that you could reproduce the experiment without having to contact the author(s) and that you can also easily check the cited literature.   In this context, there are two things that really annoy me about some of the so-called ’high impact’ established print journals and their on-line would be rivals.  First, the way in which the methods and materials section is relegated to the end of the paper, often in smaller font, and in some cases to the supplementary material section  In other journals e.g. Nature, the methods section is also very minimal and I defy anyone to repeat those experiments!  My second bugbear is the habit that some journals have, possibly to reduce space, in making you use numbers to denote references, placing them either in parentheses or superscript in the main text.

Perhaps I am alone in this, but I do like to know whose work is being cited without having to constantly refer to the references section.  What  particularly annoys me, are those journals that not only insist on numbered references but then list them in number order and not in alphabetical order!  I once wrote a review paper for Annual Review of Entomology, which has the numbering system, but subverted it by listing my references alphabetically – the editor never noticed 😉

You may say that what all these journals are doing is merely structuring the paper in the order that people tend to read them which is, I admit, a valid point. To me however, they are saying to the scientific community, perhaps not overtly, but certainly subliminally, that methods and materials are something you don’t really need to bother about, somewhat akin to those things that you store in an attic or basement, just in case you might want them at some time in the future, but probably not often, if at all.

Hidden methods

This sends a strong and erroneous message to authors that despite the methodology being the most important part of how we do our science, as long as they report the general gist of how they did things it is fine.  To referees the subversion of the methods section sends an equally strong signal; you don’t really need to spend a lot of time reading about the methodology as long as the rationale for the work is justified and that the results are significant and well presented.

As someone who works on insect-plant interactions I constantly come across inadequate methods and materials sections both as a referee and as a reader of published work.  The thing that perhaps causes me the most annoyance are descriptions of plant phenology.   Herbivorous insects have a very intimate relationship with their host plants and the growth stage of their host plant or the age of the plant tissue that they are feeding on can have very marked effects on their development, survival and fecundity (Awmack & Leather, 2002).  I so often came across methods descriptions along the lines of “10 day-old cabbage seedling” “ 3 week old pepper plant”,  “2 week-old wheat plant”, that in desperation I wrote an editorial (Leather, 2010) explaining how important it was to use a measure that didn’t depend on the temperature,  photoperiod, nutrient or water status that the plants were grown at i.e. the BCCH scale.  I also compiled a virtual issue of Annals of Applied Biology, with relevant examples drawn from the journal which has a long and distinguished history in publishing such articles.  If you can’t find your host plant in past issues of the Annals you will find that most plants have a published version somewhere, even if only on Wikipedia.  Despite my efforts however, I still often have to remind authors to describe the phenological stage of their host plants accurately and precisely.

Methods and materials, please come back, we need you!

 

References

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

Leather, S. R. (2010). Precise knowledge of plant growth stages enhances applied and pure research. Annals of Applied Biology 157, 159-161.

 

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