Tag Archives: mortality

Data I am never going to publish in peer-reviewed journals

I have got to that stage in my career where retirement is no longer a distant speck on the horizon; something that 20 years ago I never even thought about, but which now I am actually looking forward to reaching. Don’t get me wrong, I have, in the main, enjoyed what I have been paid to do for the last 40 years, but I’m looking forward to a change of pace and a change of priorities. I’m not planning on leaving entomology and ecology, or putting my collecting equipment in a cupboard, throwing my field guides away and burning all my reprints in a huge bonfire. Nor do I plan on deleting my EndNote™ files and database when I retire to our house in Languedoc-Roussillon to sit next to the pool with a never-emptying glass of red wine and gently pickle myself in the sun*. I’m just looking forward to approaching it in a different way; my plan is to stop initiating the writing scientific papers, but instead to expand on the outreach, to blog more and to write books for a wider audience. I want to spread the joys and wonders of entomology to the world, and hopefully, supplement my pension a bit to make sure that I can keep that glass filled with red wine and heat the swimming pool in the winter 🙂

I’m planning a gradual retirement, a slow(ish) canter towards the day (September 30th 2020) when I finally vacate my university office and move full-time into my converted attic in the Villa Lucie surrounded by my books and filing cabinets with a superb view of the mountains.

View

The view from my study to be – I will have to stand up to see it, but exercise is good for you 🙂

I have already reached a number of milestones, I took on my last ever PhD student (as Director of Studies) this month (June 7th) and submitted my final grant application as a PI (June 10th).

Grant

I must admit that it is a bit of funny feeling, but a remarkably rewarding one in many ways. I look at my former colleagues who have already retired productively and enjoyably, and I’m envious, so I know that I am making the right decision despite the slight feeling of apprehension. I now have a dilemma. As Jeff Ollerton points out, when you have been around a while, in my case it is almost 40 years since I started my PhD**, you build up a substantial amount of data, especially, if as I have, you have supervised over 150 undergraduate research projects, an equal number of MSc research projects and over 50 PhD students. Much of these data are fragmentary, not significant or even lost (sadly when I moved from Imperial College, they threw away the hard copies of my undergraduate projects, although I can remember what some of the lost data were about). My ten year sycamore and bird cherry aphid field study from my time in Scotland (1982-1992) remains largely unpublished and my huge twenty year sycamore herbivores data set from Silwood Park (1992-2012) is in the same boat, although parts of the data are ‘out on loan’ to former students of mine and I hope will be analysed and published before I retire.

This leaves however, the data, some of it substantial, which I would like to see the light of day, e.g. a whole set of rabbit behaviour data that I collected one summer with the help of an undergraduate and MSc student, which surprisingly revealed novel insights. Other data, perhaps not as novel, may be of interest to some people and there is a whole bunch of negative and non-significant data, which as Terry McGlynn highlights over on Small Pond Science, does not necessarily mean that it is of no use.   I have, as an example of fragmentary, not entirely earth-shattering data, the following to offer. Whilst monitoring aphid egg populations on bird cherry and sycamore trees, in Scotland between 1982 and 1992, I occasionally sampled overwintering eggs of Euceraphis betulae, on some nearby birch (Betula pendula) trees and of Tuberculoides annulatus, on an oak tree (Quercus robur) in my back garden in Peebles.

As far as I know there are no published data on the overwintering egg mortality of these two aphids. Although novel for these two aphid species, the observation of the way the egg populations behave over the winter and the factors causing the mortality have already been described by me for another aphid species (Leather, 1980, 1981). I am therefore unlikely to get them published in any mainstream journal, although I am sure that one of the many predatory journals out here would leap at the chance to take my money and publish the data in the Journal of Non-Peer-Reviewed Entomology 🙂 I could of course publish the data in one of the many ‘amateur’ type, but nevertheless peer-reviewed journals, such as Entomologist’s Monthly Magazine, The Entomologist’s Record, The Entomologist’s Gazette or the British Journal of Entomology & Natural History, which all have long and distinguished histories, three of which I have published in at least once (Leather & Brotherton 1987, Leather, 1989, 2015), but which have the disadvantage of not being published with on-line versions except for those few issues that have been scanned into that great resource, The Biodiversity Heritage Library, so would remain largely inaccessible for future reference.

I thus offer to the world these data collected from four Betula pendula trees in Roslin Glen Nature Reserve in Scotland between 1982 and 1986. On each sampling occasion, beginning at the end of October, 200 buds were haphazardly selected and the number of eggs present in the bud axils recorded. Sampling continued until egg hatch began in the spring.

Graph

Figure 1. Mean number of eggs per 100 buds of the aphid Euceraphis betulae present on four Betula pendula trees at Roslin Glen Nature Reserve Scotland***.

The number of eggs laid on the trees varied significantly between years (F = 20.3, d.f. = 4/15, P <0.001) ranging from 12.75 eggs/100 buds in 1983-84 to 683 eggs/100 buds in 1986-87. Mortality occurred at a regular rate over the winter and ranged from between 60% in 1985-86 to 83 % in 1984-85, averaging out at 74% over the five-year study.

So in conclusion, no startling new insights, but just some additional data about aphid egg mortality to add to the somewhat sparse records to date (Leather, 1992). Perhaps it is time for me to write another review 🙂

References

Leather, S.R. (1980) Egg survival in the bird cherry-oat aphid, Rhopalosiphum padi. Entomologia experimentalis et applicata, 27, 96-97.

Leather, S.R. (1981) Factors affecting egg survival in the bird cherry-oat aphid, Rhopalosiphum padi. Entomologia experimentalis et applicata, 30, 197-199.

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

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

Leather, S.R. (1992) Aspects of aphid overwintering (Homoptera: Aphidinea: Aphididae). Entomologia Generalis, 17, 101-113.

Leather, S.R. (2015) An entomological classic – the Pooter or insect aspirator. British Journal of Entomology & Natural History, 28, 52-54.

 

*although in light of the recent horrific BREXIT vote this may now not be as simple as it might have been 😦

**I must confess that I haven’t actually published all the data that I collected during my PhD. I rather suspect that this will never see the light of day 🙂

***Data from 1986-87 are not shown as their inclusion makes it very difficult to see the low years. I can assure you however, that the mortality rate shows the same patterns as the other years.

 

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Ten papers that shook my world – Way & Banks (1964) – counting aphid eggs to protect crops

The previous papers in this series (Southwood, 1961; Haukioja & Niemelä 1976; Owen & Weigert, 1976), were all ones that had an influence on my post-PhD career. This one in contrast, had a direct effect on my PhD as well as on my subsequent career, and was, I guess, greatly influential in the publication of the first book to deal with the ecology of insect overwintering (Leather, Walters & Bale, 1993). In 1964 Mike Way, one of the early proponents of Integrated Pest Management (in fact considered to be the father of UK IPM), was working on control methods for the black bean aphid, Aphis fabae.

Bean aphids

Mike had recently joined Imperial College from Rothamsted Research Station where he had been leading research on ways to reduce pesticide use by farmers and growers.   During his time at Rothamsted he had worked closely with a colleague, C.J. Banks on the black bean aphid including studies on the overwintering eggs. As they said in the introduction to their paper, published four years after their experiments; “During the British winter A. fabae survives almost exclusively in the egg stage. Egg mortality might therefore be important in affecting size of populations of this species and in predicting outbreaks”. They investigated the effects of temperature and predators on the mortality of the eggs on the primary host, spindle, Euonymus europaeus, and concluded that the levels of mortality seen would not affect the success of the aphids the following spring. By 1968 (Way & Banks, 1968) they had followed up on the idea and began to feel confident that aphid populations on field beans could be predicted from the number of eggs on the winter host; spindle bushes. The publication of this paper stimulated the setting up of a long-term collaborative project monitoring Aphis fabae eggs on spindle bushes at over 300 locations throughout England south of the River Humber, and monitoring aphid numbers in about 100 bean fields per year.   In 1977 the results were finally published (Way et al., 1977) and the highly successful black bean aphid forecasting system was born. This was further refined by using the Rothamsted aphid suction trap data (Way et al., 1981).

This was also the year that I began my PhD at the University of East Anglia, working on the bird cherry-oat aphid, Rhopalosiphum padi. In the course of my preparatory reading I came across Way & Banks (1964) just in time to set up a plot of bird cherry saplings which I monitored for the next three winters, the first winter’s work resulting in my first publication (Leather, 1980). I subsequently went on to develop the bird cherry aphid forecasting system still used in Finland today (Leather & Lehti, 1981; Leather, 1983; Kurppa, 1989).

Finnish aphid forecasts

Sadly, despite the great success of these two systems there has not been a huge take-up of the idea, although the concept has been looked at for predicting pea aphid numbers in Sweden (Bommarco & Ekbom, 1995) and rosy apple aphids in Switzerland (Graf et al., 2006). Nevertheless, for me this paper was hugely influential and resulted in me counting aphid eggs for over 30 years!

References

Bommarco, R. & Ekbom, B. (1995) Phenology and prediction of pea aphid infestations on pas. International Journal of Pest Management, 41, 101-113

Graf, B., Höpli, H.U., Höhn, H. and Samietz, J. (2006) Temperature effects on egg development of the rosy apple aphid and forecasting of egg hatch. Entomologia Experimentalis et applicata, 119, 207-211

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

Kurppa, S. (1989) Predicting outbreaks of Rhopalosiphum padi in Finland. Annales Agriculturae Fenniae 28: 333-348.

Leather, S. R. (1983) Forecasting aphid outbreaks using winter egg counts: an assessment of its feasibility and an example of its application. Zeitschrift fur Angewandte Entomolgie 96: 282-287.

Leather, S. R. & Lehti, J. P. (1981) Abundance and survival of eggs of the bird cherry-oat aphid, Rhopalosiphum padi in southern Finland. Annales entomologici Fennici 47;: 125-130.

Leather, S.R., Bale, J.S., & Walters, K.F.A. (1993) The Ecology of Insect Overwintering, First edn. Cambridge University Press, Cambridge.

Owen, D.F. & Wiegert, R.G. (1976) Do consumers maximise plant fitness? Oikos, 27, 488-492.

Southwood, T.R.E. (1961) The number of species of insect associated with various trees. Journal of Animal Ecology, 30, 1-8.

Way, M.J. & Banks, C.J. (1964) Natural mortality of eggs of the black bean aphid Aphis fabae on the spindle tree, Euonymus europaeus L. Annals of Applied Biology, 54, 255-267.

Way, M. J. & Banks, C. J. (1968). Population studies on the active stages of the black bean aphid, Aphis fabae Scop., on its winter Euonymus europaeus L. Annals of Applied Biology 62, 177-197.

Way, M. J., Cammel, M. E., Taylor, L. R. &Woiwod, I., P. (1981). The use of egg counts and suction trap samples to forecast the infestation of spring sown field beansVicia faba by the black bean aphid, Aphis fabae. Annals of Applied Biology 98: 21-34.

Way, M.J., Cammell, M.E., Alford, D.V., Gould, H.J., Graham, C.W., & Lane, A. (1977) Use of forecasting in chemical control of black bean aphid, Aphis fabae Scop., on spring-sown field beans, Vicia faba L. Plant Pathology, 26, 1-7.

 

Post script

Michael Way died in 2011 and is greatly missed by all those who knew him well. He examined my PhD thesis, and to my delight and relief, was very complimentary about it and passed it without the need for corrections. I was greatly honoured that a decade or so later I became one of his colleagues and worked alongside him at Silwood Park. He was a very modest and self-deprecating man and never had a bad word to say about anyone. He had a remarkable career, his first paper published in 1948 dealing the effect of DDT on bees (Way & Synge, 1948) and his last paper published in 2011 dealing with ants and biological control (Seguni et al., 2011), a remarkable 63 year span. His obituary can be found here http://www.telegraph.co.uk/news/obituaries/science-obituaries/8427667/Michael-Way.html

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Filed under Aphidology, Aphids, Ten Papers That Shook My World

A Winter’s Tale – aphid overwintering

Aphids that live in temperate or boreal regions have to be able to survive overwinter. Aphids, depending on species, are able to pass winter in two ways. If they are holocyclic i.e. possess an egg-laying stage, they usually overwinter as eggs. Aphid eggs are extremely cold-hardy; they have been reported to have super-cooling points of about -42oC (Somme ). If laid on a woody host, eggs are usually laid in the bud axils as in the case of the apple aphid, Aphis pomi, the black bean aphid Aphis fabae and the bird cherry aphid, Rhopaloishum padi.

aphid eggs

In some instances, such as the sycamore aphid, Drepanosiphum platanoidis, eggs are laid directly on the tree bark or in crevices in the bark or even in lichen growing on the bark.  See if you can spot the eggs in the picture below.

ovipsyc

If however, the aphid in question lives on an herbaceous host, the eggs may be laid directly on the ground, on or amongst fallen leaves or at the base of grass tussock.

The other strategy adopted by those aphids that are anholocyclic, such as the green spruce aphid, Elatobium abietinum, is to pass the winter as an active stage, either as an adult or immature nymph. Those holocyclic aphids that have anholcyclic strains are also able to adopt this strategy. Despite their soft bodies and fragile appearance, aphids have quite low super-cooling points values such as -26oC having been reported (Griffiths & Wratten, 1979).

A potential advantage of using an active overwintering stage and not an egg, is that if they survive the winter, they are able to start reproducing sooner, particularly if they are a host –alternating aphid, where the aphids hatching from eggs, have to spend time developing and reproducing on the primary woody host before being able to migrate to the secondary hosts. This also applies, to a lesser extent, to those holoyclic aphids living on herbaceous plants, although the temporal advantage is not as great. One would assume that given the relative cold-hardiness attributes of aphid eggs and adults that in a country such as the UK where winter temperatures below -10oC are both infrequent and short lasting, winter survival of aphids would be extremely high if not guaranteed. This is not the case. For example, eggs mortality of the bird cherry aphids is typically around 70-80% as shown in my first ever publication (no fancy graphics packages in those days, just Letraset , Indian ink, stencils and tracing paper). Actually people had measured aphid egg mortality much earlier than this (Gillette, 1908) but I was the first person to monitor mortality throughout the winter and show that it occurred at a steady rate irrespective of the severity of the winter.

 Egg survival

It is actually a function of the length of the winter that determines how many eggs survive, the longer the winter the greater the mortality.

Egg mortality

This level of mortality is typical for all aphid species for which I have data (Leather, 1993). Some of this mortality can be attributed to predation, but most of it is intrinsic (Leather, 1981), possibly due to cryo-injury.

Similarly, those aphids that overwinter as adults or nymphs, despite their ability to super-cool to temperatures below -20oC, experience even greater levels of mortality as shown elegantly by Jon Knight and Jeff Bale in 1986 studying overwinter survival of the grain aphid Sitobion avenae near Leeds.

Knight & Bale

In fact one wonders how any aphids at all survive winter this way, but they certainly do if the winters are mild enough, as in the case of Myzus persicae and Sitobion avenae in southern England and E. abietinum throughout most of its range (Day et al., 2010). An interesting anomaly is Iceland where hot springs abound and the bird cherry aphid is able to survive anholocyclically on grasses growing around the springs whereas in other countries with similar winter temperatures it would only be able to survive as the egg stage.

Despite the importance of winter to aphid population dynamics we still know very little about their winter ecology, our knowledge being confined to a handful of economically important species. Despite the discomfort of field work in the winter this is an area which would be very rewarding to anyone in need of an interesting and good research project.  Finger-less mittens are, however, definitely recommended 😉

Useful references

Bale, J. S. (1996). Insect cold hardiness: a matter of life and death. European Journal of Entomology 93, 369-382. http://www.eje.cz/pdfs/eje/1996/03/09.pdf

Day, K. R., Ayres, M. P., Harrington, R. & Kidd, N. A. C. (2010). Interannual dynamics of aerial and arboreal spruce aphid populations. Population Ecology 52, 317-327. http://link.springer.com/article/10.1007/s10144-009-0190-0#page-1

Gillette, C. P. & Taylor, E. P. (1908). A few orchard plant lice. Colorado Agricultural Experimental Station Bulletin, 113, 1-47.

Griffths, E. &Wratten, S. D. (1979). Intra-and inter-specific differences in cereal aphid low temperature tolerance. Entomologia experimentalis et applicata 26, 161-167. http://onlinelibrary.wiley.com/doi/10.1111/j.1570-7458.1979.tb02912.x/abstract

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

Leather, S. R. (1980). Egg survival in the bird cherry-oat aphid, Rhopalosiphum padi. Entomologia experimentalis et applicata 27, 96-97. http://onlinelibrary.wiley.com/doi/10.1111/j.1570-7458.1980.tb02951.x/abstract

Leather, S. R. (1981). Factors affecting egg survival in the bird cherry-oat aphid, Rhopalosiphum padi. Ent omologia experimentalis et applicata 30, 197-199. http://onlinelibrary.wiley.com/doi/10.1111/j.1570-7458.1981.tb03097.x/abstract

Leather, S. R. (1993). Overwintering in six arable aphid pests: a review with particular relevance to pest management. Journal of Applied Entomology 116, 217-233. http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0418.1993.tb01192.x/abstract;jsessionid=9FC2ED8174E96317F192CF42A19092FE.f03t03?deniedAccessCustomisedMessage=&userIsAuthenticated=false

Strathdee, A. T., Howling, G. G. & Bale, J. S. (1995). Cold hardiness of overwintering aphid eggs. Journal of Insect Physiology 41, 653-657. http://www.sciencedirect.com/science/article/pii/002219109500029T

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Filed under Aphidology, Aphids