Tag Archives: aphids

Not just sailor aphids, but an aphid ship too – Insect Class Gunboats

Some of you may have come across Reaktion Books and their Animal series, which as well having the usual vertebrate suspects has a refreshingly large number of invertebrate titles, for example, Moth, Ant, Mosquito just to name those gracing my shelves. I had, at one time, the ambition of adding to the collection with Aphid :-). Unfortunately, one of the requirements for inclusion in the series is what one might call a cultural dimension, and despite being fabulously awesome, aphids have not, as yet, made a huge impact on human culture.  In spite of assiduous searching on my behalf, I have not, as yet*, managed to find many instances of aphids making it into the wider human consciousness beyond their undeserved (in my opinion) reputation as mega-pests.

My count to date is a post card, a children’s book, a postage stamp, a sculpture and two poems. Sadly, I don’t feel I can count coloured plates from entomological texts, no matter how beautiful 😦

Punk aphid postcard – adapted from the cover of an issue of New Scientist published in 1977, when our PhD group at the University of East Anglia had our fifteen minutes of fame 🙂

To my knowledge, the only children’s book (or any work of fiction for that matter), with an aphid as the main character.

The World’s classiest stamp – thank you Slovenia for recognising the importance of aphids 🙂

An artist who appreciates the beauty of aphids – Aphid on rose – Beth Biggs.

Of the two poems that mention aphids, Charles Goodrich’s is, in my opinion, the winner, so I have reproduced it in full. I am much less enamoured of Greenfly from Giles Goodland’s collection celebrating insects, The Masses, so have not shared it with you.

A Lecture on Aphids by Charles Goodrich

She plucks my sleeve.
“Young man,” she says, “you need to spray.
You have aphids on your roses.”

In a dark serge coat and a pill box hat
by god it’s my third grade Sunday school teacher,
shrunken but still stern, the town’s
most successful corporate attorney’s mother.
She doesn’t remember me. I holster
my secateurs, smile publicly,
and reply, “Ma’am,

did you know a female aphid is born
carrying fertile eggs? Come look.
There may be five or six generations
cheek by jowl on this “Peace” bud.
Don’t they remind you
of refugees
crowding the deck of a tramp steamer?
Look through my hand lens-
they’re translucent. You can see their dark innards
like kidneys in aspic.

Yes, ma’am, they are full-time inebriates,
and unashamed of their nakedness.
But isn’t there something wild and uplifting
about their complete indifference to the human prospect?”

And then I do something wicked. “Ma’am,” I say,
“I love aphids!” And I squeeze
a few dozen from the nearest bud
and eat them.

After the old woman scuttles away
I feel ill
and sit down to consider
what comes next. You see,
aphids
aren’t sweet
as I had always imagined.
Even though rose wine is their only food,
aphids
are bitter.


“But what about the ship?” I hear you cry.  To cut a long story short, I was looking for images of Aphis species for a lecture, when up popped a picture of a ship, HMS Aphis. I of course immediately jumped down the internet rabbit hole in pursuit and found to

HMS Aphis https://commons.wikimedia.org/wiki/File:HMS_Aphis_AWM_302297.jpeg

my delight that during the first World War, the Admiralty commissioned a class of ships, the Insect Gunboats, for the Royal Navy designed for use in shallow rivers or inshore. Twelve of these were commissioned between 1915 and 1916. They were, in alphabetical order, not in order of commission, Aphis, Bee, Cicala, Cockchafer, Cricket, Glowworm, Gnat, Ladybird, Mantis, Moth, Scarab, and surprisingly, given the huge number of candidates to choose from, a non-insect, Tarantula.

I haven’t been able to discover why someone decided to call them the Insect class or why they choose the names they did.  Most

HMS Aphis, ship’s badges – very pleased to see the siphunculi, somebody did their research.

of them are not particularly pugnacious species with the possible exceptions of the Bee, Gnat, Ladybird, Mantis and the non-insect Tarantula.

Not sure which species of ladybird this is supposed to represent but felt that as an insect often associated with aphids it deserved a mention 🙂

Lepidoptera, Hymenoptera and Diptera

HMS Glowworm – a shame that this is symbolic rather than the actual insect 😦

Sadly, none of the Insect gunboats have survived, HMS Aphis was scrapped in 1947, in Singapore of all places, and the last one, HMS Cockchafer, was sold for scrap in 1949.

Pleased as I was to discover HMS Aphis, I am still a long way off having enough cultural references to convince Reaktion Books that Aphid is a possible title in the series. The Secret Life of Aphids, is however, a real possibility :-).  Finally, if you were puzzled about the sailor aphids I mention in the title, you can satisfy your curiosity by clicking on this link.

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Spore shedding aphids

If you were in the European silkworm business two or three hundred years ago the last thing you wanted to find in your colony were stiff dead caterpillars. Worse still would be if when you picked them up and bent them, they snapped in half and revealed a solid white or green interior, giving them the appearance of a stick of chalk. Horror stricken you realise that your beloved silkworms have been struck down by white or green muscardine disease, or if you were an Italian, calcino; in both cases the name refers to the chalk like appearance of the inside of the stricken larvae.  By the middle of the 19th century the combined effects of the industrial revolution, the revival of the Japanese silk industry and an epidemic of viral and fungal diseases had pretty much shut down the European silk industry (Federico, 1997). We now know that the muscardine diseases are caused by the entompathogenic fungi Beauveria bassiana and Metarhizium anisipoliae, although this was not realised until the early part of the 19th Century when the Italian naturalist Agostino Bassi discovered their true nature.

So what about the aphids I hear you asking? I have written earlier about the attacks that aphids have to suffer from predators and parasitoids, but that is not all with which they have to contend.  Fungal diseases (Dean &Wilding, 1973; Rabasse et al., 1982; Aqueel & Leather, 2013) also attack aphids in the same way that they attack most other insects.  In the case of aphids, it is not one of the muscardines, instead they are attacked by a number of fungi belonging to the Entomophthoraceae. The first member of this family to be recognised as a fungus was named Empusa musca (now Entomophthora muscae) by Charles de Geer in 1782 (Cohn, 1855). As the name suggests, it attacks house flies. There are, however, a number of different entomopathogenic fungi that specialise in attacking aphids, Erynia neoaphidis, and other members of the Entomophtoraceae, being the most commonly seen (Dean & Wilding,

An aphid unfortunate enough to encounter an insect infecting fungal spore and lacking the appropriate symbionts (Parker et al., 2013) is very likely to suffer a slow and lingering death as the fungal mycelia proliferate within its body.

Aphid infected by Pandora (Erynia) neopahidis https://commons.wikimedia.org/wiki/File:Pandora_neoaphidis.jpg

Pandora neoaphidis infected pea aphids (photo Tom Pope)

On landing on a susceptible aphid, the fungal spore germinates and the germ tube penetrates the aphid, either directly through the cuticle or via a nearby spiracle.  Unlike those other invidious invaders of aphids, the parasitoids, entomopathogenic fungi need very specific environmental conditions to successfully colonise their aphid hosts. The damper the better, and if the aphid is surrounded by liquid water the more likely the fungus is to be able to effect an entry (Wilding, 1969; Dean & Wilding, 1973).  More than a century ago Paul Hayhurst of Harvard University noticed that galls of the Chenopodium aphid, Hayhurstia atriplicis (then known as Aphis atriplicis) that were ruptured and had allowed water in, had a much higher incidence of diseased aphids than the intact galls (Hayhurst, 1909). Another more recent indication of this dependence on damp conditions is a mention of a high incidence of Pandora neoaphidis (described as Empusa aphidis) on Schizolachnus pini-radiatae being associated with higher than average rainfall (Grobler, 1962). 

The earliest experiment involving aphid specific entompathogenic fungi that I have been able to find is from the latter half of the 19th Century (Houghton & Phillips, 1885). 

“I placed some infected aphides under a glass with healthy specimens from my garden-beans and in a short time these became similarly covered with the same red-coloured fungoid growth. The n*****s took the scarlet fever and died.”

Their conclusion was that it was an Entomopthora species, perhaps related to, if not, E. planchoniana.

Although fungal pathogens have been shown to be able to reduce aphid populations in the field (Fluke*, 1925; Grobler et al., 1962; Plantegenest et al., 2001), their effectiveness as biological control agents on their own is variable and unpredictable (Milner, 1997).  Most often, they are used either as biopesticides, or in conjunction with parasitoids and predators (e.g. Milner, 1997; Aqueel & Leather, 2013). One of the problems that entompathogenic fungi have is ‘finding’ their hosts.  While it is known that entompathogenic fungi, as with entomopathogenic viruses, affect the behaviour of many insect that they attack (Hughes et al., 2011), by making them move to locations on their host plant where they are more likely to infect their kin, as far as I know, there is only one record of this for aphids (Harper, 1958).  Surely a productive avenue of research to follow? That said, these clever fungi have another option up their mycelial sleeves.  They are, like other fungi, able to discharge their spores explosively.  Erynia neopahidis can project its spores more than 3mm vertically and more than 5 mm horizontally (Hemmati et al., 2001). This may seem a tiny distance to you and me, but the spores only need to get further than 2 mm to get air borne and move on to other plants or plant parts.  It might be a leap into the unknown but it seems to work out all right for the fungi 🙂

References

Aqueel, M.A. & Leather, S.R. (2013) Virulence of Verticillium lecanii (Z.) against cereal aphids; does timing of infection affect the performance of parasitoids and predators? Pest Management Science, 69, 493-498.

Cohn, F. (1855) Empusa muscae und die Krankeit der Stubenfliegen  Nova acta Academiae

Caesareae Leopoldino-Carolinae Germanicae Naturae Curiosorum, 25, 301-360

Dean, G.J. & Wilding, N. (1973) Infection of cereal aphids by the fungus Entomophthora. Annals of Applied Biology, 74, 133-138.

Federico, G. (1997 ) An Economic History of the Silk Industry, 1830-1930. Cambridge University Press, Cambridge.

Fluke, C.L. (1925) Natural enemies of the pa aphid (Illinoia pisi Kalt.); their abundance and distribution in Wisconsin.  Journal of Economic Entomology, 18, 612-616.

Grobler, J.H., MacLeod, D.M. & Delyzer, A.J. (1962) The fungus Empusa aphidis Hoffman parasitic on the wooly pine needle aphid, Schizolachnus pini-radiatae (Davidson). Canadian Entomologist, 94, 46-49.

Harper, A.M. (1958) Notes on behaviour of Pemphigus betae Doane (Homoptera: Aphididae) Infected with Entomophthora aphidis Hoffm. Canadian Entomologist, 90, 439-440.

Hayhurst, P. (1909) Observations on a gall aphid (Aphis atriplicis L.). Annals of the Entomological Society of America, 2, 88-100.

Hemmati, F., Pell, J.K., McCartney, H.A., Clark, S.J. & Deadman, M.L. (2001) Conidial discharge in the aphid pathogen Erynia neoaphidis. Mycological Research, 105, 715-722.

Hughes, D.P., Andersen, S.B., Hywel-Jones, N.L. , Himaman, W., Billen, J. & Boomsma, J. (2011) Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection. BMC Ecology, 11, 13.

Milner, R.J. (1997) Prospects for biopesticides fro aphid control. Entomophaga, 42, 227-239.

Parker, B.J., Spragg, C.J., Altincicek, B. & Gerardo, N.M. (2013) Symbiont-mediated protection against fungal pathogens in pea aphids: a role for pathogen specificity. Applied & Environmental Microbiology, 79, 2455-2458.

Plantegenest, M., Pierre, J.S., Dedryver, C.A. & Kindlmann, P. (2001) Assessment of the relative impact of different natural enemies on population dynamics of the grain aphid Sitobion avenae in the field. Ecological Entomology, 26, 404-410.

Rabasse, J.M., Dedryver, C.A., Molionari, J. & Lafont, J.P. (1982) Facteurs de limitation des populations d’Aphis fabae dans l’Ouest de la France 4. Nouvelles donnees sur le deroulement des epizooties entomophtoracees sur feverole de printemps. Entomophaga, 27, 39-53.

Roditakis, E., Couzin, J.D., K., B., Franks, N.R. & Charnley, R.K. (2000) Improving secondary pick up of insect fungal pathogen conidia by manipulating host behaviour. Annals of Applied Biology, 137, 329-335.

Wilding, N. (1969) Effect of humidity on the sporulation of Entomophthora aphidis and E. thaxteriana. Transactions of the British Mycological Society, 53, 126-130.

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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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Time of year determines some, but not all, views of my blog posts

I was going to format this post as a spoof Nature communication, but not being as skilled as our students, who turn out excellently formatted mock papers for their assignments, decided not to. I did, however, go for a typical Nature title 🙂

The other day when I was looking at my blog stats I clicked on the view post stats button next to my most read post of the day, Not all aphids are vegans*, and was amused enough by the strong seasonal dynamics shown to post it on Twitter.

Not all aphids are vegans – strong seasonal dynamics

As you can see, the peaks and troughs of views strongly follow the times of year that aphids are present and absent.

As regular readers of my blog will know, I am a bit of an aphidophile. It is kind of hard to miss if I’m honest, but then aphids are fantastic and awesome, so you will get no apologies from me for loving them and writing, or talking about them whenever I get the chance to do so.

That said, not all my posts are about aphids, insects yes, but I do write about other things too, including entomological equipment, classic papers and teaching matters, and sometimes about my holidays 🙂

Given the strong correlation between aphid life cycle timing and visits to the post about biting aphids, I wondered how my other aphid posts stacked up in terms of seasonal viewing.

Aphid life cycles – bizarre, complex or what?

Somewhat surprisingly, well to me at least, the post about aphid life cycles did not show very strong seasonal dynamics, although April, when aphids start to become active, did, at the beginning of the post’s life, show a bit of a peak of interest, but has since broken down completely.  Another season aspect of aphid biology is wing formation. This is usually associated with late spring and early summer (Dixon, 1973, 1976), and in this case, the viewing history fitted appropriately.

Not all aphids have wings – seasonally appropriate

 

What about the other end of the year, autumn and winter?  As expected, my post about aphid overwintering showed the reverse pattern to the other aphid posts, people wanted to read about aphid overwintering as winter appraoched.

A Winter’s Tale – aphid overwintering

Aphid posts, as predicted, show a correlation (OK, not tested) with the time of year associated with the appropriate part of the life cycle.  We would therefore expect that posts that are more general would show no marked seasonality in their popularity. To test this I looked at first, my posts that deal with entomological equipment, pan traps, clip cages and the poster and then at two posts that fit into the teaching category.  Staring with the Pan trap, a very basic and commonly used piece of field equipment, despite a slight expectation on my part that there might be a spring peak (after all, that is when insects start flying) there was no pattern that I could see.

The pan trap – disappointingly no pattern

 

Nest I looked at the Pooter, an essential bit of general entomological kit (Leather, 2015) used by entomologists of all types. Given that this is used in both the laboratory and the field, I didn’t really expect to see any pattern jumping out at me.  I wasn’t disappointed although if you look very quickly, and not too closely, it is just about possible top convince yourself that there is an increase in views during the summer, which would fit with the general increase in insects caught in nets.

The Pooter – perhaps a slight tendency for views to increase in mid-summer

 

Next, back to aphids, this time a piece of kit that is almost, but not entirely, confined to aphidologists (Macgillivray & Anderson, 1957).  My expectation here, was that given that clip cages are almost always used in laboratories or glasshouses, that there would be absolutely no pattern in the viewing figures. Sure enough, that was the outcome.

The clip cage – no discernible patterns

Finally, the two teaching posts, first my tribute to Southwood’s classic species-area paper (Southwood, 1961).  I know that this post is used for undergraduate teaching at one university, so given the regularity of university timetabling, might have a chance of  showing a pattern;  It didn’t.

Southwood (1961) – the number of insect species associated with various trees – no pattern

Finally, a post that has attracted a modicum of attention over the years, all about what to expect in a PhD viva.  My hypothesis for this, given that most PhD projects start at the beginning of the academic year and run for four or five years before submission, was that if there was going to be an annual peak in views that it would be between October and January.  To save you the troubkle of squinting at the graph, there was no pattern.

Are PhD examiners really ogres? – no consistent peak

In conclusion, aphid posts tend to show viewing patterns consistent with the time of year and life cycle stage, other, more general posts show absolutely no pattern.

 

References

Dixon, A.F.G. (1973) Biology of Aphids. Edward Arnold, London.

Dixon, A.F.G. (1976) Reproductive strategies of the alate morphs of the bird cherry-oat aphid Rhopalosiphum padi. Journal of Animal Ecology, 45, 817-830.

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

MacGillivray, M.E. & Anderson, G.B. (1957) Three useful insect cages. Canadian Entomologist, 89, 43-46.

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

 

 

 

 

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On rarity, apparency and the indisputable fact that most aphids are not pests

I am willing to bet that when most entomologists are out for a walk spend most of their time looking at the ground or the vegetation between the ground and head height. Lepidopterists and odonatologists may be the exceptions that prove the rule, but most of us spend a lot of time looking for things lurking in dung, hiding under stones or bark, scurrying around in the undergrowth or making holes in leaves 🙂

Tell-tale signs for an entomologist that something is or has been enjoying a meal

I’m an entomologist, I’m trained to look out for signs of insect infestations; curled leaves as in the above picture tell me that almost certainly an aphid and her offspring have been at work, sticky leaves alert me to the fact that there are aphids above me in the canopy of a tree. Leaves with holes tell me that a beetle or caterpillar has been at work. Leaves spun together with a silk web tell me a similar story. Plants with their stems and leaves stripped right back inform me that sawfly, lepidoptera and beetle larvae have been at work. A fancy spiral of brown or white on a leaf tells me that a leafminer has been, or is at work. In some cases the insect may not be there when I see the damage, the curled leaves caused by an aphid or psyllid infestation remain there until leaf fall, the chances of finding a caterpillar feeding on the very obviously shot-holed leaves of a plant are slim.  Like all sensible herbivores, the culprit will be in hiding closer to the stem, only sporadically popping out to feed.  On the other hand it may have fallen victim to a visually acute predator (bird) that was attracted to the leaf by the tell-tale feeding signs, or been eaten by a predatory insect or  have been parasitized by an ichneumonid wasp.  Plants are a lot less passive than people think. By producing the equivalent of an immune response they cause the insects to move to different feeding sites to make more holes effectively advertising their presence to potential predators.  Simultaneously, the plant sends out chemical signals telling insect predators and parasites that there is a meal or host available.  An herbivore’s lot is not an easy one.

The Covid-19 crisis means that I have been working from home in a hamlet on the Staffordshire/Shropshire border.  To keep myself reasonably sane and moderately physically healthy I have been treating myself to a lunchtime walk along the bridleways, footpaths and public roads within a 5 km radius of my house. As a result I have become much more familiar with the area. One of the things that has been very obvious, apparent even, is that some plants dominate the roadside verges, cow parsley Anthricus sylvestris being one that really stands

Cow parsley – very common and abundant, occurring in huge swathes around Forton and Sutton and in this case and in many other sites along my walks, backed by the equally apparent hawthorn (Crataegusus monogyna) hedge.

out from the crowd at this time of the year. Not only is it very apparent, but it provides a great source of nectar for the spring butterflies such as the Orange Tip and the assorted bumblebees, solitary bees and hoverflies, that despite the anthropogenic pressures put upon them, still manage to make an appearance.  Nettles, as I particularly noticed when having to social distance myself from the sweaty joggers and cyclists taking advantage of the virtually deserted country lanes, also play a prominent role in the roadside plant community. Also very common, but showing a much patchier distribution and occurring in clumps, including in my garden, is the ribwort plantain, Plantago lanceolata, which is yet another so called weed*, that is perfect for pollinators.

Ribwort plantain – common but patchy and clumped – this clump in my garden where it is safe from forks and herbicides.

Although both the cow parsley and plantain were buzzing with pollinators, they were, and still are at time of writing, singularly devoid of herbivores, including my favourite aphids. Conversely, the odd scattered bird cherries (Prunus  padus) and the solitary self-seeded wild cherry (Prunus avium) in my garden are proudly sporting the characteristic leaf rolls caused by the bird cherry aphid, Rhopaloisphum padi and the cherry black fly, Myzus cerasi respectively.

Note that both these trees were not growing near any of their relatives and were surrounded and overtopped by other plant species, so as far as humans are concerned not very apparent.

This got me to wondering why it was, that, the to me, and presumably other humans, the very obvious cow parsley and plantains, were not covered in plant feeding insects, while the less apparent cherries were heavily infested by their respective aphids.  After all, according to Richard Root, large swathes of monocultures are likely to be easily found and colonised by pests. Plant apparency was first defined by the British born, American based ecologist Paul Feeny in the mid-1970s.

“The susceptibility of an individual plant to discovery by its enemies may be influenced not only by its size, growth form and persistence, but also by the relative abundance of its species within the overall community. To denote the interaction of abundance, persistence and other plant characteristics which influence likelihood of discovery, I now prefer to describe “bound to be found” plants by the more convenient term “apparent”, meaning “visible, plainly seen, conspicuous, palpable, obvious” (Shorter Oxford English Dictionary, 3rd, edition; Webster’s Concise English Dictionary). Plants which are “hard to find” by their enemies will be referred to as “unapparent”, the antonym of apparent (O.E.D. and Webster, loco cit.). The vulnerability of an individual plant to discovery by its enemies may then be referred to as its “apparency”, meaning “the quality of being apparent; visibility” (O.E.D. and Webster, loco cit.). Since animals, fungi and pathogens may use means other than vision to locate their host-plants, I shall consider apparency to mean “susceptibility to discovery” by whatever means enemies may employ” Feeny (1976).

So, even though cow parsley is highly visible and apparent to us humans, and their pollinators, because it is an annual and thus ephemeral within the landscape, it is not necessarily apparent to the herbivores that want to feed on it. Conversely, trees, such as bird cherry, although not necessarily apparent to us, are apparent to insect herbivores because they are large and long-lived. How does this affect the way in which plants avoid being found and eaten by insect herbivores?

Peter Price, another British born American based ecologist very neatly summarised Paul’s hypothesis as follows

Long-lived trees which are bound to be found by herbivores, invest heavily in costly chemical defence with broad-spectrum efficacy.   These quantitative defences are expensive but the cost is tolerable for a long-lived plant.  Short-lived plants are less easily detected by herbivores, and their best defence is being hard to find in patchy and ephemeral sites.  Low cost defences are effective against generalist herbviores should plants be found.  Instead of tannins and other digestibility reducers found as defences in long-lived plants, short-lived plants have evolved with mustard oils (glucosinolates) in crucifers, for example, alkaloids in the potato family, furanocoumarins in the carrot family (Price, 2003).

All I can say is that the quantitative defences of the trees don’t seem to be doing as good a job as the less expensive ones of the cow parsley, plantains and nettles.  As an aside, it turns out that although both cow parsley and plantain have a lot of medicinal uses, their chemistry does include some insecticides (Adler et al., 1995; Milovanovic et al., 1996). Cheap and cheerful seems to be the answer for an herbivore-free life in this case 🙂 Earlier I referred to cow parsley and plantains as being common.  What does that mean? According to Wikipedia (where else would I go?),

 “Common species and uncommon species are designations used in ecology to describe the population status of a species. Commonness is closely related to abundance. Abundance refers to the frequency with which a species is found in controlled samples; in contrast, species are defined as common or uncommon based on their overall presence in the environment. A species may be locally abundant without being common.

However, “common” and “uncommon” are also sometimes used to describe levels of abundance, with a common species being less abundant than an abundant species, while an uncommon species is more abundant than a rare species.”

In the UK we have a conservation designation, Sites of Special Scientific Interest, the criteria for selection which can be found here. To save you the trouble of reading the whole document, the way in which rarity and scarcity are defined is as follows.

Nationally Rare (15 or fewer UK hectad (10 km squares) records)

Nationally Scarce – Notable A (31-100 UK hectad records),

Nationally Scarce – Notable B (16-30 hectad records.

Local – (101-300 UK hectad records)

Okay, so what has all this to do with aphids and their pest status? As you all probably know by now I love aphids; as far as I am concerned, where insects are concerned, they are the bee’s knees**.

Unfortunately, aphids get a terrible press, most of it, in my opinion, undeserved.

Just a couple of examples of aphids getting a biblically bad press.

A few years ago, I wrote a short piece about the fact that only a minority of the so far 5600 or so aphids described, are pests, and many are very rare. The cover of this issue of New Scientist from 1977, which appeared a few months after I joined the group, very nicely sums up the question that we really ought to be asking. Here I have to confess that the article from our lab (McLean et al., 1977), made the case for aphids being pests, and it was the late Denis Owen who defended aphids (Owen, 1977).

Tony Dixon’s cereal aphid research group (of which I was proud to be a member) got more than just a mention in this issue.

Two plants that I have a particular interest in are sycamore and bird cherry, mainly because of their aphids, but in the case of the bird cherry, I love its flowers.  Now, although both have very similar distributions and occurrences to cow parsley and ribwort plantain, ubiquitous, they are much easier

Distribution of cow parsley, ribwort plantain, and sycamore and bird cherry in the British Isles (Atlas of the British Flora)

to find aphids on than both cow parsley and plantain.  On my daily walks during which I pass countless cow parsley and plantain plants, I have, so far, only found one cow parsley with aphids on and not a single plantain has shown any signs of aphid infestation . I have also, only found one nettle plant with Microlophium carnosum on it.  Cow parsley has a number of aphid species that use it as a secondary host migrating there from willows or hawthorns. Plantains also serve as host plants to aphids, some such as Dysaphis plantaginea host alternate, others such as Aphis plantaginis, do not. The latter species, if present, is almost always ant attended (Novgorodova & Gavrilyuk, 2012), which, if you know what you are looking for, makes it easy to spot.  I know what to look for and so far, have not found any! Nettles are also very common in the roadside verges, and they too have aphids that love them, Microlophium carnosum and Aphis urticata, the former a favourite prey of ants, the latter, farmed by the ants.  So far this year I have only found one small colony of M. carnosum, and believe me, I have been looking.

So what about the trees? Sycamores are a common sight on my walks, occurring both as hedges and as solitary trees or sometime in small groups. Almost all the large trees have sycamore aphids, Drepanosiphum platanoidis feeding on their leaves, and many have dense colonies of the maple aphid, Periphyllus testudinaceus, some with ants in attendance. Bird cherry is not as common on my walks and where I have found it, they have been small trees or shrubs usually on their own, and surrounded by other woody plants. Without exception, all have been conspicuously infested by the bird-cherry oat aphid.  To summarise, we have common plants that support aphids that are not regarded as rare, but find startlingly different levels of abundance of them here in Staffordshire, and in my experience, elsewhere.  At the same time that I have been actively searching for aphids, six species of butterfly that the Woodland Trust lists as common, have been hard to miss.  In order of sightings these are the Orange Tip, the Peacock, the Small Tortoiseshell, the Speckled Wood, the Holly Blue and the Brimstone, two of which, the Peacock and the Small Tortoiseshell, being nettle feeders as larvae. Despite the abundance of nettles in the hedgerows, So far I have only seen one small colony of Small Tortoiseshell larvae on the of nettles. I am, at this juncture, unable to resist mentioning that adults of the Holly Blue feed on aphid honeydew J Going back to my original point, the fact that I have seen more butterflies than aphids doesn’t necessarily mean that the aphids are less abundant, just less apparent.

There are at least 614 species of aphid in the UK (Bell et al., 2015). I am not sure how many I have seen, I stopped keeping a personal tick list many years ago, but I would guess that I have seen about half of them.  I like aphids, I look for aphids, but there are many ‘common’ species that I have never seen. I have, however, seen some of the rare ones. Four that stand out in my memory are Monaphis antnenata, Stomapahis graffii, Myzocallis myricae and Maculolachnus submacula. The first feeds on the upper surface of birch leaves (Hopkins & Dixon, 1997) and was shown to me by the late Nigel Barlow, when he was on a sabbatical at Silwood Park. Stomaphis graffii which feeds under the bark of sycamores and maples and is ant attended, was shown to me by an MSc student, Andrew Johnson, also at Silwood Park.  Myzocallis myricae, the bog myrtle aphid, only found on bog myrtle (Myrica gale) (Hopkins et al., 2002), I saw in the Highlands of Scotland, when Tony Dixon asked me to stop the car so he could go and look at a clump of bog myrtle he had spotted as we drove along between field sites. The giant rose aphid, Maculolachnus submacula, I saw in my garden in Norwich (84 Earlham Road) when I was a PhD student at the University of East Anglia.  I only found it because I wondered why there was an ant nest reaching halfway up one of my roses.  When I looked, I found that they were farming the aphids that were feeding on the lower stems.

It is important to remember that most aphids are host-specific, some feeding only on a single plant species, others being confined to a single genus with only a minority having a wide host range*** and considered pests (Dixon, 1998). Given this, it is obvious that aphids with rare host plants are also going to be rare (Hopkins et al., 2002).  Many aphids are also very fussy about their niche, either feeding on a very particular part of a plant or having a very close association with a particular species of ant.  Looking at the aphids that the two Bobs (Influential Points it seems that aphids that are rare  are also ant-attended.  Given, that many ant-attended aphids aren’t rare it would seem an interesting area to pursue. Perhaps it is the degree of ant-attendance, i.e. facultative versus obligate that is the key factor?

If you look at the list of species of insects that are regarded as endangered and worthy of conservation in the UK, the overwhelming impression is that unless they are big and pretty they don’t get a look in.  Needless to say, despite their beauty and fascinating life styles, no aphids are included in the list L

We really should be conserving aphids, not squashing them. Many provide important nutrition for ants and other pollinators, honeydew.  They are an important source of food for insects and birds (Cowie & Hinsley, 1988).  Aphids also help plants grow by feeding mycorrhizae with their honeydew (Owen, 1980; Milcu et al., 2015). Finally, as aphids are so host specific using the presence of uncommon species in suction traps could help identify sites with rare plants.

Aphids, rare, useful and much maligned, time to rethink their role.

 

References

Adler, L.S., Schmitt, J. & Bowers, M.D. (1995) Genetic variation in defensive chemistry in Plantago lanceolata (Plantaginaceae) and its effect on the specialist herbivore Junonia coenia (Nymphalidae). Oecologia, 101, 75-85.

Bell, J.R., Alderson, L., Izera, D., Kruger, T., Parker, S., Pickup, J., Shortall, C.R., Taylor, M.S., Verier, P. & Harrington, R. (2015) Long-term phenological trends, species accumulation rates, aphid traits and climate: five decades of change in migrating aphids. Journal of Animal Ecology, 84, 21-34.

Cowie, R.J. & Hinsley, S.A. (1988) Feeding ecology of great tits (Parus major) and blue tits (Parus caeruleus), breeding in suburban gardens. Journal of Animal Ecology, 57, 611-626.

Dixon, A.F.G. (1998) Aphid Ecology. Chapman & Hall, London.

Feeny, P. (1976) Plant apparency and chemical defence. Recent Advances in Phytochemistry, 10, 1-40.

Hopkins, G.W. & Dixon, A.F.G. (1997) Enemy-free space and the feeding niche of an aphid. Ecological Entomology, 22, 271-274.

Hopkins, G.W., Thacker, J.I.T., Dixon, A.F.G., Waring, P. & Telfer, M.G. (2002) Identifying rarity in aphids: the importance of host plant range. Biological Conservation, 105, 293-307.

McLean, I., Carter, N. & Watt, A. (1977) Pests out of Control. New Scientist, 76, 74-75.

Milcu, A., Bonkowski, H., Collins, C.M. & Crawley, M.J. (2015) Aphid honeydew-induced changes in soil biota can cascade up to tree crown architecture. Pedobiologia, 58, 119-127.

Milovanovic, M., Stefanovic, M., Djermanovic, V., & Milovanovic, J. (1996). Some chemical constituents of Anthriscus sylvestris. Journal of Herbs, Spices & Medicinal Plants, 4, 17–22. Eugenol – insecticide

Novgorodova, T.A. & Gavrilyuk, A.V. (2012). The degree of protection different ants (Hymenoptera: Formicidae) provide aphids (Hemiptera: Aphididae) against aphidophages European Journal of Entomology, 109, 187-196.

Owen, D.F. (1977) Are aphids really plant pests? New Scientist, 76, 76-77.

Owen, D.F. (1980) How plants may benefit from the animals that eat them. Oikos, 35, 230-235.

Price, P.W. (2003) Macroecological Theory on Macroecological Patterns, Cambridge University Press, Cambridge.

Thacker, J.I., Hopkins, G.W. & Dixon, A.F.G. (2006) Aphids and scale insects on threatened trees: co-extinction is a minor threat. Oryx, 40, 233-236.

Uusitalo, M. (2004) European Bird Cherry (Pruns padus L). A Biodiverse Wild Plant for Horticulture. MTT Agrifood Research Finland, Jokioinen.

** https://en.wiktionary.org/wiki/the_bee%27s_knees    

***Hugh Loxdale however, would argue that all insects are specialists and that so called polyphagous species are, in reality, cryptic specialist species (Loxdale, H.D., Lushai, G. & Harvey, J.A. (2011) The evolutionary improbablity of ‘generalism’ in nature, with special reference to insects. Biological Journal of the Linnean Society, 103, 1-18.)

 

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Filed under Aphidology, Aphids

An unintended consequence – Maris Huntsman: A great choice for entomological careers but not so good for farmers

I could have used Sod’s Law or Murphy’s Law as the lead in for this article, but as you will see (if you keep on reading), this story isn’t all doom and gloom 😊. During the 1960s, cereal growers in the UK and on mainland Europe, were subjected to onslaughts on two fronts, yellow rust* ((Puccinia striiformis) (Doling & Doodson, 1968) and cereal aphids (Fletcher & Bardner, 1969; Kolbe, 1969).  Although cereal aphids had been a sporadic problem in Europe for several decades previously (Kolbe, 1969,1973; Rautapää, 1976) and even earlier than that (e.g. Marsham, 1798), 1968 was an exceptional year for them (Fletcher & Bardner, 1969; Kolbe, 1969).  Presaging  Richard Root’s seminal work on crop apparency and pest occurrence, the Dutch agronomist Willem Feekes predicted that changes in agricultural practice, in particular cereal production, would lead to increased pest and disease problems (Feekes, 1967). This was further emphasised by Wilhelm Kolbe of Bayer, who suggested that the big increase in cereal production in Europe between 1950 and 1970 and the switch from oats to wheat was the cause of the cereal aphid problem (Kolbe, 1973).   Similarly, in the UK, where oats were 51% of the cereal crop in 1930, they had fallen to 11% by 1965 (Marks & Britton, 1989).

Cereal production UK

The shift in cereal crops may indeed have been a contributory factor, but I think, certainly in the UK, that we can add another factor to the equation. Over at Maris Lane**, where the Plant Breeding Institute was based at Trumpington, Cambridge, a new variety of wheat, Maris Huntsman, with good resistance to both powdery mildew and yellow rust (Ruckenbauer, 1975) had been developed and introduced as a recommended variety to farmers in 1972 (Hughes & Bodden, 1978).  By 1977 it accounted for almost 40% of the wheat sold in the UK (Hughes & Bodden, 1978), although a mere two years later, it had fallen to just over 20% (Johnson, 1992).  Based at Trumpington, entomologist Henry Lowe, had, since the late1960s been investigating the resistance of crop plants to aphids, first beans (e.g. Lowe, 1968) was at the time, investigating the resistance of varieties of wheat to aphids (Lowe, 1978, 1980). He found, as one might expect that not all cereal species and varieties were equally susceptible to aphids, and if given a free choice, the grain aphid Sitobion avenae, showed a preference for Maris Huntsman.

So what does this have to do with launching the careers of a couple of dozen entomologists? Well, back in the late 1960s Tony Dixon, then based in Glasgow, got interested in the bird cherry-oat aphid, Rhopalosiphum padi  (Dixon, 1971; Dixon & Glen, 1971), a minor pest of cereals in the UK, mainly because of its great ability to transmit Barley Yellow Dwarf Virus (Watson & Mulligan, 1960. In those countries, such as Finland and Sweden, where spring sown cereals are the norm, it is a pest in its own right, able to cause yield reduction without the help of a virus (Leather et al., 1989). Tony moved to the University of East Anglia as Professor of Ecology in 1975 and started his new career there by appointing six new PhD students. Three of these were looking at aspects of cereal aphid ecology, Allan Watt researching the biology of S. avenae and Metoplophium dirhodum, Ian McLean looking at the predators and Nick Carter modelling their populations in order to develop a forecasting system.  Research groups at Imperial College and at the University of Southampton also began to work on the problem.  Fortuitously although cereal aphid numbers had fallen since the  

Numbers of Sitobion avenae caught in the Brooms Barn suction trap (data from Watson & Carter, 1983)

populations picked up in 1974 and then rose to outbreak levels again in 1976, just as the new PhD students started their field work. I joined the group in 1977 to work on R. padi, followed in subsequent years by Keith Walters (now a colleague at Harper Adams University), John Chroston, Sarah Gardner, Nigel Thornback, Ali Fraser, Shirley Watson, Trevor Acreman, Dave Dent, and after I left for pastures new, Alvin Helden (now Head of School at Anglia Ruskin University). Similar numbers of students were appointed at Southampton, including Nick Sotherton, now Director of Research at the Game and Wildlife Conservation Trust.  There were also groups started at Imperial College and the University of Reading. There was a certain element of rivalry between the groups, Steve Wratten for example, was an ex-student of Tony’s and there was a certain degree of animosity between Roy Taylor (of Taylor’s Power Law fame) at Rothamsted and Tony Dixon, we had mini-conferences to exchange findings and generally got on well.  Allan Watt for example went to work for Steve Wratten as a post-doc before moving up to Scotland to work on the pine beauty moth alongside me.  It was a great time to be working on aphids and I think we all benefitted from the experience and I for one, am very grateful to the plant breeders for developing a  variety of wheat, that although resistant to rust and powdery mildew, is very attractive to the grain aphid 🙂

Having fun in a Norfolk cereal field; me, Allan Watt and Ian McLean (Nick Carter had the good sense to stand behind the camera).

You may be wondering why I penned this reminiscence. Well, last year, my colleague Tom Pope and I were discussing cereal aphids at coffee time (as you do), and I mentioned how Maris Huntsman had launched my career.  It just so happened that Tom had access to old, ancient and modern varieties of cereals to hand and a final year project student keen on aphids so it doesn’t take a genius to guess what happened next 🙂

Host preferences of Sitobion avenae (Dan Hawes & Tom Pope). Can you guess which is Maris Huntsman?

So, Maris Huntsman, a great choice for attracting aphids and producing entomologists 🙂 and of course a great big vote of thanks to the PBI

 

References

Dean, G.J.W. & Luuring, B.B. (1970) Distribution of aphids on cereal crops. Annals of Applied Biology, 66, 485-496.

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. & Glen, D.M. (1971) Morph determination in the bird cherry-oat aphid, Rhopalosiphum padi (L). Annals of Applied Biology, 68, 11-21.

Doling, D.A. & Doodson, J.K. (1968) The effect of yellow rust on the yield of spring and winter wheat. Transactions of the British Mycological Society, 51, 427-434.

Feekes, W. (1967) Phytopathological consequences of changing agricultural methods. II Cereals. Netherlands Journal of Plant Pathology, 73 Supplement 1, 97-115.

Fletcher, K.E. & Bardner, R. (1969) Cereal aphids on wheat. Report of the Rothamsted Experimental Station 1968, 200-201.

Hughes, W. G., & Bodden, J. J. (1978). An assessment of the production and performance of F1 hybrid wheats based on Triticum timopheevi cytoplasm. Theoretical and Applied Genetics, 53, 219–228.

Janson, H.W. (1959) Aphids on cereals and grasses in 1957. Plant Pathology, 8, 29.

Johnson R. (1992) Past, present and future opportunities in breeding for disease resistance, with examples from wheat. [In] Johnson R., Jellis G.J. (eds) Breeding for Disease Resistance. Developments in Plant Pathology, vol 1. Springer, Dordrecht

Kolbe, W. (1969) Studies on the occurrence of different aphid species as the cause of cereal yield and quality. Pflanzenschutz Nachrichten Bayer, 22, 171-204.

Kolbe, W. (1973) Studies on the occurrence of cereal aphids and the effect of feedingdamage on yields in relation. Pflanzenschutz Nachrichten Bayer, 26, 396-410.

Latteur, G. (1971) Evolution des populations aphidiennes sur froments d’hiver.  Mededelingen van de Faculteit Landbouwwetenschappen, Rijksuniversiteit Gent, 36, 928-939.

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.

Leather, S.R., Carter, N., Walters, K.F.A., Chroston, J.R., Thornback, N., Gardner, S.M., & Watson, S.J. (1984) Epidemiology of cereal aphids on winter wheat in Norfolk, 1979-1981. Journal of Applied Ecology, 21, 103-114.

Lowe, HJ.J.B. (1967) Interspecific differences in the biology of aphids (Homoptera: Aphididae) on leaves of Vicia faba I. Feeding behaviour. Entomologia experimentalis et applicata, 10, 347-357.

Lowe, H.J.B. (1974) Effects of Metopolophium dirhodum on Spring wheat in the glasshouse.  Plant Pathology, 23, 136-140.

Lowe, H.J.B. (1978) Detection of resistance to aphids in cereals.  Annals of Applied Biology, 88, 401-406.

Lowe, H.J.B. (1980) Resistance to aphids in immature wheat and barley. Annals of Applied Biology, 95, 129-135.

Macer, R.C.F. (1972) The resistance of cereals to yellow rust and its exploitation by plant breeding.  Proceedings of the Royal Society London B., 181, 281-301.

Marks, H.F. & Britton, D.K. (1989)  A Hundred  Years of British Food and Farming: A Statistical Survey. Taylor & Francis.

Marsham, T. (1798) Further observations on the wheat insect, in a letter to the Rev. Samuel Goodenough, L.L.D. F.R.S. Tr.L.S. Transactions of the Linnaean Society London, 4, 224-229.

Rautapää, J. (1976) Population dynamics of cereal aphids and method of predicting population trends. Annales Agriculturae Fenniae, 15, 272-293.

Rogerson, J.P. (1947) The oat-bird cherry aphis Rhopalosiphum padi (L.) and comparison with R. crataegellum Theo. Bulletin of Entomological Research, 38, 157-176.

Ruckenbauer, P.  (19 75) Photosynthetic and translocation pattern in contrasting winter wheat varieties. Annals of Applied Biology, 79, 351-359.

Watosn, M.A. & Mulligan, T. (1960) The manner of transmission of some Barley Yellow‐Dwarf Viruses by different aphid species. Annals of Applied Biology, 48, 711-720.

Watson, S.J. & Carter, N. (1983) Weather and modelling cereal aphid populations in Norfolk (UK). EPPO Bulletin, 13, 223-227.

Zayed, Y. & Loft, P. (2019) Agriculture: Historical Statistics. House of Commons Briefing paper 3339

 

*Yellow rust is still a  still a major problem for cereal growers worldwide

**an address that is immortalised in the names of several cultivars of crops developed by the PBI

 

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Pick & Mix 44 – some things to ponder while you practice social distancing

The Swiss do more than make cuckoo clocks – they (well some of them) subvert maps J

Great summary of the latest special issue in Insect Conservation & Diversity by Manu Saunders

We need to get out more – interesting paper on the health benefits of being outside and getting dirty

Interesting post from Miles King on education and his thoughts about why it should be student centred rather than league table centred and include getting outside more

Will the Covid-19 epidemic have a silver lining for the green economy?  Not necessarily writes James Murray of BusinessGreen

Something to visit when the pandemic is over – The Linnean Society celebrates the achievements of their first female fellows

Something to help you get through these days of social distancing – watch these springtails jump and then go outside and find some yourself, but do keep away from other peopel

The ecological mystery of a Stink Bug swarm far out to sea – what does it tell us about colonisation of the Galapagos Islands?

Somewhat related is this old post of mine about long distance migration in aphids

Finally, if you haven’t come across the word defining site Sesquiotica, I can definitely recommend it, sometimes poetry, sometimes prose, but always enlightening

 

 

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Omphaloskepsis – navel gazing in the time of Covid-19

Advance warning – there is not much science or entomology in this one, although it could be a welcome respite from Covid-19 😊

I am assured that they are gazing at their navels

A couple of days ago I was scrolling through my ‘Blogs to write’ file, clicking on titles that caught my fancy, when I came across this one that I thought looked interesting – Meaningful numbers, with a file date of almost exactly 4 years ago.

What surprises lurk inside this file?

I wondered what I was thinking about at the time so opened the file.  Imagine my disappointment when this was revealed 😊

Nothing but the title, not even a picture to help jog my memory!

So, I was none the wiser.  I knew it wasn’t about one of my pet bugbears; journals that use numbered references, because that has its own file, in fact two files, because I seem to have started writing it twice 😊 I guess an indication of how much the practice irritates me. As a referee it makes it so much more difficult to check if the authors have cited the relevant literature. 😦

I hate this so much! It goes against my sense of order, literally speaking of course 😊

 It wasn’t about how many times the word insect featured as a worldwide search term in Google Trends, although looking at the graph it is striking that the peak is in June/July, the Northern Hemisphere summer.

Worldwide Google Trends for the search term ‘insect’

 

Staying with insects, (OK there is some tangential entomology in this piece), could I have been meaning to write something about how many insects species there are, given that the estimates range from Terry Erwin’s gloriously possibly over the top estimate of 30 000 000 (Erwin, 1983) to Ian Hodkinson’s 2-3 000 000, that I consider to be very conservative indeed, with Camilo Mora and colleagues oddly calculated 9 000 000 in between.   Or, could it refer to my ten-year data aphid data sets from Scotland, still waiting to be transferred transfer from these battered notebooks to an Excel spreadsheet?

Aphid data, not meaningful until it makes it to a spreadsheet?

Certainly, they contain a lot of numbers but are they meaningful? They haven’t even made it into my Data I am never going to publish series 😊

In desperation I Googled the phrase ‘meaningful numbers’ and ended up, via this piece by Donald Byrd,

http://homes.sice.indiana.edu/donbyrd/Teach/Math/MeaningfulNumbers+SignificantFigures.pdf

on the Wikipedia page about significant figures, which, although the habit that many undergraduates have of reporting their statistical output to the millionth decimal place, is one of my other pet bugbears, was probably not what I had intended to write about, or was it?

I guess we’ll never know what the original title was all about, but on the plus side, I now have a few more ideas to turn into blogs 😊

 

References

Erwin, T.L. (1983) Tropical forest canopies: the last biotic frontier. Bulletin of the Entomological Society of America, 29, 14-19.

Hodkinson, I.D. & Casson, D. (1991) A lesser predilection for bugs: Hemiptera (Insecta) diversity in tropical rain forests. Biological Journal of the Linnaean Society, 43, 101-109.

Mora, C., Tittensor, D.P., Adl, S., Simpson, A.G.B., & Worm, B. (2011) How many species are there on earth and in the ocean? PloS Biology, 9(8):, e1001127.doi:10.1371/journal.pbio.1001127.

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Pick & Mix 41 – some links to entertain and inform

Which species do we save – so many to choose from and not enough money

The moths of Whittingehame – following in the footsteps of Alice Blanche Balfour

The science behind prejudice – do cultures grow more prejudiced when they tighten cultural norms in response to destabilizing ecological threats?

Did bird vaginas evolve to fight invading penises?

Procrastination in academia – most of us do it – here is a scientific exploration and analysis – be warned it is riddled with jargon

What goes on inside an aphid and why Nancy Moran does what she does

James Wong examines the evidence (or lack of) for an impending “agricultural Armageddon”

Here Patrick Barkham recommends some books about Nature and muses on how we as individuals can make a difference

Overlooked and underused crops – a possible solution to the food crisis?

Great pictures and story – all about swallowtail caterpillars and their defence mechanism – another tour de force from Charlie Eiseman

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Ten more papers that shook my world – When it comes to plant-insect interactions its growth stage, not age that counts Watt (1979)

This is not just about a paper, but also about mentoring!  At the beginning of October 1977, I hesitantly knocked on the door of Professor Tony Dixon’s outer office in the School of Biological Sciences at the University of East Anglia, Norwich.  Tony was to become my PhD supervisor for the next three years and my friend and colleague for the next forty plus years, but until that day I had never met him, as my interview had been conducted entirely by telephone and in those pre-internet days, unless you had met someone at a conference you really only knew them by their papers and reputation.  I knew Tony because of his great little book, The Biology of Aphids which I had bought as an undergraduate in 1975, when I realised that aphids were really cool 😊 I told his secretary who I was and she directed me through to his office.  Tony looked up, said hello and asking me to follow him, took me down to the lab where I was to spend the next three years and introduced me to a tall, moustachioed Scotsman, Allan Watt, whom I was later to discover had a wicked sense of humour, and was to become not just a colleague and collaborator, but also a great friend, a friendship that continues to this day.  Tony’s introduction was roughly along the lines of “This is Allan, he’ll tell you what to do” and he did. Allan was just starting the final year of his PhD which was, like a number of us in Tony’s lab, on cereal aphids, in Allan’s case Sitobion avenae and Metopolphium dirhodum, the two major pests of cereals in the UK at the time.  My PhD was on a less abundant (in cereal crops), but equally problematic aphid, due to its ability to transmit Barley Yellow Dwarf Virus, the bird cherry-oat aphid Rhopalosiphum padi.  Having got my aphid cultures set up and done a couple of practice mini-experiments, I asked Allan what he was doing with his aphids.  He told me that he was looking at the effect of cereal growth stage on the survival and reproduction of his two aphid species and that the age of the plant had a significant effect on the aphids and that this varied between the two species, which he published a couple of years later (Watt, 1979).  Having been immersed in the cereal aphid literature for a couple of months, I knew that no one had done this for my aphid, and even then, being a great believer in “standing on the shoulders of giants” I figured that I could do the same for my aphid, but, in that never ending treadmill of adding novelty, also look at the effect of feeding position*. Allan’s advice and help stood me in good stead, and in due course I successfully published the results of my experiment (Leather & Dixon, 1981).

So, leaving aside me getting a publication as a result of Allan’s paper, how did this shake my World?  Well, first of all, it really drove home to me that plant phenological stage was incredibly important for insect-plant interactions and that unless you know the precise growth stage at which an interaction is happening it is difficult to compare other peoples’ results to yours and each other’s. As a result, it has led me as a reviewer and reader of papers, to be very scathing of phrases such as “ten-day old wheat plant”, “week old cabbage seedlings”, “young pea plant” (Leather, 2010).  It is deeply unhelpful for anyone wanting to repeat or compare similar work.  Just a few degrees difference in temperature over a week can move a plant from one phenological stage to another. There is no excuse for this type of sloppiness.

Two seven-day old wheat plants, same cultivar, same germination date, one reared at 20⁰C the other at 10⁰C. Growth stage 12 versus Growth stage 10 (Growth stages as described by Tottman & Makepeace, 1979).

The same two plants now fourteen day sold, GS 13 versus GS 12

It is not hard to find a solution.  The World has been blessed by the invention of the BBCH** system for coding plant phenological stages (Meier et al., 2009).  This system, which now exists for most major crop plants, including trees, means that there is no excuse for anyone to ever use the phrase “ten-day old plant” or similar wording. If by some chance, your plant does not yet have a BBCH description, either describe the growth stage that your plants are at in very precise terms or take the time to codify it yourself and submit it to a journal such as Annals of Applied Biology which has a long history of publishing such articles.

To be fair, before the BBCH system came into being, people had published descriptions of plant growth stages for some of the major crops, e.g. cereals (Feekes, 1941; Large, 1954), but they were not standardised, and in some cases, too broad-brush.  The stimulus for a standardised, decimal system of coding plant phenological stages was the publication of the Zadoks scale for cereals (Zadoks et al., 1974) and the illustrated follow-up a few years later (Tottman & Makepeace, 1979), the latter being the blueprint on which phenological growth stage papers are now based.

I look forward to the day when authors understand that a precise knowledge of plant growth stage is essential to understanding insect-plant interactions and I do NOT have to chide authors for not using the BBCH codification when I review their papers.

 

References

Feekes, W. (1941) De Tarwe en haar milieu. Vers. XVII Tech. Tarwe Comm. Groningen, 560-561.

Large, E.C. (1954) Growth stages in cereals. Plant Pathology, 3, 128-129.

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

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.

Meier, U., Bleiholder, H., Buhr, L., Feller, C., Hack, H., Hess, M., Lancashire, P.D., Schnock, U., Strauss, R., Vanden Boom, T., Weber, E. & Zwerger, P. (2009) The BBCH system to coding the phenological growth stages of plants – history and publications. Journal fur Kulturpflanzen, 61, S.41-52.

Tottman, D.R. & Makepeace, R.J. (1979) An explanation of the decimal code for the growth stage of cereals, with illustrations. Annals of Applied Biology, 93, 221-234.

Watt, A.D. (1979) The effect of cereal growth stages on the reproductive activity of Sitobion avenae and Metopolphium dirhodum. Annals of Applied Biology, 91, 147-157.

Watt, A.D. & Dixon, A.F.G. (1981) The effect of cereal growth stages and crowding of aphids on the induction of alatae in Sitobion avenae. Ecological Entomology, 6, 441-447.

Watt, A.D. & Wratten, S.D. (1984) The effects of growth stage in wheat on yield reductions caused by the rose grain aphid, Metopolophium dirhodum. Annals of Applied Biology, 104, 393-397.

Zadoks, J.C., Chang, T.T. & Konzak, C.F. (1974) A decimal code for the growth stages of cereals. Weed Research, 14, 415-421.

 

 

 

*

*Rhopaloisphum padi, in contrast to Sitobion avenae, is usually found on the lower stem and leaves of cereals.

**

The abbreviation BBCH derives from the names of the originally participating stakeholders: “Biologische Bundesanstalt, Bundessortenamt und CHemische Industrie”. Allegedly, the abbreviation is said to unofficially represent the four companies that initially sponsored its development; Bayer, BASF, Ciba-Geigy, and Hoechst.

 

 

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