Thursday, 18 December 2014

Bug-hunting, leaf-twitching, data-analysing and me

Written for CISFBR (Cornwall & Isles of Scilly Federation of Biological Recorders) Newsletter

So, what’s your PhD on then?  Those immortal words which, after several years of being a PhD researcher, still manage to provoke in me a feeling of dread the moment they’re uttered.   Depending on my audience (and after a deep intake of breath), my response will vary, from ‘invertebrates, of the non-native variety’ to ‘how non-native species interact with native species’ or ‘how non-native invertebrates do their stuff in native foodwebs’.  The more scientific version/ working title of my thesis is ‘The integration of non-native phytophagous invertebrates in native interaction networks’, so now that I’ve got that out of the way, I’ll attempt to shed  some light on what that actually means, and perhaps more pertinently, what I actually do.

It all began with a Cornwall-based project proposal to investigate the indirect effects of the introduction of a non-native insect, the release of which was (is) hoped to help combat the massive ecological disaster that is the ever-increasing presence of Japanese Knotweed Fallopia japonica in Britain.  In March 2010, Defra granted approval for the host-specific psyllid Aphalara itadori to be used as a biological control agent, and its release/monitoring programme is currently underway.  Despite rigorous testing and scientific research, the deliberate introduction of a non-native species has met, not surprisingly given the popular history of past exploits, with varying degrees of (dis)approval.  I won’t go into the arguments for and against the psyllid’s use here, other than to say that, given my knowledge of psyllid ‘mechanics’ and host-specificity combined with the devastating impact of Japanese  Knotweed on native ecosystems, I know in which camp I firmly sit.

Indirect effects can probably best be described as the impact of the presence of a species on another species via an intermediary species, and as such, can be negative or positive – potentially harmful or potentially beneficial.  Despite the thorough testing carried out prior to the release of the psyllid, the indirect effects of its presence in native foodwebs/interaction networks is not known, and from an applied point of view, there is every possibility that some of these effects could prove useful in helping to effectively control other species considered ‘pests’ in certain circles.  And this is where I was to come in.

Due to a combination of funding issues and thus far negligible impact of the psyllid’s release, the above proposal soon developed into a less species-specific but still Cornwall-focused project along similar lines.   Rather ironically, considering the oft-prevailing doubts surrounding the notion of a non-native species being invited to reside amongst our very own flora and fauna, it soon became clear that Aphalara itadori is a tiny, tiny drop in the ocean of what is the presence of non-native species in Britain.  The GB Non-native Species Secretariat currently provides information for over 3000 non-native plant/animal species, describing a non-native species as ‘a species that has been introduced into the country by human intervention (either deliberately or accidentally) since the end of the last ice age’.[1]  But to put things into perspective, of these 3000+ species, only c. 10% are considered to impact negatively and/or socio-economically[2], although invasive non-native species are still designated as one of the main drivers of biodiversity loss[3]

Introduction routes for non-native species are numerous, with agriculture, aquaculture and ornamental horticulture all playing significant roles – historically, most have come from other parts of Europe but more recently, species have originated from temperate Asia and North America.  Keeping with the theme of plant-munching (phytophagous) invertebrates, as per Aphalara itadori, many examples of such exhibit host-specificity (specialist feeders), whereas others have evolved to feed less restrictively (generalist feeders).  Non-native specialist feeders require particular host-plants, and being non-native, more often than not, the latter will be a non-native species also, which leads on nicely to the role of the host-plant.
What’s so significant about Cornwall?  Well, with its southerly latitude and (in places, sub-tropical) maritime climate, Cornwall is home to many flourishing gardens, featuring a large variety of exotic plants from many different parts of the world. Add to this an increasing number of specialist horticultural nurseries and an established agricultural trade, and there exists a veritable Smörgåsbord of potential introduction means, habitats and host-plants for non-native species.  With this in mind, one of my tasks is to sample a percentage of the invertebrate population of Cornwall’s historic/municipal gardens in order to determine the presence of non-native invertebrate fauna (and performing some possibly complicated-sounding data analysis along the way).  As a compulsive recorder of all things biological, the prospect of purposefully poking my nose around Cornwall’s gardens for days on end makes me very happy; of course, this is something I already do on a routine basis, albeit rather more haphazardly.  Yes, I‘m a self-confessed leaf-twitcher – get me within 6 or so metres of a plant, and I have no choice but to turn over its leaves, check its stems and peer into its flowers to seek out resident or visiting invertebrates.  Systematic surveying aside, my leaf-twitching has already proved very rewarding, revealing all manner of previously-overlooked species, as well as enabling an insight into the microcosmic worlds that exist right under our noses.  

Now, I have another confession – before the commencement of my research, I knew very little about psyllids, and definitely don’t recall actually having seen one.  They’re interesting little critters, most closely related to aphids, whiteflies and scale-insects, and I personally think that they resemble mini cicadas, although they are far less noisy than their larger cousins.  The number of extant species in the world currently stands at 3338, just fewer than 100 of which can be found in Britain[4]. According to my records, I have now managed to see 22 of these, 6 being non-native and including one species new to Europe: Cacopsylla fatsiae or tetrapanaxae (Fig. 1) (the jury’s still out on which one it is, or even if the two species are actually one and the same), an Asian species currently thriving on Fatsia japonica and Tetrapanax papyrifer plants in West Cornwall, one species new to Britain: Agonoscena targionii (Fig. 2), a European species very much at home on Pistacia lentiscus at the Eden Project, and another species found at various locations throughout southern Britain but new to Cornwall: Acizzia uncatoides (Fig. 3), an Australian species found on Paraserianthes lophantha  (formerly Albizia lophantha) in Penzance.
Figure 1Cacopsylla fatsiae/tetrapanaxae - adult (length 3.5-4.5 mm)

Figure 2Agonscena targionii - adult (photo: C. Malumphy/Fera) (length 3-4 mm)

Figure 3Acizzia uncatoides – adult (length 1.5-2 mm)

Psyllids aren’t the only phytophagous invertebrates with which I’ve become uncommonly closely acquainted.  I’ve also befriended a particularly attractive little-known aphid species Crypturaphis  grassii (Fig.4), believed to be monophagous, feeding only on Italian Alder Alnus cordata, and native to Corsica and Southern Italy.  First recorded in the UK in 1998[5], it is found in relatively low numbers throughout Britain, and was first recorded in Cornwall in 2011[6].  Another of my aims is to investigate the potential for Crypturaphis grassii to switch hosts to one or more related (congeneric) species, by means of a series of host-preference tests, and also to find out more the species’ overall biology.  

Figure 4Crypturaphis grassii – aptera (length 2-3 mm)

Arguably one of weirdest groups of phytophagous invertebrates about which I have had the pleasure of finding out more has to be scale insects.  Highly specialised plant parasites, appearance-wise, scale insects are massively diverse (see Figure 5), with sexually mature females exhibiting neoteny, the retention of immature external morphology.  These mature females are usually immobile, feeding in situ, whereas most of the early instar nymphal stages (‘crawlers’) have functional legs and are highly mobile, seeking out a suitable feeding spot for the subsequent stages of their development.   Short-lived winged adult males occur in some species, when sexual reproduction will occur; however, as in aphids, parthenogenesis is commonplace.

Figure 5: Scale insects l-r by row:
Row 1 - Bambusaspis bambusae (non-native); Lichtensia viburni (probably native); Pinnaspis strachani (non-native)
Row 2 - Aspidiotus nerii (non-native); Carulaspis cf. minima (non-native); Dynaspidiotus britanicus (probably native)
Row 3 - Pseudococcus viburni (unknown); Saissetia oleae (non-native); Nipaecoccus nipae (non-native)
Row 4 - Coccus hespiridum (non-native); Pulvinaria floccifera (non-native); Chrysomphalus aonidum (non-native)

Linking all of the above phytophagous invertebrates are parasitoids – parasitic organisms that have often co-evolved to spend a significant portion of their life (usually egg and/or larval stages) in or on its host, ultimately resulting in the latter’s demise.  The dynamics of host-parasitoid relationships is a truly fascinating subject, and also a very useful example of indirect effects, with numerous studies demonstrating how behaviours such as predator-avoidance in one species can alter population densities, feeding behaviours, reproduction strategies and similar in another.  However, attempting to explain it further in a straightforward, let alone succinct manner is proving too much for my addled brain!

Other examples of phytophagous invertebrates subject to my scrutiny include those which live and feed inside plant tissue, such as leaf/stem-mining insects and various gall-makers.   The Horse Chestnut Leafminer Cameraria ohridella (Fig. 6) is a prime example of a non-native leaf-mining moth, first recorded in Britain in 2001/2 (Wimbledon), its distribution is increasing rapidly.[7]  It causes significant, unsightly damage to the foliage of Horse Chestnut Aesculus hippocastanum (also non-native) and related trees; however, as yet, there is no evidence of the moth’s presence having any serious impact on the tree’s survival.  Accordingly, I am about to embark on a literature search to establish what is currently known about C. ohridealla and its parasitoid complex, paying particular attention to known associations of parasitoids with native hosts, clinal variation, novel interactions with native species, etc. 

Figure 6: Cameraria ohridealla on Horse Chestnut Aesculus hippocastanum Image © Opuntia via Wikipedia Commons, 20 Jan 2013, Creative Commons Attribution.  

So, for now, that’s what I’m up to.  Needless to say, there are more projects on the horizon but then, aren’t there always?

[1] GB Non-native Species Secretariat [online] at: (accessed 17 January 2014)
[2] Roy, H.E., Bacon, J., Beckmann, B., Harrower, C.A., Hill, M.O., Isaac, N.J.B., Preston, C.D., Rathod, B., Rorke, S.L., Marchant, J.H., Musgrove, A., Noble, D., Sewell, J., Seeley, R., Sweet, N., Adams, L., Bishop, J., Jukes, A.R., Walker, K.J. & Pearman, D. 2012. Non-Native Species in Great Britain: establishment, detection and reporting to inform effective decision making NERC Centre for Ecology & Hydrology, 110pp.
[3] Millennium Ecosystem Assessment
[4] Ouvrard, D. 2014. Psyl'list - The World Psylloidea Database. [online] at:  (accessed 17 January 2014)
[5] Harrington, R. 1998. An aphid new to Britain Entomologist’s Record & Journal of Variation 110: 288.
[6] Luker, S. 2011. Crypturaphis grassii (Sternorryncha: Aphidae): first records for Cornwall Br. J. Ent. Nat. Hist 24: 205-209.
 [7] Pocock, M., Evans, D. Straw, N. & Polaszek, A. 2011. The horse-chestnut leaf-miner and its parasitoids. British Wildlife Vol. 22 Number 5 June 2011 p. 305-313.

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