Material World interview

There has been huge concern regarding ash dieback in Britain over the past week. This is potentially devastating for our environment.

With all the interest in this, it has raised the discussion on tree health in general (which was the subject of increasing research even before this outbreak). Michael was involved with a discussion on Material World on Radio 4 (1st November 2012; listen here) about the impacts of tree pathogens and what can be done.

And another word cloud

This time I've produced a wordle of the comments made by people who took part in the Mission: pest controllers. The size of each word is proportional to its frequency in the comments we received. It's heartening to see large words like 'interesting', 'enjoyable' and 'good'. We looked very closely and found the word 'boring', but it was tiny!

The wordle of comments received by people who took part in the mission: pest controllers.

Comments to Conker Tree Science

Just for fun! A word cloud of the comments that we've received via the Conker Tree Science website.

More news

I was up in Scotland at the Royal Botanic Gardens Edinburgh last week and while I was there, I had a good look out for the horse-chestnut leaf miner. There was no sign of it anywhere! Indeed, it was strange to see the horse-chestnuts looking green, unlike in the south of England where they are very definitely browner than all the other trees.

We got a mention of the project in a really nice article in Science Omega on 17th September.

Smaller conkers, says the Sunday Telegraph

Our conkers are getting smaller according to the Sunday Telegraph (16th September 2012). They feature the Conker Tree Science project, and report on an in-depth study (available here)  looking at the diminishing size of conkers due to the horse-chestnut leaf miner.

The reports says that "last week, The Sunday Telegraph conducted its own survey of dozens of conkers, found in Green Park and Hyde Park, in central London. Those which had fallen from heavily infested trees were, on average, 15 per cent smaller than those from less affected trees – with an average diameter of around 1 inch in diameter, while those from less effected trees were around 1 1/4 inches."

Just like on the straw polls run during BBC Radio 4's Any Questions, it probably ought to be stated that their survey was not 'scientific' (for instance, they don't assess whether the trees not affected by the leaf miner also started off in better health?), but it's an interesting finding. I'm quite surprised, though, that they managed to find any trees in those areas which were not very heavily infested with the leaf miner!

Making the news

You can see the ITV Meridian news report on the latest Conker Tree Science mission: bird attacks.

We were also featured on BBC Oxford television news, beamed across the whole of the south region, and on BBC Radios Oxfordshire, Berkshire and Humberside.

Derwent May wrote about the project in The Times (30th August) .

Conker tree declines

I've been asked a couple of times recently about the long term prognosis for horse-chestnut trees. The simple answer is "in the worst case scenario, it's bleak".

Here's the background to why we think that is the case:

The horse-chestnut leaf-miner (the focus of Conker Tree Science) does not kill horse-chestnut trees. It does however affect the 'photosynthetic capacity' of the trees. Over the course of a year the 'net primary productivity' (which basically means the amount of food the tree makes for itself) declines by about one-third. (That is according to two scientific papers published in 2004 and 2011.)

At the the same time that the leaf-miner has spread, another more serious disease, called bleeding canker has also spread in our horse-chestnuts. This can cause the death of the tree, and branches that have been badly affected can be dropped by the tree. Local authorities and tree owners have been carefully checking their horse-chestnut trees, and trees have been managed appropriately and in some cases they have been felled.

It is possible that the spread of the leaf miner and the effect it has on the tree's photosynthetic capacity is weakening trees, so making them more susceptible to bleeding canker, though this requires further research.

So, the bleeding canker, may ultimately lead to many horse-chestnut trees being felled. That wouldn't be so bad if trees were being re-planted. However, sales of horse-chestnut trees have declined by 98% over the past 5 years.This is presumably because few people want to replant horse-chestnut trees that look so moth-eaten (quite literally!) by mid-summer.

So, even though the leaf-mining moth doesn't kill our trees, it is intrinsically linked to the possible demise of our conker trees.

Can blue tits save our conker trees?

Today is the day we've launched our third Conker Tree Science mission! It is the Mission: bird attack and is the perfect way to do some real science while enjoying the end of the summer. (Or rather dodging the showers?)

photo by Richard Broughton

Like the other missions (the alien moth survey and pest controller missions), this is real science and we're really interested in the data that will come in. All you'll need is a few minutes next to a conker tree and the mission instructions.

So, what's it all about?

In the past, the Conker Tree Scientists have looked to see whether tiny little parasitic wasps can act as natural pest controllers. Last year though people contacted us telling us about another possible pest controller: blue tits. Several people had seen tit flocks (mostly blue tits, but also great tits) feeding on the leaves of infested horse-chestnut trees.

Could blue tits act as pest controllers of this alien leaf-mining moth? We didn't know, and thought it would be good to find out.

What do you have to do?

A bird attack on a leaf mine caused by the alien moth

In brief, you need to:

1. Get hold of a copy of the detailed instructions.
2. Find a horse-chestnut trees that is infested with the leaf-mining moth.
3. Choose a leaf from the tree. Any leaf will do. Don't select one becaue it looks particularly unusual in any way.
4. Record how much damage has been caused by the leaf-mining moth.
5. Count the number of bird attacks on the leaf.
6. Choose 3 other leaves from the same tree and make the same records.
7. Let us know what you found!

We look forward to seeing how the results look as they come in.

Better, worse or the same?

Now we are into the 2012 Conker Tree Science season, it is interesting to wonder whether this year is better or worse than previous years in terms of the level of damage caused by the moth.

One person from south Wales emailed to say that of the two trees she had been watching: 

"Both trees were very badly infected early on in the season this year with leaves shrivelling and dying following the harsh winds and weather.  However I think this has actually benefitted the trees as they have subsequently produced new leaves which, at the moment, show no signs of infection.  The trees had enough time to produce new leaves which seem to be outside the normal cycle of the moth.

   I think leaf litter may explain some of the infection but certainly is only part of the story. The weather is certainly a major factor.  2 years ago when we had quite a dry year the badly infected tree did much better and actually produced some conkers which it hasn't for a while."

I'm sure that weather does have a role in influencing moth numbers where the moths have been for several years - but what type of weather affects the moths? Is winter or spring weather more important?

Another person, from Leicestershire, also emailed to comment:

"This is to tell you that hereabouts infestation is vastly reduced from previous years. No trees are predominantly brown from a distance and on many that were heavily infested last year it is difficult to find any mines."

How is it looking in your area? Are the trees faring better or worse than last year? Feel free to add your comments below.

Welcome to Conker Tree Science 2012

Welcome to Conker Tree Science 2012!

What can you do now?

1.  Take part in Mission: pest controllers (http://www.conkertreescience.org.uk/pestcontrolmission.html). You can collect infected leaves for this mission from 3-8 July inclusive.  Bag up the leaves so the tiny insects can't escape and after 2 weeks see what has emerged from the leaf.  Help us discover how many alien moths are being attacked by pest controlling wasps. Submit your results from 18-22 July inclusive.

2.  Take part in the Mission: alien moth survey (http://www.conkertreescience.org.uk/surveymission.html). Look out for conker trees, see if they show leaf mine damage and report your results via the website http://www.conkertreescience.org.uk/surveysubmitresults.html or the Leafwatch smartphone app (http://leafwatch.naturelocator.org/). Will the moth be confirmed further north than Newcastle this year? Will this year be worse than last year for the horse-chestnut trees?

3. Visit the project blog (http://conkertreescience.blogspot.co.uk) for all the up-to-date news. There you can see a summary of the results from last year. We’ll also be keeping this up-to-date with answers to your questions.

4. Get a sneak preview (http://conkertreescience.blogspot.co.uk/2012/07/natural-pest-contollers-not-just-wasps.html) of the new mission that we will be launching this in August.

We look forward to receiving your results to help us understand more about what is happening to our conker trees.

Best wishes

Michael Pocock & Darren Evans

P.S. Please forward this email to anyone who may want to know what is happening to conker trees.

What about the leaf litter?

From time to time we've had queries about leaf litter under horse chestnut trees, specifically whether it is a problem and, if so, what should be done about it.

It was for this reason that we invited people to record the vegetation under their trees in 2011 when recording the amount of damage that the moths had done. The final analysis is close to completion, but a look at the preliminary results suggests that:

The presence of mown lawn under horse chestnut trees, which was taken as a measure that leaf litter would not have been present over the winter*, is related to a reduced amount of damage recorded for any particular location and time.

In other words - the data people collected strongly suggests that clearing leaf litter is worth it to reduce damage to your tree!

2 trees just 50m apart, photographed on 2nd July. The one on the left had leaf litter under it during the winter. The one on the right did not have leaf litter under it during the winter. Of course, the presence of leaf litter may not be the only factor affecting how much damage there is from the horse-chestnut leaf miner, but it could have been important.

(* Of course, some trees with other types under the tree canopy could have had their leaf litter cleared away, but our observations suggest that this would be a minority. If we had been able to take that into account that would have strengthened our results. So, why did we not directly ask people whether there had been leaf litter under the tree the previous winter, or whether it had been cleared away? The answer is that we wanted this project to be open to anyone - so they could answer all the questions even if passing a tree they had never seen before.)

Natural pest contollers - not just wasps?

In Conker Tree Science we've been focussing on the tiny wasps that could act as natural pest controllers for the horse-chestnut leaf-miner. It's an incredible demonstration of the way in which we can rely on insects that are quite so small.

However, evidence is emerging (partly thanks to those who submitted photos via the Leafwatch app) that there may be bigger, fluffier pest controllers around! It seems that birds (probably blue tits and great tits) are preying upon the pupae of the moth, by ripping open the leaf mines.

Here you can see where the bird (probably a blue tit) has ripped open the leaf to prey upon the leaf-miner pupa.

We thought this was worthy of investigation, so we are working on a new mission: bird attacks for people to take part in during August and September. Just like the other two missions, this is a way for anyone to get involved in genuine scientific research. Register to receive updates about this mission and how to take part.

More apps for invasives

If you like the idea of recording invasive wildlife with your smartphone, then you'll probably like the new Plant Tracker app.

The idea developed from the success of the Conker Tree Science Leafwatch app. The Environment Agency saw how well it worked and realised that something similar would be ideal for tracking invasive plants. For some species, in some rivers, this would be especially important because it could allow Environment Agency staff to go and control the plants, so stopping them spreading and causing a problem.

The app is designed for people to report the presence of three invasive plants:

• Himalayan balsam 
• Japanese knotweed 
• floating pennywort 

Although the app is currently focussed on the Midlands region, we'd welcome records from anywhere to support its roll-out to Environment Agency regions across the country.

As the press release states, This is the latest app that has come from IT Services R&D at the University of Bristol. It was funded by the Environment Agency and University of Bristol, in collaboration with the Centre for Ecology & Hydrology.

What to do with the leaf litter?

We've had so much interest from people wanting to know what can be done to help their conker trees. So, at the beginning of 2011, we extended Conker Tree Science so that people could help us find out if clearing leaf litter really does help reduce the amount of damage on a tree. And the answer appeared to be a clear  'yes'.*


So, if clearing leaf litter is worth it, then what should be done about it?


Firstly, it is worth noting that general leaf litter is a fantastic ecological product that allows the recycling of nutrients and provides shelter and food sources for a wide range of animals, plants, fungi and all other sorts of microscopic creatures.


But, the horse-chestnut leaf-miner overwinters in the leaf litter and emerges in the spring to attack the leaves of horse chestnut trees.


Nigel Straw and colleagues at Forest Research produced a report showing that to effectively kill the moth pupae it is neccesary either to:

1. Cover the leaves in a layer of soil to stop the adult moths emerging. To quote from the Forest Research website, you will need to "cover the leaves with a 10cm layer of soil or 15-30cm layer of other plant material, and leave the heaps undisturbed until the end of May".
2. Compost the leaves at a high temperature. (The easiest way is via a commercial composting scheme, e.g. through your local council.)
   

Once the leaf litter is well rotted (so at least a year old, once all the moths have died) then it should be safe to use as normal compost.

* Why do we say 'appeared to be' and not 'is'? Well, the answer is because the formal statistical analysis of this is still on-going. We'll have the answer soon.

LeafWatch smartphone app

Making observations of the amount of damage that the leaf-mining moth has done to trees, means that you have to remember to submit what you saw and where you saw it when you get home and turn on your computer.

What would be perfect would be if people had a little device to make those records while they were looking at the tree. It would be even better if it would record their location automatically, and even allow them to submit a photo of one of the leaves, while they were there.

Aha! Smartphones would be the perfect tool!

...And so was born the idea of the LeafWatch app.

Mission: alien moth survey

How long? A minute. 
When? Anytime from mid June to late autumn.
How? Make observations and (1) enter records on the website, or (2) use the LeafWatch app for smartphones.
Why? Does the damage caused by the moth increase with the length of time that it has been present in a location?

Anecdotal evidence suggests that the amount of damage caused by  leaf miner increases over the first few years that the moth has been present in a locality. For example, many horse-chestnut trees in London are almost completely defoliated by early August, so it looks like autumn has come early, but currently in parts of south Devon, horse-chestnut trees only have a speckling of leaf mines by the middle of September.

Part of the aim of our science is to provide data to confirm anecdotes such as these, and to estimate precisely how quickly the levels of damage increase with the length of time that the moth has been present.

We have asked people since 2010 to score how much damage is being done to the horse-chestnut tree leaves. They can enter their location and date so that we can assess the damage. Since 2011 people can also get involved with the LeafWatch app. For those who have smartphones, this is a really convenient way of gathering records - each record is associated with a photograph (which helps us confirm

What do we do with the records?

Records of the moth's spread
Firstly, the distribution of many animals and plants in this country is recorded in 10 x 10km squares (based on the Ordnance Survey grid), and the horse-chestnut leaf-miner is no different. Forest Research have been collating the 10 x 10km square records of the horse-chestnut leaf-miner to monitor its spread. We pass on any confirmed records from new 10 x 10km squares to Forest Research to help with our understanding of its spread. (We confirm records with a photograph, which is either requested via the Conker Tree Science website for new squares, or is automatically included in the record from the LeafWatch app.)

Records of its damage
Secondly, we are assessing how the amount of damage to the leaves is affected by the length of time that the moth has been present. This is clearly shown on the LeafWatch app website.

We are also doing statistical analysis to confirm the observations, while taking account of the time of year (because the amount of damage increases throughout the year as the moths reproduce). The statistics we are using is a fairly complex method called ordinal regression.

Results from 2011: summary

During 2011 we had two missions running: the alien moth survey and the pest controller mission. People could take part in both missions via our website, and they could take part in the alien moth survey via the LeafWatch app for iPhones and Android smartphones.

Mission: alien moth survey

Website results for the alien moth survey, 2011

We had 710 records from 250 people via the website (but many more took part via the smartphone app). From the snapshot of the results at the end of the season we can see that the leaf-mining moth is widespread over most of England, although it appears less abundant in the south-west of England. In Wales the records are less widespread, but we cannot tell if that is because they are fewer leaf-miners or fewer people sending in records. Again, there are few records in the north of England, but this does fit with other people's findings that it has not spread right into the north of England.

We had received positive records from as far north as Newcastle, Carlisle and Dundee, but only the record from Newcastle has been confirmed with a photograph. So, up until the end of 2011, the horse-chestnut leaf-miner still had not been confirmed in Scotland.

Mission: pest controllers

Website results for the pest controller mission, 2011

We had 383 results from 120 people via the website. This is a more involved study than the alien moth survey and has to be started in a one week period at the beginning of July. However, from the comments we received, those people taking part really enjoyed it.

Like last year, there was, overall, a very small number of pest controllers that emerged.

One person noted that there was a big difference in the numbers of pest controllers reared from trees that were very close together, which is an intriguing finding.

Although the graph shows a huge proportion of pest controllers in the square covering Cornwall, it is worth noting that these graphs do not show the 'sample size'. We received just two records from Cornwall, and both had quite high numbers of pest controllers. We received a record from Bath with a similarly high number of pest controllers, but lots of other records with very few pest controllers, which evens out the results. Of course, it may also be something specific about Cornwall - but in science it is wise not to base conclusions on small sample sizes.

About the moth 2

Where has it come from?

The horse-chestnut leaf-miner was discovered in the Balkans (near Lake Ohrid in Macedonia) in the late 1970s. It was then discovered in Austria and from these two focal points, the moth has spread rapidly throughout Europe.

The spread of the moth in Britain

The spread of the horse-chestnut leaf-miner. Data from Forest Research

Thanks to the efforts of Nigel Straw and Christine Tilbury at Forest Research, we have a good record of the spread of the moth since its arrival in west London in 2002.

It has spread quickly through Britain, so that by the end of 2011 it was widespread south of the Pennines. Its distribution in south-west England and Wales is patchy than elsewhere in sourthen England, this is probably due to the smaller number of horse-chestnut trees in these area and that the leaf-miner has only recently arrived in these regions.

How quickly does it spread?

Studies across Europe suggest that the moth spreads at an average rate of about 30km per year.

How does it spread? 

The moth can spread by flying. It is a very small moth and probably is a weak flier. However there can be so many adult moths emerging from the leaves of an infested tree that just by chance a few inidividuals may manage to travel a mile or two.

The main way in which the moth spreads long distances is probably by 'hitch-hiking' on vehicles. Our anecdotal evidence supports this notion. A couple of years ago I was looking round a south Devon coastal town for the horse-chestnut leaf-miner and the only place I found it was in the car park of a holiday resort, suggesting it had hitch-hiked with holiday-makers. A few months later I was photographing a horse-chestnut tree, then walked back 20 metres, got in the car and discovered several of the moths had come in the car with me.

Thanks to Forest Research for allowing us to use their distribution data in the Conker Tree Science project.

About the moth 1

The horse-chestnut leaf-mining moth

The moth whose caterpillars are causing the damage to horse-chestnut trees is the horse-chestnut leaf-mining moth, which has the scientific name Cameraria ohridella.

It is known as one of the 'micro moths', to distinguish it from the typical 'macro moths', which are the larger moths often attracted to light.

A mating pair of horse-chestnut leaf-mining moths. © Dave Kilbey

The adult moth

The adult moth is tiny - just a few millimetres long - and very attractive, with white stripes on glossy bronze wings. Many people we have spoken to are surprised that the moth is so small. When the adults emerge, there can be so many flying close to a horse-chestnut tree that the tree appears to shimmer.

Its leaf-mining larvae

It is the larvae (or caterpillars) of the horse-chestnut leaf-miner that do the damage and feed on the leaves of the horse-chestnut. Many caterpillars are external feeders, but the horse-chestnut leaf-miner is different. Its larvae actually live inside the leaf and they 'mine' the leaf forming what are called, unsurprisingly, leaf mines. As they feed on the green tissue on the inside of the leaf, they leave the upper and lower layers of the leaf (the 'epidermis) intact, so the larvae remain protected.

The remaining epidermis of the leaf is translucent, which is why the leaf mines look whitish when they are fresh. After a few weeks the epidermis of the leaf mine dies and turns brown.

Each larvae produces a singe leaf mine, which eventually ends up about the size of half a person's finger. When infestations are large, the mines coallese and the larvae form groups searching for the remaining green tissue.

The larvae have incredible adaptations for living inside a leaf. They are have flattened so they can easily move about in the leaf mine and they have chisel-shaped heads with pointed moutparts so they can easily eat the fresh green tissue at the edge of the leaf mine.

Mission: pest controllers

Conker Tree Science

Can tiny parasitic wasps help to save our conker trees?

Believe it or not there are dozens of different kinds of tiny wasps (only distantly related to the stinging wasps that we are so familiar with) that attack the horse-chestnut leaf-miner. These wasps are so small that they lay their eggs inside the leaf-miner as it is eating the horse-chestnut leaf from the inside out! The developing wasp larvae eat the leaf-miner from the inside out and then burst out of the caterpillar, in the process killing it and so acting as a natural pest controller.

Can these potential pest controllers actually help by parasitising enough of the leaf-miners to control it's numbers? Given that we have so many of the leaf-miners in this country it would seem that they cannot, but we are interested in finding out more about them.

Stephen Turner - The art of the horse-chestnut

Stephen Turner has produced a fascinating blog about his experience as artist in residence at Sturovo in Slovakia (Hungarian / Slovakian border) over the past 6 months.

Conkers painted in watercolour made from the tree itself, from Stephen Turner's blog of his artistic residency in Slovakia.

He has been creating a visual art project about the leaf mining moth and the horse-chestnut in these locations which has involved mapping the location and spread of the disease amongst this species of tree in Sturovo and Esztergom (i.e. both sides of the river Danube) and he has produced a lovely narrative of his discoveries and creations.

Featuring in the Observer Ethical Awards

As part of the Observer Ethical Awards, Lucy Siegle, who runs the awards, wanted something for voters to do once they had voted. She invited me (Michael Pocock) and Darren Evans to create an invasive species citizen science project. Of course, being so involved in Conker Tree Science, we had to include the horse-chestnut leaf-miner as one of the featured species!

We chose to make sure that people were invited to submit records for all the 10 species to recording schemes that were already running, so that the data really would be useful and that the excellent work so many organisations are doing will get promoted. It was just a shame that the Observer project was promoted during the winter when many of the species were dormant. We hope that people will continue to report these species during this summer and that it will raise awareness of the potential problems of invasive species.