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Why these missions?

We want to find out about the alien moth species, because it is damaging our horse chestnut trees, and spreading so fast. We need your help because we need lots of information from all around the country. Only by asking members of the public and pupils, can we get enough information?

What question is answered by the missions?

We are asking how far the alien moth has spread, and how well the pest controllers are keeping it at bay. We think the pest controllers are taking time to get to grips with this new species, and so expect there to be more pest controllers in areas where the moth has been present for longer.

Questions about taking part

I want to take part, but I can’t find an infected tree. What should I do?
If you live in Scotland, central or northern Wales, or southern Cornwall, you may not be able to find an infected tree this year. Please do take part in mission: alien moth survey – information about non-infected trees is important.

I’m trying to do the survey mission, but I can’t find anything, what am I doing wrong?

The alien moths may not have reached your area yet. Lucky you! Please record your negative records anyway.

Why are you interested in records of trees without the moth?

Our aim in mission: alien moth survey is to find out how far the moth has spread in the UK, in summer 2011. Negative records are much better evidence than a lack of positive records, so please take part, even if you cannot find any infected trees in your area.

Nothing is coming out of my leaf, what should I do?

Look carefully; the insects are very small. If you really can’t see anything, please wait until late July 2011 before recording your results. If no insects hatch, you should record that.

Questions about the insects

Is the alien moth harmful?

Not at all to humans, but it is very harmful to horse chestnut trees!

Do the pest-controlling wasps sting?

No. They are related to the black-and-yellow stinging wasps, but not the same species. They are beneficial insects.

Should I release my moth after the mission?

Yes, if you want to, and if you are releasing it close to where you collected the leaf. If you are in an area were the moth not yet found, it would be better to squash it, to avoid helping its spread throughout the UK. It is, after all, an invasive alien species.

How can I tell the insects apart?

The adult moth is reddish-brown and white. The pest controllers have clear wings, and are shiny. See the detailed instructions for more information. Both types of insects may be dead when you try to identify them.

Questions about the alien invasion

Where does the invader come from?

The alien moth was first found in the UK in 2002 and came from continental Europe. Adults probably hitched a ride in a car or somebody’s luggage – they are very tiny so could easily go unnoticed.

Why is the moth only found on horse chestnut trees?

The alien moth is sometimes found on other species, but it evolved on and is adapted to live on horse chestnut trees.

How long will it take for a cure to be found?

Researchers are not looking for a cure but trying to understand the invasion better. There are lots of other invasive species which may affect our environment, and understanding how they interact with native species is crucial.

Questions about conker trees

Is the game of conkers really under threat?

Maybe. Conker trees which are infected still produce lots of conkers, but they are small and unlikely to be competition winners.

Why are most of the leaf mines near the bottom of the tree?

The alien moths overwinter as pupae in the leaf litter under the tree. In spring, the first generation adults hatch, mate, fly upwards, land on leaves and the females lay their eggs. They probably simply select the nearest suitable leaves, so in early summer, most of the damage caused by the caterpillars hatching from those eggs are near the bottom of the tree. Second generation moths lay their eggs higher on the tree so that the damage spreads up trees as the summer progresses.

How can I save my conker tree from damage?

There is not much you can do, but removing all the leaf litter in autumn may help to reduce the level of infection. You will need to do this every year to minimise the damage to your tree. Any pesticide you spray onto the tree would kill not only the alien moths but also the beneficial native insects. A treatment, based on garlic extract, for bleeding canker, is available. It may also make treated trees less attractive to the alien moths, but there is no clear evidence for this.

I can see some blotches on horse chestnut leaves, but how can I be sure they were caused by the moth?

Damage caused by the leaf miner is distinctive, especially until mid-July. Mines are entirely whitish or pale green, sometimes with a brown spot near the center. After mid-July, the adult moths emerge, and the empty mines turn brown. The pattern of mines remains the same, and new, pale mines can often be found.
If only the tips or edges of the leaf have shriveled up and turned brown, or if the patches are brown with yellow around them (see the photo of leaf blotch, a fungal infection, on the right), the damage was not caused by the moth.
If the tree has signs of bleeding on the trunk or branches, as well as yellowing, shriveled leaves, it may have bleeding canker, which is caused by another fungal pathogen, Phytophthora, as well as by a bacterium, Pseudomonas syringae PV aesculi.

I have noticed conker trees dying and being cut down. Is this because of the moth?

No, probably not, but it may be due to bleeding canker, which does kill the trees. Also, trees infested with the alien moth may become more susceptible to canker and other diseases, but nobody knows for sure.

Does the moth damage or kill the tree?

Yes, it damages the tree and reduces the size of the conkers, which means that trees growing from those conkers are small and weedy. The moth also may kill young trees, and cause mature trees to be susceptible to diseases which do kill them.

My conker tree is infested, should I cut it down?

Unless the damage is very unsightly, or the tree is very young, you should not consider cutting down the tree.