Hi Andy
Oh how I hate media coverage of such things. They always try to sensationalise things.
It's not known exactly how it arrived but almost certainly by man. Before it's arrival here it had been spreading across Europe at a rapid rate, far quicker than is the norm for such expansions. It was first found in the UK in the Wimbledon area of London and I was one of a team of people sent down to check it out and confirm its presence and the extent of the 'infestation'. It was clear that it had been present for more than just one year, given the numbers of moths and mines.
Within minutes of arriving we and our bags were covered with the adult moths. There were moths covering the outside of the cars and even a number inside, having got it during the brief time it took to get out of the car.
The leaf mines were distributed across a wide area but not on trees away from the roadside. In fact, the heaviest infestations were on trees in people's driveways, above where cars were parked.
One year later I re-visited the site and others in the area and the infestation by now was enormous. I left the original site and headed to a nearby area that I knew was infested and was next to a railway station. I saw tens of 1000s of moths flyng around and the air above the platform was thick with them. As soon as a train arrived, many flew into the carriages and were transported to who knows where along the route.
It is also thought that long-distance lorries also brought them in as infested leaves in the wheel arches, etc. When I left the site I counted the number of moths on the outside of my car - 36. When I arrived at my next destination 3 miles away (where it was already present), they were all still present on the car despite travelling at speeds up to 30mph, and two had even found each other and were mating.
I also have a theory to explain the concentration of moths at the original site that were in people's driveways - transportation by children picking up the leaves.
The leaves, being so large, can support a large number of leaf mines and there are several generations per year, so the population can quickly build up.
A lot has been said about the moths killing off the trees. In my opinion this is rubbish. Infected leaves are still on the tree in autumn and are still slightly green, so are still photosynthesizing. Leaves infected with Guignardia, however, are crisp, brown and crumpled - effectively dead. It is this, plus bleeding bark disease, that is killing off the trees.
Abroad it was found that the population levelled off after about 10 years. Parasitic wasps started to infect the larvae, Blue and Great tits also discovered that the emerging pupae were an easy food source, both having an effect on the numbers of moths.
The best way to control the moth is to sweep up and burn (in situ) all the leaves in the autumn. This drastically reduces the potential population at the start of the following year - but this is time-consuming and therefore espensive so councils, etc., are loathe to do it. Composting the leaves doesn't help as some pupae survive and are therefore reintroduced into new areas wherever the compost it used.
Martin
