2008 saw the continued spread of the moth and increased infestation levels at existing sites. The Horse Chestnut Leaf Miner has continued it's spread and new records of infestation levels were reached in 2010. Now Horse Chestnut trees are conspicuous from early July for their brown, withered-like leaves caused by hundreds of leaf mines per leaf, giving the impression that Autumn is arriving earlier as a result. Surprisingly though, it seems that the effects on the Horse Chestnut, are purely cosmetic.

The Horse Chestnut Leaf Miner (Cameraria ohridella) was only discovered near Macedonia in 1985. It was originally known from Greece in the 1970's, but not recognised as a separate species until 1985. It then spread rapidly to other European countries, before reaching the UK (at Wimbledon, south-west London) in 2002, but was considered likely to have arrived the previous year due to the number of mines found. Accidental transportation via either road or rail, was thought to be a contributing factor in helping the moth reach the UK. Since 2002, it has been found over much of the south-east UK, reaching the neighbouring counties of Derbyshire and Leicestershire in 2005.

Following checks with other UK entomologists, it was revealed that there were in fact no Nottinghamshire records of this invasive moth to date and the Nettleworth record was later confirmed as Nottinghamshire's first by John Langmaid. We made a more accurate count of the number of mines present at Nettleworth Manor the following morning, reaching around 15/20 mines on the two Horse Chestnuts present. Further searches were conducted and we found an increasing numbers of mines on three other trees nearby. Most of the mines found at the time were on foliage growing in sheltered locations, often well under the tree canopy and in shade. Side shoots from the trunk are also affected.

However, higher infestation rates were then discovered at Oxton, suggesting that C. ohridella had definitely arrived there in 2006, or possibly even late 2005. The trees in the centre of Oxton were found with an infestation rate of a minimum of 250 mines per tree.

Of the locations checked in 2007, trees at Oxton and Caunton had much higher levels of C. ohridella infestation than anywhere else. But it was believed at the time, that many south-east Nottinghamshire sites would have shown infestations of similar levels. An appeal at the time for records from this part of the county proved to be unsuccessful, so this was never confirmed.

A year on and a return visit to Caunton in mid-September 2008, showed just how quickly infestation levels have increased. Large proportions of the lower branches of the same trees, were now almost devoid of any green leaf area following a succession of broods throughout the year. There was also evidence that leaves higher up the trees were also becoming more heavily infested as females searched for suitable egg laying sites.

Previously unaffected sites such as Edwinstowe and Debdale Lane in Mansfield, which had remained free of the moth until 2009, now have infestation levels more or less in line with those found at Oxton and Caunton back in 2007.

The sharp rise in infestation levels is possible because the moth is triple-brooded within a single year, so the multiples of population increases are huge following the first appearance of mines on any tree. Now on warm sunny days, heavily infested trees and the immediate vegetation can be literally swarming with several hundred adults.

The long-term threat by C. ohridella infestation to one of our most easily recognised trees is not fully understood and the moth's rapid colonisation of the UK, has been closely monitored by the Forestry Commision. Current evidence suggests that there is no decline in tree health and that trees are capable of producing new growth later in the year. Trees seem to survive repeated infestations OK and the damage is largely cosmetic (there can be hundreds of mines per leaf) Most damage occurs too late in the growing season to adversely affect the tree. Horse Chestnut trees of the red flowering variety are considerably less affected.