A clean bill of health for the Horse Chestnut Leaf-miner?

I have recently been sent a copy of a paper by researchers from Forest Research (part of the Forestry Commission as was) on the impacts of the Horse Chestnut Leaf-miner Cameraria ohridella and the bleeding canker disease on Horse Chestnut trees (Straw, N.A. & Williams, D.T. in Agricultural and Forest Entomology (2013), DOI: 10.1111/afe.12020).

The forestry mafia have had it in for this moth ever since it arrived in Britain (as they do for virtually any new insect that turns up if it feeds on a tree or shrub). There was all sorts of nonsense written, even that it would destroy the game of conkers in this country! Strangely, no mention was ever made of the fact that Horse Chestnut is not native and is of virtually no commercial value. Unfortunately, many other people and organisations jumped on the bandwagon and I well remember Surrey Wildlife Trust printing a Forestry Commission press release in its magazine (presented as editorial) that told everyone how awful C. ohridella was and what steps everyone should take to try to get rid of it.

Presumably all this anti- activity was stimulated by the discoloration that the moth causes to Horse Chestnut leaves.

My opinion has, unsurprisingly, always differed from the mainstream. To me, the evidence that it had arrived in Britain by other than natural means was tenuous and circumstantial in the extreme. It is an attractive moth and provided a substantial food source for insectivorous species on a tree that was previously virtually sterile.

The latest research looked at what impact C. ohridella has had on Horse Chestnut trees. The abstract starts by stating that 'The leaf miner Cameraria ohridella and bleeding canker disease (BCD) are invasive organisms causing severe damage to horse-chestnut trees in Europe' [my emphasis]. So no change to forestry propaganda there then. But then the results: 'C. ohridella damaged up to 75% of the total leaf area [of Horse Chestnut] but it had no influence on stem radial growth or general tree condition' [my emphasis again]. Further, it stated 'Trees with higher rates of leaf miner damage generally had a lower incidence of BCD and there was no evidence that C. ohridella either facilitated the spread of the disease or accentuated its impact'.

I find it rather difficult to reconcile the actual results with the initial abstract statement and would suggest that independent peer reviewers should have requested changes.

Will these results, which in effect give a clean bill of health to the Horse Chestnut Leaf-miner, put a stop to all the negative comment about the moth? Probably not, but at least the facts are now known.