Our research highlights the danger of selecting trees for resilience to ash dieback at the expense of resistance to insects that threaten this iconic UK tree speciesDr Christine Sambles, University of Exeter Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Caused by the hymenoscyphus fraxineus fungus, the disease is capable of killing young trees in a single season, and older trees over several years.Screening replacement trees in order to plant only those resistant to the disease is seen as the “best hope” of saving Britain’s ash population.Since 2013, the Forestry Commission has planted around 155,550 trees across 14 locations in the South East in an attempt to find out which types are disease resistant.But the new research from the universities of Exeter and Warwick suggests the types able to resist the fungus also have very low levels of the chemicals needed to defend against insects.In particular, it leaves them defenceless against the Emerald Ash Borer beetle, which has already devastated vast tracts of ash in the US and is currently spreading westwards across Europe. It means choosing saplings on the basis of their ability to withstand dieback could simply replace one lethal problem with another.“Our research highlights the danger of selecting trees for resilience to ash dieback at the expense of resistance to insects that threaten this iconic UK tree species, said Dr Christine Sambles, who co-led the research.Ash is Britain’s most common hedgerow tree, with 60,000 miles of tree lines, and the second most common woodland tree after oak.An infection of dieback is usually fatal for a tree, and the disease can be spread on the wind and by the movement of infected logs.The Forestry Commission has said its strategy to secure the long-term future of Britain’s ash trees lies in understanding the species’ genetic structure and how some varieties can survives dieback.However, the team from Exeter and Warwick also examined in the differences in the chemical composition between tolerant and susceptible ash trees.“Plants use a vast range of chemicals to defend against fungal attack, and the primary objective was to identify differences which could be used to screen young ash trees and choose the best ones for replanting, said Professor Murray Grant, from Warwick.“Our findings underline the need for further research to ensure that we select ash trees resilient to present and future threats.”Emerald Ash borer, a beetle which kills ash trees within two or three years, is not yet in the UK but is high on the Government’s plant risk register.In October the Woodland Trust announced it would launch an accreditation and labelling scheme for trees sold at nurseries as a guarantee that they have been grown in Britain from British seed.The “Buy British” initiative is intended to try to prevent foreign pests entering UK woodlands.An estimated six million trees were brought into Britain in the past three years, including 1.1 million oaks. Attempts to stall the spread of Ash dieback may backfire because trees selected to withstand the disease are particularly vulnerable to deadly attacks by insects, new research reveals.The “unexpected” data has prompted warnings from scientists about the hidden dangers of screening projects, such a major initiative currently being run by the Forestry Commission.The current outbreak of dieback, also called Chalara, was first detected in a nursery in Buckinghamshire in 2012, leading to fears the UK ash tree population could be all but wiped out.