Experts have warned infestations of oak processionary moth will continue to spread despite a new strategy aimed at containing the pest.
In March, the Forestry Commission moved from a policy of working to eradicate the species from the core outbreak zone in west London to trying to contain it.
Rather than residents and councils in the zone - covering Brent, Ealing, Richmond, Hounslow and Hammersmith and Fulham - being statutorily required to remove or spray caterpillars and nests, those within a new 10km buffer-zone are now responsible for treatment.
But Tony Kirkham, head of the arboretum at Kew, said despite the new control measures the pest was likely to become a national problem. "It has become pretty well established in west London despite efforts to control it and outbreaks outside London have already been reported."
Kirkham suggested that removing nests in the buffer zone would not be enough because they were very hard to spot, but more effective treatment may not be financially viable.
"The only control is to do the kind of spraying we have done at Kew, but I don't know how realistic that is in the current climate," he added.
He said the application of Deltamethrin on affected trees in Kew in 2010 had been 99.9 per cent successful, resulting in the use of less aggressive pesticides this year. "But they will always creep in from neighbouring areas so we simply can't eradicate it," he warned.
An outbreak was also reported in Pangbourne, Berkshire, in October last year. West Berkshire Council is working with the Forestry Commission to attempt to eradicate it.
Resources are key
Dave Lofthouse, Chair, London Tree Officers Association
"If we are only looking at treating the buffer zone then it is no longer eradicable but simply controllable. If there were sufficient resources, eradication could be feasible. Local authorities and our members will continue to treat the pest but many private tree owners are unlikely to do so without an enforcement notice."