'Christmas trees' provide a new home

Several of the conifers growing in our garden when I was young were old Christmas trees, planted out having served their festive purpose. As such, I used to refer to any suitably shaped conifer, regardless of origin, as a Christmas tree. Today, a wide range of conifers are used for Christmas trees and, indeed, for other ornamental purposes. One of these, the leyland cypress, has made the headlines on occasion when neighbours have fallen out of over the size of hedge this tree can achieve. The Leyland cypress was first created as a hybrid, by crossing Monterey and nootka cypress, but it now occurs alongside many other cultivars.

The widespread establishment of these new cypresses has opened up opportunities for a number of different insect species, including several moths. Juniper is our only native member of the cupressaceae (the family of conifers which includes the cypresses) but other members are native to southern Europe and these support a number of moth species not originally found in Britain. However, over the last 60 years several species have established themselves here. The first of these reached us in 1951, when a Dr Blair discovered Blair’s shoulder-knot feeding on a Monterey cypress on the Isle of Wight. By the 1960s this species had reached the mainland and began to spread inland. It now occurs across much of Britain, reaching as far north as Tyneside and southwest Scotland. Blair’s shoulder-knot had been extending its range from the Mediterranean around the Atlantic coast of France and, from there, it was a short hop across the English Channel.

Other species to reach us include the cypress pug and the cypress carpet, arriving in 1955 and 1984 respectively. Although now well-established, both species have failed to penetrate very far north and are restricted to the extreme south of England because they are prone to winter frosts. A number of smaller moths, just a few millimetres in length, have also reached our shores to exploit the new cypress resource. One of these, Argyresthia trifasciata, is a stunning little fellow, with golden wings across which run three white bands. Its caterpillars feed within conifer shoots and the shoot tips soon turn brown, leaving a clear sign that the moth has colonised a tree. Although such species may have been able to extend their European range northwards thanks to global climate change, they could not survive here without the presence of the cypresses. Other species have been assisted by the international trade in conifers, piggy-backing on trees imported from North America. The cypress tip moth that is established around Ipswich almost certainly arrived this way. At least one native species has been reported feeding on cypress and others may follow.