The interdependence of trees and insects comes to mind in a report by Butterfly Conservation that investigates the food supply of a rare butterfly.
The loss of the English elm from Dutch elm disease has affected the numbers of the White-letter Hairstreak.
This butterfly feeds on elm flowers and is now on the DEFRA UK 'priority' register as a result of its scarcity.
Efforts are being made to find a substitute within the elm family that is resistant to Dutch elm disease.
A report this year by the Butterfly Conservation Hampshire and Isle of Wight Branch into different elm varieties has been published. The goal is to find a suitable tree that adapts to UK conditions and could be a host plant to feed the White-letter Hairstreak.
There are thirty to forty species of elm across the world. The butterfly has been known to feed on Wych elm which is an elm variety less attractive to the disease carrier, the elm bark beetle, than the English elm.
As a result, some Wych elms escaped the Dutch elm disease of the 1970s.
Andrew Brookes of Portsmouth University, who ran the butterfly study, titled Disease resistant elm cultivators 2010 Elm Report download), with thirteen varieties of elm, writes that as yet their value to the butterfly is not proven as the trees have not flowered.
On another note, many hoped that a replacement for the English elm had been found. However, this was premature.
Andrew Brookes described these replacement trees as nearly all having Asiatic ancestors, so in many ways were unlike, and not replacements, for the European elms.
While their leaves and shapes may resemble more familiar elms, such as the American or the field elm, they don't grow to such heights.
“Many of these trees differ in appearance to their European counterparts often significantly smaller with uncharacteristic foliage," he said.
"Ergo. These trees would not, for all their virtues look at home in the wider English countryside – and should only be planted as ornamentals in urban parks."
Putting it differently was one expert, Eric Collin, of the French Institute for Research in Science and Technology.
Of the elm species known and loved in Europe, he said: “No European elm is resistant to elm disease but some are a little less sensitive than the majority of elms”.
Journalist, Mark Seddon, who has been tracing the development of the well-loved elm said that 'a disease resistant English elm has yet to be grown'.
Sadly, these trees may not replace the English elm. However, they may very well help improve numbers of the struggling White-letter Hairstreak butterfly population. In itself, lifting the threat to a once common butterfly is no small achievement.
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