This edited article about originally appeared in Look and Learn issue number 715 published on 27 September 1975.
The small, flying beetle alighted on the trunk of a large elm tree, to be joined soon afterwards by another of the same species. The pair of beetles were both less than 6mm long but they were to be responsible for the premature death of the great elm in which they laid their eggs. They were elm bark beetles (scolytus scolytus), a species which has destroyed more than half the elms in Southern England during the last few years. The female began to burrow into the bark until she reached the sapwood. Then the male took over and constructed a nuptial chamber in which pairing took place. He then left the female to continue burrowing a vertical tunnel just under the bark. As she worked her way upwards, the female laid single eggs at regular intervals on both sides of the tunnel.
A week or so later the eggs hatched into small white grubs (larvae). These grubs immediately began eating into the wood, constructing tunnels of their own roughly at right angles to the main one and carefully avoiding the tunnels of their neighbours. The tunnels naturally broadened as the grubs grew bigger. When they were fully grown they stopped feeding and each made a little chamber in which to change into a pupa. Eventually, when the adult beetles emerged from their pupal cases, they gnawed through the bark to the surface and flew off in search of other elm trees.
Although the beetles are blamed for killing the elms, it is not their burrows which do the damage but a fungus which is carried from one tree to another by the beetles.
The spores of this fungus are so small that a microscope is needed to see them. Just one of these minute specks, however, carried on the foot of a bark beetle, can develop in the sapwood of a healthy tree and gradually spread through the whole tree.
The first sign of the disease is the leaves on a few branches turning prematurely yellow and dying.
In its early stages, the epidemic might have been stopped by cutting down infected trees and burning them but now it is too late and, unhappily, there is no effective known remedy.
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