Insects Feeding on “Slime Flux” of Trees

A SIMILAR phenomenon may be seen at the present time in the collection of elms at Kew. The trunk of a fine specimen of Ulmus parvifolia has for some weeks past-but more especially during August and September-been the daily rendezvous of hundreds of wasps and bluebottles. As is the case with the trees at Ettington, the attraction is the sweet sap that exudes from the trunk. It is a mistake, however, to blame the wasps for the damage that is being done to the trees. They do not cause the outflow of sap, but are merely there feeding on it. A piece of bark has been removed from the tree at Kew and microscopically examined. It was found to be suffering from what is commonly known as ``slime flux'', the bark being saturated with sugary moisture. The primary cause of this somewhat obscure disease appears to be a yeast, which finds its way to the cambium layer by means of a wound. Often, as in the Kew instance, ingress has been facilitated by the borings of an elm beetle. The yeast sets up a decomposition of the cells, and starchy, ultimately sugary, products are formed, which exude from the trunk in solution. It is this which attracts the multitude of wasps, bluebottles, and other insects. It is evident from the odour of the bark that a certain amount of fermentation is going on, and the presence of alcohol is further indicated by the behaviour of the wasps, which, after feeding for some time, become stupid and lethargic.