The following article has been prepared at the request of the CRIMSON by J. W. Chapman 2G., an expert on insect pests, with the intention of showing the condition of the trees in the Yard, and what is being done to preserve them.
Those who are familiar with the Yard--as all of the students and alumni are--know that it can be divided into two parts, an east and west part, the dividing line being Thayer, University and Weld Halls. The magnificent old elms stand on the west section, while the eastern part, being newer, has a greater variety of trees, namely: elm, ash, maple and oak, which are younger and in much better condition, than the former ones.
The trees of the Yard have been practically free from insect pests in past years and it is only during the last few years that there has been any trouble at all. The first troublesome insect was the elm-leaf beetle. It is a small beetle which feeds on the leaves of the elms, in its larval stage, appearing in such numbers as to strip the trees entirely of their foliage, thereby killing them. The trees in the west part of the Yard were attacked by this pest and considerable damage was done before they were overcome.
These elm-leaf beetles undoubtedly weakened the elms to a very great extent and it may be that this paved the way for other destructive insects which have followed.
The leopard moth, which was first noticed in June 1909 is an imported European pest, and is only injurious in its larval stage. The life of the larva is two years. It makes its way into the tree by boring through the bark where it may make great furrows in the growing layer, thus girding the limbs, or it may burrow deeper into the heart of the tree. Its burrows show that it migrates often, from one part of a branch to another or to a different one altogether.
While cutting the leopard moth larvae from the limbs of the elms last fall, a small beetle was found, which has since been identified as the European elm bark-borer--scolytus multistriatus-marsh. In Germany it is known as the "splint kafer" and it is one of their most injurious pests. It enters the bark and the newly hatched larvae work in the splint of the live wood causing the bark to loosen and eventually fall off. Scores of trees in the Yard and about Cambridge have been examined and without exception all of them are infected.
One very readily sees that it is difficult to say just what particular insect is doing the most damage. It is more likely that it is the combined effort of all of them that is causing the trouble.
Insecticides fail to reach either the leopard moth or bark-borer. And such a spraying as the trees got when attacked by the elm-leaf beetle may have something to do with the apparent absence of insect enemies of the two above-named species. For the spraying of the trees could have easily killed their parasites, which might have been lurking about on the trees at the time the spray- ing was done. And one thing that favors this theory is,--the leopard moth is worst in that part of the Yard which was the most carefully sprayed.
Another natural enemy of these insects are the birds. A careful examination of the Yard shows that birds' nests are conspicuous by their absence. Occasionally one sees a bird, but it's rarely, and they do not live among us. For the English sparrow and grey squirrel have completely driven such birds as the flicker and woodpecker away. Here is a conflict of sentiments, trees vs. squirrels. And the result is, many squirrels, few birds. Few birds, many insects. Many insects, few trees.
The work of determining the life histories of these insects is being carried on as speedily as conditions will permit. Plans are also being made to put out trap trees and electric light traps in the spring. Further it is hoped that parasites of the leopard moth can be procured from Europe. And it has already been tried and so far has resulted in failure, because the larvae are very hard to find during the winter.
It is true that some of the elms may be lost but the care they had during the summer will save the majority of them, and if the ravages of these insects can be checked the trees are good for years to come.
Full details and description of all the insect pests of the Yard elms will appear in a preliminary paper from Bussey Institution in a short time. It is hoped that enough will be known about them at that time so that an intelligent campaign can be conducted against them, exterminating them entirely, thus saving the trees