National Geographic : 1914 Jul
Photo from U. S. Department of Agriculture TRAYS IN WHICH TINY FLIES, Schedius (EGG PARASITES), WERE REARED IN THE LABORATORY AT MELROSE HIGHLANDS, MASS. Each tray is stocked with I,ooo,ooo gipsy-moth eggs. About 90,000 parasites were reared in each tray for colonization in the field in 1913 (see also page 66) the streets and in the gardens and in the orchards, and the forest attack is becom ing more and more alleviated by these means. But it is not intended that we should rely upon parasites and diseases alone to protect the forests. Careful studies of the feeding habits of the gipsy moth in particular have shown that, al though when full grown it attacks almost all sorts of living vegetation, when young it can live successfully upon but a few plants. It must grow large and strong before it can eat and assimilate the leaves of most trees. A pure stand of pine or any other conifer, for example, cannot be harmed by the gipsy-moth, and the same may be said of hickory, maple, chestnut, alder, beech, and of mixed for ests of these kinds of trees; but where a mixed forest contains oaks and gray birches, then it will suffer, because these two kinds of trees are the preferred food plants of these destructive leaf-eaters. It results therefore that practical meth ods of thinning can often be adopted that will almost perfectly protect a mixed for est, and experiments have shown that mixtures of chestnut, ash, red maple, pine, and hickory are practically uninjured by the gipsy-moth. In these cases the oak scrub has been cut out and the larger oaks and gray birch have been removed.