National Geographic : 1914 Jul
and it was thought that the species spread only while in the caterpillar stage, by crawling upon trolley cars, upon automo biles and other vehicles, and upon the clothes of pedestrians, and that it was thus carried for the most part along the main traveled highways and thus gained a large spread. In consequence, for several years the attention of the government workers was focused upon these main traveled roads. and the roadsides were cleaned up to a depth of from 50 to 1oo feet, and the trees that were left were banded and sprayed, leaving the roadsides in such condition that there was no possibility of caterpillars falling upon passing vehicles or persons. It is undoubtedly true that by this means a far greater spread than has occurred was prevented. A MOTH AEROPLANE More recently, however, it has been discovered that a very important means of spread had been overlooked. As the young caterpillar of the gipsy - moth hatches from the egg it spins down on warm days suspended by a silken thread, is caught up by the wind and carried sometimes for miles before it succeeds in attaching itself to a tree or shrub. Large-scale experiments in the last two or three years, conducted by erecting enormous wire screens (see page 41) at various distances to the windward from infested woods, the screens being coated with a sticky substance, have shown that many young caterpillars are carried in this way to a distance of six miles or more. This discovery has altered the methods of endeavoring to prevent the further spread of this insect, and as a result the operations are now carried on most in tensively along the border of spread, es pecial attention being given to colonies that occur on hillsides, since young cater pillars from these colonies are more likely to be spread to great distances by the wind. Another method of preventing the spread of the gipsy-moth is the inspec tion of products shipped from the in fested region. This measure is very im portant and has been carried on with increasing care year after year. A per fected system has been inaugurated by the comparatively recently established Photo from U. S. Department of Agriculture THIS TUBE CONTAINS I,600 TINY FLIES, Schedius kuvance The flies, when liberated, will deposit their eggs in the eggs of the gipsy-moth, thus de stroying the latter (see page 66).