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Page:Popular Science Monthly Volume 72.djvu/416

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412
POPULAR SCIENCE MONTHLY

Moth and Brown-tail Moth.—If parasitic insects (hymenopterous and dipterous) are at the present time behind the predatory ones, it does not make their efficacy any the less that the work that they accomplish is not so immediate and is less easily brought about.

Everybody knows how some ladybirds will free a tree from plant lice or scale insects, while there is some trouble in observing how a parasitic insect lays its eggs in the interior of a caterpillar. Moreover, while the victims of a predaceous insect are killed immediately, the insects pierced by the hymenopterous insect continue in most cases to feed and grow, and it is only in the following generation that the good work can be seen. Finally, to appreciate the just value of parasites, it should be remarked that several species, in certain cases more than thirty, live at the expense of a single plant-feeding species and join forces to hold it in check. To reestablish the equilibrium in a country into which a plant-feeding species has been imported, not only one of these parasitic species, but as many as possible, should be sought for and should be naturalized.

In a few years we will be much more certain concerning the advantages to be drawn from the utilization of these beneficial species.

No experiment in any case can be better conceived to illustrate this question than the gigantic undertaking now carried on by the government of the United States which has for its object the importation of the European parasites of Bombycids, up to the present unmasterable scourges, which ravage without interruption the trees of Massachusetts.

These two insects, Liparis dispar and L. chrysorrhœa, are European insects which have been accidentally introduced into Massachusetts, the first in 1868, and the second in 1890. It is difficult to imagine the intensity of the ravages of these two insects. The damage occasioned by the first of them, which is popularly known in America under the name of the gipsy moth, is to-day celebrated in certain localities, notably in the suburbs of Medford, which was the first point of infestation. The caterpillars became so abundant that all the trees in the parks, woods and public streets were entirely defoliated, and presented, in mid-summer, a winter aspect. These trees, deprived of their vitality, were killed by thousands. In certain suburban quarters, one could see the walls of the houses carpeted with caterpillars, and the roads themselves so invaded that it was impossible to walk without crushing them by hundreds. A special committee was started to organize the fight, and from 1889 to 1895, $525,000 was spent in work against the destruction of this species. For the year 1897 alone, $150,000 was voted by the legislature.

As to chrysorrhœa, known to Americans under the name of the brown-tail moth, although it has shown itself extremely injurious, it is