382 



SCIENCE. 



[Vol. XIV. No. 357 



the gypsy-moth {Oouria dispar Linn.) of Europe; but as the 

 moths were emerging, and laying their eggs for next year"s brood, 

 there was nothing to recommend at that time except to destroy the 

 moths and their eggs as far as possible, and prepare for the 

 destruction of the caterpillars when they first appear next spring. 



There is a statement in the second volume of the American En- 

 tomologist, p. 1 1 1 (published in 1870), and also in Riley's " Second 

 Missouri Report on Insects," p. 10, that " only a year ago the larva 

 of a certain owlet moth {Hypogymna dispar), which is a great pest 

 in Europe both to fruit-trees and forest-trees, was accidentally intro- 

 duced by a Massachusetts entomologist into New England." 



Mr. Samuel Henshaw and Dr. Hagen of Cambridge both state 

 that the entomologist who introduced this insect was Mr. L. Trou- 

 velot, now living in Paris, but at that time living near Glenwood, 

 Medford, where he attempted some experiments in raising silk from 

 our native silk-worms, and also introduced European species for the 

 same purpose. 



It seems, then, that this was an accidental introduction, but that 

 they have now become acclimated, and are spreading, and doing 

 so much damage as to cause very great alarm. 



The gypsy-moth is abundant in nearly all parts of Europe, north- 

 ern and western Asia, and it even extends as far as Japan. In this 

 country it occurs only in'Medford, Mass., occupying an area in the 

 form of an ellipse about a mile and a half long by half a mile wide. 

 This represents the territory where the outbreak occurred, and 

 where the insects were very abundant. Without doubt, they are 

 distributed in smaller quantities outside of this ellipse, but how far 

 it is now impossible to tell. 



This insect was reported as feeding upon the leaves of apple, 

 cherry, quince, elm, linden, maple, balm of Gilead, birch, oak, 

 willow, wisteria, Norway spruce, and corn. The food-plants 

 given in Europe are apple, pear, plum, cherry, quince, apricot, lime, 

 pomegranate, Imden, elm, birch, beech, oak, poplar, willow, horn- 

 beam, ash, haze'-nut, larch, fir, azalea, myrtle, rose, cabbage, and 

 many others. Curtis, in his "British Entomology," states that 

 they are sometimes very destructive in gardens. Professor W. P. 

 Brooks reported this insect as very abundant in Sapporo, Japan, in 

 1883, and gave strawberry as a food-plant in addition to those 

 mentioned above. 



The fact that this insect has now been in this country for the 

 last twenty years, and has not only held its own, but has multiplied 

 to such an extent as to cause the entire destruction of the fruit- 

 crop and also to defoliate the shade-trees in the infested region, is 

 sufficient cause for alarm. The citizens of Medford are immedi- 

 ately interested, but the entire Commonwealth and country are 

 threatened with one of the worst insect pests of all Europe. In 

 1817 the cork-oaks of southern France suffered severely from the 

 attacks of this insect. One of the papers of that time stated that 

 the beautiful cork-oaks which extended from Barbaste to the city 

 of Podenas were nearly destroyed by the caterpillars of the gypsy- 

 moth. After having devoured the leaves and young acorns, they 

 attacked the fields of corn and millet, and also the grass-lands and 

 fruit-trees. 



In 1878 the plane trees of the public promenades of Lyons were 

 nearly ruined by this same insect. Mr. Fernald states that only 

 last summer he saw the moths in immense numbers on the trees 

 in the Zoological Gardens of Berlin, where the caterpillars had done 

 great injury: and the European works on entomology abound with 

 instances of the destructiveness of this insect. When its long list 

 of food-plants is considered, it will be seen how injurious this in- 

 sect may become if allowed to spread over the country, and become 

 established. 



The opinion was expressed to him by prominent entomologists 

 in Europe, that, if the gypsy-moth should get a foothold in this 

 country, it would become a far greater pest than the Colorado 

 potato-beetle, because it is so prolific, and feeds on so many dif- 

 ferent plants, while the potato-beetle confines itself to a small 

 number. 



In Europe eleven species of V\\^ Ichneunionida, and seven species 

 of flies {Tachina), have been known to attack the eggs and cater- 

 pillars of this moth ; but it is not known that there are any parasit- 

 ic insects in this country that destroy it. Undoubtedly our pre- 

 daceous beetles and bugs destroy more or less of them, and 



mud-wasps and spiders are also to be counted among their 

 enemies. 



All the masses of eggs should be scraped from the trees and 

 other places where the females have deposited them, and burned. 

 Crushing is not sufficient, as possibly some might escape uninjured. 

 This should be done in the fall, winter, or early spring, before the 

 eggs hatch. It is not at all probable that one will find all the egg- 

 masses even with the most careful searching on the trees in a small 

 orchard ; but, when one remembers that this insect deposits its 

 eggs on all kinds of shade and forest trees also, it appears a hope- 

 less task to exterminate this pest by an attempt to destroy the eggs. 

 It is a habit of these caterpillars, after they have emerged, to cluster 

 together on the trunks or branches of the trees between the times 

 of feeding, and this affords an opportunity of destroying vast num- 

 bers by crushing them ; and after they have changed to pupas they 

 may be destroyed wherever they can be found. The female moths 

 are so sluggish in their flight, and so conspicuous, that they may 

 be easily captured and destroyed as soon as they emerge ; yet any- 

 one or all of these methods which have been employed in Europe 

 are not sufficient for their extermination. At best they will only 

 reduce the numbers more or less, according to the thoroughness- 

 with which the work has been done. Mr. Fernald could not learn 

 that any attempts have ever been made in Europe to destroy this 

 insect by means of poisonous insecticides, and it is to this method 

 that we may look for positive results in this country. 



If all the trees in the infested region in Medford be thoroughly 

 showered with Paris-green in water (one pound to a hundred and 

 fifty gallons) soon after the hatching of the eggs in the spring, the 

 young caterpillars will surely be destroyed ; and, if any escape, it 

 will be because of some neglect or ignorance in the use of the in- 

 secticide. It will be absolutely necessary to shower every tree and 

 shrub in that region ; for, if a single tree be neglected, it may yield 

 a crop sufliciently large to eventually restock the region. 



We can hardly feel confident that all these insects can be ex- 

 terqiinated in one year ; but if this work of showering the trees be 

 continued during the months of April and May for two or three 

 years under competent direction, we have no doubt but that they 

 may be entirely destroyed. 



This is, in the opinion of Mr. Fernald, the cheapest and surest 

 method of exterminating this pest, but its effectiveness depends 

 entirely upon the thoroughness and carefulness with which it is 

 done ; and those who do the work must have authority to shower 

 the trees not only on public, but on private grounds. 



As this insect was introduced into this country by an entomolo- 

 gist who carelessly allowed it to escape, the same thing may occur 

 elsewhere if the people of Medford allow the eggs or caterpillars to 

 be sent out of the town. The only proper thing to do with such a 

 dangerous and destructive enemy is to burn it. 



Several different common names have also been given to the in- 

 sect in Europe, as the "sponge-moth," the "gypsy-moth," the 

 "great-headed moth," the " fungus moth," and others. 



ELECTRICAL NEWS. 

 Specific Inductive Capacity. — Mr. W. A. Rudge writes 

 on the above subject to Nature as iullows : " On p. 669 of Ganot's 

 ' Physics ' (eleventh edition) the following statement is found : ' At 

 a fixed distance above a gold leaf electroscope, let an electrified 

 sphere be placed, by which a certain divergence of the leaves is 

 produced. If, now, the charges remaining the same, a disk of sul- 

 phur or of shellac be interposed, the divergence increases, showing 

 that inductive action takes place through the sulphur to a greater 

 extent than through a layer of air of the same thickness.' If this state- 

 ment were correct, there should be less electric action on the side 

 of the ball farthest from the electroscope when the dielectric is in- 

 terposed. To test this, I arranged an experiment as follows : The 

 knob of a charged Leyden jar was placed midway between two - 

 insulated plates of metal, each plate being in connection with an 

 electroscope. The leaves of each electroscope now diveiged to an 

 equal extent. A plate of ebonite was now placed between the 

 knob of the jar and one of the plates. If the' statement above 

 quoted is correct, the leaves of the electroscope in connection with 

 this plate should show an increased divergence, but the reverse 



