5 164 APR 29 1914 Issued January 17, 1913. U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ENTOMOLOGY-CIRCULAR No. 164. L. O. HOWARD, Entomologist and Chief of Bureau. THE GIPSY MOTH AS A FOREST INSECT, WITH SUGGESTIONS AS TO ITS CONTROL. 67364°-13- -1 BY W. F. FISKE, OTRY WASHINGTON: GOVERNMENT PRINTING OFFICE : 1913 BUREAU OF ENTOMOLOG Y. L. O. HOWARD, Entomologist and Chief of Bureau. R. S. CLIFTON, Executive Assistant. W. F. TASTET, Chief Clerk. F. H. CHITTENDEN, in charge of truck crop and stored product insect investigations. A. D. HOPKINS, in charge of forest insect investigations. W. D. HUNTER, in charge of Southern field crop insect investigations. F. M. WEBSTER, in charge of cereal and forage insect investigations. A. L. QUAINTANCE, in charge of deciduous fruit insect investigations. ROLLA P. CURRIE, in charge of editorial work. MABEL COLCORD, in charge of library. PREVENTING SPREAD OF MOтнs. LABORATORY. (At Melrose Highlands, Mass.) A. F. BURGESS, in charge of biological investigations. W. F. FISKE, in charge of parasite and disease investigations. KENNETH W. BROWN, C. W. COLLINS, J. J. CULVER, JOHN E. DUDLEY, Jr., HARTLEY R. GOOCH, CHAS. W. MINOTT, F. H. MOSHER, HAROLD A. PRESTON, E. A. PROCTOR, JOHN V. Schaffner, Jr., M. B. Shepherd, C. W. STOCK well, J. N. SUMMERS, W. B. Turner, Reginald WoolDRIDGE, assistants. FIELD WORK. D. M. ROGERS, in charge of Eastern territory. L. H. WORTHLEY, in charge of Western territory. HAROLD A. AMES, I. L. BAILEY, HENRY N. BEAN, FRANK W. GRAVES, Jr., H. L. MCINTYRE, D. G. MURPHY, CHARLES E. TOTMAN, H. W. VINTON, assistants. 1.5. Dept. of Agi. 8-26-1929 1 CIRCULAR No. 164. Issued January 17, 1913. United States Department of Agriculture. BUREAU Of entomolOGY. L. O. HOWARD, Entomologist and Chief of Bureau. THE GIPSY MOTH AS A FOREST INSECT, WITH SUGGESTIONS AS TO ITS CONTROL.1 By W. F. FISKE, THE GIPSY-MOTH SITUATION: PAST AND PRESENT. It has been said of the gipsy moth that the caterpillar is almost omnivorous so far as foliage is concerned, and the early reports published by the State Board of Agriculture of Massachusetts abound in references confirmatory of this statement. It is in fact incontrovertible, from the mass of evidence furnished by these reports as well as by the contemporaneous accounts in the press, that the gipsy moth was formerly almost unique amongst injurious insects in its ability to destroy all sorts of vegetation. Upon the occasion of its historic outbreak in Medford and Malden, beginning about 1889, and again in the larger outbreak following a few years after the extermination work was concluded in 1900, not only forest, shade, and ornamental trees but orchards, gardens, and fields were defoliated and devastated. And when the food supply was exhausted the starving caterpillars, by force of numbers alone, constituted a veritable plague, rendering the streets almost impassable to pedestrians, massing upon and entering houses, and infesting the bedrooms, the kitchens, and even the dining tables as well as all outdoors. It is needless to state that these conditions no longer prevail. Caterpillars there are, during their season; egg masses in varying abundance are everywhere to be found in neglected woodlands, and thousands of dead and dying trees stand as evidence that unless it be rendered still further innocuous the gipsy moth is still a very living factor to be considered in the future of American forestry. But the accounts of its earlier depredations seem all but incredible when compared with conditions to-day. It is no longer prominent as a field and garden pest. 1 A consideration of the parasites of the gipsy moth (Porthetria dispar L.), the "wilt" disease, and the natural resistance of certain species of trees to attack by the gipsy moth, as applied to the management of forests. 1 As an orchard insect it is not infrequently eclipsed by the American tent caterpillar. Even the forests have suffered less than early predictions would have led one to expect. It is certain that the situation has become measurably improved within recent years. area. CAUSES OF THE IMPROVED CONDITIONS. This obvious improvement is in part only apparent and in part very real and due to a variety of causes. The apparent amelioration is due to the fact that the gipsy moth is at present most active in a belt of towns beyond the limits of the densely populated metropolitan Were Boston's parks again to be infested as formerly; were the forests in the Middlesex Fells, for example, to be defoliated, a wave of remonstrance would arise which might be heard halfway across the continent. But a thousand acres of forest in the sparsely populated and financially poor towns 30 to 50 miles away may be repeatedly defoliated and ultimately destroyed without creating more than a ripple in comparison. And this latter is precisely what is taking place at the present time. It will be necessary to wait until in its slow progress the gipsy moth invades another great metropolitan area before popular interest will be aroused to an extent comparable to that existing in Massachusetts a few years ago. The real amelioration so noticeable in the metropolitan district, and distinctly in evidence everywhere, is due to at least four main causes: (1) The perfection and standardization of the methods for artificial repression; (2) the death of a large proportion of the more susceptible trees or their removal from the infested woodlands; (3) the importation of parasitic and predatory insect enemies; and (4) the development of the "wilt" disease. As it is intended at this time to consider the gipsy moth strictly as a forest insect no mention need be made of the methods for artificially suppressing it. On account of their expense these methods can not be used in forests other than those which it is desired to protect for æsthetic and sentimental reasons. RESULTS OF PARASITE IMPORTATION. There are about 30 species of insect enemies of the gipsy moth which appear to be of importance in checking its increase in Europe and Japan. All of the promising species have been imported and colonized under more or less satisfactory conditions in America. Not all have successfully accommodated themselves to their new environment. About one-third of the total appear to have done so and to be steadily increasing in efficiency in accordance with their powers of multiplication and dispersion. It was hoped that more of them would acclimatize themselves; it was feared that the number might be less. On the whole, the results are decidedly satisfying, and the State of Massachusetts and the United States Department of Agriculture have no cause to regret having undertaken the unexpectedly formidable task of parasite importation. Within a territory centering a little to the northward of Boston, it may be conservatively stated that fully 50 per cent of the eggs, caterpillars, or pupæ of the gipsy moth, in the aggregate, were destroyed by imported parasites in 1912. The territory over which the imported insect enemies have spread is not yet very extensive, but it is extending notably from year to year, and there is every reason to believe that the mortality to which the gipsy moth is already subjected in this central portion of the infested area will eventually be considerably increased throughout its whole extent. Some additional work will be done toward assisting in the dispersion of certain species, and it may be that a new attempt will be made to import under more satisfactory conditions certain others which appear not to have established themselves as the result of earlier attempts. Otherwise the work of parasite importation may be considered as completed. THE "WILT" DISEASE OF THE GIPSY MOTH. More than to the parasites, more than to the perfection of the methods of artificial suppression, the amelioration in conditions is due to the "wilt" disease. This is a malady similar to or suggestive of the flacherie of the silkworm. According to recent investigations it is due to parasitism by a bacterium which has been described under the name of Gyrococcus flaccidifex by its discoverers, Messrs. Glaser and Chapman, working under the direction of Dr. W. M. Wheeler, of the Bussey Institution. While it is not positively proved that this bacterium is the cause of the disease, there are no good grounds for doubting and many for believing that it is. Confirmation is expected as the result of further cooperative investigations now under way by the Bureau of Entomology and the Bussey Institution. Although we know very little of the bacterium, we know much of the malady. According to the most trustworthy observers it first appeared about 1903 or 1904 in certain of the worst infested forests, and by 1907, when the present writer first became associated with the gipsy-moth work, it was everywhere in evidence throughout the infested area. It seemed slightly to increase in the years immediately following and to have reached a climax about 1911. At the present time, fortunately, there is nothing to indicate that it is at all likely to become much if any less effective in the immediate future. We do not yet know how the caterpillars originally become infected, but once infected there is hardly room for doubting that the organism itself is conveyed from one generation to another through the egg. Simple infection is by no means sufficient to cause death. On |