/ 1 4- U. S. DEPARTMENT OF AGRICULTURE, BUREAU OF ENTOMOLOGY CIRCULAR No. 164. L. O. HOWARD. Entomologist *nd Chief oi Bureau. THE GIPSY MOTH AS A FOREST INSECT. WITH M SeESTIOHS kS TO lis CONTEOL. BY W. F. FISKE, 673W-13 1 WA4HINCTON : GOVERNMENT WIINTINO OFFKE : 1(11 BUREA U OF EKTOMDWa Y. L. 0. Howard, Entomologist and Chief of Bureau. C. L. Marlatt, Entomologist and Acting Chief in Absence of Chief. R. S. Clifton, Executive Assistant. W. F. Tastet, Chief Cleric. F. II. Chittenden, in charge of truck crop and stored product insect investigations. A. I). Hopkins, in charge of forest insect investigations. W. I). 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. E. V. Phillips in charge of ha culture. Rolla P. Currie, in charge of editorial work. Mabel Colcord, in charge of library. Preventing Spread of Moths. laboratory. (At Melrose Highlands, Mass.) A. F. Burgess, in charge of biological i /instigations: 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. II. Worthley, in charge of Western territory. Harold A. Ames, I. L. Bailey, Henry X. Bean. Frank W. Graves, Jr., II. L. McIntyre, D. G. Murphy, Charles E. Totman, H. W. Vinton, assistants. ii Circular No. 164 I nited States Department of Agriculture, BUREAU OK ENTOMOLOGY. L. O. HOWARD, Entomologist and Chief of Bureau. Till QIPST MMTII AS v FOHKsl INSECT, WITH SUGGESTIONS kS TO ITS CONTROL By W. I'. FisKi Agi mi OIFST-MOTB Mil \ii<>\. PAST \\i> PRESENT. It has been said of the gipsy moth thai the caterpillar is almosl omnivorous so far as foliage is concerned, and the earrj reports ] >u I >- lished by the State Board <>l' Agriculture of Massachusetts abound in references confirmatory of this statement. It is in facl incontro- \ ertible, from the ma— of evidence furnished by these reports as well as by the contemporaneous accounts in the press, thai thegipsj moth was formerly almosl unique amongst injurious insects in its ability to destroy all sorts of vegetation. Upon the occasion of it- historic outbreak in Medford and Maiden, beginning about 1889, mid again in the larger outbreak following a few years after the extermination work was concluded in 1900, not only forest, -hade, and ornamental t fees hut Orchards, gardens, and Held- were defoliated and deva-t at ed. Ami when the food supplj 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 kitchen-, and even the dining tables as well as all outdoors. It i- needless to state that these conditions no longerprevail. ( later- pillars there are, during their season ; egg masses in varying abundance are everywhere to be found in neglected woodland-, and thousands of dead and dying tree- -tand as evidence that unless it he rendered -till further innocuous the gipsy moth i- -till a very living factor to be considered in the future of American forestry. Bui the accounts of its earlier depredations seem all hut incredible when compared with condition- to-dav. It i- no longer prominent as a field and garden pesl nstderattao < noth (Porthr/ria dhpar I It" disease, natural raa ol trees to attack by thi I I . .*{ are decidedl) satisfying, and the State ol Massachusetts and the United States Department of Agriculture have qo cause to regrel having undertaken the unexpected!) formidable task of parasite importation. Within a territory centering a little to the uorthward of Boston, it may be conservative^ 9tated thai fulrj 50 per cent of the eggs, caterpillars, or pupa? of the gipsy moth, in the ate, were destroyed by imported parasites in 1912. The territory over which the imported insect enemies have spread is uol yel verj exten- sive, but ii is extending not a hi \ from year to year, and there is e\ ery reason to believe thai the mortality to which the gipsj moth is already subjected in this central portion of the infested area will eventually be considerably increased throughout it- whole extent, ae additional work will be done toward assisting in the dispersion of certain species, and it may be thai a ne\t attempl will be made to import under more sal isfactorj conditions certain others which appear uol 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 QEPS1 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 "will " disease. This is a malady similar to or suggestive of the flacherie of the silkworm. According to recent investigations it is i\uv to parasitism by a bacterium which has been described under the name t>( Qyrococeus Hacddifex by its discoverers, Messrs. Glaser and Chapman, working under the direction of Dr. W. M. Wheeler, of the Busse) Institution. While it is uot positively proved thai this bacterium is the cause of the disease, there are no good grounds for doubting and many for believing thai it is. Confirmation is expected as the resull 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 <>f the malady. According to the mosl trustworthy observers it first appeared aboul 1903 or 1904 in certain of the worsl infested forests, and t>\ 1907, when the present writer lir-t became associated with the gipsy-moth work, it was everywhere in evidence throughout the infested area. It seemed slight ly to increase in the year- immediately following and to have reached a climax aboul 1911. At the present time, fortunately, there is nothing to indicate that it is at all likely to become much if any le>» effective in the immediate future. We do not yet know how the caterpillars originally become infected, hut once infected there is hardly room for doubting thai the organ- ism itself is conveyed from one generation to another through the Simple infection is by no mean- sufficient to cause death. On 4 THE GIPSY MOTH AS A FOREST INSECT. the contrary, if conditions are otherwise favorable an infected cater- pillar will live, complete its transformations, and (it is believed) transmit the germs of the disease directly to its offspring. Under these circumstances generation could follow generation, and in the course of time the race of gipsy moths might gradually be purged of the disease, so that eventually only a few individuals would carry it. This would all be changed were the infected caterpillars to become weakened through any other cause. Under such circumstances an apparently healthy individual will sicken and die, and in a surpris- ingly short time the entire contents of its body will be resolved into a black liquid containing countless myriads of the germs of disease where before there were but few. Death is particularly likely to ensue upon the topmost twig of the tree, and the disintegrated bod}* of the victim, breaking of its own weight, permits the black poison to defile the foliage below. Another caterpillar feeding upon this foliage contracts the disease and, provided it also be weakened through any other cause, it quickly dies, and the process is repeated. It is very evident that the more abundant the caterpillars chance to be in a given forest the greater the chance that the disease will be thus transmitted; the more these caterpillars chance to be weakened through a lack of suitable food the more likely the}' are quickly to succumb and transmit the malady to their fellows. It thus results that when a forest is threatened with defoliation by infected cater- pillars the disease becomes epidemic and spreads with astounding rapidity. A yet more important cause for the development of the "wilt " than partial defoliation is to be found in unfavorable food. It used to be easy to rear caterpillars in the laboratory upon lettuce, for example, when they were free from the taint of the disease, but it is practically impossible to do so to-day, if American eggs are used. With foreign eggs, collected from a locality where the wilt is not prevalent, this did not prove to be the case in the course of experiments recently conducted at the Gipsy Moth Parasite Laboratory, which it is pro- posed to repeat the present year. Nor is lettuce an exception among foods. The same may be said of practically all herbaceous plants, and, fortunately, of a considerable variety of trees and shrubs. Herein lies the most potent cause for the less destructive character of the gipsy moth in recent years, according to the opinion of the writer — an opinion which it is expected will be abundantly confirmed in the course of the coming summer. And herein lies the real secret of the practical resistance of certain species of trees to gipsy-moth attack. Till: UIPS1 Moiii \- \ PORES! INSECT. 5 \i; 1 11 li I M I riUZATION 01 i ill WILT " I h seems necessarj to emphasize the foregoing statement that the resistance of certain species of trees is directly due to 1 1 m ■ suscepti- bility of caterpillars, feeding upon the foliage of these trees, t<> death through the "wilt" disease, and thus incidentally i<> emphasize 1 1 1< • \cr\ greal importance of the disease itself. Since this disease is believed to result from parasitism l>\ a specific bacterium, tin- propo- sition of increasing its efficiency through infecting the caterpillara artificiallj with cultures of th< v bacterium al mice suggests itself. This possibility is largely precluded if equal emphasis be laid upon tin" real character of the disease, bo far as we are able to (let ermine it , either through intensive study of the organism believed to be respon- sible or tlirough observations upon its activities in the field. At the presenl time wherever caterpillars ;ire to be found, infected caterpillars have been found also upon everj occasion when search for them has been made. Furthermore, even though the infection were proved to he w ind-horne. as has heen contended and there is room for doubl regarding this mosl essentia] fact every particle of reliable evidence indicate- that slightly infected caterpillars remain reasonably healthy. The condition of the caterpillars upon the arti- ficially protected trees along the roadsides in localities where an epi- demic o( the disease prevails in the main body of the forest i-. or ought to be, sufficient evidence of this. Notwithstanding thai these caterpillars are forced to feed upon trees which have heen sprayed, and notwithstanding that through artificial suppression alone are they prevented from stripping the trees, those which escape death amid the various dangers by which they are artificially encompassed remain remarkably healthy, and with comparatively rare exceptions there i> an increase in cumbers of the fresh egg masses each tail over the number which escaped the creosote brush the preceding spring. Rather elaborate experiment-- have heen carried on in thepa-t to determine whether the disease could he practically transmitted through infected food, and with one not a hie exception those who have conducted such experiments have concluded that artificial utilization of the disease in this manner i- impracticable. If the writer is not mis- taken ir was Dr. Roland Thaxter. of Harvard University, a specialist of high Standing upon the vegetable parasites of insects, who was the lirst actually to experiment along this line, and who was the first to he convinced of it> futility. In 1908 Dr. Herbert Johnson, work- ing for the State of Massachusetts in cooperation with Harvard University, conducted an elaborate series of field experiments to test this theory, hut with no more promising results. Further investigation and experimentation were conducted coop- eratively by the State of Massachusetts and Harvard University 6 THE GIPSY, MOTH AS A FOREST INSECT. under the direction of Dr. E. A. Murk and Dr. Theobald Smith. working more or less independently, and still the results were nega- tive 1 . The present writer, in connection with the work of parasite importation, conducted experiments of a similar nature but with the usual outcome. The difficulty in every case was due to the fact that it was impossible to secure healthy caterpillars for either the experiment or its check. It made no difference whether the cater- pillars were fed with the infected food or not, large numbers would die in any event, and there seemed to be no noticeable difference between the mortality in the experiments and in the checks. It remained for Mr. William Reiff, at one time a laborator}- assist- ant in the Bussey Institution, to claim success where others had failed. His experiments were, in their essential characters, like those of his predecessors. He fed some caterpillars upon an unfavorable food, and they contracted the disease and died, exactly as had resulted in' all other recent attempts to rear caterpillars in the laboratory from American eggs. When the sick and dead individuals were placed upon badly infested trees in the field a mortality was noticed among the other caterpillars in the vicinity. The fact was cheerfully ignored that a similar mortality might be observed in every other locality where the same degree of infestation prevailed, and no attempt was made systematically to determine exactly what happened in these other places. In this most important respect the experiments con- ducted by Mr. Reiff differed from those conducted by Dr. Johnson. Such a series of check observations has been made the past sea- son, quite incidentally, hi connection with the field-observation work fts conducted by Mr. A. F. Burgess of the Bureau of Entomology. The final results of this work for the season are not yet available, but the writer, who has personally visited the majority of the observation points, of which perhaps 20 per cent chanced to be in the immediate vicinity of disease plantings of the summer before, has been abso- lutely unable to distinguish a single point of difference between the treated and the untreated localities. In every badly infested locality complete or partial defoliation with all its attendant consequences resulted. The severity of the injury differed notably in different localities, as was to be expected, but if extreme instances were to be cited it would not be difficult to select localities where no disease was planted in which conditions at the close of the season were very much better than in others where plantings had been made. Nor is there anything unusual anywhere in the infested territory to differentiate conditions this fall from those prevailing a year or two ago. In fact it is the writer's personal impression that rather more pine has been seriously injured in 1912 than in 1911, and that the con- dition of the oak is worse than he has ever seen it before. In short, nothing whatever that is tangible has yet come to the attention of I III. i.ll'.M \ln I II VS v pokes r INSECT. , anyone associated with the Bureau of Entomo liich can be used in Biipporl of the contention that the disease ma} be rendered more efficient through artificial dispersion. The extensive experiments con ducted by the State of Massachusetts in 1912, in pursuance of its policy in investigate thoroughly every possible method of ridding its forests of the gips) moth, would appear to have resulted exactly as did the earlier and less elaborate aeries r lucted \<\ Dr. Johnson and others \\iii.\i CONTROl 01 I'll I " QIPS1 MOTH \lti:n\u A large portion of the past two years has been spenl by the writer abroad in studying the gips} moth in its original habitat. The objects of this over-sea work were several. Ii was desired more exactly to determine the part played by the parasites in holding the gips) moth in check in the European forests and to ascertain whether all the important species of parasites had been discovered. Were promising new species found, attempts wen to be made to ship large quantities to America for experimental colonization. Above all. it was hoped to learn whether the assumption upon which the parasite work had originally been undertaken was well grounded; that is, whether all the factors responsible for the natural control of the gipsj moth in the European forests were presenl and active in America, saving only the parasites. 'The results of this work are in part supplemented and in part confirmed by the observations of Mr. L. II \Vuitl,le\ . who has spenl the better part of a year abroad, and in part the\ are pertinent to this discussion. It was found that the invasion of the greater pari of Europe by the gipsy moth some three to se\en years ago had spent its force, and that, although small cumbers of the inseel might be found in aearl) every oak foresl visited in Italj and Germany, it was found abundant in verj few. It was difficult to ascertain definitely what had occurred to check this general invasion, bul it is certain that a disease similar in all its external manifestations to the American "wilt" (and also to the well-known and beneficent ' ' w ipfelkrank- heit " of the nun moth 1 had prevailed in many localities, including some in Kussi;i. Italy, and Germany. It seemed to have heel) epi- demic in all nf the localities which had been badly infested by the gipsy moth. It was also evident that following the enormous decrease in cum- bers brought about l>\ this epidemic there was nothing like the phe- nomenal increase of the straggling remainder so frequently observed in America. Instead, when an innocuous minimum was reached this desirable condition was maintained for an indefinite and some- times for a protracted period. It appeared highly probable and this 8 T11K GIPS1 MOTH AS A FOBBST INSECT. probability was supported by definite confirmatory evidence — that the failure of the moth immediately to increase was due as much as anything to the parasites; and a wholly unexpected and phenomenal rate of parasitism was found to prevail in some localities. Inci- dentally several species of parasites until then unrecognized as impor- tant or promising were found and large numbers were shipped to America. The role played by the parasites, however, was obviously less important than had been assumed when the work of parasite impor- tation was inaugurated. Generally speaking, it appeared that though the increase of the moth was prevented or retarded through para- sitism, it was principally if not invariably through disease that an actual outbreak was checked. This was borne out by the circumstances associated with two local outbreaks in southern Italy: One in Sicily, in the extensive cork- oak forest of San Pietro, near Caltagirone, and the other in the communal forest of the town of Gioia Tauro, in Calabria. In both of these localities, and particularly in the latter, the parasites were abundant and varied. In neither were they able to prevent the rapid increase of the moth, much less to bring about a decrease. In both the defoliation of a large portion of the forest was absolutely complete, and in neither was the "wilt" disease operative. The conditions in the foresl of San Pietro were the more interesting and instructive because the invasion there was of no less than 12 years' standing. At no time, according to the statements of the local authorities, had the entire forest been defoliated at once, but the invasion would sweep back and forth over it, so that the trees were defoliated about every second or third year. Here in this Sicilian forest all the amazing stories told of the gipsy moth upon the occasion of its historic outbreak in Maiden and Med- ford were abundantly substantiated. There were no streets and very few houses, but there were a few gardens, fields, orchards, and vineyards, and an abundance of wild plants, shrubby and herbaceous. Of them all, wild and cultivated, hardly a dozen species were immune from attack. There were places where at times the ground was black with the caterpillars as they came out of the forest, which no longer afforded them either food or protection, and invaded the fields and open spaces. Here the combination of burning sand and blazing sun resulted in the agonizing death of myriads, and their dead bodies could have been swept up by the bushel. Neither in 1911 nor in 1912 was a single caterpillar dying of the wilt observed. Parasites were abundant each year, destroying approximately 90 per cent, which was far from sufficient to prevent increase. Each year the millions which died of starvation and 1 HE <.li'M MO I ii 18 \ l ORES i I N 3E( I . exposure dried up without showing traces* oj the decomposition in\ ariabh associated « n h i he ''will As a resuh , in the worst infested port ions of the f oresl there w be very iVw eggs, but the caterpillars would always be remarka health} the next Beason, and as the parasites would be attracted to the inure badrj infested parts of the foresl the rate of increa i i where would be Bimpl} astounding, In the Calabrian foresl the invasion had not passed beyond its preliminary stages in 1911, but l>\ 1912 it had reached it- mi mum. Here conditions were the same, pxcepl thai as the surround- ing fields offered better protection from the glaring sun the cater- pillars coming oul of the foresl lived longeranddid more damage to the crops. The trees in both forests were absolutel} stripped of foli whenever there were sufficient caterpillars and not left, as they commonly in America, where the disease is prevalent, with a sprinkling of partly eaten leaves. All kinds seemed to suffer alike. There were no conifers except a few cypress (related to and with foliage very like our white cedar which gre\s along an agave hedj bordering the Sicilian forest. These were stripped as bare as the oaks. In no locality other than these two, whether European or Amei i< has the writer been able to find the gipsy ninth unaccompanied by disease. Ii is the prevalence of such extraordinary conditions and their similarity to those w tiicfa prevailed in America before the devel- opment of the disease which serve to convince him thai the present improved conditions are so largely asions l ["he pa 1. The dis i I'll"- chars* tor of t hi fori The parasites are promising to become about as efficient here as in the European forests, and it musl not l>c forgotten that m> more has been claimed for them than that thej would render the gips) moth as innocuous here as in it-- original habitat. The disease, t<>". is about as efficient here as it is abroad. Perhaps it is not too much, then, to demand that forest conditions in America be made to conform a little more nearh to those of the countries in winch the gipsj moth is native, particularly to those of 1 • main . Tli i- does no1 by any means imprj the adoption of European foresl methods en masse, but rather that the forests be given a little better attention and that provision be made f< >r the actual or inevitable invasion by the u r ip^.\ ninth through the elimination <>f those tn most likely t<> be injured and their replacement by others less 3us ceptible and not infrequently mine valuable. As a matter of fact this removal and replacement is taking place automatically in the territory thai has been longest infested, bul the natural process i- Tim often accompanied by unnecessary destruction of other trees and unnecessary pecuniary loss. RELATIVE SUSCEPTIBILITl •>! AMERICAN FORES! iREES TO QIPSY MOTH \ I r \i K As has been stated, at the time when the firsl real invasion by the gipsy moth in the United States was at it- height it was believed that scarcely any forest, shade, or fruit tree was resistant to it- attack. And. as has been explained, the appearance of disease, fol- lowing a period of uninterrupted increase of the moth, was accom- panied by a change in tln> respect. That this change was \rvy largely due to the disease is further indicated by the similarity of the conditions prevailing in certain Sicilian and (alahrian for to-day to those prevailing in Medford and Maiden in 1889 The relative susceptibility of certain tree-, to injury and the relative immunity of others is therefore very largely due to, and dependei t upon, the presence of disease. But since i he disease is everywhere and bids fair to remain until possibly the gipsy moth i- freed of its taint through a long -erics of generations passed under ideally healthy and favorable surroundings, there seems t.> be no reason why the neces- sary dependence should not he placed in it without fear of serious consequences. 12 THE GIPSY MOTH AS A FOREST INSECT. At the same time the writer is averse to committing himself to the extent of stating positively that the methods of forest management to be suggested further on will invariably prove successful. Ho wishes to emphasize the truth as he sees it. thai the relative freedom from injury of certain type- of forest is dependent upon the "wilt," and that their continued well-being will largely depend upon the persistence of this malady. lie wishes further to emphasize his belief that an increase in the efficiency of the parasites will add to the variety of the forests which may he cultivated to advantage, but that it will not result in pro- tection to all the types which at present are to he found in the area of infestation. The suggestion that experiments hi' conducted to determine the practicability of the "reserve-tree" method of culti- vating oak is made only on the assumption that the parasites will eventually render more efficient aid than at present and in a le>s limited portion of the infested territory. In 1908 Mr. A. II. Kirkland, in his third annual report as superin- tendent of work against the gipsy and brown-tail moths, first called attention to the apparent resistance of white pine unless associated with hardwood trees. A year later Mr. L. II. "Wort blew his acting successor, published in the next report the results of experiments winch showed that this was indeed the case, and that pure stands of pine might he protected at a very reasonable expense. Partly in pursuance of this idea, and partly independently, Messrs. 1). M. Rogers and A. F. Burgess, of the Bureau of Entomology, after observing the activities of the moth in the field, concluded that in addition to pine most of the other conifers, and certain hardwood trees as well, might he considered as sufficiently resistant to escape serious injury. Ash, hickory, and maple were mentioned, and recommenda- tion was made jointly in Bulletin 87 of this bureau that such trees he planted in place of those which were destroyed. These recommendations, made in 1910, were succeeded by further observations by employees of the Bureau of Entomology and the Massachusetts State forester's office with the result that by the fall of 1911 several important additions had been made to the list. Exact information, however, was lacking, and because of the obvious need for it a series of investigations was inaugurated under the direction of Mr. Burgess. These were so planned as to demon- strate not only what happened when caterpillars were confined to certain soils of food indoors, hut exactly what happened following invasion of different types of forest out of doors. More than 250 observation points were selected, representative of every type of pure and mixed forest which could he easily located within the infested area. In addition to pure stands of pine, oak. and birch, for example. I III 0IP8> Mmi ii \- \ i 0R1 BT INSECT. 1 ■ "• mixed Btands of oak and pine, birch and pine, oak and birch, etc., w ere Belectod. \ circle hhi feel in diameter was laid off around h central tree in the midst of the foresl selected, every tree included was numbered, and notes were made covering its species, size, general condition, and degree of infestation. The total number <>f egg masses t" be found within the circle was recorded, and their increase or decrease from year to year, together with the actual extent of injury resulting in ee of bad infestation, was to be taken as the measure of resistance offered bj thai particular type of forest. Although tin- work is n<>! yel complete, the results already Becured are too pertinent and valuable to be reserved until its conclusion. Rather for convenience than because the proposed classification i- altogether natural the inure common shade and foresl trees of New England ma\ be separated into groups in accordance with their wsceptibilit) to injury. The Bret of these groups consists of those trees upon w bich the ninth following its establishment norma II \ increases to the poinl of complete or nearly complete defoliation. After the first defoliation the moth's numbers may be very greatly reduced or the} may remain practically the same. In the one case one or more years may elapse before de- foliation is repeated. In the other, the forest ma\ be defoliated for several year- in succession. In either case the trees are likely to be severely injured and to die. This group, bo far as known, is composed exclusively of the various oaks, with the possible but not proved exception of the shrubby Bpecies These may be considered as representing the most favored food plants of the gipsy moth. The second group consists of those tree- which appear to be espe- cially favorable to the increase of the moth immediately following its establishment. Almost always, however, at about the time when defoliation would result were the colon] to remain healthy, it receives a set hack. The trees are rareh completely s< ripped, and though they may be from one-half to three-fourths defoliated for several successive years, death rarely follow-. The most notable representatives of this group are several of the tree willows and the gray birch. It i- possible thai some other trees will eventually he included; hut none other 30 commonly encoun- tered in the territory at pre-ent infested by the gipsj moth will Compare directly with birch or willow These, through the protec- tion which they afford to incipient colonic- of the gipsy moth, act a- incubators or breeders. In the third group are to he placed t ho-e trees upon which the gipsj moth rarely increases to the extent usual upon gray birch 01 willow. Upon Borne it will increase until a fair degree of infestation 14 THE GIPSY .MOTH AS A FOREST [NSECT. results, l)iit rarely to the point of noticeable defoliation. Upon others it will barely hold its own, and upon a few there wiJ] be a decrease in abundance following any considerable degree of accidental infesta- tion. These trees are what is here called resistant, and nearly all of them are practically that, so long as the "wilt " remains as efficient as it is at present. In this group are to be placed the pines; the spruces; in all prob- ability fir; hemlock, with scarcely a doubt, though it is notably more favorable than pine as a food plant: the junipers and cedars: doubt- fully larch: some, but perhaps not all, of the poplars; chestnut: probably beech: yellow birch, black birch, and probably paper birch: apparently all the species of hickory; butternut: sycamore: Ameri- can elm, and probably the other species of elm: apparently hack- berry; sassafras: catalpa; the various species of ash: black locust and honey locust: black cherry and bird cherry: probably mountain ash: all the indigenous and probably the European species of maple, although the Norway maple is more liable to attack than others: boxelder; tupelo; horse-chestnut; ailanthus; tulip tree, and undoubt- edly many other of the less commonly planted shade and ornamental trees. A few of the more common trees have not yet been definitely placed, notably basswood or linden, ironwood. and hop hornbeam. RELATIVE SUSCEPTIBILITY OF MIXED FORESTS. It would thus appear that in a territory in which both disease and parasites, or disease alone, is prevalent the gipsy moth becomes peculiarly an enemy of oak, and this is true in so far as pure stands of trees are concerned, or of isolated trees. It is not so true of mixed stands, however, as was pointed out by Mr. Kirkland and by Mr. Worthley in respect to pine mingled with hardwood, and these mixed stands may generally be considered just a little more resistant than would be a pure stand of the least resistant tree and considerably less resistant than a pure stand of the most resistant tree which goes to make up any considerable portion of the mixture. Thus a pine and oak forest is slightly less liable to injury than a pure stand of oak and much more liable than a pure stand of pine. The same might be said of an oak and hickory mixture or one of oak and chestnut. The reason is that the caterpillars, increasing uninterrupt- edly upon oak. will finally be forced to leave it and will strip other trees upon which they would not increase to anything like a similar extent if they were forced to feed upon them for generation after generation. They do not always do this, it is true, but they do it very often, particularly when the oak is abundant and scattered evenly throughout the forest. I ill. GDPB1 HOTS 18 \ i 0BE8T tv-M i . 1 B Since hemlock i- better liked Mian pine l>\ tin- caterpillars, a mixed growth of oak ami hemlock is much more likely in he destroyed com- pletely than :i mixed growth «>t' oak ami pine: ami since graj birch i- ii< » i -i. favorable a food plant as oak, a birch and pine mixture ie not nearly ><> likely In Buffer a- a mixed -land of nak ami pine. Apparent!} no fear oeed he felt as to the safety of anj mixture whatever of which all the component parts could he considered as resistant it" they were Btanding in pure growth. As •<> the greater resistance of an oak tree when Btanding Burrounded l>> chestnut ami hickory, a- compared with another of the same Bpecies and vigor surrounded by oak. there is room for Further investigation. It can only he -aid that the protection thus afforded i<> oak through being associated with other tree- i- not particularly Btriking. RELATION or UNDERBRUSB TO THE FOREST. li i- interesting, in connection with the relative resistance of forest trees, to note that the aprouts and, t>> a Ie-- extent, the seedlingB, are not bo liable to injury a- are Larger tree- of the same Bpecies. This i- tine even of pine, mile— the writer ha- misinterpreted his field observations. Il i- al-o true thai for the nio-t part tin- common species ol -liruh- to he found growing a- u.nderhru-h in a forest air unfavorable BS food for tin- gipsy moth that i- to -ay. they ma\ he classed with the resistant species of trees. It i- certainly logical and. to that extent, reasonable to suppose that underbrush will he found to play quite an important part in the protection of the forest. Caterpillars falling from tree- in a pure -land of oak devoid of underbrush will find their way back to oak and be little tin- worse for the adventure. Caterpillars falling in a similar manner in a forest full of underbrush will not find their way hack bo readily, and the eating of strange food for h time will render them Ie— resistant to disease, more likely to die. and therein more likely to transmit the germs of disease to their fellows. It is a subject well worthy of further study ami experimentation and one to which it is hoped to devote considerable attention in the course of the coming year, the mote -o since it ha- special bearing upon the suggestion that oak might possibly he protected by adopt- ing the method ot cutting so a- to leave reserve trees. BE] \TIY1. RESISTANCE OF DIFFERENT TREES OF tut SAME SPECIES. It would appear from numerou- observations that certain indi- vidual trees (of red oak. for example) are much better able to with- stand the attack ot the irip^y moth than others of the same species growing in the same wood lot. These tree-, although they are sub- jected to the same degree of defoliation, will live when all around 16 THE GIPSY MOTH AS A FOREST INSECT. them die and even take on new life and vigor through coming into a larger share of light and space. It is yet to be determined whether these trees are more resistant or whether, through standing in some favored pockets of richer soil, they simply survive through the pos- session of a more vigorous constitution. It is undoubtedly true that vigorous, rapidly growing trees are more resistant than other trees of the same species less vigorous and less rapidly growing. Thus oak trees around the border of an infested wood lot, with more room to expand their roots and branches, not infrequently live when all or nearly all the more crowded indi- viduals in the depths of the wood lot die. It is also true that isolated trees withstand a greater degree of defoliation than those in dense growth. Advantage seems to have been taken of this principle in the method of growing oak formerly in vogue in Germany, for, if the writer is correctly informed, the finest and largest oaks in the Empire are grown more or less isolated and parked. When the relative immu- nity of young sprouts is also considered, a very logical reason is suggested for the fact that the method of leaving reserve trees, scattered over a territory devoted principally to the growth of sprouts or coppice, finds so much favor in certain parts of Europe. The-e reserve trees are left practically isolated in the forests which have come to the writer's personal attention, and the sprouts, for which there is a read} 7 market, unfortunately lacking in America, are cut at quite frequent intervals. SUGGESTIONS FOR THE MANAGEMENT OF FOREST LANDS WITH REFER- ENCE TO THE GIPSY MOTH. It is by no means to be understood that because of the gipsy moth all the oak in this country is foredoomed to destruction, but atten- tion must be called to what is undoubtedly the truth, that unless parasitism or disease, or something else not at present recognized as a variable factor in the natural control of this pest, develops to an extent unknown in either America or Europe, pure and mixed stands of oak will be seriously injured. Not only is the oak itself liable to injury, but also other trees mixed with it. It is yet too soon to state definitely whether, in localities where there is no oak, other trees may not act as breeders of the moths to an equally disastrous extent. For instance, the paper birch in the north woods may so foster it as to bring about the defoliation of adjacent spruce. The results of field-observation work in occasional bits of forest in the infested territory when 1 spruce and birch occur are not in themselves sufficient to settle the question, because condi- tions so far from the large body of boreal forest can not be considered i in-: i.ll-s\ Mm ii \> \ i (mm ST INBBOT. 17 as rralh typical. s.> far as they go, however, they indicate thai the gipsy moth is not to l)<" feared outside the range of the oak dr in forests inside that range provided the oak, and possibly one or two other species of unimportant trees, be eliminated. There are, therefore, two phases of the complex problem of gipsy- moth control in forests which must be considered. Firet, how best to eliminate the oak and -ecure it- replacement by other ami, if possible, more valuable trees; and, second, how besl to proteel the oak from aerious injury in localities where little else can he grown to adi antage. In a large portion of the area at present infested by the lt i j > - > moth the solution is almost absurdly simple. This is the natural home of the white pine, one of the most valuable timber trees to be found in the whole Temperate Zone. In a way the oak is an interloper. Over a large part of New England the white pine was once preeminent . and it would become so again were the country to be deserted by civilized man. The pine reproduces freely, if given half a chance, hut there are thousands of acres in the aggregate in which a natural reproduction of pine is being retarded, destroyed even, through the mare circumstance that the oak chanced to secure a running start, by sprouting, when the Land was last cut over. The German forester who would permit such conditions to prevail would be considered hopelessly, even criminally insane. Under such circumstances oak is to be considered a- a weed, and the advent of the L'ip^y moth as a blessing when, a-- sometime-- happens, it takes the oak and leaves the pine. If it would always do jusl that and nothing more it- progress mighl be watched with a certain degree of complacency. But it does not always stop at that and, what i> worse, injudicious cutting not infrequently results in greater damage than would be done by the gipsy mot h it-elf. The larger pines are apt to be cut or broken down, and the -mailer one-, unable to compete with the rapidly growing oak sprout-, are quickly in no better condition than before. The natural program, therefore, in every pine and oak mixture, i- so to eliminate the oak a- to afford the pine a better opportunity to take possession of the ground. How thi- may he-t be accom- plished depends entirely upon the individual characteristics of any particular wood lot. And. furthermore, it i- strictly a problem in applied forestry and one for the forester, not for the entomologist, to solve. In a great many localities where the white pine doe- not grow naturally, or in winch it has been destroyed through injudicious cut- ting and extensive forest tire-, there is to be found a stand of oak mingled with other hardwoods. In these forests tin- solution is not reached quite so easily or -o satisfactorily. Chestnut (saving only 18 THE GIPSY MOTH AS A FOREST INSECT. for the possible injury by the blight), hickory, paper birch, sugar maple, and ash all find conditions greatly to their liking in one or another part of New England, and all are desirable substitutes for oak. There are certainly some, and probably numerous localities in which, through nothing more than the exercise of a little care and intelligent management, the oak may be removed and its natural replacement by these other hardwoods may be secured with a mini- mum of expense. It is in the pure stands of oak, or in those of oak mingled with much less valuable trees, all too frequently to be found throughout the infested area, that the problem becomes acute. Here the land must be allowed practically to go to waste, or planting must be resorted to, or else some attempt must be made to maintain a growth of oak. The most simple method would seem to be the leaving of reserve trees. The chances at present are that this may not work very well, but unless the relief which we have every reason to expect through the further development of the parasites be denied us, there is a chance that in the near future it will prove to be a fairly satisfactory, cheap, and eventually remunerative alternative to permitting the forests to be entirely destroyed. It must not be forgotten that when the oaks are left to die from the gipsy-moth attack they very rarely sprout, and a pure oak stand is apt to degenerate into a thicket of gray birch or something even less intrinsically valuable. If the oak be thinned in advance of the gipsy-moth invasion the sprouts will be resistant for a period of years at least, perhaps until the parasites become so efficient that they wall protect the stand of reserve trees. It is even possible, if the thinning be done far enough in advance of the inva- sion, that the reserve trees will have increased sufficiently in vigor to resist the attack of the moth until the parasites shall have multi- plied sufficiently to hold it in check. All these suggestions are to be treated as such and as nothing more. The author is no forester and can not pretend to recommend, but only to suggest. He has had the advantage, however, of four years' study of the insects injurious to American forests under the direction of the foremost forest entomologist in America, and through subsequent study of the gipsy moth in America and abroad has reached certain pretty definite conclusions. The gipsy moth is distinctly a menace to our forests, but it is really no more to be feared than any one of several forest insects native to tins country. If the situation be rightly viewed, and a serious attempt be made to cope with it, it is certain that the results will redound not only to the benefit of the forests in general but to that of the country at large. I ill QIP81 \i"i ii IB A 1 OR] BT INSECT, I '» 1111: i\i\iim\m 1:1 .i,H ii.-i MIA i - 01 Mil Mil \TH>\ The immediate requirements of the situation are thai the work be conducted in a hearts spirit of cooperation among all concerned. For tin' purpose of solving t li<' problems associated with the elimina- tion of oak and its replacement by other and, if possible, more valuable trees the Bureau of Entomology has allied itself with the United Stales Forest Service and hopes also to continue in hearty accord with the various State foresters most immediately concerned. The further investigation of the "wilt" disease will l>e conducted l>\ the Bureau of Entomology and the Bussej Institution working together. Additional information concerning the relative resist- ance of various t ices standing singly, or in pure or mixed growth, will be compiled by the Bureau of Entomology, which will also concern itself to discover exactly whal progress is being made by thi> imported parasites and predatory enemies. These lines of investigation, observation, and research are all being directed with one single end in view, hov besl to protecl the forest. Of greal importance, also, is the work intended to restrict the spread of the gipsy moth beyond the boundaries of New England. A certain amount of natural spread can not l>e prevented, especially through uiml. but it U hoped entirely to eliminate the danger of an immensely more rapid spread through artificial channels, upon Qursery Btock, forest products, etc., shipped from infested to oonin- fested territory. It is also hoped considerably to retard the slow and inevitable natural dispersion, even though it is impossible entirely to prevent it. The natural progression of tlie moth to the westward, which is the most to be feared and also the easiest to retard, will be more effectively controlled if the woodland colonies along the western frontier, and for that matter over the whole infested area, are sup- pressed. It is from these that the wind spread largely comes about. The longer they can be kept down, the less the likelihood of their becoming a source of infestation to the country beyond. Especially along the frontier the colonic-, .ire at first feu ami scattered, and while everything within reason will be done toward their suppression, there is believed to be justification for asking the active cooperation of foresl owner-- directly interested. If through a modification in their methods of h andling their property they can save themselves from what would now appeal- in many in-~t.ii to be certain loss; if they can at the same time put their fort in such condition a- not only to protecl them in the future but also to render them more intrinsically valuable; and. finally, if they can render a not inconsiderable public service through helping to 20 THE GIPSY MOTH AS A FOREST INSECT. retard the progress of the moth into territory not as yet infested, the request for such cooperation would appear to be well justified. This project, to bring good out of the evil that has resulted through the establishment of the gipsy moth, by combating it through methods which would make American forests more valuable than they have ever been before, is no mere vision. Evidence enough of its practicability in the case of the mixed stands of oak and pine already referred to is easily found and sufficiently convincing. That other types of natural forests may be handled so as to make the outcome advantageous to the forest owner as well as to the whole country, it is only reasonable to expect. The Forest Service and the Bureau of Entomology will attempt to do their share of the work, through cooperative study of the technical aspects of the problem. Experimental and demonstrative work must precede definite recommendation, and in this the aid and assistance of the forest owners themselves must be secured. If a spirit of hearty cooperation can be established and maintained it would seem as though the problem would all but solve itself. Approved: James Wilson, Secretary of Agriculture. Washington, D. C, November J, 1912. ADDITIONAL COPIES of this publication il may be procured from the Superintend- ent of Documents, Government Printing Office, Washington, D. C, at 5 cents per copy UNIVERSITY OF FLORIDA 3 1262 09216 5637