/ PAEASITES OF THE GYPSY AND BROWN-TAIL MOTHS INTRODUCED INTO MASSACHUSETTS. Sl--i^ 4^^.-1^, < 1 ° c o 5" ^ w Q c8 : ffi : a : 14 ■3 ■ o '■ a o ■ a) : m ■ o ■ 53 : o ■ o ■ ^ : u. ■ 1^1 P^ : 6 5"5 1s| 00 Anastatus bifasciatus, Schediua kuvana? • > 3 O Crossocoaniia sp Theronia atalautte, Chalcis obscurata, GYPSY AND BROW^^-TAIL MOTHS. 17 How thev work iu effecting the control of the moth in their native country is best indicated in the table, which, while it needs explanation, tells the story much plainer than it would be possible to tell in words. Opposite the name of each parasite, extending across a certain number of the vertical columns, is a dotted and a solid line. The vertical columns indicate different stages in the development and transformations of the gypsy moth, as egg, caterpillar and pupa, and these are still further divided into caterpillars of different sizes and eggs and pupee of different ages and conditions. At the head of each column is stated the approximate number of days during which the indi- vidual gypsy moth remains in that particular stage. The dotted line following the name of the parasite indicates those stages in the life of the gypsy moth during which it is liable to be attacked by the parasite in question, and it will be seen that in a number of instances, as, for example, Chalcis and Theronia, this period is exceedingly short. The solid line indi- cates the stages in the life of the gypsy moth during which it is likely to contain the parasite in its body. This, it may also be noted, varies considerably. Crossocosmia, for example, gains lodgment in the active caterpillar while it is only about half grown, and the extension of the solid line across all of the columns which stand for the later caterpillar stages, as well as for all of the pupal stages, indicates that the larvae of this para- site do not leave the host caterpillar until after it has trans- formed to a pupa, and until the moth would naturally have emerged had the pupa remained healthy and unparasitized. The main fact, which it is particularly desired to emphasize, is that every stage in the transformations of the gypsy moth, from the time the eggs are first deposited until the caterpillars are full grown and transformed to pupse, is subject to the attack of one or more parasites. It is also liable to attack at any time throughout this period except during the cold weather in the winter, when there is no insect activity. This is exactly w^hat is meant by the sequence of parasites, and, in the opinion of those most thoroughly informed, it is the condition which it is absolutely necessary to bring about in America before complete cjontrol can be effected. 18 IMPORTED PARASITES. PARASITES OF THE GYPSY MOTH IN EUROPE. Table 2 is similar in construetioii and illustrates the para- sitism of the gypsy moth in Europe. There are at least 22 species, and possibly one or two more of slight importance, known to attack the moth in various European countries, and of these, 15 are considered to be important. Of the 22, 2 are identical in all respects with 2 which occur in Japan, and are considered to be the same species. Six or 7 are quite distinctly ditferent from any which have yet been received from Japan, and it is impossible to separate the remainder from +he Japa- nese species by habit and method of attack alone. The most of them, however, appear to be different in their final appear- ance as adults, and are considered, for the present, as repre- senting different species. There are several reasons why there should be a longer list of European than of Japanese parasites, principal among which is the greater variety of climate represented by the dift'erent European countries. Some of the parasites are confined al- most exclusively to the Mediterranean region, others to Russia and eastern Europe generally, while others are more common in the northern, central and Avestern portions. It is almost cer- tain that other parasites will be found in other parts of the Jap- anese empire from which small quantities of parasite material have been received, but it is very doubtful if any of importance will be added to the list from European sources. It will be noted, if the table is scrutinized, that exactly the same conditions as regards the sequence of parasites obtain in Europe as in Japan. As in the table first given, every stage of the moth from the newly deposited egg to the pupa is open to attack by one or more species of parasite, and the sequence is perfect. GYPSY AND BROWN-TAIL MOTHS. 19 ■3 < 00 a o < Pi Pre- pupa, 2 Days. < 02 < > -a" *f CO g Q c3 : : a : ■ b Q : ■0 • 1 t Q a • -0 sr; ■ cj : c .■ 1 ^ : fe : 6 o — PARASITES. Anastatus bifasciatus, Apanteles solitarius, , 1 > "3 Ij a C3 a =? p. Blepliaripa scutellata, .... Compsilura concinnata, .... Zygobothria gilva, Carcelia gnava, Trieholyga grandis, .... Tachina larvarum Parasetigena segregata, .... Ichneumon disparis Theronia atalantse, Chalcis flavipes Monodontomerus aereus, Calosoma sycophanta, .... 20 IMPORTED PARASITES. PARASITES OF THE GYPSY MOTH IN AMERICA. There is just one parasite of the gypsy moth in xVmeriea, na- tive to the country, which ranks in importance with the least of those included in the tables of Japanese and European para- sites. This is Theronia, and the native species is so similar in habit as to be indistinguishable from the other species of the same genus which attack the same host in Europe and Japan, and it cannot as yet be stated with assurance that it is not the same. It is literally the least important of all of the parasites listed, and the maximum effectiveness in America is, if any- thing, less than in any foreign country. It cannot be credited with destroying more than 1 in 30 or 1 in 50 of the pupie, on the average, and never more than 1 in 10 under the most fa- vorable conditions ever observed. A table of the native para- sites of the gypsy moth (leaving out the rare and inconsequen- tial species), prepared for comparison with those of the Euro- pean and Japanese, would consist of this species and no other, and the difference is obvious. In Table 3 are listed all of the parasites which have been received from Europe or Japan in sufficient numbers to make possible satisfactory colonization in America. There are 4 or 5 more which have been liberated in small numbers, or which are on hand ready for liberation in the spring, including Tachina japonica and CJinlcis ohscumfa. Japanese representatives of the European species, and having nearly identical habits. There are also on hand at the laboratory a large number of the hiber- nating puparia of Parasetigena segrecjata and Crossocosmla sp., both of which are parasites of some promise, and neither of which has vet been colonized. GYPSY AND BROWN-TAIL MOTHS. 21 ^ g 5^ Si, (TO K 5 < i < i o < •< 00 ^ Q im oa fa Q Pre- pupa, 2 Days. " ■ : 1 O •«: t. CB .J < > < J5 d o 5 Q 3 9 a 1 Blepliaripa scutollata Compsilui'a concinnata, .... Zygoljotliria gilva Carcelia gnava, Tricholyga grandis, .... Tachina larvarum Therouia fulvescens, .... Chalcis flavipes, Monodontomerus aereus, Calosoma sycophanta 22 IMPORTED PARASITES. It is not by any means assnred that all of those parasites are established here, bnt it is possible that they are, or that they will be before another season passes. Some that are known to be living in the field, and which are apparently in a very good way toward becoming permanent fixtnres in the American fanna, have had their freedom for less than one year ; and there is no assurance that a species is established nntil it has completed at least one cycle of the seasons unprotected in the open. A few of them, as will be shown later, will be the better for artificial assistance in dispersion, etc. One, Chalcis, onght to be imported in larger numbers, bnt with this one possible ex- ception, each that is listed has been liberated under the most favorable circumstances which it is possible to provide. Especial attention is called to the fact that the sequence is complete as it stands. Every stage of the moth is provided with a parasite which will attack it, if given the opportunity, and in every respect the table compares favorably with that illustrative of the Japanese parasites or of the European. It represents, in this most important respect, the climax of the endeavors of the past five years, and it has been accomplished only during the ])ast five months. If the writer were assured of the firm estab- lishment of each of the species listed, and that each would be- come as efficient in Massachusetts as it is in the countries from which it came, he would state without reservation that the work of parasite introduction was successfully accomplished. The reader must not confuse the accomplishment of parasite introduction with the accomplishment of the end which it is desired to achieve. It goes without saying, when the halnts of the parasites are taken into consideration, that the few paltry thousands, which it has been possible to secure through methods of importation which were the best which experience could devise, must be allowed sufiicient time to increase to the millions and billions necessary to cope with the tremendous quantities of gypsy moths which are everywhere in evidence throughout the infested district, wherever the ex]iensive methods of hand suppression have not been employed. Fortunately, this increase, if it follows colonization, will be by geometrical progression, exactly as has been the case with the gypsy moth; and it will, most fortunately, be much more rapid Kn;. -2. — An;ist;itus H'lvatlv cnlar.nL'i Fid. 3. — Anastatus: hilnTiiatin,^ larva from gyiisy niotli eg.n' ureatlv enlarged. GYPSY AND BROA¥N-TAIL MOTHS. 23 than it was in the case of the gypsy moth, owing to the greater dispersive powers of nearly all of the parasites. With one exception, they more nearly resemble the brown-tail moth in this respect, being gifted with the power of flight ; and, as is well known, the territory covered by this insect is mnch more extensive than that covered by the gypsy moth, althongh the latter was introduced into America more than twenty years earlier. Another enormons step in advance, which has marked the progress of the work the present season, is the accnmnlation of certain valuable data which throw much-needed light upon the subject of parasite dispersion, and which have tended more than anything which has come about since the earliest beginning to encourage those who have been charged with direction of the work. For the first time it is possible to calculate, with some foundation upon fact, the probable outcome of the under- taking. It is difficult to do this on the small amount of abso- lutely authentic information at hand, and to vouch for the accuracy of the conclusions with any degree of assurance ; but the attempt has been made, and will appear in the concluding paragraphs. First, in order to make more clear the ground which supports these conclusions, a brief account of each of the introduced parasites of the gypsy moth will be given. Xo attempts have been made to go into technical detail concerning the lives and habits of these several species, further than is necessary to give a general idea of their methods of attack, and of the hopes and fears which are felt for the future of each. Pakasites of the Egg. Anastatus hifasciatus. This minute parasite (Fig. 1 ) attacks the newly deposited eggs of the gypsy moth during the brief interval which elapses before the embryonic caterpillars develop. Its eggs (Fig. 2) are deposited singly, one in each individual egg of the host, and its larva? feed upon the substance of the host eggs and become full fed in about three weeks. They then enter on a long rest- ing stage, snugly ensconced within the limited confines of the 24 IMPORTED PARASITES. shc41 (Fig, C), and do not resume activity until the middle of the following summer, ten months later. The transformations to pupa (Fig. 4) and adult (Fig. 1) follow in the course of two or three weeks, the latter emerge, and in a few days are ready to deposit eggs for another generation within the newly deposited eggs of the next generation of the gypsy moth. There is thus but one generation of the parasite each year, and its life cycle, which corresponds to the annual cycle, is correlated exactly with that of the insect which serves as its host. It is a native of both Europe and Japan, and is sometimes a common and effective parasite in either country. It is very unevenly distributed, however, especially in Europe, and a great many lots of eggs have been received which did not contain any of the parasite. For two years large numbers of egg masses were imported from various European and Japanese localities, and not a single specimen was secured. Finally, in the spring of 1908 it issued almost simultaneously from Russian and from Japanese eggs, and was soon determined to be a primary parasite. About 500 individuals were liberated that summer, but under conditions which were unsatisfactory in many re- spects, and no reproduction in the field resulted, so far as has been determined. Encouraged by the knowledge that there was ai> egg parasite which could be secured through the winter importation of eggs, — a fact which was far from being established \\p to the rearing of the first specimens of Anastatus, ■ — ■ larger imj>ortations from numerous localities were made during the winter of 1008— 01). As before, only a part of these shipments were productive, but among them was one consisting of five sacks of about 1,000 egg masses each, from Professor Jablonowski of Budapest, which were collected in five different Hungarian localities. From three of these only an insignificant quantity of parasites was secured, one lot being entirely unparasitized. From two, how- ever, was secured by far the largest number of egg parasites ever received from any source, there being more than 80,000 all told. It illustrates very well the uneven distribution of the species in Europe. These, together with some others from other sources, were liberated in five colonies, in quite widely separated localities Fi(i. 4.— Aiiastatiis: puiia from Kyi'sy niotli ej^s, greatly enlarged. Fig. .">. — ^(iicdii/s l-iiniiiif : .laiiane^ii; iiarasitc of gypsy iiiotli eggs, adult female, greatly enlarged. GYPSY AND BROWN-TAIL MOTHS. 25 within the infested area. In every instance they attacked the freshly deposited eggs of the moth with avidity, and reproduc- tion in the field under perfectly natural conditions resulted. At the present time there are many thousands of the larva? of the parasite hibernating in the open in the immediate vicinity of the colonies, exactly as they would do in their native land, and there is hardly room to doubt that they will issue next summer in the normal manner. In one respect only is the insect disappointing. It appears to resemble the gypsy moth, in that the females do not fly. The utmost endeavors have been made to determine accurately the distance to which it travelled from each of the points where it was liberated, and the results indicate that 100 feet is about the limit. This is a rate of dispersion slower than that of the gypsy moth itself, and it would take a great many years for the parasite to spread over the entire infested area. Additional importations will be made during the present winter, and it is hoped that a large number of colonies will be established next summer, but no immediate benefits can be expected. ScJtedius Jiuvance. Most fortunately it is not necessary to depend exclusively upon the Anastatus as a parasite of the eggs of the gypsy moth, for in Japan there is another (Fig. 5) with similar habits, in so far as the object of its attack is identical ; outside of this fact, it is different in many important particulars. Instead of con- fining its attack to the freshly deposited eggs, it rather prefers those in which the embryonic caterpillars have developed, and, since these caterpillars are fully formed, and so far as appear- ances go ready to hatch within three weeks after the eggs are deposited in the summer, Schedius is actually a parasite of the unhatched caterpillar, rather than of the egg. Instead of re- quiring a full year to complete the life cycle from egg to adult, it completes a generation once every three or four weeks during the warmer part of the summer, or in the winter if kept in rooms properly warmed. It is thus able to go through at least two generations during the fall, after the eggs of the moth have been deposited, and before cold weather puts a stop to its activity. 26 IMPORTED PARASITES. The history of its introduetiou into America is most interest- ing, and, except for the fact that it was so Lmg delayed in ex- ecution, forms one of the most satisfactory episodes in the entire work of parasite introduction. As long ago as the spring of 1907 a few dead adults w^ere se- cured in an importation of gypsy egg masses received during the winter from Japan, but none were living on receipt. During the winter next following larger importations were made, and many thousands of eggs, from wdiich some parasite had issued, were found, but not a single living specimen was obtained. It was evident that it completed its transformations and issued in the fall, and that, if it hibernated in the eggs, it was warmed to activity while the packages were in transit to America, and the adult parasites either died or escaped en route. In the fall, winter and spring of 1908-09 a large quantity of eggs of the gypsy moth were received from Japan, the shipments beginning early in the fall and continuing until nearly time for the caterpillars to hatch in the spring. The first, received in September, contained hundreds, possibly thousands, of the para- sites, which had issued from the eggs en route, and all of which, as usual, had died ; not a single living individual was received. Specimens were referred to Dr. How-ard, who found that they i'e]iresented an entirely new and hitherto undescribed species, which he named after Professor Ivuwana, w^ho collected and sent the eggs from which they had issued. A single pair of living specimens rewarded the careful attention which was lavished upon the importations received later in the fall and during the winter, and it was not until April, 1909, that a mated pair could be secured. During that month a total of 11 individuals issued from cages containing Japanese eggs recently received. This small number served as the beginning of a series of ex- ]ieriments in propagation, which succeeded so well that in Au- gust several thousands were available for liberation in the field. In September and again in October additional colonies were es- tal)lished, and during the fall, some r)0,000 in all Avere given their freedom. After September the bulk of those reared were kept for exten- sive propagation work in the laboratory, and at the present time (Februarv 1) a conservative estimate of the numl)er in various Fig. 6. — Gypsy motli eg^ niiiss, show- ing exit holes ot Schedius, enltirged .•il>out four times. GYPSY AND BROWN-TAIL MOTHS. 27 stages in the rei^roduction cages is 2,000,000. It is bv no means sure that the species will go through the winter in the open as successfully as is hoped will he the case ; but no obstacle threat- ens to prevent the liberation of several millions of the parasite during the summer of 1910. The reproduction of the parasite in the field, as a result of the earlier attempts at colonization, has been far in excess of expectations. The rate of reproduction in the laboratory, which averages only about ten-fold each generation, was greatly ex- ceeded, and hundreds of thousands of eggs were kno\\ni to be parasitized in the immediate vicinity of the colony sites. In the one colony which has been most carefully watched the para- sitized eggs (Fig. 6) average some 30 to the mass everywhere within a radius of 50 yards, and the masses in a few places are so thick as to hide the liark on the trees. Beyond 50 yards the numbers fall off very rapidly ; Init the s]iecies has been found several hundred yards from the ]ioint of liberation, in striking contrast to Anastatus, which traveled only 100 feet. It is hoped that a strong colony will be established in evevy town in the infested district during the coming summer ; and if the same rate of dispersion indicated during the past fall con- tinues, and the parasite demonstrates its ability to exist under American conditions during the entire year, it should be gen- erally established throughout the iufested area in two or three years more. It must not be forgotten, however, that it has not yet proven itself adaptable to American conditions at all seasons. Like the other eQ:g parasite, Anastatus, the only known host is the gypsy moth ; but, unlike that species, its life is not correlated to that of its host. It is not known how it passes the winter, and, al- though living adults issue within a few days from eii:g, masses brought in from the vicinity of the colonies in December, it is possible that they will not survive the cold weather which is bound to follow in January and February.^ There is also a possibility that in Japan there is some other sort of egfi subject to its attack, in which it passes a generation during the early * This statement was written in December. It has since been found that all of the larvae and pupse of the parasites perished during the cold weather in January, but that adult parasites, of which there are known to be many in the field, lived through it. Whether they will survive the remainder of the winter is yet to be demonstrated. 28 IMPORTED PARASITES. summer, before the eggs of the gypsy moth are available, and that there will be no native insect which will give what may prove to be some such necessary aid to its continued existence. Parasites of the Catekpillak. Glyptapanteles fulvipes. Although this was almost the first parasite of the gypsy moth which attracted any attention in Massachusetts, and the first which it was attemj^ted to import after the beginning of active work, it was one of the last to be liberated under satisfactory conditions, and its establishment in America is not yet certain. Extraordinary methods were necessary to bring it to America living and healthy, and it was not until Prof. Trevor Kincaid, who was selected by Dr. Howard as the best available man for the purpose, visited Japan, and personally superintended the collection and shipment of the cocoons, that success was achieved. The story of Professor Kincaid's experiences and of the difficul- ties which he met and overcame is interesting. He was accorded groat and material assistance by the Japanese entomologists, and the work inaugurated by him in 1908, was continued with even greater success in 1909, The adult parasite (Fig. 7) deposits a number of eggs be- neath the skin of the active caterpillars, and any stage, from the first to and possibly including the last, may be attacked. The larva?, hatching from the eggs, become full grown in from two to three weeks, and then work their way out through the skin of the still living caterpillar (Fig, 8) within the body of which they fed. Each spins for itself immediately afterward, f(U- its better protection during its later stages, a small white cocoon. The number of parasites nourished by a single host varies in accordance with its size. There may be as few as 2 or 3 in very small caterpillars, or 100 or more in those which are nearly full grown. The unfortunate victim of attack does not, as a rule, die im- mediately after the emergence of the parasite larvje and the spin- ning of their cocoons, but it never voluntarily moves from the spot. Its appearance, both before and after death, surrounded by and seeming to brood over the cocoons, is peculiar and char- acteristic, and once seen can never be mistaken (Fig. 9). Fl( i./!//i/i/p(intt/(>!i f/ilriji,.-i : Japani'sc and Kuropeaii cattT- pillar parasite, ailult, urcatly cnlarned. Fk;. .'^. — Glyptapanteles: larva? leavi gyiisj- moth caterpillar, colarged. Fiu. 1). — (ilyptapaiiteles : dead gypsy moth caterpillar surroimded by cocoons of parasite, slightly enlarged. GYPSY AND BROWN-TAIL MOTHS. 29 There is ample opportunity for two generations of tbe para- site annually upon the caterpillars of one generation of the gypsy moth. This is the rule in the countries to which it is native, and is to be expected in America. The parasite was described from Europe more than seventy- five years ago, and has been known to be a parasite of the gypsy moth for a long time. Later it was described under a different name from Japan, and the Japanese parasite was for a time considered to be different from the European. Abso- lutely no differences in life and habit which can serve to sepa- rate the two are known, and, as the adults are also indistinguish- able in appearance, they are considered to be identical. It has been the subject of frequent mention under the name of Apanteles, as well as of Glyptapanteles, in the various reports of the superintendent of moth work, from the first to the fourth ; and Dr. Howard, in the account of his first trip to Europe in the interests of parasite introduction, tells of its occurrence in the suburbs of Vienna. Largely on account of the fact that it is much more conspicuous than many of the other parasites, it has attracted more general attention. The Rev. IT. A. Loomis, a missionary, and resident of Yokohama, was the first to call attention to its importance in Japan, and made several unsuc- cessful attempts to send it to America. Dr. G. P. Clinton, mycologist of the Connecticut Agricultural Experiment Station, who visited Japan in 1909, observed the parasite at work, and reported most favorably upon its efficiency as a check to the moth. Numerous other attempts on the part of European and Japanese entomologists, including one elaborate experiment, which involved the shipment of a large wire-screened cage con- taining a living tree with gypsy caterpillars and the parasite, were made, but with uniformly ill success. Upon every oc- casion the parasites all emerged from their cocoons and died en route. When every other means failed, Professor Kincaid, as already stated, was deputed to visit Japan, and to make all necessary arrangements for the transportation of the parasite cocoons in cold storage to America. The arrangements which he perfected provided for continuous cold storage, not only en route across the Pacific, but during practically every moment from the time 30 IMPORTED PARASITES. the cocoons were collected in the field in Japan until they were received at the laboratory in Melrose. Events justified the adoption of every precaution, and, with all the care, only a small part of the very large quantity of cocoons which he col- lected reached their destination in good condition. Hundreds of thousands were collected and shipped, and less than 50,000 were received alive, — nearly all in one shipment in July. The season in Massachusetts was early, and nearly all of the gypsy caterpillars had pupated by that time, so that there was no opportunity for the parasite to increase in the field upon this host that season. In 1909 the sites of the colonies were fre- quently visited, but not a single parasitized caterpillar was found which could be traced to colonizations of the year before. Keen disappointment was at first felt, but later developments have tended to throw a more encouraging light upon the situa- tion. In 1909 importations were continued, through the magnificent efforts of Prof. S. L Kuwana of the Imperial Agricultural Experiment Station, at Tokio, with much more satisfactory results. In 1908 the season in Japan was very late, and it was not practicable to send any of the cocoons of the parasite until June and July ; while in America the season was early, and by that time all of the caterpillars, as has already been stated, had pupated. In 1909 the season was rather early in Japan and correspondingly late in America; and besides, through special effort, Professor Kuwana was enabled to send a few thousands of the cocoons of the first generation, which reached the labora- tory early in June. About 1,000 adults emerged from these cocoons after receipt, and the most of them were placed in one colony in a cold situation on the l^orth Shore, where the cater- pillars were greatly retarded, and where there were still some in the first stage. The remainder were colonized in warmer localities, where the caterpillars were one stage farther advanced. Immediate success followed the planting of these colonies. Within three weeks cocoons were found in each, and the number of parasitized caterpillars was gratifyingly large. A very care- ful investigation was conducted, to determine the pro]3ortion which was attacked by native secondary parasites ; and. while this was so verv laroe in one instance as seriously to jeopardize GYPSY AND BROWN-TAIL MOTHS. 31 the success of the experiment, it was not so large in the others. There were several thousands of this first generation known to have developed in the open upon American soil, which issued from the cocoons some four or five weeks after the colonies were established, hut in only that one on the North Shore, where the caterpillars were in the first and second stages when the parasites were liberated, was there a full second generation. Here the larger caterpillars were again attacked, and an abundant second generation of the parasite followed, ^feanwhile, additional shipments of cocoons of the second Japanese generation were received early enough to permit of a generation in the open upon the native caterpillars, and sev- eral other colonies were successfully established. It is kno^^^l that there were many thousands of the parasite issuing in at least five diiferent localities during August, but immediately thereafter they were completely lost to sight, and it is futile to hope to recover traces of them before another spring. Until the late summer of 1909 nothing occurred to indicate that this parasite would be likely to fly for any great distance from the point of its liberation ; and, as has been already stated, it was looked for in vain in the summer of 1909 in the imme- diate vicinity of the colonies of the year before. In -July, 1909, a strong colony was planted in an isolated woodland cnlony of gypsy moths in the town of Milton. It was rather confidently expected that it would attack these caterpillars so extensively as to destroy the major portion ; but it was the cause of some surprise, when the locality was visited after the parasites of the new generation had mostly issued from the affected caterpillars, to find a smaller number of cocoons than there were individuals liberated in the first place, and only about one-fourth, perhaps less, of the caterpillars attacked. The circumstance was as dis- couraging as anything which had gone before, and for a few days nothing happened to change its complexion. Then, to the intense surprise of the writer, Mr. Charles W, Minott, field agent of the central division, sent to the laboratory a hona-fide example of the parasite, which had been collected in the Blue Hills reservation, upwards of a mile away. There was no pos- sible source except the ]\Iilton colon> , and a spread of upwards of a mile in somethino' under a week was indicated bevond dis- 32 IMPORTED PARASITES. pute. At almost the same time the brood of Monodontomerus was found for the first time in pupoB of the gypsy moth in the field ; and when the history of this species is considered, in the connection which it bears toward the circumstances surrounding the recovery of the Glyptapanteles so far from the j)oint where it was liberated, the whole situation is altered. Granted that the parasite disperses at the rate of one mile in each week of activity, and that it is able to adapt its life and habits to the climate and conditions in America, the chances are, that, instead of looking for it in the immediate vicinity of the points of colonization, it is quite as likely to be found almost anywhere in the infested area within 25 miles of Boston. If it is thus generally distributed, very large numbers in the ag-gregate may exist, and it may increase at a rate as rapid as that of Monodontomerus, and at the same time escape detection until the summer of 1911 or 1912.^ This is not only possible, but probable, unless a number of careful observers assist in the recovery of the parasite next sea- son; and if any one should chance, at any time during the summer, to discover parasite cocoon masses similar to those fig-ured, and will collect them and forward them in a small box to the gypsy moth laboratory, Melrose Highlands, Mass., the service will be greatly appreciated. There are a great many native parasites of native caterpillars which are very similar and in some instances indistinguishable from those of the Glyptapanteles, but none of these have ever been recorded as attacking the gypsy moth. The one great fear in conne<3tion with the introduction of this most important parasite is that it will not find all of the natural conditions necessary for its continued existence in Massachu- setts. Its life during the fall and its whereabouts during the winter are equally a mystery ; and even the Japanese entomolo- gists, w^ho are the keenest of observers, resident in a country where it is a relatively common insect, are wholly unable to sug- gest a reasonable solution. It has been recorded upon a variety 1 The occurrence of the cocoons in the near vicinity of the colony sites immediately following the liberation is most natural, and in perfect harmony with the wide dispersion. The female parasites as soon as they emerge are ready to deposit a small part of the eggs which they will eventually deposit if they live and have opportunity. After the deposition of this part, it is necessary for them to wait an appreciable time before they are ready to deposit any more. Fiiir0|ii';ii) ]i;ir;isitt' of .u'vpsy and l)rci\vii-tail iiiotli ciilcrpillai's, adult, eulargi'd. Flu. U. — cii,ilri:irii,rijns: Kuropoaii | lara site of gypsy luotli iiuii:l>, adult, greatly euUli-ged. GYPSY AND BROWN-TAIL MOTHS. 39 white eggs upon the larger caterpillars of the gypsy moth in certain localities each year so abundantly as periodically to at- tract attention : but the identity of these eggs cannot be deter- mined, since the maggots which hatch from them rarely go through to maturity. The reasons for this extraordinary state of affairs have not been accurately determined, but in some way the caterpillars of the introduced insect are not fitted to the needs of the maggots of the native parasite. It has been stated that the native species occasionally com- pletes its gTOwth and transformations upon the gypsy moth, and, since it is impracticable to separate the adults with certainty, there will be no way of following the progress of the imported species in America until it shall become a great deal more com- mon than the native in this connection. It is unquestionably too soon to look for such conditions at the present time, but it is rather confidently expected that within a few years Tachina larvarum will become an efficient link in the sequence of para- sites which it is hoped to establish. There is a species of Tachina in Japan, indistinguishable in habit from the European species, and apparently rather more effective. The adults are different, however, and quite easily distinguished from either the American or the European. A small number have been liberated, and it is possible that they will be heard from in the future. It is also expected that a larger number will be imported and liberated the coming sea- son, so that, if the European species for any reason should fail to come up to expectations, the position which it might other- wise occu])y will not remain vacant. Zygohothria r/ilva and Carcdia gnava. Through the efforts of ]\I. Rene Oberthiir of Rennes, very large shipments of gypsy caterpillars and pupae were received from France in 1009 in much better condition than any con- siderable shipments ever received before. Largely because of the satisfactory condition of the material on receipt, and partly because the two parasites named above are more common in the Mediterranean region than in northern or central Europe, several thousands of each were imported and colonized under the happy circumstances which accompanied nearly all of the 40 IMPORTED PARASITES. colonizations in 1909. Both had been received before, and both had been colonized, but in insignificant quantities and nndei- conditions which left mnch to be desired. It is consid- ered, therefore, that the first satisfactory and possibly the first effective colonization of these jDarasites was accomplished last year. Both are Tachinids, and similar in many respects to Tachina, Compsilnra, etc., bnt differ from all others and from each other in many minor particnlars in their life and habits. In relative importance, as determined by the frequency of their occurrence abroad, they are about equal in rank, and compare favorably in France with any other Tachinid parasites except Blepharipa. It is ho])ed that both will establish themselves in America, but their ability to do so remains to be proven, and it is hardly to be expected that either will be recovered before 1911 or 1912, unless some of the earlier and relatively very unsatisfactory colonizations should have resulted more favorably than is now believed to l)e the case. Parasites of tup: Pupa. Theronia sp. There are at least 10 species of large, wasp-like parasites which attack the freshly formed pupa? of the gypsy moth, and the caterpillars just previous to their transformation, and which belong to the genera Pimpla and Theronia. All of them are very general in their host relations, and will attack the pupa^ of almost any moth which they encounter under the proper con- ditions ; but none of them, with the exception of the several varieties or species of the genus Theronia, have ever occurred so abundantly in any lots of imported gypsy pu]X"e as to justify a position among the important parasites of the gypsy moth. As parasites of the brown-tail, the several species of Pimpla are quite effective both in Europe and America ; and Theronia is also a broAvn-tail parasite, but of relatively less importance. There are three species or varieties of Theronia, inhabiting respectively Europe, Japan and America, and all are very sim- ilar in appearance and habits. The American species, Theronia fulvescens, appears to have reached its maximum effectiveness Fig. 1."). — Cbalcis: full-growu larv;i from gypsy moth pupa, rreatlv enlarged. Fig. 16. — Chalcis: pupa from gypsy moth pupa, greatly enlarged. Fiii. 17. — Chalcis: gypsy moth pup:v, showing exit liolo of the parasite, enlarged. GYPSY AND BROWN-TAIL MOTHS. 41 in America, and without exceeding in this respect the Japanese or the European species in their respective countries. A few of the European Tlieronia atalantce have been liberated in America, but nothing more is expected of it than of Tlieronia fulvescens; and, as a matter of fact, it will be difficult to deter- mine whether it is established or not, owing to the very close resemblance between the two. Theronia will help a little in the ultimate control of the gypsy moth in America, but it is not to be expected that it will ever become of greater efficiency than it is at present. It is gen- erally distributed throughout the infested area. CJialcis flavipes. One of the most effective parasites of the tussock moth in cer- tain more southern localities is a native species of Chalcis (Fig. 14) which is not very common in any connection in New Eng- land. If, as is altogether probable, the gypsy moth extends its southern distribution into the range of Chalcis as a common parasite, it is not at all unlikely that it will be attacked by it. In southern Europe and in Japan are other species of Chalcis similar to the native species in appearance and habits, and some- times quite effective parasites of the pupae of the gypsy moth. They are always solitary, and notwithstanding that there is sub- stance enough in an average gypsy pupa to nourish several in- dividuals, there is no record of more than one ever emerging from one host. The eggs are deposited in the freshly formed pupa, and apparently the individual host is open to attack for a period of only about three days in the course of its life. The larva (Fig. 15) feeds upon as much of the contents of the pupal shell as it desires, and then transforms to a pupa (Fig. 16). The adult emerges later through a large, ragged hole gnawed through the pupal shell. (Fig. 17.) The European species, Chalris flavipes, was imported in some numbers in 1905, but at that time was supposed to be an enemy of the Tachinids which were primary parasites of the moth, and none were liberated. In 1000 and 1007 none were received, and no opportunity arose to investigate the relations existing between the moth and the parasite. It was not known that it was so closely confined in its geographical distribution at that 42 IMPORTED PARASITES. time, and since no gypsv moth pupae were received in good con- dition from any of the Italian or French collectors, its impor- tance was not recognized. In 1908, for the first time since 1905, a quantity of gypsv moth pupffi was received from Italy, through the courtesy of Professor Leonard! of the School of Agriculture, Portici, and from them quite large numbers of the parasite were reared. At first, with the recorded secondary parasitism of the species in mind, considerable care was exercised to prevent the escape of any of the specimens until their true relation to the gypsy moth should be established. At last, after a rather tedious series of microscopic studies, supplemented by dissections of the para- sitized pupse, it was definitely demonstrated that the Chalcis which issued from the Tachinid puparia were different from those which came from pupa direct ; in other words, there were several species of the genus Chalcis, closely resembling each other in their appearance, but differing entirely in their habits. One of them was, beyond further dispute, a primary parasite of the gypsy moth, and was immediately liberated in the field, while the others were destroyed as fast as secured. In 1909 a few more were received in importations of gypsy pupa? from Italy and France, and another small colony was established. It is known definitely that reproduction in the field followed immediately after, but there is insufficient assurance that the species is acclimatized in America, since it has not been recovered a full year after its colonization. If it disperses as rapidly as do most of the parasites, it will be some years before it is again recovered as the result of the last summer's coloniza- tion. During this period it is hoped that additional importa- tions will make it possible to establish larger and stronger colonies of what, if it can exist here, is very likely to become a parasite of some importance. In both 1908 and 1909 Chalcis flavipes was carried through all of its transformations in gypsy moth pup?e in the laboratory ; and, but for the fact that a supply of host pupse cannot be pro- vided except during a very limited season each year, it would be practicable to institute propagation work similar to that which has been so successful with Schedius and Calosoma. Only about one month is required for the complete life cycle from Fig. 1.-^, — .\ronodonl.oineriis ncrcus : European iiarasitc of jrypsy aud brown-tail moth iniiiu', aihilt female, greatly eulargecL GYPSY AND BROWN-TAIL MOTHS. 43 egg to adult. It is very probable that the adults live for a loug time, like those of Monodontomerus, and they may hibernate. Monodontomerus aereus. The females (Fig. 18) deposit their eggs (Fig. 19) in the freshly formed pup£e of the gypsy moth and of the brown-tail moth, several in each individual host. The larvse (Fig. 20) feed and subsequently undergo all of their transformations within the pupal shell, of which they usually consume the entire con- tents. (Fig. 21.) A little later than the time when the moth would have issued, had the parasitized pupa remained healthy, the Monodontomerus adults escape through a small hole in the dried pupal shell. (Fig. 22.) From 5 or 6 to 15 or 20 come from each. The males die soon after, but the females live all winter, and are not able to deposit eggs for another generation until the summer following. When cold weather approaches they seek the shelter afforded by the hibernating webs of the brown-tail caterpillars, and remain well protected in the silken chambers during the winter. They come forth in the spring as soon as the weather becomes warm enough to stir them into activity, and in the course of the period intervening between their resumption of activity and the pupation of the brown-tail and gypsy, they develop their eggs and are ready for the attack. A considerable number of the adults of this parasite, all, with- out exception, fertilized females, issued from the large number of brown-tail hibernating nests which were imported from vari- ous European countries during the winter of 1005-06. A part were given their freedom in the spring, but as it was soon found that the species were not in any way an enemy of the hibernating brown-tail caterpillars, and as their parasitism of the pupse of the gypsy moth and brown-tail moth was not indicated at that time, their liberation was discontinued. In 1906 and 1907 small numbers were reared from imported cocoon masses of brown-tail, but under conditions which told nothing concerning their host relations. Upon several occasions small numbers have been reared from the puparia of Tachinid parasites of the gypsy moth, and it was feared that the parasite might prove to be habitually secondary, instead of primary. Like Chalcis, Monodontomerus is more common in southern 44 IMPORTED PARASITES. Europe, and the small quantities of gypsy and brown-tail pnpse which were received in 1900 and 1007 from those countries where it was most abundant made any attempts to investigate its life and habits difficult of execution. The females would never evince any interest in gypsy or brown-tail pupae in the laboratory, and all of the many reproduction experiments which were made failed utterly. This was subsequently found to be due to the fact that their eggs were undeveloped, and it was not until a careful series of microscopic dissections were made that this insuperable obstacle to success was discovered. In 1908 the same importation of gypsy moth pupae from Italy which served to establish the host relations of Chalcis served also to establish the primary character of the parasitism by Monodontomerus. It was reared from the gypsy moth pupae direct, and in such numbers as to indicate that it was a parasite of considerable importance ; and great regret was felt that it had not been liberated in larger numbers upon the first oppor- tunity. It was hardly considered probable at that time that the small number liberated during the early spring of 1906 would succeed in establishing themselves. In the winter of 1908-09, large numbers of the hibernating nests of brown-tail were collected from various localities, as they had been each winter since the beginning of the Avork, and from these nests issued a very few hibernating females of Monodon- tomerus, exactly as they had previously issued from nests simi- larly collected in Europe. The circumstance was as unexpected as it was gratifying, and indicated that the parasite had mul- tiplied rapidly in the field, because similar collections of even larger quantities of brown-tail nests had not produced the para- site the year before. Steps were immediately taken to determine the distribution of the parasite, and the surprise was greater when it was discovered to be sparingly but generally dis- tributed over an area of approximately 500 square miles, ex- tending in nearly every direction, but farthest to the west, from the original point of liberation. In the summer of 1909, when the proper season had arrived, it was recovered for the first time as a parasite of the gypsy moth in the field. Although it was not very common, it was found to be generally distributed, exactly as indicated by the collections Fig. 19.— Mouodontoni- orus: egg, greatly en- larsred. Fi<;. '20. — Monodoiitoiiioriis: larva I'roui ?;> psy inotli impa, ,^i'eatl>' ciilarijcd. Fi<;. '21. — Monodontonierus: inii>a from gyi>sy moth liupa, greatly enlarged. Fii;. •.'■_'. — .MoiiodonliiiiuTiis: gypsy moth |iupa, showing exit hole li't'i by [larasite, greatly enlarged. GYPSY AND BROWN-TAIL MOTHS. 45 from brown-tail iiests the winter before. The percentage of the gjpsy pnpffi destroyed was negligible ; but the fact remained that the j)arasite was on the increase, since exactly the same methods employed in previous years had produced no such results. Great curiosity was felt as to the jDrobable character of the results of winter work in the recovery of the hibernating females in the winter nests of brown-tails in the fall of 1909, as this would provide the first opportunity to determine the rate of an- nual increase and of dispersion. The work was begun as soon as practicable, and, while the results are not yet complete, they are more favorable than was at any time anticipated. In brief, the insect is now known to be distributed over an area of ap- proximately 3,000 square miles. Every portion of the Com- monwealth north and east of Boston to the New Hampshire line, and as far west and southwest as Leominster, Shirley and Dover, is included in this territory. It is certain to be in New Hamp- shire, but to date none have been received from that State, and the western limits of its distribution have not been determined. Everywhere in the area which was not included in its known distribution last year it is about as common as it was in any place the winter before. Within the limits of the territory in which it was known to occur a year ago it has increased at least twenty-five-fold during the year. At this rate, if unchecked, it would be abundant enough to destroy all of the gypsy and broA\m-tail pupse in three years more. Since this, for various reasons, is highly improbable, it is likely that it will reach its maximum effectiveness within the centrally infested areas by that time. Judging from the best which it is known to do abroad, this will be the destruction of something like one-fourth of the gypsy and brown-tail pupa\ It is not al^road, and cannot be expected to become in America a parasite of as great import- ance as Glyptapanteles or Blepharipa, provided these species become as thoroughly acclimatized ; ])ut it promises to become a very valuable parasite, occupying, as it does, a position in the sequence of ]>arasites which would otherwise be vacant except for the ineffective Theronia or the less certainly efficient Chalcis. 46 IMPORTED PARASITES. PROGRESS OF THE PARASITES IN MASSACHUSETTS. Before it is possible accurately to predict the progress of an insect in a new country, it is necessary to know, iirst, the average rate of increase under the new conditions; and, second, the average rate of dispersion. ISTeither may be determined other- wise than by actual observation in the field. In the countries to which the insect in question is native, the rate of increase is balanced more or less perfectly, and, although it always fluc- tuates somewhat in relative abundance from one year to another, there is no permanent gain or loss. The dispersion of an insect in a country where it is native and generally distributed is im- possible of determination ; the progeny of any given parent or of the parents within a given area are at once confused with the progeny of parents in any part of the surrounding country into which they may chance to spread. The introduction of an insect into a new country is usually followed by a steady increase, which is sustained until it has established a balance with the native insects ; or by a steady decrease, which results in its final extinction. There are a few instances on record in which the progress of an introduced insect has followed neither path. The Chinese lady-bird (Chilchonis similis) was introduced into Georgia in 1902 as an enemy of the San Jose scale, and for one year in- creased at a very rapid rate, and spread over a considerable territory from the point where it was liberated. It passed the first winter successfully, and for a time bade fair to become so numerous as to be of valuable assistance in the fight against this scale; but in 1904 its numbers showed a decided decrease, and at the present time it appears not to be at all common. The causes for this are very obscure, and no satisfactory explanation has ever been advanced. The history of the Oriental moth in Boston, where a few years ago it appeared to have become firmly established, is an- other case in point. At the present time it is far from common, and it is very possible that eventually it will become extinct. It will never he known how many insects have been introduced into America from abroad, but the number is undoubtedlv far GYPSY AND BROWN-TAIL MOTHS. 47 in excess of those which have become temporarily or permanently abundant enough to attract attention. It has never been expected that all of the parasites and predatory enemies of the gypsy and brown-tail moths which have been introduced into Massachusetts would continue to exist here. It has always been expected that certain of them would do so, and the only cause for uneasiness as to the ultimate success of the work has been the fear that not enough different kinds of parasites could be secured for colonization, or, if colonized, that not enough to form a natural and effective parasitic sequence would be able to continue to exist. At the present time there is no parasite of the gypsy moth, and only one or more of the brown-tail, of which it can be said that the progress is unsatis- factory. Just what the progress is, or whether there is any actual progress, is not known in every case ; but, as will be shown, it may be very satisfactory, and at the same time in- conspicuous. In the beginning it was expected that increase, if it followed colonization, would be rapid ; but it was not thought that many of the several species would be likely to fly very far from the point of liberation until they had increased for several genera- tions. Had these expectations been fulfilled, practical results would have been apparent, locally, within three or four years. So far as it is possible now to state, the rate of multiplication has generally been gratifyingly rapid ; but it has been accom- panied by a rate of dispersion so much greater than was ex- pected as to materially change the aspect of the situation. It is now evident that, if success follows the work of parasite in- troduction, the parasites will become practically effective over a considerable portion of the infested area, and possibly through- out its whole extent, at about the same time. In order better to illustrate this point, a theoretical example may be taken of an insect introduced into a new country, Avhere it increases at the rate of twenty-five-fold annually, and spreads from the point of liberation at the rate of about 10 miles an- nually. It is supposed that 1,000 individuals are liberated in a territory where they can be spread in every direction, and where their increase will be unhampered for a period of six years. 48 IMPORTED PARASITES. Lest any one shonld think that the figures and diagrams as given are fanciful, and the result of pure speculation, it is well to state in the beginning that they represent, as accurately as the available information will permit, the progress of Monodon- tomerus in the field. The territory covered is not quite as ex- tensive as indicated by the first diagram, owing to the fact that a large part of it is, or would be, open sea; but the recovery of the parasite from the field indicates that it has spread at a rate of approximately 10 miles annually to the west and north, and that its increase, which was about twenty-five-fold during the summer of 1909, has been maintained at that rate since its liberation. It is not known exactly how many of the parasites were liberated originally, the notes which were made at that time apparently having been lost. Tentatively, the figures are set at 1,000. The rate of dispersion, provided it was dependent upon the activities of the insect, and not upon chance or accidental agen- cies, would be about as rapid during the first year from a colony of 1,000 as though it were very abundant. The territory covered by the insect during the six years would therefore be represented by a series of six concentric circles, the smallest of which would have a radius of 10 miles, and each of the others of multiples of 10 u}^ to 60. The area given in acres, and for convenience sake in round numbers, over which the insect would range each year from the first to the sixth, respectively, would be as indi- cated in Diagram I. Increase numerically, at the rate of twenty-five-fold annually, Avould be at a very much more rapid rate, and is indicated by the several squares in Diagram II. It would be impossible to illustrate this increase diagrammatically for the entire six years without the use of a large chart, because the square which would indicate the number of the insects which would result from the sixth year's increase would have sides between 3 and 4 feet long. The figures for six years would be : — 1906, 1,000 1907 25,000 1908, 625,000 1909 15,625,000 1910 390,625,000 1911 9,725,625,000 DiAtiKAM I.— Illustrating the dispersiou of an introduced insect for six years, at the rate of approximately ten miles per year. n DiAijKAM II. — Illustrating the uunierical iucrease of an iutroduced iusecl for tour years, at the rate of tweuty-flve-fold each year. 1906. 1 individual tu -'oO acres. 1907. 5 individuals to 200 acres. 1908. fi9 individuals to 200 acres. 1909. !)Tt; individuals tJ ■< 1 O O S CO 3 o • O : u] : a ■ 13 a b.1 a . 2 s d .2 ; 5S 1 a O o •< iJ 3 s Zygobolhria nidicola, .... Pteromalus egregius, .... Parexorista chelonia?, .... Dexodes nie;ripes, ..... Compsilura concinnata,* Eupeletoria magnicornis, Zenillia libatrix Pales pavida Tachina larvarum, .... Anomalon exile, .... 56 IjMported parasites. o ^ oq ^M c B « O g g .s o •-" ^ 5 _ee _c3 UE f^ PARASITES Gypsy and Bro\/vn-Tail Moths INTRODUCED INTO MASSACHUSETTS A WHERE THEY COME FROM WHAT THEY ARE DOING A GENERAL SURVEY OF THE WORK By W. F. FISKE Agent and Elxpert, Bureau of Entomology, U. S. Department of Agriculture UNDER THE DIRECTION OF F. W. RANE, STATE Forester ^ ^m