Technical results from the Gipsy moth parasite laboratory


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Technical results from the Gipsy moth parasite laboratory
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L. O. HOWARD, Entomologist and Chief of Bureau.



Assistant in Biology, Sheffield Scientific School, Yale University,

In Charge of Gipsy Moth Parasite Laboratory, Bureau of Entomology.

ISSUED MARCH 22, 1911.



L. 0. HOWvARD, Entomologist and Chief of Thtreau.
C. L. MARLATT, Entomologist and Acting Chief in Absence of Chief.
R, S. CLIFTON, Exeutive Assistant.
W. F. TASTET, Chief Clerk. F. 11. CHITTENDEN, in char-ge of truck crop and stored product insect investigations. A. D. HlOPKINS, in charge of forest insect investigations. AV. D. HUNTER, in charge of southern fielat crop insect ivesigations.
F. M WEBTERin charge of cereal and for-age insect investigations.
AL.QUAINTANCE, inl charge of dec(iduous1 fruit insect ivest iga tions. F. l1'. PhIL11LIPS, ill charge of bee culture. 1). Ml. Roc;i uls, ill charge of prcccnting sprecad of moths, field work. !%'.OLLIA P. C7URRIE, in charge of editorial work. MAPELJ COL.CORD, Ii bir naa.



AN. F. FisKE, in charge;7c A. F. BUNCESS, HI. L. VIERECK, C. W. COLLINS, R. WOOLDIDG, JNO. i9. ruOHILL, C. W. STOCKWVELL, H. E. SMITH, assistants.


.1). M. ROGES, carg; I:1. B. DALTON, H. W. VrINTON, D. G. MlURPHY, I. .
IAILEY, I. L. M\CINTYI'E, assistants.


Introduction ---------------------------------------------- 25
General conditions ------------------------------------------------- 27
Collections of gipsy-moth pupve for maggots of Sarcophagidae ----------- 27
Experiments with adult Sarcophagidm---------------------------------29
Experiments with first-stage maggots on living and dead material- -------30 Relation of decomposition to oviposition ---------------------------- 30
Conclusion -------------------------------------------------------- 31

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U. S. D. A., B. E. Tech. Ser. 19, Pt. III, Issued March 22, 1911.


III. Investigations into the Habits of Certain Sarcophagid e.
Assistant in Biology, Sheffield Scientific School, Yale University.
That there are among the Sarcophagide a number of species which, to all intents and purposes, are primary parasites of grasshoppers is a fact concerning which there is no ground left for argument. Whether the young larvve of these flies bear-a relation to the living host which is in any way comparable to the extraordinary intimacy which characterizes the relations between the tachinid parasites and their hosts is beside the present question. They assuredly do gain access to the living body of their host, and after a time destroy it, and by so doing qualify themselves to be considered among the insect parasites.
There are numerous species of the Sarcophagidee which have been reared in association with the gipsy moth (Porthetria dispar L.). Each year after the caterpillars have pupated and when the moths are beginning to emerge, interested persons have found pupae with the shell apparently unbroken, the contents in a state of decomposition, and an active sarcophagid larva luxuriating in the surroundings thus provided. The condition of the pupa containing the sarcophagid is always different from that of a pupa containing a tachinid maggot, but the distinction is not instantly apparent nor easily described. To the ordinary observer the pupa containing the sarcophagid answers perfectly to the description of a pupa destroyed by a tachinid, and each year it has been necessary to explain anew the difference between parasite and scavenger. That sarcophagid maggots found under these conditions are always scavengers and never parasites has never seriously been questioned.
It must be admitted, however, that in thus rather summarily consigning the whole group of sarcophagids to the r6le of scavengers, in so far as their relations to the gipsy moth were concerned, there has been an undercurrent of uneasiness lest among them should eventu'Introduction by W. F. Fiske, in charge of Gipsy Moth Parasite Laboratory, Bureau of Entomology, Melrose Highlands, Mass.
794040---11 -25

ally be found some which created rather than took advantage of the conditions under which they were encountered. It required hardly any stretching of the imagination to conceive of sarcophagid maggots deposited upon living pupae, effecting an entrance, and eventually bringing about the death and decomposition of the host. From time to time tentative attempts to acquire more definite information were made, but without positive results one way or the other. Large numbers of gipsy-moth puppe, apparently living, were collected in the open and upon one or two occasions sarcophagid maggots were subsequently found, but there were always very satisfactory explanations for their presence other than that they were parasitic, and it was increasingly evident that if such experiments were to be decisive, they would have to be conducted with exceedingly great care. Several attempts were also made to keep the adult sarcophagids reared from gipsy-moth pupv imported from Europe or Japan until they reached their full sexual development and were ready to deposit their brood, but there were a good many things to learn about the best way of conducting an experiment of this sort and none of them was successfully concluded.
In the summer of 1910 the question of Sarcophaga in its relations to the gipsy moth was rather suddenly reopened as the immediate result of a study in parasitism conducted by Mr. P. I. Timberlake, of this laboratory, upon the "pine tussock moth which was causing some injury to pine in northern Wisconsin. The results of his studies, which will be published in another part of this bulletin, were such as strongly to indicate the parasitic character of certain sarcophagids and to suggest that they were, in effect, of rather considerable importance in the control of this moth.
This, when taken in connection with the fact that a vastly larger number of sarcophagids were continually being received in shipments of gipsy-moth puppe from Europe and Japan than would be secured from an equal number of similar pupve collected in America, was a circumstance which could no longer be overlooked. The evidence was such as materially to support a contention that among the European sarcophagids occurred species which were primarily enemies of the gipsy moth. If, as did not seem so very improbable, there existed in Europe such an important group of dipterous parasites of gipsy-moth pupw, no time should be lost in attempting to secure their introduction into America.
Most unfortunately it is impossible in this case, as in a great many others, to conduct the necessary investigations to the best advantage. Independent European entomologists can not, of course, conduct elaborate investigations along lines wholly outside of their own affairs, and the establishment of a European branch of the Gipsy Moth Parasite Laboratory has never been considered as practicable.


As usual we were forced to do what could be done with 'such opportunities as were offered. It was decided to institute at once a new series of studies upon the relations of the American sarcophiagids, to the gipsy moth, and to conduct them so carefully that if they dlid not produce positive results they would at least possess negative valuev.
Fortunately the services of Mr. Patterson were available at that time, and the affairs of the laboratory were in such condition as to permit him to give the work his undivided attention. For the first time it was possible to conduct the experiments, which he will describe himself, with the adequate attention to detail which is absolutely necessary if the results are to be considered as decisive. His results seem to justify the retention of the ideas previously held. in so far as they can be justified b y a study of American conditions. It is sincerely to be hoped that in the very near future similar investigations may be conducted in Europe, since the only other additional studies which seem worth while in America will be of the sarcophagids in relation to other lepidopterous hosts, and the findings, whatever their character, would not be directly applicable to the problem of gipsy-moth parasite introduction.

Since the establishment of the Gipsy Moth Parasite Laboratory in 1905 considerable interest has been excited each year from the number of sarcophagids reared in connection with gi psy-moth pupcT, and even more from the larger percentage of sarcophagids received from gipsymoth pupaw imported annually from Europe and Japan. It would seem probable from the above that certain species of sarcophagids had always been parasitic, or else that they had within recent years developed the parasitic habit, which is the more likely; hence, instead of having to depend wholly upon dead material as a host they had joined the ranks of certain of the Tachinidee in waging war against one of the most injurious insect pests that has ever invaded New England, the gipsy moth. During the last few years certain tentative experiments have been made at the laboratory, but all this work, while it proved rather interesting, was not convincing, and gave neither positive nor negative results. In the summer of 1910 conditions again became favorable for further investigations into the *habits of native Sarcophagidae and the writer attempted to determine, by the series of experiments which follow, whether any of these flies are parasitic in habit, or whether they are scavengers on the gipsy moth.
Collections were made of gipsy-moth pupaw from localities in towns within a radius of 10 miles of the laboratory. The smallest collection contained 225 and the largest 790 pupee, each of which was care-

fully examined and placed into one of two separate lots, namely, the live and active, or the dead, abnormal, and inactive. A few small collections were also made of active prepupal larvae which were kept separate from the other lots. All of these lots were placed in small pasteboard boxes about 8 by 5 by 4 inches, with tight covers, and were examined almost daily for either maggots or puparia of Sarcophagidae, or parasites, and the moths as they issued from the pupae were removed and killed. The small number of pup.e from which no moths issued was dissected for parasites at the close of the experiments. Three thousand two hundred and fifty-seven pupae and prepupal larvae were collected for the experiments, 300 of which were active prepupal larvae, 591 were dead and inactive pupae, and the re-' maining 2,366 were active pupae. No sarcophagids were reared from the lots of active pupae and active prepupal larve, but 2 puparia of the tachinid parasite Compsilura coneinnata Meig. developed from one of the lots of the active pupa and 14 were secured from the prepupal larva. This parasite of the gipsy moth and brown-tail moth was introduced from Europe and liberated in eastern Massachusetts. It has become so well established here, according to the best authorities and records, that it is now distributed over more than 200 square miles of the infested territory.
From the dead and inactive pupae, as might have been expected, sarcophagids were obtained, as well as other species which work as scavengers or parasites. This material yielded 4 third-stage maggots and 1 second-stage (dead) maggot of the Sarcophagidue; 4 puparia and 1 third-stage maggot (dead) of Compsilura concinnata; 1 Exorista blanda 0. S.; 2 third-stage maggots and 1 second-stage tachinid maggot of an unknown species; 14: fonodontomerus adults and 2 pupae of the same; 8 pupae of Gaurax anchora Loew (?) ; and I adult and 4 pupae of Theronia and 5 Dibrachys (dead) in 1 gipsy moth pupa. A special lot of 5 prepupal larvae was collected, and on dissection 2 proved to be alive, 2 dead, and 1 had pupated while being brought in from the field. In one of the live prepupals a second-stage maggot of Cornpsilura concinnata was obtained, while the other was not parasitized. One of the dead prepupals produced 3 third-stage maggots of the Sarcophagidae, while the other, as well as the freshly formed pupa, contained no parasites.
The above experiments riot only uphold, but seem rather to strengthen the old belief that the sarcophagids are simply scavengers. Another point of interest in this line of investigation is that tlere are sometimes found in a single pupa more than one parasite, which often belong not only to entirely distinct and separate genera, but even to entirely distinct and separate families. This point was well illustrated in making one of the collections, when the posterior end of a


dead gipsy-moth pupa was accidentally broken off in removing it from the tree, thus disclosing within its almost empty case 2 third-stage maggots, one Compsilura concinnata and the other a sarcophagid. This may be very satisfactorily explained by the fact that this pupa, when in the caterpillar stage, was first parasitized by Compsilura concinnata, and after reaching the pupal stage the maggot within became large enough to kill the pupa. The decomposition which resulted furnished a favorable place for the oviposition of a female sarcophagid. In various other cases, when it appeared as an almost absolute certainty that maggots of the Sarcophagidao came from living material, their presence could be accounted for in some such way as the above. The following experiments with the native sarcophagids will also go to strengthen and substantiate the above theory.
Collections were made of these flies for reproduction experiments from different localities in the infested area. Each collection was kept separate in cylindrical wire screen (one-twelfth-inch mesh) cages, 10 inches in height by about 4 inches in diameter. The top consisted of a circular piece of wood, to which was tacked the wire screen, while the lower edge of the screen fitted into a groove in the wooden base. This arrangement allowed the quick removal of the base and furnished easy access to the cage. A sprig of leaves, with the stem wrapped with cotton batting, was inserted in a tube of water attached to the inside of each cage, and this was sprayed with a solution of sugar and water twice daily, which furnished food for the flies. At first only active prepupal larvae of the gipsy moth were placed in these cages. They pupated in a day or two and were alowed to remain there for several days, where the flies could have free access to them, before they were transferred to jelly glasses, which were covered with cheesecloth. These were kept under observation for sarcophagid maggots until the moths emerged or the pupoe died, in which cases they were always dissected. All these experiments gave negative results, showing almost conclusively that these flies did not oviposit on living pupae. The writer then added some badly decomposed caterpillars to the living ones in the cages and observed in a short time that the female flies deposited tiny maggots on the dead material, but not on the living, although frequently they crawled over the live pupae until these wriggled, which seemed to frighten the flies away. The living material from these experiments was also placed in jelly glasses, but all finally gave negative results. All dead material was now placed in the cages and first-stage maggots were obtained quite plentifully and appeared to be perfectly healthy.

Some of these maggots were placed on mature active pup., but in every instance they showed little, if any, desire to bore through the pupal cases. This would probably be an impossibility, as the exterior of the pupoe is tough and hard, but the maggots did not enter even the soft prepupal larvae. In both cases the pupw- and prepupal larve were greatly disturbed and irritated when maggots were crawling on them, and they wriggled violently, dislodging the maggots. If they were placed on a soft, freshly formed pupa the maggots at once would make frantic attempts to bite into it, but without success; although, in one instance, when the membrane which holds the wing cover to the body of the pupa became ruptured, the maggot took advantage of this opportunity of concealment and crawled beneath, and although the maggot was still on the external surface of the pupa it caused such an irritation by its movements that a dark secretion oozed out, coming either from the pupa, maggot, or both, and in the course of a few hours the wing cover became sealed to the body of the pupa, so that only the anal stigmata of the maggot were lefC exposed. After the lapse of about 12 hours the pupa was found to be dead, and in 18 or 20 hours the maggot disappeared into the body of the pupa. A dissection was made the following day. The maggot was found dead midway in the body of the pupa. This would seem to indicate that the environment which the maggot found within the pupa was not favorable for its development.
To further illustrate the above idea the writer took active pupae, making a puncture about midway in the body of each, and allowed a live maggot to crawl in, but in all cases the maggots died, showing that they can not live under such circumstances. However, a few came out of the pupae and died on the outside. Similar experiments were made on dead material with entirely different results. In most cases the maggots went in without experiencing any difficulty and usually survived, which showed that they were in a natural environment.
It was observed that the flies would not oviposit on freshly killed material in the cages, even though the females had been ovipositing previously on older decomposing caterpillars. This would seem to refute the parasitic theory and would tend to show that the material must reach a certain stage of decomposition before the females would. oviposit. Selecting the only cage where females were ovipositing the writer removed all the old material and replaced it with a single freshly killed caterpillar. The flies at once ceased to oviposit,


although they would crawl about over it. Two (lays later the writer observed one of the female flies in this cage spending the most of her time crawling about over this caterpillar. A little later she began to make a buzzing noise with her wings and was feeling here and there with her proboscis over the body of the decomposing caterpillar. Proceeding to the anterior portion of the caterpillar a few segments back of the head she succeeded in puncturing the decaying skin with her proboscis, and then moving along far enough so that the end of her ovipositor was directly over this puncture she slowly deposited a maggot which immediately, true to its instincts, worked its way through this puncture into the body of the caterpillar. Several maggots were deposited by this fly, and later a second female was observed to oviposit on the caterpillar in the same incision. This not only indicates that a certain stage of decomposition must be reached, but that the skin of the caterpillar must be either broken, or in such a condition that the female fly can puncture it with her proboscis before she will oviposit, thus allowing an opportunity for the maggots to crawl into the dead host. There were a few living pupve in this cage, and although the females not infrequently crawled about over them, they did not attempt oviposition. This was the case with a freshly killed caterpillar which was placed beside a dead specimen upon which flies were ovipositing, but when decomposition reached the proper stage, the flies began to oviposit freely. It must be stated here that the true source of the flies in the cage with which this last experiment was tried was unknown, and that they were selected only for the reason that they happened to be the only flies available that were ovipositing. They were secured from a jar containing dead European Calosoma beetles which had been exposed for several weeks to the attack of various species of sarcophagids. It is possible that these flies might have been imported from Europe, but this is extremely doubtful.

These experiments indicate very conclusively that the sarcophagids in New England do not destroy living gipsy-moth larvoe or pupo in the field. From a collection of 2,666 specimens not a single sarcophagid was reared.
In cages the flies would not oviposit on healthy or recently killed caterpillars or pupe, but did so freely after they became slightly decomposed.
First-stage maggots, when placed artificially within living pupae. failed to develop in every instance, showing that the conditions were not favorable for their growth.

When living and decomposing larvea or pupoe were placed side by side in a cage, the flies selected the latter on which to oviposit, and normal larvae developed.
In conclusion it must be understood that the writer has not attempted to work with any one species of the Sarcophagidoe, nor to separate them into species, but, on the other hand, he has worked with them only as a family, taking for granted that if any of these flies are ever parasitic on the gipsy moth, they would naturally be found in the infested localities. Although all the experiments have given negative results, yet they are nevertheless of economic importance, because in Europe and Japan, where sarcophagids are more commonly associated with the gipsy moth than in this country, it is possible that there may be several species that have the parasitic habit. If so, foreign investigations should be hastened, for if introduced into America these parasitic sarcophagids would be an important addition to the natural enemies of the gipsy moth.


UNIVERSITY OF FLORIDA 3 1262 09229 6317

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