TECHNICAL SERIES NO. 20, PART VI.
U. S. DEPARTMENT OF AGRICULTURE,
B13TREA 0TI O" ENTOMOLOGOA-V.
L. O. HOWARD, Entomologist and Chief of Bureau.
TECHNICAL PAPERS ON MISCELLANEOUS
VI. CHALCIDIDS INJURIOUS TO
S. A. ROHWER,
ISSUED FEBRUARY 10, 1913.
GOVERNMENT PRINTING OFFICE. A 1 1913.
Digitized by the Internet Archive in 2013
U. S. D. A., B. E. Tech. Ser. 20, Pt. VI. F. I. I., February 10, 1913.
TECHNICAL PAPERS ON MISCELLANEOUS FOREST INSECTS.
VI. CHALCIDIDS INJURIOUS TO FOREST-TREE SEEDS.'
By S. A. ROHWER,
For a long time entomologists were loath to give up the theory that all chalcidids were parasitic, and most of the species which attacked the seeds of forest trees were originally described as being parasitic on some other insect which either lived within the seeds of the trees or lived within the cones, but in 1893 Wachtl recorded definitely that Megastigmus spermotrophus lives within the seeds of Douglas fir and is phytophagous. Even after this statement entomologists were loath to believe that any chalcidids are not parasitic, and many of the foremost authorities on these insects believed up to the time of their death that some day it would be proven that all chalcidids, with the exception of certain few belonging to the genus Isosoma and its allies, are parasitic. Of late years, however, most entomologists have come to believe that the phytophagous habit in many of the chalcidids is not uncommon. We know at present phytophagous species of the family Collimanida (olim Torymids), of the subfamilies Collimanina and Megastigmine, and of the family Eurytomide, the phytophagous species being in the tribes Isosomini and Eurytomini. To these also may be added certain genera which have been assigned to the family Perilampidse.
The species that attack seeds of forest trees are confined to the Collimanide, and most of them belong to the subfamily Megastigmine. Summing up the literature on phytophagous Chalcidoidea belonging to this family, it is possible to outline the life history of every species which may live within the seeds of forest trees. This would be as follows: The egg is laid in the early summer or late spring,
SAlthough certain hymenopterous insects belonging to the superfamily Chalcidoidea have been shown to be very injurious to the seeds of certain forest trees, very little work has been done on these insects in America. The present paper is a rdsumd of the literature which deals with these insects, with a bibliography of the literature. It is prepared to facilitate the work of field men and to call the attention of entomologists in general to the damage done by these insects.
71311*-rr vi-13 157
158 MISCELLANEOUS FOREST INSECTS.
the larva feeding within the seed until it reaches maturity, passing the winter within the seed as a prepupal larva, transforming into a pupa early in the spring, and emerging as an adult in time to oviposit in the rather young seeds of the trees. The egg-laying habit of some of the chalcidids which attack the seeds of shrubs or vines differs in a measure from that of those attacking the seeds of trees; for instance, the grape-seed chalcidid (Evozysoma vitis Saund.) oviposits in the seeds that are quite hard, and the only way that the female is able to deposit eggs within the seed of the grape is by finding a soft portion of the shell which is known as the chalaza. This is also the case with the seed chalcidid of Virginia creeper (Prodecatoma phytophaga Crosby). The oviposition of species of Megastigmus which live within the seeds of coniferous trees has never been observed, but owing to the heavy, leathery texture of the cones it is possible that oviposition occurs when the cones are very small.
Species of chalcidids feeding within the seeds of various plants have proven in some cases to be of much economic importance. A few examples will suffice to show this. Forty pounds of apple seed planted at Budapest failed to give even a good standing of apple seedlings, the seeds having been destroyed by the apple-seed chalcidid (Syntomaspis druparum). The seeds of the Douglas fir usually gathere(d in Aberdeenshire, Scotland, and amounting to over 300 bushels were, according to a letter from Mr. John Crosier published by MacDougall in 1906, not worth gathering, owing to the attack of the Douglas fir seed chalcidid (Megastigmus spermotrophus). According to a letter published by Riley in 1893, the seeds of the silver fir (Abies pectinata) in the forests of Denmark were so completely destroyed (luring the years 1886 and 1888 by species of the genus Megastigmus that not a single healthy seed could be found. As a great many of the species of Megastigmus which are troublesome in Europe come from the seed of the American conifers it is very likely that difficulty will be found in North America on account of the attacks of these insects. No parasite of the species of the genus Megastigmus is as yet known.
SYNTOMASPIS DRUPARUX (Boheman).
This species, which normally attacks the apple but is known to attack the seeds of mountain ash (Sorbus scandiea, and probably Sorbus latifolia) and hawthorn (Crategus), is very elaborately treated by Crosby in his paper entitled "Certain seed-infesting chalcid flies," where an account is given of practically the entire life history of this insect. The egg is deposited by the female within the seed of an apple when the apple is about three-fourths of an inch in diameter. The young larva feeds within the seed and develops until it hibernates s a larva within the see(d, plupatiln early in the spring and emerging as l atilt il JuneA. As this s ~'ies 1 Ilot of any economIic importance
CHALCIDIDS INJURIOUS TO FOREST-TREE SEEDS. 159
so far as forest trees are concerned, no more details concerning it need be given, but any one wishing to obtain information regarding this insect may consult the above-mentioned paper by Crosby.
Ichneumon nigricornis Berger, 1803, p. 141. Torymus druparum Boheman, 1833, p. 361. 9 J Syntomaspis pubescens (Foerster) Mayr, 1874, p. 103. (There is some doubt as to this being the same.)
Mokrezecki, 1906, pp. 390-392, figs. 1-2. Syntomaspis druparumr (Boheman) Gu6rin-AlM6neville, 1865, pp. 83-85.
Thomson, 1875, p. 76.
Horvath, 1886, p. 127.
Schlechtendal, 1888, p. 416. Dalla Torre, 1898, p. 294.
Crosby, 1909, pp. 369-375, figs. 67-76. MEGASTIGMUS SP.
A species of Megastigmus is recorded by Riley through rearings conducted by Borries, from the Japanese Abies roariesii. Nothing more is known about this species.
Megastigmus D. Riley, 1893, p. 360.
MEGASTIGMUS BREVICAUTDIS Ratzeburg.
This insect is considered by its original describer as probably a parasite of a gall fly inhabiting the fruit of mountain ash (Sorbus scandica), but Crosby has proven the species as entirely phytophagous in habit, and has reared it from seeds of Sorbus aucuparia. Crosby describes the larva as white, smaller than the larva of Syntomaspis druparum, from which it may be distinguished by the mandibles having four teeth on their inner margin and by the absence of brown tubercules on the face. The oviposition habit and the egg of this species are unknown, but it may be presumed that they are similar to those of the foregoing species.
Megastigmus brevicaudis Ratzeburg, 1852, p. 225.
Dalla Torre, 1898, p. 286.
Crosby, 1909, pp. 375-377, figs. 78-79. MEGASTIGMUS STROBILOBIUS Ratzburg.
The original describer of this insect considered it to be parasitic on Tortrix strobilotina, but since then it has been shown by Judeich and Nitsche that this species lives, as do other species of Megastigmus, within the seeds of plants, this species choosing the amabilis fir (Abies
160 MISCELLANEOUS FOREST INSECTS.
amabilis). They also state that this species is distinct from Mega&tigmus spermotrophus, and that the larva is about 4 millimeters long, whitish in color, and that the mandibles have three inner teeth. Crosby records this species in Abies pectinata. Riley records it from Hooker hemlock (Tsuga mnertensiana hookeriana) and from Abies
Megastigmus strobilobius Ratzeburg, 1848, p. 182.
Judeich and Nitsche, 1893, p. 704; 1895, p. 1339. Riley, 1893, p. 260.
Crosby, 1909, p. 368.
3Megastigms pictus (Foerster) Mayr, 1874, p. 138.
Cameron, 1879, p. 138.
Dalla Torre (in part), 1898, p. 287.
MEGASTIGMUS PINUS Parfltt.
This species was considered by its original describer to be a parasite on some species of Cynips which infested the seeds of the bristle-cone fir (Abies venusta) (according to the original describer this was considered as Picea bracteata), of a new species of Tsuga, and of the noble fir (Abies nobilis). In the original account "etc." is added after the foregoing list, which implies that other coniferous seeds are attacked by this insect. Riley, in referring to material reared by Mr. Borries, of Copenhagen, Denmark, adds that this species has been reared from the seeds of Shasta fir (Abies magnifica), from the white fir (Abies concolor), from the grand fir (Abies grandis), and from the amabilis fir (Abies amabilis), but as Riley allows great variation within this species it may be that some of these rearings actually contained some of the other species of Megastigmus. Other than the above mentioned list of food plants nothing is published concerhing the biology of this species.
Megastzynus pinus Parfitt, 1857, pp. 5543, 5629, 5721.
Dalla Torre, 1898, p. 287.
Riley, 1893, p. 360.
Cro'Sby, 1909, p. 368.
MEGASTIGMUS SPERMXOTROPHUS Wachtl.
This insect was originally described in 1893 by Wachtl, and at that time Wachtl stated with assurance that this species of Megastigmus was phytophagous and lived within the seeds of the Douglas fir (Iseidotsuga taxifola). Since then two papers have treated this insect in some detail. The first of these was by MacDougall in 1906. MacDougall knew the larva and felt reasonably sure that this species was p)hytopihagous. Some of his statements as to emergence are not without interest; he states that from a lot of seeds harvested in October. 1904, he found larva- in May, June, July, August, September, Octo-
CHALCIDIDS INJ UR10US TO FOREST-TREE SEEDS. I 61
ber, and November, 1905, and seemed to be of the opinion that the great variation in the dates of emergence of this insect was (ue to the irregularity of the hatching of the eggs and the coming to maturity of the larvoe. It may be, however, that the females which had emerged in the receptacle containing the seeds oviposited within the seeds, thus accounting for the larvv found in the months of July, August, September, October, and November, 1905, when the larvve which would be adults in the spring of 1906 should be feeding within the seeds. MacDougall does not give sufficient information to make his statement concerning variation in emergence conclusive, while rearings by Crosby, Crosier, and Wachtl confirm this last supposition.
The egg has been obtained by Crosby by dissection of a female and is described by him as "white, smooth, and spindle-shaped with a very long pedicel at the anterior end and the vestige of one at the opposite end. Length of body of egg, .36 mm.; tail-like process, .9 to 1.2 mm." The larva described by Crosby is as follows: "The full-grown larva is yellowish white with brownish mouth parts; its length varies from 2.5 to 3.5 millimeters. The surface is smooth without apparent sculpture, and the hairs are very sparse and microscopic in size. The inner margin of the mandibles is provided with three sharp teeth." The pupa is described by Crosby as follows: "The pupa is yellowish white and in the female has the ovipositor curved over the back and reaching to about the middle of the thorax. Length of female pupa, 3 mm.; of male, 2.5 mm."
The oviposition of this species is unknown, and the shape of the egg after having been deposited is not known. Neither has this insect been recorded as having been reared from the seeds of any Douglas fir raised in the United States. All seeds from which it has been reared were collected in Aberdeenshire, Scotland, on the estate of Mr. John Crosier. In this statement we must except the seeds from which the species was reared by Wachtl, as it is presumed that these were collected somewhere in the northwestern United States. Crosby also records the larvve within the seeds of Douglas fir in Colorado, but these seeds came from a nursery firm and definite locality could not be secured.
Up to the present time this is the most injurious chalcidid on forest trees which has received the attention of any entomologist. The attention which this insect has received in America, with the exception of the work done by Crosby, has been nil. MacDougall recommends as protection from this species that the cones be gathered as soon as ripe, and that, as soon as they will permit, the seed be thrashed from them, and that this be fumigated without delay with bisulphid of carbon. No experiments have been published concerning the results of such fumigation, but except for killing the larve within the seed and preventing another generation of adults this method can not be considered as valuable.
162 MISCELLANEOUS FOREST INSECTS.
jMcgastigmus spermotrophus Wachtl, 1893, p. 26, pl. 1.
Dalla Torre, 1898, p. 287.
MacDougall, 1906, pp. 52-65, 2 pls. Crosby, 1909, pp. 379-380, figs. 85-89.
Up to the present time there are seven species of chalcidid flies which are known to attack the seeds of the following forest trees: fSorbus scandica.
Mountain ash..................................... Sorbus aucuparia.
Amabilis fir.......................................Abies amabilis.
W hite fir...........................................Abies concolor.
Great silver fir......................................Abies grandis.
Shasta fir.........................................Abies magnifita.
Bristlecone fir................................... Abies venusta.
Noble fir..........................................Abies nobilis.
Three exotic firs.................................. Abies pectinata.
Hooker hemlock...................................Tsuga mertensiana hookeriana.
Unknown Tsuga................................... Tsuga sp. (?)
Douglas fir........ ...............................Pseudotsuga taxifolia.
Of these seven species the eggs of two are known, the larvae of four, the pupal of two, the oviposition habit of one, and the emergence dates of three. The only species of which the life history has been completely traced is that of the apple-seed chalcidid (Syntomaspis
druparumt) which is also known to attack the seeds of mountain ash .
The following bibliography is believed to be reasonably complete for all the literature received in Washington up to November 1, 1912, dealing with chalcidid flies which are phytophagous within the
seeds of forest trees.
lsO:. B;Enrm, F1RAN(AIS.-Extrait des observations sur un ver qui so trouve dans
l'intforieure des p6pins de la pomme d'api.
Paris, Ann. 12, p. 141.
Is::i. lOiuEMA, CARH. .-Skandinaviska Pteromaliner.
1879. CAMmRON, P.-On some new or little known British Hlymenoptera.
Ent. Soc. L ond., pp. 107-119.
1912. CRAwFoRD, .1. C.-De (riptions of new Hlymenoptera No. 5.
Nat. Mu1.. vol.-13, pp. 163-188.
Change of the name JToryNmid to Collmanldw.
CHALCIDIDS INJURIOUS TO FOREST-TREE SEEDS. 163
1909. CROSBY, CYRUs R.-On certain seed-infesting chalci-flics.
Cornell Univ., Coll. Agr., Dept. Ent., pp. 367-388, pls. 1-2, figs 67-98.
Original notes on a number of seed-infesting chalcidids, with many figures.
1898. DALLA TORRE, C. G. DE.--Catalogus Hymnopterorum, vol. 5, pp). 285-2S7,
1865. GUtRIN-MENEVILLE, F. E.--Note sur un chalcidite sorti des pepins dIune
1886. HORVATH, G.-yntomaspis drniparum Boh.
125-127, pp. xvuii-xix.
1895. JUDEICHI, J. F., AND NITSCHE, H.-Die Chalcididen.
1.906. MAcDOUGALIJ, R. STEWART.-- Megastigmus spermotrophus Wachtl, as an enemy
of Douglas fir (Pseudotsuga tax ifolia).
Vol. 19, pp. 52-65, 2 pls.
Notes on this species, with remarks on the habits of chalcidids in general. 1874. MAYR, GuSTAV .-Die curopaischen Torymiden hiologisch und systemat isch
1906. MOKREZECKI, S.-Beitrag zur Kenntnis der Lebensweise von Syntornaspis
pubesens Fiirst., druparuin (Boh.) Thorns.
Vol. 11, pp. 390-392, figs. 1-2.
1857. PARFITT, EDWARD.--Description of a new hymenopterous insect, found
amongst seeds of various species of pine in California.
Original description of Meqastigmus pin us.
1857. PARFITT, EDWARD.-Description of the male of .11egastigmuts pin u..
1848. RATZEBURcJ, J. T. C.--Die Ichneumonen der Forstinsekte-n, vol. 2, p. 182: vol.
3, p. 225! 1852.
1893. RILEY, C. V.-Is Jfegastiglh us phytophagic?
1908. RODZLANKO, W. W.--Commentatio de Torymidis quarum larvoe i-n seminihus
pomacearum vitam agunt.
A separate publication giving a review of the literature and some original observations on Syntoinaspi& druparum.
1879. SCHLECHTENDAL, D. H1. R. VO-N.-Entomologisch e Alifzeichnungen.
1888. SCHLECHTENDAL, D. H. R. voN.-'Uber das vorkommen phytophager Schlupfwespen.
1893. WAcHTL, FRITz A .--Ein neuer Jfegastigrnus als Samenverwiister von Psevidotsuga don glasii Carr.
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