TECHNICAL BULLETIN NO. 230 MARCH, 1931 UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C. MACROCENTRUS GIFUENSIS ASHMEAD, A POLYEMBRYONIC BRACONID PARA- SITE IN THE EUROPEAN CORN BORER By H. L. PARKER ^entomologist, Dici^ton of Cereal and Forage Insects, Bureau of Entomology^ CONTENTS Pr.gc Page Discovery in Europe and identity of the Biology—Continued. species 1 Average size of colony and proportion of Geographic distribution and host relations... 2 sexes _ 44 History of polyembryony in Hymenoptera.. 2 Parthenogenesis 46 Techi ic 'ollowed .- 6 Consideration of the zones in which Macro- Explanation of symbols used in the illust^^l- centrus gifuensis occurs_ _ 47 tions 7 Physical characteristics; 47 Description of Macrocentrus giftiensis 8 Climet'-c characteristics _ 48 The adult '. , 8 Seasonal history 49 The egg 9 Seasonal history of the host 49 The lar va 9 Seasonal history of the pi rasite 49 The prepupa and pupa 23 Experimental data 51 The cocoon 23 Laboratory breeding expor'ments 52 Biology. 24 Mortality in roaring of field material 52 E mergence 24 Summary of duration of vyrious stages,. 53 Light reactions 24 Kapidity of spring development 53 Feeding 24 Mortality in the prepupal pnd pupal Oogénesis 24 stages 55 C opulation. - 24 Cold storage of overwintering host larvae Oviposition 25 containing parasites 55 Segmentation of the egg 29 Cold storage of cocoons .- 56 Growth and developniert of tiie egg 30 Macrocentrus gifuensis as a controlling factor |H Pseud ogcrms :JG of Pyrausia nubilalis 56 Cyst formation. 38 Limiting factors 57 Larval habits 38 Recommendations 57 EiTect of parasite on iiu.it larva 42 Summary 58 Spin'ing L'nd pupation ._ 43 Literature cited 61 DISCOVERY IN EUROPE AND IDENTITY OF THE SPECIES 3iacrocentrus gifuensis Ashm.,^ a primary parasite in the larva of the European corn borer {Pyraustci nubilalis Hübn.), was found in common mugwort, Artemisia vulgaris L. {29),^ in the Armorican zone of western France by W. Gamkrelidze, of this laboratory, while on an exploration trip during the summer of 1925. ^ The work reported in this bulletin was done at the European I'arasite Laboratory of the Bureau of Entomology at Hyërcs, Var. France, from April, 1927, to October, 1929. The writer expresses his gratitude to Paul Marchai for examining and criticizing the microscopic preparations and drawings; to C. F. W. Muesebeclj and A. B. Gahan for help with the identity and description of this species ; to Esther Hart for her drawings of the adult and cocoons ; to W. R. Walton, W. R. Thompson, and E. Rabaud for help with the manuscript; to V. Malama for the photomicrographs; and to A. M. Vance, H. D. Smith, and Th. Malama for help in various ways. ^Family Braconidae, order Hymenoptera, class Insccta. 3 Italic numt>ers in parentheses refer to Literature Cited, p. 61. 24081—31- 2 TECHNICAL BULLETIN 2 3 0, TJ. S. DEPT. OF AGRICULTURE Further study by the writer soon revealed the fact that this species was an important primary parasite, and exportations to the United States for colonization were begun the following year. At first it was believed that this species was M. ahdoimnalis Fab., and in an earlier publication {^9) it was so designated. The writer has not examined the type of M. abdominalis, but A. B. Gahan has compared specimens from P. nubilalis with the type of M. gifuensis and believes that they are the same species, while he considers M. àbdomincdis to be a distinct species. GEOGRAPHIC DISTRIBUTION AND HOST RELATIONS This species has been reared by the writer from liost larvae taken from Artemisia in the Sequanian (south), Armorican, and Central zones in France, and from corn in the Danaprisian (north) zone in Russia. W. B. Cartwright has reared it in Japan from P. rmhilalk taken in corn and hemp. Hergula (7) has bred from larvae taken from corn at Kraljevec and Bjelovár in Jugoslavia a species of Macroceñlrus which he claims is identical with that bred from Tours material. It is quite likely that this is also M. gifuensis. So far as is known it has not been reared from other hosts than P. nubilalis. It is possible, however, that M. gifuensis has often been misidentified as M. ahdomwMlis and that, consequently, some of the biological and descriptive data in publications on M. ahdom- inalis pertain in reality to M. gifuensis. As there is no definite proof of this condition at present, such data can not be definitely incorpo- rated in a paper devoted exclusively to M: gifuensis. HISTORY OF POLYEMBRYONY IN HYMENOPTERA The discovery of polyembryonic development in the parasitic Hymenoptera by Paul Marchai and his subsequent studies and those of F. Silvestri are so well known and have been cited so oft«n that it is not necessary to go into detail concerning these matters. For the purpose of completeness, however, it is considered desir- able to cite here the forms known to reproduce by polyembryony as well as those suspected of such reproduction. It is pointed out that most workers on tlie Hymenoptera suspect that a great many of the vast group of Encyrtidae, whose biology is as yet unknown, will be found to reproduce in this manner. Polyembryony in the Braconidae.'' more especially in the genus Macrocentrus, was suspected as early as 1913 by Cushman (3). In 1927 Voukassovitch (30) supposed it to exist in M. ahdo-minalis, a parasite of Psarmnotis hyalinalis Hbn. Later, Thompson and Parker ißd) held it probable that M. gifuensis (then erroneously called M. dbdoininalis) reproduced in this manner. This bulletin leaves unclarified many aspects of the reproductive activities of M. gifuensis, such as oogénesis and the origin of the germ-cell determinant, the maturation divisions of the female pro- *Fink (5) describes the transformation and change in shape of the egg of M. anoylivora, but he gives no data on the segmentation or the structure of tlie gernis and embryonic membranes. After a careful study of Fink's remarks on the euperparasitism, etc., in this species the writer considers it possible that there is polyembryony in M. ancuHvara. In all events the matter should be investigated more closely. MACEOCENTRUS GIFITENSIS^ A POLYEMBRYONIC PARASITE 3 nucleus, the conjugation of the male and female pronuclei, the con- jugation of the germ-cell determinant, and early divisions of the primary cleavage nucleus.^ The vs'riter holds, however, that he has demonstrated the following points: (1) The differentiation of the egg into a pregerm composed of a paranucleus (probably derived from the polar nuclei) which directs and governs the trophamnios, and germinativo or true embry- onic cells which give rise to embryos; (2) the division by fission of the primary germ accompanied by a division of the paranucleus to form the secondarjr germs, which again divide to form morulae, which demonstrate (3) polyembryony in M. gifioensis. A summary of our knowledge of polyembryony among the para- sitic Hymenoptera is presented in Tables 1 and 2. ^ Thip phase of development will be made the subject of further researches. TECHNICAL BULLETIN 2 30, V. S. DEFT. 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