The Male Genital Tube of Some of the Species of the Genus Scymnus (Coleoptera, Fam. Coccinellidae).
Psyche 34(5):167-170, 1927.
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VOL. XXXIV. OCTOBER 1927 No. 5
THE MALE GENITAL TUBE OF SOME OF THE SPECIES OF THE GENUS SCYMNUS (COLEOPTERA, FAM.
The genus Scymnus is one of the largest in the family Coc- cinellidse and one in which the species are very hard to determine on account of their remarkable uniformity in appearance. The adult beetles are small, ranging from 1.1 mm. to approximately 3 mm. in length, rounded to oblong-oval in shape, pubescent, with six ventral abdominal segments showing, and the legs free. The color markings are quite constant, "Color characters have their utility in the separation of species of Scymnus, but some care and no little experience is required in their use" (Horn 1895). Casey (1899) in his revision of the Coccinellidse used color to a great extent in the separation of the species. The prosternal carinse and the abdominal plates or metacoxal lines are other characters which are very useful in this group. The secondary sexual characters of the male are quite distinct in most of the species, but have been mentioned in the description of very few of the species.
Leng (1920) lists one hundred and nineteen species from North America, sixty-five of which were described by Casey, seventeen by Leconte, fourteen by Horn, ten by Mulsant, four by Fall, three by Crotch, three by Melsheimer, one by Blatch- ley, and one by Say. Casey believed that the number of species would be increased in the future instead of decreased. Nothing has been done with the genus Scymnus since Casey's "Revision of the American Coccinellidas," except the description of four species by Fall and one by Blatchley.
Contributions from the Entomological Laboratory of the Bussey Insti- tution, Harvard University, No. 276
The genitalia of the male are usually accepted as being the final criteria for species about whose validity there is any doubt. A study of the genitalia will also show the degree of relationship between species in a group. With these facts in view the present study was undertaken in the hope that significant variations might be found in the cedagus of species having only slight ex- ternal differences.
Since it is very easy to make erroneous determinations in this group, the present paper includes only that material which was compared with the types. All the species were described by Lecont except five, and the specimens were carefully compared with the Leconte types in the Museum of Comparative Zoology at Cambridge. The other five species were identified by Le- conte, and were included in his collection. As my identifications agree with his, I felt safe in using these species in my investiga- tion.
I wish here to thank Mr. Nathan Banks for his kind gene- rosity in allowing me the use of the collection in the Museum of Comparative Zoology. I am also greatly indebted to Mr. C. A. Frost who loaned me his collection with permission to dissect any of the specimens which I might see fit to use for such pur- poses.
In a previous paper (Wilson 1926) the structure of the Coccinellid cedagus was described in detail. The general struc-
ture of the oedagus of Scymnus is similar to that of other Coc- cinellids. The basal lobe surrounds the median lobe and is very variable in shape. In such forms as Scymnus americanus Muls., the basal lobe is quite similar to that of Brachyacantha ursina Fab., which is one of the simplest of the forms described in that paper.
The material here presented seems to fall naturally into four groups, and if a study of the whole genus could be made it would probably be possible to separate the genus into several groups, each group showing some relation to the other groups. The oedagus of quadritceniatus Lee. is particularly interest- ing because the proximal end of the median lobe is not flattened and expanded as in the other species. The median lobe is also
19271 The Male Genital Tube of the Genus Scymnus 169 less chitinized and is looped around the median strut. The
lateral lobes are large as compared with the basal lobe. In the second group which consists of americanus Muls.,' punctatus Mels., cervicalis Muls., and lerminatus Say, the proxi- mal end of the median lobe shows specific variations. In fact
the proximal end of the median lobe, and the basal lobe, are the structures which are most variable in all the groups. The oedagus of nanus Lee., semiruber Lee., cinctus Lee., and hcemorrhous Lee., are larger than the cedagi of the second group. All of the drawings were made at a magnification of about 115 diameters, except in the case of americanus and puncticollis, which were magnified about 85 diameters. The proximal end of
the median lobe in nanus and semiruber are somewhat alike, and resemble that of terminatus to a certain extent. The same area in cinctus and hmorrhous has in addition a small area, in the upper portion of which are found alternate bands of thick and thin chitin.
The basal lobe is also much modified in cinctus and hcemorrhous. It extends through the basal piece, and beyond it anteriorily, for a short distance. Possibly if more material were available, there would be two groups instead of one, nanus and semiruber belonging to one, and cinctus and hmorrhous to the other.
The basal lobe of puncticollis Lee., consobrinus Lee., and tenebrosus Muls., is much expanded, and very much larger than the lateral lobes. The shape of the basal lobe is also rather com- plicated in structure and projects beyond the basal piece an- teriorily. At the distal end of the median lobe there are several stiff, bristle-like projections which point forward. There are also specific differences in the proximal end of the median lobe. If we consider the genitalia of consobrinus and tenebrosus it would appear that these species are closely related, while in the key they fall into separate groups, and their relation would never be suspected. The genitalia of the Coccinellidae are rarely ex- truded and are rather difficult to dissect out, for this reason they will never be of any value as key characters, as in the case of other groups. However, further study of the genitalia of the genus Scymnus will undoubtedly show the relationship between the various species.
170 Psyche [OC~O bet
Casey, Thomas L. 1899. A Revision of the American Cocci- nellidee, Journ. New York Ent. Soc., VII, 138-160 Crotch, G. 8. 1874. Revision of the Coleoptera Family Cocci- nellidae, London 1-311
Horn, G. H. 1895. Studies in Coccinellidee, Tran. American Ent. Soc., XXII, 81-114
Leng, Charles W. 1920. Catalogue of the Coleoptera of America North of Mexico,
Sharp, D. and Muir, F. 1912. The Comparative Anatomy of the Male Genital Tube in Coleoptera. Tran. Ent. Soc. London, 477-639
BL. Basal lobe
BP. Basal piece
LL. Lateral lobe
ML. Median lobe
MS. Median strut
EXPLANATION OF PLATE VI.
Scymnus quadritceniatus Lec.
Scymnus americanus Muls.
Scymnus punxtatus Mels.
Scymnus cervicalis Muls.
Scymnus terminatus Say
Scymnus nanus Lee.
Scymnus semiruber Lec.
Scymnus cinctus Lee.
Scymnus hamorrhous Lee.
Scymnus puncticollis Lee.
Scymnus consobrinus Lee.
Scymnus tenebrosus Muls.
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