The genus Isocybus is considerably problematic because there are very few specimens in collections, and I have only a dozen or so from various scattered regions. It's a moot question as to whether there are more species, simply because there are not enough representatives from any one region to provide insights about variation, hosts, ranges, or any other useful data. I have provided a reformatted version of Fouts" redescription, and several illustrations based on specimens available to me. The reference to their being raised from willow is the only one I have seen from this country. If so, it seems that there should be many more specimens available. The willow records may actually be from a Platygaster species that was misidentified as Isocybus. Perhaps P. obscuripennis Ashmead.
Whatever the case may be, there is clearly a great deal of variation in topography, but no apparent substantial difference for distinguishing species. That may change with more study, in the future.
DIAGNOSIS (reformatted and modified from Fouts (1924))
Isocybus Foerster.
Isocybus Foerster, Hym. Stud., Heft 2, 1856, p 114. Four species.
Genotype: (Platygaster ruficornis Walker) = Platygaster grandis Nees. By original description.
This genus is closely related to Platygaster Latreille and Trichacis Foerster. It may be separated from the former only by the shape of the head which is more or less cubical, very full behind and above the eyes. As in Trichacis the scutellum is of an irregular shape, never smoothly rounded above and evenly sculptured, and has a more or less distinct tuft of hair above. In Platygaster the pubescence is scattered and alwavs denser on the sides than on the top. The abdomen is six segmented in the female and seven in the male. The second tergite is not densely pubescent proximally and has two basal foveae.
Foerster designated as type the species described by Walker' under the name Platygaster ruficornis Latreille. P. ruficornis (Latreille) Walker is not Latreille's species and has been synonymized with Platygaster grandis Nees by Dalla Torre. In the National Museum there is one specimen from Europe labeled "Essex, England (Isocybus grandis Nees." I do not know who labeled the specimen but it agrees pretty well with Nees' description. Compared with specimens of canadensis (Provancher) I can find few differences, none fundamental, the most important of which are the slightly coarser sculpture of the mesonotum and the darker color of the antennae.
Only one species is known from North America. The two others included in this genus by Ashmead do not agree with the diagnosis given above and are placed elsewhere. Platygaster pallipes Say is retained as a doubtful speoies in Platygaster. Isocybus longtwentris Ashmead is redescribed in the same genus.
Platygaster canadensis Provancher, Addit. Fauna Ent. Can. Hym., p. 181.
Monocrita canadensis (Provancher), Ashmead, Can. Ent., vol. 19, 1887, p. 126.-
Cresson, Syn. N. Amer.Hym., 1887, p. 49.
Isocybus canadensis (Provancher) Ashmead, Bull.. 45, U. S. Nat. Mus., 1893, p.
329.-Brues, Bull. 22, Conn. Geol. Nat. liist. Survey, 1916 (1917), p. 541.
Isocybus nigriclavus Ashmead, Bull. 45, U. S. Nat. Mus., 1893, p. 328.
Isocybus pallipes (Say) Ashmead, Can. Ent., vol. 19, 1887, p. 132.-Cresson,
Syn. N. Amer. Hym.,, 1886, p. 2S0.-Ashmead, Bull. 45, U. S. Nat. Mus.,
1893, p. 328. (Misidentification of Say's species, see p. 109.)
Isocybus pallipes (Say) Brues, Bull. 22, Conn. Geol. Nat. Hist. Survey, 1916
(1917), p. 541.
Female.-Length 4 mm. Head two-thirds as wide as long, as wale as the thorax, very full behind the eyes, the cheeks being highly convex and much wider than the eyes; occiput and vertex shagreened, the former emarginated, sometimes punctate rugose; frons rugose, finely set with twisted raised lines, reticulated; cheeks sometimes with a sculpture similar to that found on the frons, frequently shagreened, without raised lines; antennal projection depressed down the middle, notched anteriorly.
Scape slender, long and curved, extending above the dorsal surface of the head; pedicel as long as joint four, shorter and wider than three which is three times as long as wide at apex; joints five to nine wider than four, a little longer than wide, cylindrical; ten as long as three, subacute apically, the upper side curved near the apex.
Thorax nearly twice as long as wide, more or less flattened above, higher than wide; pronotum roughened and strongly punctate above on the sides; mesonotum usually mostly. polished, sometimes mostly sculptured like the frons; notauli deep, complete; lateral lobes coarsely shagreened along their inner margin, posterior margin of mesonotum with long hairs projecting over the scutellar fovea; scutellum transverse, roughened, with a large central space densely covered with short whitish hairs, lateral margins of scutellum very high and sharp, projecting above the surface of the scutellum; propodeum rather finely roughened, densely covered with erect long white hair; median carinae close together and parallel.
First tergite as wide as long, slightly narrowed anteriorly, roughened and covered with erect white hair on each side of the median area; median area well defined, widened flask-like anteriorly, much longer than wide; abdomen obovate, a little over twice as long aswide, wider than the thorax, as long as the head and thorax united; second tergite two-thirds as wide as long, three-eighths as wide at base as at apex, without sculpture of any sort; basal foveae deep, not especially large, as long as the first tergite, pubescent; tergites three to six finely shagreened, united three-tenths as long as the second, the third a little the longest.
Wings brownish, extending half the length of the second tergite past the apex of the abdomen.
Black; antenna and legs (except last six joints of the former and the coxae) brownish yellow, shining; antennal club brown, coxae black.
Male.-Length 3 mm. Pedicel one and one-half times as long as wide; as long and as wide as joints three and four; joint three elongate and more or less triangular; four cylindrical, slightly widened below at apex; five cylindrical, a little longer than wide, as wide as four at apex; joints six to nine as wide as four, becoming gradually longer distally; ten very long and acute apically, nearly as long as eight and nine united, three times as long as wide.
Abdomen sculptured as in the female, spatulate, a little over twice as long as wide, as long as the head and thorax united; tergites three to seven finely shagreened, thickly pubescent, united one-third as long as the second.
Wings extending the length of the second tergite past the apex of the abdomen. Coloration as in the female; flagellum, including the pedicel, usually brownish, sometimes yellow.
Type locality.-Ottawa, Canada.
Other localities.- Greeley, Colorado; Algona, Iowa; Texas; Michigan.
Type.- One of Provancher's male paratypes is in the National Museum (Cat. No. 25427). The types of I. nigriclavus are also in the National Collection (Cat. No. 2306).
Besides the types mentioned above the National Collection has a number of specimens from the Agricultural College in Michigan. Several of these specimens are recorded as having been reared March 10, 1887, from a gall on willow. The others bear only the labels, "June 3, 1887," and "Ag. Coll. Mich."
References:
Fouts, R.M. 1924. Revision of North American Wasps of the subfamily Platygasterinae.Proc. U.S. Natl. Mus. 63 (15): 10-12.
Whether or not there is more than one species of Isocybus in the U.S. is still an unknown, and a more detailed study of each variant may prove one way or another. For this I began working up the mouthparts of this and closely related genera, using light microscope methods. The study is greatly eased by using CMC (carboxy methyl celluslose) as a dissecting medium and as a mountant.
As a dissecting medium, I add flourescein and mercurochrome, which is somewhat picked up by the tissues in processing and in the slide preparation. CMC must be liberally applied to a finished slide, however, and then sealed with a permanent varnish or lacquer. Use lots of CMC!
The specimens are cleared for long periods, sometimes weeks, in saturated KOH solution, then the heads are removed to tiny Syracuse dishes of water, which is changed several times over a two or three day period. They are then infiltrated with watery CMC, which gradually thickens, to which I continue adding thicker CMC. This I then partially solidified under a halogen lamp. The rest of the specimen is similarly treated and set aside in a separate dish after infiltration.
When the head has set up and is reasonably immobile, the maxilla and labium are removed using microneedles. This work is better done on the slide to avoid transferring the specimens. CMC viscosity is adjusted with water or heat at all stages to suit my purposes. When ready, I dry the specimen in the drop of CMC, apply a generous amount to a cover slip, then invert the slide onto it. This way, the specimen remains more or less permanently fixed to the spot and refuses to float around on the slide. The slides can be examined immediately unless oil immersion is required, for which I wait a few days.
My methods are only slight modifications of those used by Leeuwenhoek, ie, I may examine the specimens at only 2 or 2.5 times his magnifications, though often not over 200x . And most certainly, the same results may be achieved using "caustic potash", carbolic acid, mineral spirits, vinegar, wine and varnish with a trace of cochineal. Of course, I have a few advantages that Leeuwenhoek lacked, such as low magnification oil immersion objectives, good condensers with high numerical apertures, and a website.
If we stop to think about it, Latreille named Platygaster in 1809, but it had certainly been known long before that time. The old microscopists examined everything that was tiny, in just about every way possible under the sun. This was probably no different. It's quite likely that these mouthparts and every other detail of this group were examined long before being reported, but no one had a website, and therefore everything was relegated to the shelf. Where it stayed. Only the super-filtrate was ever published.
I have another obvious advantage in that while reviewing my manuscript before it goes to the website, I can settle down with a bowl of hot chili with habeneros, nachos, and sardines resting in Louisiana hot sauce. This, with a cup of steaming coffee, is a great aid to staying alert for the review, and may enhance the vitality of the final report. I must also add that jalepenos and habeneros will also greatly enhance the flavor of even the meanest, most mundane coffee… these are "adjuvants. Leeuwenhoek had none of these advantages.
A footnote here: using strong, saturated solutions of KOH is not the usual procedure in most insect anatomy studies, but is just right in these. In this way, I accidentally discovered that certain genera develop characteristic holes in the head, long before any other membraneous areas have disappeared; in Inostemma, square holes over the ocelli and in the face; in Isocybus, crescentic holes over the lateral ocelli; in Trichacis, a wedge shaped hole in the frons. This happens with considerable regularity. So far, no holes have occurred in Platygaster, Leptacis or Synopeas. You may imagine how the key couplets might appear for this character.
At first the holes in the head were only a curiousity, I thought a fluke, but then recalled that Masner presumes the ovipositor to be extruded by hydraulic pressures caused by pumping actions of the head and propleura. How so? Examining the internal texture of the Isocybus head shows a thick, convoluted mat of wrinkles all over the front, sides, and most of the back, but very thin and relatively nonconvoluted texture over the lateral ocelli. That doesn't answer the question, but may give a clue about why the holes occur. In some Inostemma specimens, it appeared that the head capsule might have somewhat thickened ridges similar to the "H" shaped lines on heads of Mymmaridae. That remains to be investigated. Perhaps it is still only a fluke, but I feel it worth mentioning here.
The maxillary stipes and labium are quite uniform throughout the Platygastrinae. The cardines vary in length and shape to a considerable degree. In Isocybus, the galea and lacinia are fused into a large ovoid piece, half with strong setation, half membraneous and without. I have labeled the parts according to my interpretation, but this based on the diagram of Synopeas sp., also included here. The galea is the outer lobe, the lacinia the inner lobe, both attached to the stipes by a thickened ridge. Synopeas, as well as other Platygastrini that I have so far examined, have a laciniate lacinia. Aha! It's not as obvious in Isocybus, wherein both are fused and the lacinia is only weakly laciniate, and has a basal lobe. In dissections, the stipito-galeal muscle is seen attached to a longitudinal sclerotic bridge running through the midsection of the galea, but I omitted it from these diagrams for clarity.
There are two maxillary palpomeres, one labial, in Isocybus. The large strong setae are concentrated at the apices of each. The glossa is bilobed, with a subapical transverse row of four setae, and one arising slightly above those. This is similar to that of Inostemma, except that the tip of the glossa in Inostemma is four lobed in those that I have examined. The tip of the glossa in Isocybus is covered with fine, feathery elongate lacinia, . which need to be studied at higher magnifications than my little "Platyskop" provides.
I am uncertain about the exact number of glossal setae in the subfamily. Synopeas and some Platygaster species appear to have only three setae in a transverse row, and one above. I insist to myself that this is due to faulty technique and breakage, but to date have not found the socket for a fourth seta, and have to report only three subapical setae in the transverse row. This will probably change with experience and further dissections. Likewise, I have not yet detected lobes at the tip of glossa in Platygastrini or Synopeadini except for the Isocybus sp. (known to me as I. canadensis (Prov.) The Isocybus also has 4 frenal hooks, instead of two as found in most Platygastrini, and may not actually belong in the tribe at all. I have cleared specimens in CMC set aside for further work on this possibility. Presently, I am guessing that Isocybus should be placed outside Platygastrini. We will likely see how this stands in another couple of centuries.
The figures show the overall relationships of the maxilla and labium, views of the galea-lacinia, palpi, and very slightly diagonal view of the cardo. The shape of the latter will probably have some generic import later. This is elongated in the Inostemma sp. studied so far (North American). Also, in Inostemma, so far, the labial palp is elongated and sinuate, with a sharp sub-basal bend.
