W. M. Wheeler.
Two Mermithergates of Ectatomma.
Psyche 37:48-54, 1930.

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Psyche
[March
TWO MERMITHERGATES OF ECTATOMMA
Since the publication in 1928 of my review of the modi- fications induced by Mermis parasites in various species of ants, two additional cases have been reported, one by Strelnikov (1928) in a Ponerine ant, Pachycondyla striata, from Paraguay, and one by myself (1929) in a Formicine ant, Camponotus (Tansentyrmex) punctatus from Argen- tina. Two other interesting mermithergates have just come to light among some ants collected by Mr. Nathan Banks and Mr. P. J. Darlington. One of these belongs to the typical Ectatomma tuberculatum Olivier, the other to its variety punctigerum Emery. As long ago as 1890, Emery (1890 a) mentioned a peculiar worker of the typi- cal E. tuberculatum, which we now know must have been a mermithergate, but he merely cites it as "analogous" to a similar specimen of Neoponera villosa with small head and voluminous abdomen.
The mermithized specimen of the typical E. tuberculatum was taken by Mr. Banks on July 15, 1924, near the tropical laboratory on Barro Colorado Island, Panama. It measures nearly 16 mm. and is of the same brownish ferruginous color as normal workers from the same locality, but with the gaster distinctly darker. The head is smaller and nar- rower, with scarcely an indication of the posterior angles and with very slightly larger and more convex eyes. Ocelli lacking. Antenna1 scapes extending half their length be- yond the posterior corners of the head and the mandibles slightly narrower. Thorax shaped as in the normal worker but slightly less robust, with distinct, blunt teeth on the epinotum. Petiolar node more strongly compressed antero- posteriorly. Postpetiolar and gastric segments, especially Contribution from the Entomological Laboratory of the Bussey Institution, Harvard University, No. 334. Pachi 37:48-54 (1930). hup ttpsychc rinclub nrg/17/37-048 html



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19301 Two Mermithergates of Ectatomma 49 the first, enlarged and distended with Mermis. Legs de- cidedly longer than in the normal worker. Head sculpture peculiar in that the longitudinal rug= are finer, closer together and decidedly more numerous on the front than in the normal worker. The reticulate rugse on the sides of the vertex in the latter are also replaced by such longitudinal rugse. Thoracic sculpture as in the nor- mal worker. Petiolar node transversely rugulose and not irregularly rugose above. Postpetiole and gaster more opaque throughout, finely and densely striate, with a satiny lustre ; the striae transverse and converging behind on the postpetiole, longitudinal on the gastric segments. Venter more shining but very finely and transversely, though more superficially striate throughout. The sculpture of the ab- domen therefore resembles that of the normal worker tuberculatum.
The pilosity of the mermithergate is quite normal.
Although the typical form of E. tuberculatum is a com- mon ant over a large portion of the Neotropical Region from Southern Mexico to Southern Brazil, its two varie- ties, acrista Forel and punctigerum Emery have a much more restricted distribution. The var. acrista is known only from Paraguay; Emery (1890 b) described punc- tigerum from a couple of workers taken by Simon at San Esteban, Venezuela. It is certainly the common, if not the only form of the species in Trinidad, where it has been taken by Prof. R. Thaxter and myself, and Dr. George Salt and Mr. Darlington brought me specimens of it from Northern Colombia. The worker differs from that of the typical tuberculatum in coloration, being decidedly darker and more brownish, and in the sculpture of the postpetiole and first gastric segment, the coarse, sparse punctures on which are larger, more impressed and interrupt the striated sculpture. Moreover, the striation on the first gastric seg- ment is much feebler than in the typical tuberculatum and becomes obsolete on the sides, so that the whole segment is decidedly smoother and more shining. The female punc- tigerum (undescribed) is scarcely paler than the worker, with very similar abdominal sculpture though in some spec- imens the striat-ion on the first gastric segment is even



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Psyche
[March
Fig. 1. Ectatomma tuberculatum Olivier var. punctigerum Emery. a, normal worker in profile ; b, head of same, dorsal view; c, head of normal female; d, mermithergate in profile; e, head of same.



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19301 Two Mermithergates of Ectatomma 51 feebler and the surface, therefore, even smoother and more shining.
The punctigerum mermithergate (Fig. 1d.e) was cap- tured by Mr. Darlington on April 20,1920 at St. Augustine, Trinidad, together with three normal workers of the vari- ety. Were it not for this association ,the specific identity of the parasitized specimen might be doubtful, though its cephalic and thoracic sculpture is clearly of the E. tuber- culatum type. The specimen measures 16.6 mm. in length and is longer than the average normal worker which meas- ures only about 10-12.5 mm., but the proportions of the head, thorax and abdomen are very different. In the mer- mithergate the head measures only 3.2 mm. in length, in- cluding the mandibles, the thorax 4 mm., the abdomen 9.4 mm. The corresponding measurements of the normal large worker are: head 3.5 mm., thorax 4.5 mm., abdomen 4.5 mm. Though the head and thorax resemble those of the normal worker they are therefore decidedly smaller and more slender. The head, excluding the mandibles, is nearly square, very slightly longer than broad, with very feebly rounded sides and the posterior angles merely rounded-rec- tangular and not sharply, rectangular or even distinctly cornuate as in the normal worker. Eyes larger, more pro- tuberant, nearly hemispherical. There are no traces of ocelli. Antenna1 scapes extending nearly half their length beyond the posterior corners of the head (only two-fifths in the normal worker), mandibles somewhat narrower. Be- sides its smaller and more slender dimensions the thorax differs from that of the normal worker in having the lateral tubercles of the pronotum more acute and less auriculate, the median tubercle or projection narrower and more sharply defined. The base and declivity of the epinotum form a less distinct obtuse angle and the epinotal teeth are reduced to mere denticles. Petiole very similar to that of the normal worker but the node slightly more compressed anteroposteriorly. Postpetiole and gaster much larger and more voluminous, owing to their containing a large Mer- mis, the compact coils of which are visible through the dis- tended intersegmental membranes. The hypertrophy af- fects not only the postpetiole and first gastric segment but also the deflected second, third and fourth gastric segments,



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52 Psyche [March
which in the normal worker and even in the female are much shorter and telescoped into one another. Anteroven- tral projection of the postpetiole less developed than in the normal worker and female; legs as long as those of the former.
Sculpture peculiar; the longitudinal rugae on the front and vertex decidedly less coarse, denser and more numer- ous than in the normal worker, with the reticulate rugae between the front and eyes also much finer; rugules on the median portion of the clypeus more numerous; striae on the mandibles somewhat coarser. On the thorax the rugse are distinctly finer and more definitely transverse; those on the posterior portion of the pronotum also transverse, not coarse and irregular as in the normal worker. The rug2 on the petiolar node are finer and symmetrical. On the post- petiole and gaster the sculpture is quite unlike that of E. tuberculatum and much like that of E. quadridens Fabr., the tergites of all the segments being finely and regularly striate, so that the surface is subopaque, with a faint satiny lustre. The strise on the postpetiole are arcuate anteriorly, longitudinal in the middle and transverse posteriorly; on the first gastric segment longitudinal anteriorly and trans- verse behind; on the second and third gastric segments transverse and more oblique on the sides. The fourth seg- ment is more shining, with finer and less distinct striae. The coarse punctures on the postpetiole and first gastric segment are small, inconspicuous and scattered, as in E. quadridens and therefore very different from those of punc- tigerum or the typical tuberculatum.
Pilosity as in the normal punctigerum worker, but less abundant, especially on the abdomen.
Coloration decidedly darker; dark brown, almost black- ish, with brownish yellow clypeus and mandibles, the former streaked with fuscous in the middle, the latter fus- cous externally. Femora, terminal tarsal joints, tips of scapes, apical halves of antenna1 funiculi and borders of gastric segments reddish brown; a spot on the middorsal region of the postpetiole and one on the corresponding re- gion of the first gastric-segment more yellowish. The specimens described in the preceding paragraphs are obviously modified workers, without any perceptible female



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8
19301 Two Mermithergates of Ectatomma, 53 (queen) characters. Even the enlargement of the abdomen is quite unlike that of the normal Ectatomma female, since in this caste the gaster is shaped like that of the worker, though more voluminous, especially in the region of the postpetiole and first gastric segment. The mermithergates are interesting for two reasons, first, because they so clearly illustrate the compensatory decrease in the size of- the head and, in Darlington's specimen, also of the thorax as a result of the hypertrophy of the abdomen, which har- bors the Mermis, and second, on account of their close re- semblance in coloration, abdominal sculpture, and, I may add, also in the shape of the posterior portion of the head, to another species of the same genus, E. quadridens. This singular resemblance may, I believe, be most readily ex- plained on the supposition that the specific characters of quadridens are probably more nearly those of the ancestral species of Ectatomma and that in the mermithized speci- mens these characters have been activated as a result of metabolic disturbances set up during metamorphosis by the parasite. To have produced such a pronounced effect on the characters of the adult ant, the young nematode must have entered its body cavity during the larval stage. Recently Vandel (1927) has maintained that in Pheidole pallidula infection of the prepupa by the Mermis is sufficient to pro- duce a rnermithergate, but his evidence for this contention is very meager. I have called attention to the fact (1928) that the larvae of the Ponerinse and Formicise (Lasius) spin cocoons before the prepupal stage and that it is therefore very improbable that the young nematode would wait to bore through a tough envelope when it could so easily and directly enter the unprotected, thin-skinned larva. That this is actually what happens, has been shown by Dr. N. A. Cobb, our well-known authority on the nematodes, who writes me that he has found the larva of Allomermis myr- mecophila Bayliss-"in the body cavity of a queen grub of the dark-colored Lasius from Falmouth, Lasius niger neoniger." Falmouth, Massachusetts, is the locality in which Dr. A. H. Sturtevant found the many mermithized queens (mermithogynes) of Lasius described in my paper of 1928.




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54 Psyche [March
Literature
Emery, C.
1890. a. Studii sulle Formiche della Fauna Neo- tropica I. Formiche di Costa Rica. Bull. Soc. Ent. Ital. 22, 1890, pp. 38-80, 5~1~.
Emery, C. 1890. b. Formicides. Voyage de M. E. Simon au Venezuela (Dec. 1887-April 1888) 7e Mem. Ann. Soc. Ent. France 1890, pp. 55-76.
Strelnikov, T. D. 1928. Mermis Parasitism in Pachydondyla triata. Psyche 35, 1928, pp. 199-200, 1 fig. Vandel, A. 1927. Modifications determinees par un nema- tode du genre, "Mermis," chez les ouvrieres et les sol- dats de la Fourmi "Pheidole pallidula" Nyl. Bull. Biol. France Belg. 61, 1927, pp. 38-48, 3 figs. Wheeler, W. M. 1928. Mermis Parasitism and Intercastes among Ants. Journ. Experim. Zool. 50, 1928, pp. 165- 237, 17 figs.
Wheeler, W. M. 1929. A Camponotus Mermithergate from Argentina. Psyche 36, 1929, pp. 102-106, 1 fig.



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