G. C. Wheeler and J. Wheeler.
The Ant Larvae of The Myrmicine Tribes Basicerotini and Dacetini.
Psyche 61:111-145, 1954.

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PSYCHE
Vol. 61 December, 1954 No. 4
THE ANT LARVAE OF THE MYRMICINE TRIBES
BASICEROTINI AND DACETINI
BY GEORGE C. WHEELER AND JEANETTE WHEELER Department of Biology, University of North Dakota We have treated these two tribes together because they were considered as one tribe (Dacetini) by Emery (1922) and by Wheeler (1922). Recently Brown1 (1949) sep- arated out several genera to form a new tribe Basicerotini. Our studies of the larvae of three of these genera corrobo- rate this separation, for they differ as a group from the Dacetini (as restricted by Brown) in body hairs, mandibles and maxillae. However, one might with equal justification split the larvae of the Dacetini (sensu strictiore) into three groups, which would differ from each other to at least as great a degree.
Tribe BASICEROTINI Brown
This tribe comprises some three dozen species in seven genera : Basiceros, Aspididris, Creightonidris, Rhopaloth- rix, Octostruma, Heptastruma and Talaridris. About half the species are in Rhopalothrix, which is Neotropical, Indo- malayan, Papuan and Australian; the remaining genera are strictly Neotropical.
The larvae of the Basicerotini are a homogeneous group, if one can apply that adjective to only two types, for the larvae of Basiceros and Aspididris are generically indistin- guishable. The tribe may be characterized as follows :- Moderately stout. Thorax and first two abdominal somites strongly curved ventrally. Anus ventral. Somites distinct on the anterior half, indistinct on the posterior. Spiracles small. Body hairs numerous; short to long; uni- Ill




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112 Psyche [December
formly distributed (except that some part of the midventral surface is naked), denticulate and of two types : (1) short and flexible; (2) a few long and slightly curved or flexible. Cranium vaguely subhexagonal in anterior view, but with the 'occipital border impressed at the middle. Clypeus bulg- ing. Antennae minute. Head hairs long, flexible and den- ticulate. Ventral border of labrum spinulose, with two or three sensilla ; posterior surface spinulose. Mandibles rather long and narrow, slightly curved medially ; with one apical tooth and two teeth on the inner border; some part of the surface furnished with a few ispinules or den- tides. Each maxilla divided into two parts by a trans- verse lateral impression, the basal half swollen laterally and bearing the palp, the distal spinulose (at least in part) and bearing the galea; palp and galea digitiform. Labium with all surfaces spinulose; palp a low knob bearing five sensilla; an isolated sensillum between each palp and the opening of the sericteries ; the latter a short transverse slit. Hypopharynx spinulose.
Genus Basiceros Schulz
Moderately stout. No neck, but thorax and first two abdominal somites strongly curved ventrally. Body hairs moderately numerous, of at least two types: (1) short, denticulate and flexible ; (2) moderately long, denticulate and slightly curved. Labrum trilobed. Mandibles with two very stout medial teeth on the inner border; basal third of inner surface with minute spinules in arcuate subtransverse rows. Maxillae large; palp with four apical sensilla. Labium large.
Basiceros sp.
(PI. 10, figs. 16 and 17)
Body moderately stout; diameter greatest at abdominal somite IV, decreasing gradually to I, then increasing slightly to the mesothorax; thorax and first two abdominal somites strongly curved ventrally. Anus ventral. Spiracles small, mesothoracic slightly larger than the rest. Integument of ventral surface of thorax with spinules in transverse rows. Body hairs moderately numerous and uniformly



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19541 Wheeler and Wheeler- Basicerotini and Ducetini Ant Larvae 113 distributed.
Of at least two types: (1) denticulate, flexible, short (about 0.16 mm) , without alveolus and articular membrane, probably the more abundant type; (2) den- ticulate, slightly curved, moderately long (about 0.25 mm), with alveolus and articular membrane.
Cranium vaguely
subhexagonal in anterior view; a third broader than long; occipital border impressed at the middle ; genae and clypeus numerous subtransverse rows; posterior surface of each of which bears a spinule. Head hairs moderately numerous, long (0.108-0.26 mm) , flexible and denticulate. Labrum short (breadth 2.3 times length), trilobed, anterior sur- face of each lateral lobe with eleven minute hairs and/or sensilla, ventral border of each lateral lobe with two con- tiguous sensilla ; whole ventral border spinulose ; posterior surface spinulose, the spinules near the lateral borders isolated and rather long, the remainder minute and in numerous subtransverse rows; posterior surface of each lateral lobe with a cluster of four sensilla. Mandibles moderately sclerotized; long and narrow, slightly curved medially; apical tooth slender, slightly curved and round pointed; two much stouter teeth projecting inward from the inner border; basal 1/^ of the inner surface with minute spinules in short arcuate subtransverse rows. Maxillae large, with a lateral swelling bearing the palp and a para- boloidal apex bearing the galea; apex spinulose; palp digitiform with four apical sensilla (two encapsulated and two with a spinule each) ; galea digitiform with two apical sensilla. Labium large, with all surfaces spinulose, the spinules in short subtransverse rows; palp a low knob with five apical sensilla (two encapsulated and three bear- ing a spinule each) ; opening of sericteries a transverse slit. Hypopharynx spinulose. (Material studied : one dam- aged semipupa from "Hamburg Farm", Costa Rica ; worker identified by Dr. W. L. Brown as B. sp. near singularis (F. Smith). )
Genus Aspididris Weber
Moderately stout. No neck, but thorax and first two abdominal somites strongly curved ventrally. Body hairs
moderately numerous, denticulate and of two types: (1) short and flexible; (2) long, curved or flexible, about a



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114 Psyche [December
dozen on each somite (except abdominal somites IX and x). Mandibles with two moderately stout medial teeth; a small patch of minute spinules on the medial surface just above the middle.
Maxillary palp with five sensilla.
Labium large.
Aspididris militaris Weber
(PI. 6, figs. 11-15)
Body moderately stout; diameter greatest at abdominal somites v and VI, decreasing to I, then increasing slightly to the mesothorax, then decreasing rapidly to less than the diameter of the head. Thorax and first two abdominal somites strongly curved ventrally; dorsal profile C-shaped, ventral J-shaped. Anus ventral. Leg and wing vestiges present. Spiracles small, mesothoracic slightly larger than the rest. Integument of the ventral surface of the thorax and abdominal somites I and 11 spinulose, the spinules in rather short subtransverse rows. Body hairs numerous and uniformly distributed except for a naked strip on the midventral surface of the thorax and abdominal somites I and 11.
Of two types:
(1) short (about 0.19 mm), flex-
ible, denticulate, on all somites, without alveolus and arti- cular membrane; (2) long (about 0.32 mm), curved or flexible, denticulate, with alveolus and articular membrane, about a dozen on each somite except abdominal somites IX and X. Cranium vaguely subhexagonal in anterior view; a third broader than long ; occipital border feebly impressed at the middle; clypeus bulging. Antennae minute, each with three sensilla, each of which bears a spinule. Head hairs moderately numerous, long (0.09-0.193 mm) , flexible EXPLANATION OF PLATE 6
Rhopalothrix gravis Mann, Figs. 1-10. - 1, head in anterior view, X76; 2, left mandible in anterior view, X148; 3, left mandible in posterior view, X148; 4, immature(?) larva in side view, X32; 5 and 6, two types of body hairs, X 185; 7, left maxilla in anterior view, X235; 8, left maxillary palp in anterior view, X470; 9, left labial palp in pos- terior view, X470; 10, profile of mature larva in side view. (After Men- ozzi, 1936).
Aspididris militaris Weber, Figs. 11-15.-11 and 12, two types of
body hairs, X109;
13, larva in side view, X20; 14, left mandible in an- terior view,
X95; 15, head in anterior view, X53.




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116 Psyche [December
and denticulate. L,abrum bibbed; breadth about twice the length; anterior surface of each lobe with seven minute hairs and/or sensilla; ventral border of each lobe with two contiguous sensilla and numerous rather long isolated spinules ; posterior surface spinulose, the spinules near the lateral borders isolated and rather long, the remainder minute and in numerous subtransverse rows ; posterior surface of each lateral lobe with two isolated and a cluster of four sensilla. Mandibles heavily sclerotized; moderately long and narrow, slightly curved medially ; apical tooth moderately stout, slightly curved and round-pointed ; two moderately stout teeth projecting inward from the inner border; a small patch of minute spinules (in short rows) on the inner surface just above the middle. Maxillae with a slight lateral swelling bearing the palp and a paraboloidal apex bearing the galea ; apex spinulose, the spinules rather long and in short rows, elsewhere short and isolated; palp digitiform with one lateral (bearing a spinule) and four apical (two encapsulated and two with a spinule each) sensilla ; galea digitiform with two apical sensilla. Lab- ium large, with all surfaces spinulose, the spinules in short subtransverse rows; palp a low knob with five apical sen- silk (three with a spinule each) ; an isolated sensillum on each side of the opening of the sericteries; the latter a short transverse slit. Hypopharynx spinulose. (Material studied: two larvae from British Guiana, courtesy of Dr. Neal A. Weber.)
Genus Rhopalothrix Mayr
Thorax and first two abdominal somites forming a stout neck which is strongly curved ventrally; rest of abdomen much plumper; posterior end broadly rounded. Body hairs numerous, denticulate and of two types: (1) slender. flexible, short to moderately long; (2) stout, slightly curved, with hooked tip, in a narrow irregular band around the middle of each somite. Labrum small. Mandibles with two medial teeth, the subapical small, the proximal large ; with three or four denticles on the distal half of the poste- rior surface. Maxillae large; palp with five sensilla.



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19541 Wheeler and Wheeler-Basicerotini and Dacetini Ant Larvae 117 Rhopalothrix gravis Mann
(PI. 6, figs. 1-10)
IMMATURE: Length about 2.8 mm. Somewhat stout; thorax and first abdominal somite forming a neck which is strongly curved ventrally, remainder of abdomen with the dorsal profile curved and the ventral nearly straight; posterior end broadly rounded. Anus ventral, with a dis- tinct posterior lip. Spiracles rather small. Integument of the ventral surface of the thorax and abdominal somites I and 11 with a few short transverse rows of minute spi- nules. Body hairs numerous and uniformly distributed, except scarce on the ventral surface. Of two types: (1) slender, flexible, denticulate, short to moderately long (0.09-0.11 mm), without alveolus and articular membrane, on the dorsal and lateral surfaces, the more abundant type; (2) stout, of nearly uniform diameter, slightly curved, with a short sharp apical hook, denticulate, short to long (0.09-0.22 mm), with alveolus and articular membrane, in a narrow irregular band around the middle of each somi te. Head moderately large ; cranium somewhat broader than long, vaguely subhexagonal in anterior view, but with the occipital border strongly impressed at the middle ; cly- peus bulging. Antennae minute, each with three sensilla, each of which bears a spinule. Head hairs few, long (0.09- 0.14 mm), flexible and denticulate. Labrum small, breadth twice the length, feebly bilobed; anterior surface of each lobe with 4 or 5 minute hairs and/or sensilla; lateral bor- ders with isolated coarse spinules ; ventral border of each lobe with minute spinules in short rows and with one isolated and two contiguous sensilla ; posterior surface of each lobe with two isolated and two contiguous sensilla; whole posterior surface spinulose, the spinules minute and in numerous rows, the rows transverse on the middle half. Mandibles heavily sclerotized, long and slender, slightly curved medially; apical tooth long and rather slender; with two teeth projecting inward from the inner border (the distal small and the proximal large) ; with 3 or 4 denticles on the distal half of the posterior surface. Maxillae large; each divided into two parts by a transverse lateral impres- sion, the basal part swollen laterally and bearing the palp,



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118 Psyche [December
the distal part spinulose, bearing the galea and having a conoidal apex; palp digitiform with five sensilla (two apical and encapsulated, three subapical and bearing a spinule each) ; galea a slender frustum bearing two apical sensilla. Labium densely spinulose, the spinules in short subtransverse rows; palp a low knob with five sensilla (two apical and encapsulated, three subapical and bearing a spinule each) ; an isolated sensillurn between each palp and the opening of the sericteries; the latter a transverse slit. Hypopharynx densely spinulose, the spinules long and in numerous transverse rows. (Material studied: three larvae from Costa Rica.)
Menozzi, 1936, pp. 84-85: "Descrizione delta larva matura di R. Schmidti2 n. sp. Ipocefala, col corpo di forma subclaviforme, con la porzione anteriore stretta, subci- lindrica e coi segment! distinti, quella posteriore 6 rigon- fiata ed i limiti dei segmenti non sono distintamente segnati. Di colore bianco sporco, col capo cremeo e con le porzioni sclerificate del pleurostoma, del margine an- teriore del clipeo, nonch6 delle mandibole e del peritrema degli spiracoli tracheali di colore ocraceo piU o meno in- tenso. Cranio visto dal dlorso pic largo che lungo, oppure cosi largo che lungo se ad esso si comprende anche il labbro superiore, coi lati arrotondati e leggermente convergenti in avanti e col margine occipitale lievemente impress0 nel mezzo; le lunghe setole di cui esso 6 provvisto sono fine- mente barbellate . . . Aree antennali di forma triangolare, situate sublateralmente sulla linea medio-trasversale del cranio, fornite ciascuna nel mezzo di tre sensilli, a1 centre dei quali si erge una piccola appendice spiniforme che 6 ben visibile anche alla semplice osservazione binoculare della larva in toto. I1 clipeo appare circoscritto ai lati da un sottile ispessimento sclerificato, che per trasparenza sembra come una semplice piega tegumentale, ma che trovandosi in tutti gli esemplari esaminati, non mi pare dubbio che tali pieghe segnano effettivamente i margini laterali di esso. I1 labbro superiore, separate dal clipeo da un leggero solco, 6 trasverso, coi lati fortemente arrotondati alla base e col margine anteriore incavato nel mezzo. Dorsalmente esso 6 provvisto di un certo numero di sensilli chetici ; . . . ventral-



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19541 Wheeler and Wheeler - Basicerotini and Dacetini Ant Larvae 119 mente la superficie 6 tutta cosparsa di piccoli processi tegu- mentali dentiformi, nonch6 di 6 papille bacilliformi collocate in numero di tre ad ogni lato della incavatura mediana del margine anteriore e di due aree sensoriali le quali, portano due sensilli ciascuna, di cui uno molto pih grande dell'altro. Le mandibole sono robuste, del doppio pih lunghe che larghe e tridentate. Le mascelle appaiono ciascuna come formate di un unico pezzo, di mode che lo sclerite stipetale, quello cardinale e il cardine non sono differenziati, o almeno, non sono riuscito, come tali, ad individuarli. Palpo mascellare un poco piti lungo che largo, provvisto di tre setolette, due nel lato anteriore ed una in quello posteriore, ed apicalmente di due vistosi sensilli a forma di flabello. Galea del doppio piti lunga che larga, gradatemente ristretta dalla base all'api'ce, f ornita distalmente di due sensilli bacillif ormi che sorgono ciascuno da una rispettiva area rotondeggiante sclerificata e ben distinta dal resto della membrana cir- costante. Labbro inferiore piti lungo che largo, di un terzo circa sporgente oltre le mascelle, coi lati ed 11 margine anteriore pressoch6 diritti. Palpo labiale cost lungo che largo, con una setoletta per ciascun lato, un sensillo placoide a1 dorso e due all'apice di forma simile a quelli del palpo mascellare. Tanto le mascelle che il labbro inferiore nella superficie orale non hanno alcuna setola o peluzzo, mentre in quella dorsale hanno un certo numero di peluzzi dis- scminati nel lato esterno delle mascelle e lungo la linea longitudinale mediana nel labbro inferiore. Tutto il corpo della larva 6 cosparso di setole eguale a quelle del capo, inoltre gli wotergiti 1-8 sono forniti di tre aptochete ciascuno . . . Sistema tracheale olopneustico, con 10 paia di spiracoli, dei quali due paia nel torace e lotto paia nell'ad- dome, situati nella regione pleurale di ciascun segmento. Lunghezza della larva naturalmente curvata mm. 2, 3; lunghez. del capo senza il labbro superiore mm. 0,62, larg- hezza mm. 0,93." Fig. 2 (p. 84), larva in side view and head in anterior view; Fig.
3 (p. 85), details of mouth
parts and a hair.
Tribe DACETINI Fore1
This tribe (in the restricted sense) comprises about 300 species in 29 genera, according to Dr. W. L. Brown (in



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120 Psyche (December
lift.). The largest genus is St~~migenys with some 200 species; next is S'mithZStru-ma., with about 56 species; the other genera are quite small with fewer than ten species each. The tribe is essentially tropical but a few genera range into the warmer parts of the North Temperate Zone, The adults form "an aberrant and sharply distinct group belonging to the subfamily Myrroicinae, as is demonstrated by the structure of the abdominal pedicel and the male genitalia" (Brown, 1953b, p. 465). They show an extreme reduction in the number of antenna1 segments; head shape, head hairs and mandibles could be characterized as bizarre. Their larvae - in contrast - are quite ordinary and far less specialized than the larvae of many other ant genera. The larvae of the Dacetini are a heterogeneous group but not more so than most other tribes of Myrmicinae. Daceton is easily separated. Stmmigenys and Smithis- truma are quite distinct from other genera, although they are not distinguishable from each other. The remaining genera in our collection, althoug-h more similar to each other, are still something of a melange. This grouping
of the larvae confirms somewhat Brown's recent (1953b) division of the Dacetini into subtribes: Dacetiti (indud- ing Daceton.) ; Orectognathiti (including- Orectognathus) ; Epopostrumiti (including Epopostm, Mesostntwm, Alis- tmm and Clarkistnima) ; and Strumig-eniti (including Strumtgenys and SmithzStruma). The tribe may be char- acterized as follows :-
E-SPLAN-ATION OF PLATE 7
Daceton ai'migemm tLatreUle), Fie. 1-14. -1, head in anterior view, X36; 2, left mandible in lateral view, X86; 3, mature larva in side view, ~8; 4, left mandible in anterior view, XtSt; 6, head in side view, X36; 6-8, 10 and 11, bifid-tipped body hairs, X185; 9, simple body hair, X185; 12, labrum (left half of drawing shows posterior view, right half, anterior view), XIS; 13, very young larva in side view (him omitted), X8; 14, young larva in side view, X8.
Epopostrwuw sp. from Victoria, Figs. 15-19.-15, left mandible in anterior view, ~185; 18, head in anterior view, X-109; 17' larva in aide view, X30; 18 and I&, two types of body bwa, XI&. Epopostmma sp. from South Australia. Fig. 20, left mandible in an- terior view, X185.




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122 Psyche [December
Anus ventral. Spiracles small. Body hairs of the most abundant type bifid, and except in Clarkistruma, denti- culate. Head hairs few (20-30), except moderately nu- merous (52) in Daceton. Labrum small ; posterior surface spinulose. Mandibles subtriangular in anterior view; with one apical and (except in Daceton) two medial teeth; no spinules or denticles on the surfaces. Maxillae usually without spinules (occasionally a few present). Palp a conspicuous protuberance bearing five sensilla (usually two encapsulated and three bearing each a spinule), except in Strumigenys and Smithistruma. Galea tall and rather slender. Anterior surface of labium spinulose ; palp re- sembling maxillary palp but shlorter; an isolated sensillurn between each palp and the opening of the sericteries; the latter a short transverse slit. Hypopharynx spinulose. Brown, 1953b, p. 467: "NO dacetine was ever observed to feed the larvae by regurgitation . . . Food delivered to and fed upon by the Australian dacetine larvae consisted only of Collembola."
Genus Daceton Perty
Somewhat stout; thorax and first two abdominal somites strongly curved ventrally but not forming a neck; diameter greatest at abdominal somites IV and V, decreasing grad- ually to the anterior end and more abruptly to the posterior end, which is round-pointed ; dorsal profile C-shaped, ventral J-shaped. Body hairs numerous. Of two types : (1) short, nearly straight, with short-bifid tip, each branch recurved and bearing short denticles; (2) very few, widely scattered, simple, minute. Antennae moderately large ; with three to five sensilla each. Head hairs short, simple or with short-bifid tip. Posterior surface of labrum with 16 sensilla.. Daceton migerm (Latreille)
(PI. 7, figs. 1-14)
MATURE WORKER LARVA : Length about 12 mm. Some- what stout; thorax and first two abdominal somites strongly curved ventrally but not forming a neck ; diameter greatest at abdominal somites IV and V, decreasing gradually to the anterior end and more abruptly to the posterior end,



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19541
Wheeler and Wheeler - Basicerotini and Dacetini Ant Larvae 123 which is round-pointed ; dorsal profile C-shaped, ventral J-shaped. Anus ventral. Leg, wing and gonopod vestiges present. Spiracles small. Integument apparently without spinules. Body hairs numerous and uniformly distributed, except for the naked midventral surface; the longest and stoutest hairs border this naked area. Of two types: (1) short (0.105-0.175mm), nearly straight, with short-bifid tip, each branch recurved and denticulate; (2) very few, widely scattered, simple, minute (about 0.009 mm). Head small; cranium about as long as broad; vaguely subpen- tagonal in anterior view, with a small dorsal projection