Two new subarboreal species of the ant genus Strumigenys (Hym., Formicidae) from West Africa.

Reprinted from Volume 107. January I February! March 1971
Date of publication, 27th August, 1977.

ENTOMOLOGIST'S MONTHLY MAGAZINE 59

TWO NEW SUBARBOREAL SPECIES OF THE ANT GENUS
STRUMIGENYS (HYM., FORMICIDAE) FROM WEST AFRICA

BY B. BOLTON

Two species of the dacetine ant genus Strumigenys F. Smith, are
described as new. Both are subarboreal nesters and foragers and have
been found in both Nigeria and Ghana in cocoa plots (Theobroma
cacao L.). S. cacaoensis sp. n. is a member of the 5. rogeri Em. group
centred on the Ethiopian Region, whilst 5. pallestes sp. n. appears to
be a member of the S. lyroessa (Roger) group, centred on the Indo-
Australian Region.

I am grateful to Dr. A. B. S. King of the Cocoa Research Institute
of Ghana for the donation of his specimens and information concerning
5. cacaoensis.

The abbreviations standardised by Brown (1953) are used here as
follows: TL, total length; HL, head length; HW, head width, CI
cephalic index; ML, mandibular length; MI, mandibular index, WT/
Weber's length of alitrunk; SL, scape length.

Strumigenys cacaoensis sp.n. (fig. 1)

Holotype worker: TL 2.7, HL 0.83, HW 0.72, (CI 87), ML 0.38, (MI 46). WL 0.76,

Head massive, general shape as shown in fig. 1. Dorsum of head at clvpeal apex
and between frontal carinae concave, convex posterior to this, with the dorsal
surface of the occipital lobes weakly concave. Preocular notch present profound
extending throughout the thickness of the head as a vertical groove and present on
the dorsolateral cephalic border. Eyes well developed, their outer borders convex
more or less pointed in front and freely projecting into the space provided by the
preocular notch. Antennal scrobes indistinct behind the eye, their ventral borders
not defined. Scapes of antennae weakly swollen, the greatest width occurring proximal
of the midlength. Funiculus distinctly 5-segmented, segments 2 and 3 about as
broad as long, the apical segment 0.31 mm, slightly longer than the preceding se<*-
ments taken together. s ' t "

Mandibles narrow at the base, broadening apically, their outer margins weaWv
convex, interrupted by a slight concavity in the basal third of their length Preapical
mandibular armament of two short teeth situated close together and close to the
apex, the distal tooth slightly longer and more acute than the proximal \pical
dentition not clearly visible in the holotype in which the mandibles are closed but
m three paratype specimens with open mandibles the apical armament is found to
be asymmetrically developed. Dorsal tooth of the apical fork about 12 mm the
ventral component about 0.8 times this length. The right mandible bears a minute
intercalary denticle at the base of the inner (dorsal) border of the ventral spiniform
tooth. On the left mandible this denticle is also present, along with a short spiniform
intercalary tooth about 0.4 times the length of the dorsal component of the apical
fork and situated just below it. What can be seen of the apical armament of the
holotype agrees with this description.

Alitrunk slender; weakly marginate laterally, maximum width of pronotum
ca. 0.36 mm, about half the maximum head width. Pronotum in dorsal view narrowly
rounded m front, without well-defined humeral angles. Promesonotal suture absent
Propodeal spines moderately long, acute, weakly upcurved and divergent connected
by an extremely narrow lateral strip running down the declivitv to 'a pair of small
triangular lamellae at the base of the declivity.

Petiole with a long peduncle, the node narrowly rounded in profile Spongiform
appendages absent, the mid-ventral strip reduced to a vestige. Post petiole move
broadly rounded above, its tergite bordered by a thin lamelliform strip, broadest
posterolaterally. A small ventral appendage present.

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Mandibles weakly sculptured, shining. Head, alitrunk and pedicel everywhere
opaque, very finely and densely punctate, with a granular appearance. Punctures
on the dorsum of the head slightly more coarse than those on alitrunk and pedicel.
Dorsum of promesonotum overlaid by a sparse, very fine longitudinal rugulation.
Gaster dully shining. Basigastric costulation of first tergite fine and dense, extending
about half the length of the segment.

Head with numerous small appressed spatulate hairs, densest around the margins
of the occipital lobes and sides of head behind eyes, and in a broad median longitud-
inal band from the occiput to the frontal carinae. Larger spatulate hairs on the

Figs. 13. 1, Strumigenys cacaoensis sp.n., holotype worker, head in dorsal
view, pilosity and right antenna omitted; 2, S. pallestes sp.n., holotype worker,
head in dorsal view, pilosity and right antenna omitted; 3, S. pallestes sp.n., paratype
worker; left mandible.

anterior clypeal margin directed weakly towards the midline; those on the scapes
curved apically. Promesonotum with one pair of clavate hairs and a sparse ground
pilosity of closely appressed small spatulate hairs. Petiole and postpetiole each
with a pair of clavate hairs placed posterodorsally, the postpetiole also with a smaller
pair situated anterodorsally. Gaster with six transverse rows of clavate hairs of
which 4 rows are on the first tergite. Colour uniform medium brown.

Paratype workers agree closely with the holotype but on some specimens the
promesonotal rugulation is more distinct and somewhat more coarse. The shape and

ENTOMOLOGIST S MONTHLY MAGAZINE 61

size of the propodeal spines vary slightly, one specimen has straight spines, noticably
broader than in the holotype. Range of cephalic dimensions in paratype workers
shows: HL 0.83-0.86, HW 0.72-0.76, ML 0.38-0.40, CI 87-89, MI 46-47.

A paratype female (alate) has dimensions, HL 0.86, HW 0.79, ML 0.40, CI 92,
MI 46, the head somewhat broader in proportion to its length than in the workers!
An infuscated area present around each ocellus and a V-shaped infuscated strip
connecting the median to the posterolateral ocelli. Eyes well developed. Dentition
as worker but the apical intercalary denticle on each mandible better developed.
Alitrunk with flight sclerites; dorsum of mesoscutum with distinct fine longitudinal
rugulation. Propodeal spines straight, the lamellae running from them to the tri-
angular basal lamellae better developed than in worker. Node of petiole weakly
excised medially, the midventral strip better developed. Other characters as worker.

The type series, including holotype, twelve paratype workers and
the paratype female discussed above were taken from a nest in a shallow
rot-hole in the trunk of a cocoa tree (Theobroma cacao), about 5 feet
above ground level and at the point of divergence of two main branches
at Gambari Experimental Station of the Cocoa Research Institute of
Nigeria (Ibadan) Nigeria, 10 July, 1969. Holotype and 7 paratypes
(including the female) to be deposited in the British Museum (Natural
History) London; the remaining 6 paratypes to the Museum of Compara-
tive Zoology, Harvard College.

At the time of collecting, no workers were observed on the tree
outside the nest. The bark of the tree was wet due to a recent rain storm.
Apart from the above, three workers and an alate female were collec-
ted on 28 August, 1970, at Tafo, Ghana from the stub of a rotten cocoa
branch about 3 feet above ground level. The workers agree well with
the above description and their cephalic dimensions fall within the
range stated above, but in all three the distal preapical tooth on both
mandibles is considerably larger than the proximal, which is reduced
to a minute denticle. This is also true of the female which is larger than
the paratype female (HL 0.90, HW 0.81) but otherwise similar.

The species has also been collected by Dr. A. B. S. King of the
Cocoa Research Institute of Ghana (November, 1969, Tafo, Ghana)
who obtained workers by using a pyrethrum knockdown technique on
'Amazon' cocoa. Dr. King reports that the species is present in 2 or 3
of every 1000 knockdowns performed.

In the two specimens retained by him the preapical mandibular
armament is similar to that described for the type series.

The form of the mandibles, alitrunk and head places the species in
the Strumigenys rogeri group, and the presence of a well-developed
preocular notch shows it to be related to a smaller series of species
including S. rogeri itself as well as S. grandidieri Forel, londianensis
(Patrizi), bernardi Brown, pretoriae Arnold and rufobrunea Santschi.
Of these species S. cacaoensis is apparently closest related to S.
grandidieri of Malagasy with which it agrees in head form, indistinct
antennal scrobes, preocular notch represented on the dorsolateral border
of the head, preapical mandibular armament and sculptural details.
It differs from S. grandidieri in the following respects:

taller; dimensions of .S. grandidieri given bv Brown (1954- 1?) are TI 5 02
HL1. 33, ML 0.69, CI 76, MI 52. " ' -- .

2. Presence of an intercalary tooth and denticles in the apical mandibular armament
absent in S. grandidieri.

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In the key given by Brown (1954: 10-12) S. cacaoensis will run out
at the second part of couplet 3, where it immediately separates as the
distal preapical tooth is larger than the proximal.

From the circumstances of the three collections made of 5. cacaoensis
it is apparent that the species is a subarboreal nester and forager, and
the occurrence of workers individually in pyrethrum knockdowns from
cocoa trees indicates diurnal activity. Ground searching and Berlese
funnel samples have failed to reveal the species. Alate females are in
the nest in July-August but have not been recovered from light traps.

Strumigenys pallestes sp. n. (figs. 2-3)

Holotype worker: XL 2.1, Hi. 0.56, HW 0.40, (Cl 72), ML 0.1'), (ill J4) SL 0.24
WL 0.55.

Preocular notch absent; eyes small, their maximum diameter slightly less than
the maximum width of the scape, invisible in dorsal view. Antennal scrobes deep,
well defined, with a short median longitudinal carina anteriorly, extending half
the distance between the antennal insertion and the eye. Antennal scapes weakly
curved posteriorly in the basal third of their length, the greatest width approximately
at the midlength. Apical funicular segment 0.21 mm about 1.3 times the length of
the preceding four segments together. Holotvpe with mandibles fully closed, the
blades enclosing a large vacuity, attennuated basally. Mandibles very broad at the
base, tapering apically; the external border convex, suddenly inflected towards the
midline close to the base. Internal borders weakly concave. Preapical dentition of
two acute teeth, the distal shorter than the proximal, both slightly recurved. Re-
maining features of mandibular structure noted from a paratype worker with open
mandibles. Internal margin of blade with a massive, translucent triangular basal
lamella, its apex directed posteriorly. This structure is concealed by the clypeus
when the mandibles are closed (fig. 3). Basal width of blade including lamella about
0.08 mm, so that the mandible is only 2.5 times longer than its basal width. Apical fork
of mandible with a long dorsal and a shorter, more stout ventral tooth. An adventit-
ious tooth arises from the ventral base of the ventral component of the apical fork
and a minute denticle is present between the two.

Alitrunk dorsally broadest in front, maximum width about 0.26 mm, weakly
margined laterally. Pronotum broadly rounded anteriorly, the sides convergent
throughout the length of the promesonotum, weakly divergent on the propodeum.
Posterior portion of mesonotum gently sloping to metanotal suture which is not
impressed. Propodeum sloping to the spines which are broadly triangular and
lamelliform, each subtended by a very broad (0.07) infradental lamella, which is
weakly convergent through the depth of the declivity.

Peduncle of petiole long and narrow in dorsal view, the node about 4 times
broader than the peduncle at its mid-length. Anterior margin of node shallowly
excised in dorsal view, the sides diverging to about the midlength and converging
behind. Postpetiole subovate, scarcely broader than petiole. Fungiform appendages
massively developed on both segments. Petiole with a very deep midventral strip
and a large posterolateral appendage, connected to its counterpart on the opposite
side by a narrow strip behind the node. Postpetiole with large posterolateral and

' --' - - - dages.

-,.,/al segment with a dorsal anterolateral translucent lamelliform prom-
inence on each side, projecting to the posterior portion of the lateral fungiform
appendages of the postpetiole, and upon which the basigastric costulae arise.

Mandibles weakly shining; head finely and densely punctate. Alitrunk more
weakly and superficially punctate, overlaid on the promesonotal dorsum by a fine
longitudinal rugulation. Dorsum of petiole node shiny, with some very weak trans-
verse striation. Postpetiole unsculptured, smooth and polished. Basigastric costulae
radiating from the anterolateral projections on each side of the first tergite, about
0.5 times the length of the tergite.

Dorsum of head with abundant short spatulate hairs. Dorsolateral margin of
head behind level of eyes with longer, anteriorly curved hairs. Dorsum of promesono-
tum with numerous short spatulate hairs, mostly curved towards the midline, and
with 5 pairs of long erect clavate hairs situated on the dorsolateral margins. The

ENTOMOLOGIST S MONTHLY MAGAZINE 63

longest of this series projecting laterally from the humeral angles. Propodeum
devoid of hairs except for a small flattened hair in front of each spine.

Both segments of pedicel with two transverse rows of clavate setae, the posterior
petiolar row with 4, posterior postpetiolar with 6 hairs. Caster with seven rows of
long erect clavate hairs with 8-10 per row.
Colour uniform medium brown.

Paratype workers agreeing with holotype. In one specimen the promesonotal
rugulation is more distinct, the puncturation more effaced. Range of cephalic
measurements: HL 0.52-0.56, HW 0.38-0.41, (CI 72-74), ML 0.18-0.19, (MI 34-35).
Paratype female (alate) with headlength at maximum of worker range width some-
what greater. HL 0.56, HW 0.44 (CI 79). Other measurements, TL ca. 2.2 mm.
ML 0.20, (MI 36), SL 0.24, WL 0.86. Answering to description of worker but eyes
better developed, maximum diameter about 0.09-0.10. Alitrunk with flight sclerites,
the mesokatepisternum unsculptured. Longitudinal rugosity on mesoscutum very
weak. J

Type series of holotype, six paratype workers and an alate female taken from an
old moss-covered rot-hole in the trunk of a cocoa tree (Theobroma cacao) about 4
feet above ground level. Wood in the rot-hole very moist and friable, in places reduced
almost to soil. Taken at the Cocoa Research Institute of Ghana, New Tafo, Eastern
Region of Ghana on 22 July, 1970. Holotype and 4 paratypes (including female)
m British Museum (Natural History) London, 3 paratypes to Museum of Comparative
Zoology, Harvard College. A series of nine workers taken from a rot-hole in a cocoa
tree trunk about five feet above the ground, 13 June, 1969 at Gambari Experimental
Station of the Cocoa Research Institute of Nigeria (Ibadan) agree with the above
description but are somewhat lighter in colour and more weakly sculptured. The
postpetiole shows faint traces of longitudinal striation close to the dorsolateral
margin. Dimensions fall within the range given for paratypes above.

The affinities of 5. pallestes are at present in doubt. The mandibular
armament is similar to that of the South African 5. marleyi Arnold,
from which it differs as follows:

1. Smaller. Brown (1954) gives the following measurements for S. marlevi HL 62
ML 0.22, WL 0.60, CI 76-77, Ml 35-36.

2. Maximum eye diameter in S. marleyi distinctly greater than maximum width of
scape. In S. pallestes the eye diameter is slightly less than the scapal width.

3. Promesonotum in S. marleyi devoid of specialised erect hairs. In S. pallestes
the promesonotum is bordered on each side with five erect clavate hairs of
which the first projects laterally.

Brown (1954: 25) considers 5. marleyi to be convergent on members
of the 5. lyroessa group of the Indo-Australian region in mandibular
structure, but neither he nor Arnold (1917: 378) mentions the presence
in S. marleyi of a massive triangular lamella at the internal base of
each mandible. This character is however noted by Brown (1948) in
members of the S. lyroessa group. It is therefore possible that 5. pallestes
is a member of the last named group of species, and if so is its first
member to be recorded outside the Indo-Australian region.

The nest sites of S. pallestes indicate a subarboreal habit. No
individuals were noted ouside the nests at the times of collection, and

.. .

Whether this indicates nocturnal foraging is open to doubt as the species
is small enough to be glued to the tree by the surface tension of the
pyrethrum droplets. Alate females are in the nest in July, but have not
yet been recovered from light traps. The species has not been taken
from Berlese funnel samples of leaf litter or log mould.

REFERENCES

Arnold, G., 1917, A monograph of the Formicidae of South Africa Ann S Afr
Mus., 14 (3): 271-402. Brown, W. L. Jr., 1948, A preliminary revision of the higher

04 ENTOMOLOGIST S MONTHLY MAGAZINE

Dacetini, Trans. Am. ent. Soc., 74: 101-29; 1953, Revisionary studies in the ant
tribe Dacetini, Amer. Midi. Nat., 50: 1-137; 1954, The ant genus Strumigenys Fred.
Smith in the Ethiopian and Malagasy Regions, Bull. Mus. comp. Zool. Han., 112
(1): 1-34.

Cocoa Research Institute of Ghana, New Tafo, Ghana.
Present address: British Museum (Natural History), London.
April 1st, 1971.