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Nesting and foraging habits in the arboreal ant Atopomyrmex mocquerysi ANDRÉ, 1889 (Hymenoptera: Formicidae: Myrmicinae)

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Atopomyrmex mocquerysi ANDRÉ, 1889 is a West-Central African wood-excavating myrmicine species whose colonies construct galleries in the main live branches of their host trees, causing the distal parts of these branches to dry out. In southeastern Cameroon, this species was mainly found in woody savannahs that are burned annually. It was also present in the canopy of a secondary forest, but was relatively rare on trees growing along forest edges and entirely absent from the canopy of an old-growth forest. It was absent from oil palm and coffee tree plantations, rare on cocoa trees, present on 0.2% to 5.3% of the avocado, guava, mango and Citrus spp. trees monitored, and frequent on safoo trees (12.4%). A fire in a mango plantation seems to have favored its presence. The colonies generally exploit Aleyrodidae, Aphididae, Coccidae, and Stictococcidae. Workers forage for prey diurnally, mostly on the ground. Their predatory behavior is characterized by detection through contact. Workers recruit nestmates at short-range (within range of an alarm pheromone), rarely at long-range, after which they spread-eagle the prey and immediately cut it up on the spot. Individual workers retrieve the prey pieces. Unlike other territorially-dominant arboreal ants, A. mocquerysi is a threat to host trees because, in addi-tion to being a wood-excavating species, its workers only slightly protect the foliage of their host tree from herbivorous insects since they mostly hunt on the ground.
Flow diagrams of the behavioral events observed when Atopomyrmex mocquerysi workers attempted to capture grasshoppers of two size ranges: (A) 3 - 5 mm long, n = 60; (B) 15 - 20 mm long, n = 60. nearby nestmates, the discovering workers left the prey to recruit at long-range (8.3% of the cases for small prey versus 60.0% for large prey; Fisher's Exact-test: P < 0.0001). For this, they released the prey and returned to the nearest main column or to the nest, laying a scent trail. In both types of recruitment, each time several recruited workers reached the prey, and then seized it by an append- age and pulled backwards, spread-eagling it. A positive feed- back effect occurred when the first recruited workers in turn attracted new nestmates. The morphological characteristics of the pretarsus, especially the horn-shaped claws and large adhesive pad (Fig. 3A), enable the ants to grasp the sub- strate well while spread-eagling prey. Workers never use any stinging behavior probably because of the very short, spatula-shape of their sting (Fig. 3B). While some workers continued to immobilize the prey by stretching it, the others immediately cut it up and retrieved the small pieces. Only 15% of the small grasshoppers were cooperatively trans- ported as whole individuals. Finally, we noted that A. mocquerysi workers had a high rate of successful captures, especially of large prey (Fig. 2). Discussion Because it is most likely a woody savannah dweller, Atopomyrmex mocquerysi is also able to nest in some tree spe- cies found in secondary forests, but not in old-growth for- ests. Tree crop plantations can also offer this species a good nesting opportunity, but this seems to vary with climatic conditions, as we noted in other African areas. Indeed, B UYCKX (1962) and L ESTON (1973) reported the highest proportions of trees attacked by A. mocquerysi in cocoa and coffee tree plantations. Therefore, A. mocquerysi col- onies can compete for space with typical territorially-dom- Fig. 3: Electron micrographs of the pretarsus (A) and the inant arboreal ant species in secondary forests and tree spatula-shaped sting (B) of a major worker of Atopomyr- c rop plantations. This competition is possible because ant mex mocquerysi .
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Myrmecological News 12 109-115 Vienna, September 2009
Nesting and foraging habits in the arboreal ant Atopomyrmex mocquerysi ANDRÉ, 1889
(Hymenoptera: Formicidae: Myrmicinae)
Martin KENNE, Renée FENERON, Champlain DJIETO-LORDON, Marie-Claire MALHERBE,
Maurice TINDO, Paul R. NGNEGUEU & Alain DEJEAN
Abstract
Atopomyrmex mocquerysi A
NDRÉ, 1889 is a West-Central African wood-excavating myrmicine species whose colonies
construct galleries in the main live branches of their host trees, causing the distal parts of these branches to dry out. In
southeastern Cameroon, this species was mainly found in woody savannahs that are burned annually. It was also present
in the canopy of a secondary forest, but was relatively rare on trees growing along forest edges and entirely absent from
the canopy of an old-growth forest. It was absent from oil palm and coffee tree plantations, rare on cocoa trees, present on
0.2% to 5.3% of the avocado, guava, mango and Citrus spp. trees monitored, and frequent on safoo trees (12.4%). A fire in
a mango plantation seems to have favored its presence. The colonies generally exploit Aleyrodidae, Aphididae, Coccidae,
and Stictococcidae. Workers forage for prey diurnally, mostly on the ground. Their predatory behavior is characterized
by detection through contact. Workers recruit nestmates at short-range (within range of an alarm pheromone), rarely at
long-range, after which they spread-eagle the prey and immediately cut it up on the spot. Individual workers retrieve the
prey pieces. Unlike other territorially-dominant arboreal ants, A. mocquerysi is a threat to host trees because, in addi-
tion to being a wood-excavating species, its workers only slightly protect the foliage of their host tree from herbivorous
insects since they mostly hunt on the ground.
Key words: Cameroon, wood-excavating ant, nest site selection, pest ant, predatory behavior, rhythm of activity, life
history.
Myrmecol. News 12: 109-115 (online 17 February 2009)
ISSN 1994-4136 (print), ISSN 1997-3500 (online)
Received 12 October 2008; revision received 30 November 2008; accepted 2 December 2008
Dr. Martin Kenne (contact author), Département de Biologie des Organismes Animaux, Faculté des Sciences de l'Uni-
versité de Douala, BP 24157, Douala, Cameroon. E-mail: medoum68@yahoo.fr
Dr. Ren
ée Feneron, Laboratoire d'Ethologie Expérimentale et Comparée (UMR-CNRS 7153), Université Paris-Nord,
F-93430 Villetaneuse, France.
Dr. Champlain Djiéto-Lordon, Laboratoire de Zoologie, Université de Yaoundé 1, BP. 812 Yaoundé, Cameroon.
Dr. Marie-Claire Malherbe, Laboratoire d'Ethologie Expérimentale et Comparée (UMR-CNRS 7153), Université Paris-
Nord, F-93430 Villetaneuse, France.
Dr. Maurice Tindo, Département de Biologie des Organismes Animaux, Faculté des Sciences de l'Université de Douala,
BP 24157, Douala, Cameroon.
Dr. Paul R. Ngnegueu, Laboratoire de Zoologie, Université de Yaoundé 1, BP. 812 Yaoundé, Cameroon.
Prof. Dr. Alain Dejean, Écologie des Forêts de Guyane (UMR-CNRS 8172), Campus agronomique, BP 709, 97379 Kourou
cedex, France.
Introduction
Arboreal-nesting ants represent a major component of the
fauna in the canopies of rainforests and tree crop planta-
tions; among them, territorially-dominant arboreal species
have very populous (several thousands of individuals) and
polydomous colonies, and are very aggressive toward other
dominant ants at both the intra- and interspecific level (D
E-
JEAN & al. 2007a). As a consequence, competition for space
results in a mosaic distribution pattern of their territories,
creating what has become known as an "arboreal ant mo-
saic" (L
ESTON 1973, BLÜTHGEN & STORK 2007, DEJEAN
& al. 2007a).
Until now, the foraging behavior of territorially-domi-
nant, African arboreal ants has been well-documented only
for Oecophylla longinoda (L
ATREILLE, 1802) (see DEJEAN
1990, H
ÖLLDOBLER & WILSON 1990, WOJTUSIAK & al.
1995), Tetramorium aculeatum (M
AYR, 1866) (see DJIÉTO-
LORDON & al. 2001) and Crematogaster sp. (RICHARD &
al. 2001). All of these species feed principally on hemi-
pteran honeydew, extrafloral nectar when available, and
prey. Since they consume different arthropod taxa, they
have frequently been used as biological control agents (D
E-
JEAN & al. 2007a).
A
mongst myrmicine ants, the genus Atopomyrmex
(Formicoxenini tribe) is widely distributed in woody savan-
nahs and forested areas of the Afrotropical region (T
AYLOR
2006). Three species have been described: A. calpocaly-
cola S
NELLING, 1992 has only been reported in Came-
roon, whereas the two others, A. cryptoceroides E
MERY,
1892 and A. mocquerysi A
NDRÉ, 1889, have been widely
noted in Central and West Africa (T
AYLOR 2006). These
wood-excavating ants are typically present in tree crop plan-
tations and forests, where they damage the main live branch-
es and trunks (B
UYCKX 1962, LÉVIEUX 1976, KENNE & al.
2003). Their nests are composed of a network of parallel
galleries that causes the distal parts of the occupied branches
to dry out. Consequently, the presence of Atopomyrmex
colonies is harmful to their host trees so that species of this
genus are considered to be pest ants, especially for coffee
and cocoa trees on which the infestation spreads to all of
the branches and may lead to the death of the infested in-
dividuals (B
UYCKX 1962).
The scattered information available on the biology of
A. mocquerysi shows that it is a dominant arboreal spe-
cies (L
ESTON 1973). A 7-year old nest contains more than
60,000 adults and 25,000 larvae (L
ÉVIEUX 1976). Workers
forage in columns on adjacent trees, including shrubs, and
on the ground to collect food such as prey, hemipteran hon-
eydew or extrafloral nectar, sap, plant resins, seeds and leaf
fragments (L
ÉVIEUX 1976, 1977).
In this study, we: (1) verified if A. mocquerysi nests in
only a limited number of cultivated trees, or if it is a gen-
eralist, (2) examined what kinds of hemipterans workers
attend, (3) studied the workers' daily activity cycle, and (4)
investigated their predatory behavior to compare it to that
of other dominant African ants.
Materials and methods
Study sites: These st
udies were carried out between 1995
and 2006 in forested zones of Cameroon on host trees sit-
uated on the campus of Yaoundé University (3° 53' N, 11°
30' E), in Minkoméyos (3° 59' N, 11° 28' E), Matomb-
Brousse (3° 53' N, 11° 4' E), Ebodjié (2° 38' N, 9° 53' E),
Kala (3° 50' N, 11° 21' E), around Buéa (4° 15' N, 9° 22'
E), Muéa (4° 35' N, 9° 36' E) and Batchenga-Nzi (3° 51' N,
11° 42' E). The region is characterized by a "tropical mon-
soon" climate (Köppens's standard climatic classification)
with a roughly constant annual temperature (averaging from
26.1°C in February to 22.8°C in August) and continuously
high levels of atmospheric humidity (varying from 71% in
January to 82% in July and August); variations in monthly
precipitation range from 5.6 mm in January to 383.3 mm
in October.
Field research on A. mocquerysi colonies was conducted
in the region of Yaoundé along forest edges (to a depth of
15 m; a total of 9 km monitored), in the crowns of 41 trees
in a 60-year old secondary forest (0.78 ha; Matomb-Brouse),
on 167 large trees (40 - 45 m tall) in an old-growth forest
(Ebodjié) using the canopy raft and the canopy sledge (see
D
EJEAN & al. 2007a), and over 5 ha of a woody savannah
(Batchenga-Nzi). The same kind of research was conducted
in tree crop plantations not treated with insecticides situ-
ated around Buéa, Muéa and Yaoundé. We monitored in
total: 615 oil palm trees Elaeis guineensis J
ACA. (Areca-
ceae), 400 coffee trees Coffea robusta L. (Rubiaceae),
5,133 cocoa trees Theobroma cacao L. (Sterculiaceae),
659 mandarin Citrus deliciosa T
EN. and orange trees C. sin-
ensis L. (Rutaceae), 412 safoo trees Dacryodes edulis (G.
D
ON) LAM. (Burceraceae), 591 guava trees Psidium guaja-
va L. (Myrtaceae), 560 mango trees Mangifera indica L.
(Anacardiaceae) and 49 avocado trees Persea americana
M
ILL. (Lauraceae).
1
For the tree crop plantations managed by the Institut de
Recherche Agricole pour le Développement (IRAD) situat-
ed in Minkoméyos, sunlight reaches the ground all around
the mango trees so that the grasses growing between them
are cut regularly. Nevertheless, a fire from the neighbor-
ing area spread to the mango tree plantation, burning these
grasses. We then verified whether the fire triggered a re-
sponse in the associated ant species of these trees by com-
paring data before and 1 year after the fire (n = 204 trees).
Host plants and honeydew collection: An inventory
was conducted during both the dry and rainy season at
different sites around Yaoundé, including the urban zone,
plantations and an old, secondary forest. This enabled us to
catalogue the hemipterans this species exploited; voucher
specimens were deposited in the Museum National d'His-
toire Naturelle, Paris. Voucher specimens of ants were de-
posited in the Museum of Natural History, London.
Daily activity cycle: This study was carried out on
three colonies found on the University campus. Their
daily rhythm of activity was recorded over two 24-hour
periods using the method developed by L
ÉVIEUX (1976):
we drew a mark on the main foraging trails (situated on the
trunks of host trees) used by the workers to reach the ground
or neighboring trees where they forage for food, and count-
ed the number of workers entering and leaving the nest.
Each observation lasted 3 minutes and was repeated every
hour. Two series of measurements were conducted during
the rainy season, and two others during the dry season. To
evaluate the relationship between ant activity and environ-
mental conditions, the air temperature and relative humi-
dity were measured each hour using a thermohygrometer
placed one meter above the ground.
Hunting strategies: We studied the predatory behav-
ior of the workers from five mature nests (they produce
winged sexuals) located on the University campus. A ply-
wood board (30 × 40 cm) placed on the ground at the
base of each tree served as an experimental hunting arena.
Experiments began one week after we judged the board to
be well integrated into the foraging territory of the ant col-
ony. Small (3 - 5 mm long; n = 60; a size similar to that of
a worker) and large (15 - 20 mm long; n = 60) live grass-
hoppers (Tettigoniidae) were used as prey. The tibia of their
hind legs were cut off to prevent them from jumping away
and escaping, since it was not our purpose here to study
their anti-predator strategy.
For each test (repeated 60 times), we used a protocol
perfected during our prior research on the predatory behav-
ior of other territorially-dominant arboreal ants (R
ICHARD
& al. 2001, DEJEAN & al. 2008b). The sequence of behavi-
oral acts was recorded from the introduction of the prey
into the centre of each hunting arena until their capture and
retrieval to the nest (three to five trials per day, two to five
days per week). At least 30 minutes separated two trials.
Data sheets containing the full repertoire of the behavioral
sequences were first established during preliminary experi-
ments. We recorded the behavioral acts performed by the
hunting workers when faced with the prey: detection, anten-
110
Tab.
1: List of hemipterans attended by A. mocquerysi workers and their host plants. Workers frequently attend hemi-
pterans on plants surrounding their host trees, especially the invasive vine, eupatoire.
1
= economically important plant
species;
2
= imported, invasive species.
Hemiptera
Family
Species
Host plant
Species (Family)
Vegetal organs
Aleyrodidae undetermined Citrus spp.
1
(Rutaceae) Leaves
Aphididae Aphis spiraecola PATCH, 1914 Eupatorium: Chromolaena odorata L.,
1759 (Asteraceae)
2
Leaves; twigs and buds
Coccidae Inglisia conchiformis MASKELL, 1879 Soursop: Annona muricata L., 1753
(Annonaceae)
1
Fruits; leaves; branches
Stictococcidae Stictococcus sp. Bitter leaves: Vernonia amygdalina
DEL., 1826 (Asteraceae)
1
Leaves; twigs and buds
nal palpation, attack, seizure, stinging, immobilization, nest-
mate recruitment, spread-eagling, cutting up, and trans-
porting the prey. The part of the prey body seized by the
ants discovering the prey was noted. The data recorded
permitted us to build flow diagrams with transition fre-
quencies between behavioral acts. Percentages (correspond-
ing to these transition frequencies) were calculated from
the overall number of cases.
Morphological analysis: Whole, dead A. mocquerysi
workers were mounted on aluminum stubs and coated with
a mixture of 80% gold and 20% palladium to be exam-
ined with a scanning electron microscope (Leica Stereo-
scan 440; Solms, Germany). The structure of the pretarsus
and the sting apparatus was studied in order to compare it
with those of other arboreal ant species.
Statistical analysis: As normality and equal variance
tests passed in all of the comparisons, mean values (± SE)
were compared using Student's t-test and correlations be-
tween parameters were determined using Pearson's cor-
relation coefficients (SigmaStat 2.03 software). Percentages
were compared from the core results using Fisher's Exact-
test (StatXact-3 software).
Results
D
istribution of the A. mocquerysi colonies: We did not
record any A. mocquerysi colonies in the canopy of old-
growth forest at Ebodjié, although we had direct access
to the canopy (167 tree crowns monitored). At Matomb-
Brousse, the colonies were extremely dispersed along the
forest edges (nine colonies noted for 9 km of forest edge;
about 1% of the trees; n 900 trees), whereas we noted
three colonies in a study of 41 trees in a 60 year-old sec-
ondary forest (7.3% of the trees). Their density was com-
paratively high in the woody savannah at Batchenga-Nzi,
where we noted 58 colonies for five hectares monitored
(about 11.6% of the trees; n 500 trees).
In tree crop plantations, A. mocquerysi was absent from
oil palm trees (n = 615 trees) and coffee trees (n = 400
trees), rarely noted on cocoa trees (0.7% of 15,133 trees),
avocado trees (2.0% of 49 trees), guava trees (3.0% of 591
trees), mango trees (3.2% of 560 trees) and mandarin or
orange trees (5.3% of 659 trees), but had a greater pre-
sence on safoo trees (12.4% of 412 trees).
The fire in the mango plantation in Minkoméyos seems
to have favored the presence of A. mocquerysi (6 trees
efore versus 31 trees 1 year after the fire; n = 204 trees;
Fisher's Exact-test: P < 0.001), while we did not note any
variation in the parts of the plantation that were not burned
during this period (M. Kenne, unpubl.).
b
Workers attended hemipterans belonging to four spe-
cies from the Sternorrhyncha suborder on both host and
adjacent trees (Tab. 1). These hemipterans proliferated on
only four out of 56 closely-monitored trees, and consisted
of Aleyrodidae on orange trees, Aphididae on Eupatorium,
Coccidae on soursop trees, and Stictococcidae on bitter
leaves.
Daily activity cycle: Atopomyrmex mocquerysi wor-
kers foraged during the day, but some residual activity
was recorded in two nests at night during the dry season
(Fig. 1). The correlation between the number of ants en-
tering and exiting the nest each hour was significant dur-
ing both the dry season (Pearson's correlation coefficient:
r = +0.864, P < 0.0001, n = 72) and the rainy season (r =
+0.559, P < 0.0001, n = 72), illustrating a regular flux. The
flow of workers was positively correlated with air tempe-
rature and negatively correlated with air humidity (Tab. 2).
In terms of the number of ants leaving the nests, the colo-
ny's investment in foraging varied seasonally, with more
workers observed on the main foraging trail during the dry
season (mean
S.E.: 30.2 4.6 workers per 3-minute ser-
ies and per day, n = 72) than during the rainy season (19.4
2.6 workers, n = 72; Student's t-test, t = 2.03, df = 142,
P = 0.044).
Hunting behavior: During their period of activity, re-
gardless of the season, A. mocquerysi workers foraged for
prey on the ground, and only infrequently on the tree foli-
age. In the savannah, scout workers discovering ripe figs re-
cruited nestmates to capture all of the agaonid pollinators
taking shelter inside of the figs, and then cut the figs them-
selves into small pieces that they then retrieved.
Workers patrolling the hunting arena that we installed at
the base of the trees moved in a sinuous path with their
antennae wide open and pointed toward the ground. The fol-
lowing sequence was observed (Fig. 2). Whatever their
size, prey were mostly detected by contact, and only rarely
from a distance (1 to 6 mm; 3.0 ± 0.3 mm; n = 27). After
brief contact, the ants seized the prey; after detection from
a distance, they antennated it (Fig. 2). All prey were seized
by an appendage (a leg or an antenna), but antennated prey
were sometimes seized and then released, so that some of
them were lost. When a prey escaped after antennal contact,
the workers searched for it by noticeably increasing their
111
Fig. 1: Daily rhythm of foraging activity for Atopomyrmex mocquerysi workers during both the dry and the rainy sea-
sons. Workers leaving or returning to their nest were counted during 3 consecutive minutes each hour. Microclimatic
parameters (i.e., air temperature and relative humidity) were also recorded.
Tab. 2: Pearson's correlation coefficient between the flow rate of A. mocquerysi workers on the main trail and values for
microclimatic conditions during the daily rhythm of activity during both the dry and the rainy seasons. * P < 0.05; ** P <
0.01; *** P < 0.001.
Dry season (n = 24) Rainy season (n = 24)
Temperature (°C) Relative humidity (%) Temperature (°C) Relative humidity (%)
Nest 1: Leaving 0.633 *** -0.536 ** 0.509 * -0.599 **
Returning 0.791 *** -0.743 *** 0.814 *** -0.849 ***
Global traffic 0.739 *** -0.667 *** 0.753 *** -0.826 ***
Nest 2: Leaving 0.634 *** -0.576 ** 0.245 ns -0.334 ns
Returning 0.819 *** -0.752 *** 0.876 *** -0.894 ***
Global traffic 0.772 *** -0.706 *** 0.653 *** -0.723 ***
Nest 3: Leaving 0.521 ** -0.420 * 0.439 * -0.540 **
Returning 0.735 *** -0.663 *** 0.709 *** -0.776 ***
Global traffic 0.649 *** -0.559 ** 0.630 *** -0.723 ***
All nests pooled (n = 72):
Global traffic
0.710 ***
-0.636 **
0.650 ***
-0.728 ***
speed and the sinuosity of their path, so that they recov-
ered the prey in a few seconds.
After this solitary phase, a collective phase occurred
with the arrival of several nestmates recruited at short- (the
discovering worker did not leave the prey) or long-range.
uring short-range recruitment, workers foraging in the vic-
inity of the nestmate that discovered and seized a grass-
hopper changed the sinuosity of their paths so as to head to-
ward the discovering worker, probably because that worker
released an alarm pheromone. Indeed, in all cases these in-
dividuals firstly antennated the discovering worker's abdo-
men before helping to capture the prey. In the absence of
D
112
Fig. 2: Flow diagrams of the behavioral events observed when Atopomyrmex mocquerysi workers attempted to capture
grasshoppers of two size ranges: (A) 3 - 5 mm long, n = 60; (B) 15 - 20 mm long, n = 60.
nearby nestmates, the discovering workers left the prey to
recruit at long-range (8.3% of the cases for small prey ver-
sus 60.0% for large prey; Fisher's Exact-test: P < 0.0001).
For this, they released the prey and returned to the nearest
main column or to the nest, laying a scent trail.
In both types of recruitment, each time several recruited
workers reached the prey, and then seized it by an append-
age and pulled backwards, spread-eagling it. A positive feed-
back effect occurred when the first recruited workers in turn
attracted new nestmates. The morphological characteristics
of the pretarsus, especially the horn-shaped claws and large
adhesive pad (Fig. 3A), enable the ants to grasp the sub-
strate well while spread-eagling prey. Workers never use
any stinging behavior probably because of the very short,
spatula-shape of their sting (Fig. 3B). While some workers
continued to immobilize the prey by stretching it, the others
immediately cut it up and retrieved the small pieces. Only
15% of the small grasshoppers were cooperatively trans-
ported as whole individuals.
Finally, we noted that A. mocquerysi workers had a
high rate of successful captures, especially of large prey
(Fig. 2).
Discussion
Because it is
most likely a woody savannah dweller, Ato-
pomyrmex mocquerysi is also able to nest in some tree spe-
cies found in secondary forests, but not in old-growth for-
ests. Tree crop plantations can also offer this species a good
nesting opportunity, but this seems to vary with climatic
conditions, as we noted in other African areas. Indeed,
B
UYCKX (1962) and LESTON (1973) reported the highest
proportions of trees attacked by A. mocquerysi in cocoa
and coffee tree plantations. Therefore, A. mocquerysi col-
onies can compete for space with typical territorially-dom-
inant arboreal ant species in secondary forests and tree
rop plantations. This competition is possible because ant c
Fig. 3: Electron micrographs of the pretarsus (A) and the
spatula-shaped sting (B) of a major worker of Atopomyr-
mex mocquerysi.
113
m
osaics are dynamic, changing as the trees age: the trees
are first occupied by "ground-nesting, arboreal-foraging"
species, and then by arboreal nesting Oecophylla longino-
da, Tetramorium aculeatum and A. mocquerysi, followed
by Crematogaster sp. (K
ENNE & al. 2003, DEJEAN & al.
2008a). Like O. longinoda and T. aculeatum, A. mocque-
rysi was absent from an old-growth forest and present in a
secondary forest, but was rare along forest edges (D
EJEAN
& al. 2007a, this study). The fact that savannahs are burned
annually, and that a fire in a mango tree seems to have fav-
ored the presence of A. mocquerysi over that of O. longi-
noda and T. aculeatum (whose colonies were destroyed by
the flames), suggests that this species is able to withstand
fire due to its nesting habit. Indeed, we observed A. moc-
querysi foraging on the ground several times one or a few
days after savannahs were burned; we even saw columns
forming between the host trees to large arthropods and earth
worms killed by the fire, illustrating that this ant also has a
scavenging behavior.
The nests of wood-excavating ants usually cause the
distal parts of the occupied branches to dry out. Conse-
quently, their presence is harmful to host trees. In our study,
host tree selection was noted in plantations, and, like other
live-wood-nesting ants (see M
ONY & al. 2007), A. mocque-
rysi can be an agricultural pest on tree species of econo-
mical importance, mostly safoo trees, but also on sour-
sop, guava, mandarin, mango, and orange trees.
Differences in climatic conditions can explain why we
noted a typically diurnal, unimodal pattern of foraging ac-
tivity for A. mocquerysi workers which differed from the bi-
modal rhythm described in the Ivory Coast (L
ÉVIEUX 1976).
Indeed, cues from the physical environment are known to
override the specific circadian rhythm affecting foraging
activity rhythms (H
ÖLLDOBLER & WILSON 1990, ORR &
C
HARLES 1994).
All of the dominant arboreal ant species studied so far
attend large numbers of honeydew-producing hemipterans
(M
AJER 1993, BLÜTHGEN & STORK 2007, DEJEAN & al.
2007a). In Central and West Africa, they typically forage in
the canopy where they mostly attend Stictococcidae (T
AY-
LOR 2006), whereas A. mocquerysi, adapted to the savan-
nah, mainly hunts on the ground and surrounding vegeta-
tion, and mostly exploits Aleyrodidae, Aphididae and Coc-
cidae – all known vectors of plant diseases (M
AJER 1993).
Because ants consume a proportion of these hemipterans,
under natural conditions the latter do not proliferate and the
amount of sap the host plant loses is generally counterbal-
anced by the protection the ants provide it from defoliat-
ing insects (S
TYRSKY & EUBANKS 2007). Nevertheless, in
plantations a vicious cycle can lead to the proliferation of
hemipterans that directly affects the host trees or indirectly
affects them through the transmission of diseases (M
AJER
1993).
Although A. mocquerysi workers can forage on the trees
(see also L
ÉVIEUX 1976), here we show that they usually
hunt on the ground, while other territorially-dominant ar-
boreal ant species mostly hunt in tree crowns. Host tree
protection is therefore reduced to the sole territoriality of
the workers (see also D
EJEAN & al. 2008a), so mostly in the
area immediately around the nest and along the trails to
the ground.
As with other typically territorially-dominant arboreal
ants, A. mocquerysi workers mostly detect prey by contact
(D
EJEAN & al. 1994, ORIVEL & al. 2000, DJIÉTO-LORDON
& al. 2001, R
ICHARD & al. 2001, DEJEAN & al. 2008b). By
contrast, Oecophylla workers group ambush prey, some-
thing facilitated by the detection of prey by sight, and hence
operate at greater distances (D
EJEAN 1990). The reaction of
A. mocquerysi workers towards escaping prey (i.e., increas-
ing their speed and the sinuosity of their path) seems to be
a general pattern in predatory ants and enhances the chances
of finding the prey again, particularly on the ground. In
tree foliage prey can escape by flying away or letting them-
selves fall (K
ENNE & al. 2000, ORIVEL & al. 2000, KENNE
& al. 2005).
The A. mocquerysi workers' predatory behavior is based
on spread-eagling prey following short-range recruitment.
This seems to be general in dominant, arboreal ants whose
hunting workers are always surrounded by several nestmates
situated within the range of a recruitment pheromone. Long-
range recruitment is used only in certain situations (D
E-
JEAN 1990, HÖLLDOBLER & WILSON 1990). The ability of
the workers to spread-eagle prey is facilitated by well-de-
veloped adhesive pad arolia, and horn-shaped claws on their
pretarsus (W
OJTUSIAK & al. 1995, DJIÉTO-LORDON & al.
2001, O
RIVEL & al. 2001, RICHARD & al. 2001, this study).
Like O. longinoda, A. mocquerysi workers never use
venom (D
EJEAN 1990); here this behavior is associated with
a short spatula-shaped sting which is used to lay recruit-
ment trails, like in the genus Pheidole (D
EJEAN & al. 2007b).
By contrast, both T. aculeatum and Crematogaster sp. (both
Myrmicinae) generally sting their prey several times. Only
O. longinoda workers retrieve prey as whole individuals,
whereas others, including A. mocquerysi, cut them up, with
individual ants retrieving the small pieces (W
OJTUSIAK &
al. 1995, D
JIÉTO-LORDON & al. 2001, RICHARD & al. 2001).
In conclusion, A. mocquerysi is a diurnal species that
nests in certain tree species of economic importance. Wor-
kers attend hemipterans belonging to taxa known to be
vectors of plant diseases. Furthermore, unlike other domi-
nant arboreal ant species that hunt mostly on tree crowns,
A. mocquerysi workers hunt mainly on the ground, reduc-
ing host tree protection and reinforcing its status of pest-
ant due to its nesting habits.
Acknowledgements
W
e would like to thank Danièle Matile-Ferrero and Barry
Bolton for the identification of the hemipterans and ants,
respectively. We are grateful to Jérôme Orivel and Ian
Robottom for useful comments and to Andrea Dejean for
proofreading the manuscript. This research was supported
by a project of the French Ministère des Affaires Etran-
gères (CORUS program, research agreement 02 412 062).
Zusammenfassung
Atopomyrmex moc
querysi A
NDRÉ, 1889 ist eine westzen-
tralafrikanische, Holz aushöhlende Ameisenart der Myrmi-
cinae. Ihre Kolonien bauen Galerien in den lebenden Haupt-
ästen ihrer Nestbäume und verursachen so das Absterben
der distalen Teile dieser Äste. Wir haben diese Art im süd-
östlichen Kamerun vor allem in Savannen mit Baumbe-
stand, der jährlich abgebrannt wird, gefunden. Ebenfalls
wurde die Art im Kronenbereich eines Sekundärwaldes ge-
funden, war aber vergleichsweise selten auf Bäumen des
Waldrandes und fehlte völlig im Kronenbereich eines Alt-
bestandes. Die Ameise wurde in Ölpalmen- und Kaffee-
114
115
plantagen nicht gefunden, war selten auf Kakaobäumen,
wurde auf 0,2 bis 5,3 % der untersuchten Avocado-, Gu-
ave-, Mango- und Zitrusbäume gefunden, und war häufig
(12,4 %) auf der Baumart Dacryodes edulis. Ein Feuer in
einer Mangoplantage scheint der Ameise zuträglich gewe-
sen zu sein. Kolonien von A. mocquerysi pflegen tropho-
biotische Beziehungen zu Aleyrodidae, Aphididae, Cocci-
dae und Stictococcidae. Die Art ist auch räuberisch. Ar-
beiterinnen fouragieren tagsüber nach Beute, vor allem am
Boden. Das räuberische Verhalten ist durch Erkennen von
Beute durch Kontakt gekennzeichnet. Arbeiterinnen rekru-
tieren Nestgenossinnen auf kurze Distanz (innerhalb des
Wirkungsradius von Alarmpheromonen) und nur selten auf
weite Distanz. Rekrutierte Arbeiterinnenteams immobili-
sieren die Beutetiere indem sie deren Extremitäten ausein-
anderziehen. Sie zerteilen sie sofort, und die Teile werden
dann von einzelnen Arbeiterinnen werden. Im Gegensatz
zu anderen territorial-dominanten, Bäume bewohnenden
Ameisen stellt A. mocquerysi durch das Aushöhlen des
Holzes eine Bedrohung für die bewohnten Nestbäume dar,
die wegen des Beutejagens am Boden durch den nur gerin-
gen Schutz des Laubes nicht ausgeglichen wird.
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