International Association for Ecology

Territory Defense by the Azteca trigona: Maintenance of an Arboreal Ant Mosaic Author(s): Eldridge S. Adams Reviewed work(s): Source: Oecologia, Vol. 97, No. 2 (1994), pp. 202-208 Published by: Springer in cooperation with International Association for Ecology Stable URL: http://www.jstor.org/stable/4220605 . Accessed: 21/09/2012 17:16

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http://www.jstor.org Oecologia (1994) 97:202-208 Springer-Verlag 1994

ORIGINAL PAPER

Eldridge S. Adams

Territory defense by the ant Azteca trigona: maintenance of an arboreal ant mosaic

Received: 16 November 1992 / Accepted: 19 November 1993

Abstract Mosaics of exclusive foraging territories, pro- Introduction duced by intra- and interspecific competition, are com- monly reported from arboreal ant communities Ant communities are often highly structured due to in- throughout the tropics and appear to represent a recur- tra- and interspecific competition (H?lldobler and ring feature of community organization. This paper Wilson 1990). The "ant mosaic hypothesis" suggests documents an ant mosaic within mangrove forests of that interspecific competition produces a recurring pat- Panama and examines the behavioral mechanisms by tern of community organization among arboreal which one of the common species, Azteca trigona, main- throughout the world's tropics (Leston 1973a, b; Majer tains its territories. Most of the mangrove canopy is 1972,1976a, b; Room 1971, 1975a, b). A central claim of occupied by mutually exclusive territories of the ants A. this hypothesis is that the numerically dominant ant trigona, A. velox, A. instabilis, and Crematogaster bre- species within the forest canopy defend mutually exclu- vispinosa. When foraging workers of A. trigona detect sive foraging territories, which nearly fill available workers of these territorial species, they organize an space. Such territorial ant mosaics have been document- alarm recruitment response using pheromonal and tac- ed among canopy ants in lowland tropical forests in tile displays. Nestmates are attracted over short dis- various regions of the world, especially in agricultural tances by an alarm pheromone originating in the py- settings (Way 1953; Brown 1959; Room 1971, 1975a, b; gidial gland and over longer distances by a trail Majer 1972, 1976a, b; Leston 1973a, 1978; Jackson pheromone produced by the Pavan's gland. Recruits are 1984). simultaneously alerted by a tactile display. No evidence The behavioral mechanisms underlying the forma- was found for chemical marking of the territory. Major tion of territory mosaics are in most cases poorly under- workers are proportionally more abundant at territory stood. Although intra- and interspecific aggression have borders than on foraging trails in the interior of the been observed frequently among tropical arboreal ants colony. The mechanisms of territory defense in A. trigo- (e.g., Way 1953; Brown 1960; Vanderplank 1960; Majer na are remarkably similar to those of ecologically 1976b), there have been few investigations of the mecha- analogous ants in the Old World tropics. nisms by which territory mosaics are produced (but see H?lldobler and Wilson 1978; H?lldobler 1979, 1983; ? ? ? Key words Ants Territoriality Azteca Ph?romones Salzemann and Jaffe 1990). Studies from the New World tropics are particularly uncommon. Colony defense in- volves the coordinated actions of hundreds or thou- sands of workers, linked together by diverse forms of communication (H?lldobler and Lumsden 1980). This paper reports that the mechanisms of communication which allow the maintenance of mosaics are remarkably E. S. Adams1 similar for two distantly related ant genera for which Department of Zoology, University of California, detailed information is available. California USA Berkeley, 94720, This study examined territory defense by the abun- Smithsonian Research Institute, Tropical dant ant Azteca and its APO Miami 34002, USA Neotropical trigona (Emery) congener A. velox (Forel). Field experiments and obser- Present address: vations were conducted within a naturally occurring ant 1 Department of Biology, mosaic to document the nature of the mosaic, to deter- University of Rochester, Rochester, NY 14627, USA mine how these ants organized territory defense, to de- 203 termine the role of caste in defense, and to test for the had been collected was used to assay responses to the gland ex- tracts. A of the donor of A. was collected presence of a territorial pheromone (H?lldobler and fragment colony trigona and transferred to a container, Wilson laboratory measuring approxi- 1978). mately 30 ? 50 ? 20 cm. The colony was provided with a paper- covered foraging arena marked with a grid of lines spaced 3 cm apart. For each test, 10 ?? of fluid containing the contents of one worker's gland were used to mark a randomly selected square. Methods After allowing 1 min for the ethanol solvent to evaporate, the ants within the marked were counted. As a control, Study site and species standing square some squares were marked with ethanol alone. For A. a similar was conducted in the field. In each Studies were conducted in forests near Coco Solo, velox, assay mangrove 10 of the contents of two workers' Colon Province, on the Atlantic coast of the of Panama trial, ?? extract, containing Republic were to a 1 cm2 area of bark near a occu- from 1983 to 1989. characteristics are described by glands, applied densely Vegetation trail. After 1 min for the ethanol to Adams and Levings (1987). Ants were identified by R. Snelling pied foraging waiting evapo- the number of ants near the treated area and main- and vouchers have been deposited at the Los Angeles County rate, standing was counted. Ethanol was used as a Museum of Natural History. Because the of Azteca is in taining aggressive postures control. need of revision and Vinson 1989), these identifications (MacKay For statistical data for A. velox were may be subject to change. analysis, log-transformed in order to equalize variances among responses to the four cate- gories of extracts. This was not necessary for data from A. trigona. The T-method was used to evaluate Mapping unplanned comparisons among the means (Sokal and Rohlf 1981). Maps of foraging territories were made near ground level ( < 2m In mangrove forests, ants are usually from height). prevented Glandular source of the trail walking on the ground by tidal flooding. Nonetheless, colonies of pheromone Azteca spp. and other arboreal ants often forage near the water Extracts were as described above. A 25 ? 40 cm surface and rely upon connections near this level to travel from prepared platform was covered with and in the field near a test tree to tree. The lateral extent of each colony's foraging area was paper placed colony of A. or A. velox. A 1-2 m connected the determined by following foraging workers and by searching the trigona bridge platform to a route of the test Ants were baited to base of each tree for activity. When foraging workers were not major foraging colony. one end of the with beef until a of at least 100 discovered during visual scans, baits of tuna or beef were placed platform group workers had collected around the bait. Artificial trails 25 cm in and monitored for 2 hr. Intraspecific boundaries were located for were then drawn across the with a Azteca spp. (but not for a co-occurring territorial ant, Cremato- length paper syringe, leading outward from the bait. of extract the gaster brevispinosa [Mayr]) by transferring workers among baits Twenty ?? containing glands from four workers were used to each trail. Control trails and foraging trails to determine if fighting occurred. The edges of prepare were drawn with 20 of ethanol. each territory were marked with colored flagging and mapped ?? The ants each trail were counted a 3 min from central trees using a compass and tape measure. following during period. For statistical analysis, the reciprocals of counts of A. velox were used in order to equalize variances. Due to the lack of variation in A. to two of the Caste participation response by trigona categories trails, Kruskal-Wallis test was used instead of ANOVA. To compare the caste distribution of ants defending territory bor- ders and ants in other parts of the territory, workers were collect- Territorial ed at different sites from 10 territories of A. trigona. The borders pheromone of neighboring territories are defended by dense groups of work- colonies of A. were chosen. Within the ers, whose behavior differs from that of foraging workers in the Twenty trigona foraging area of each a circle of filter 15 cm in diameter was interior of the territory (Adams 1990). For each colony, workers colony, paper attached to a tree trunk with dense trails of A. were collected by rapidly pressing a strip of tape across a border foraging trigona. The resident ants soon established trails across the disks. defense group so that ants were removed before alarm responses paper The disks were retrieved after ten and the of ants could change the group composition. A group of workers was days responses to three of were measured in the field: collected in the same manner from a major foraging trail in the types paper (1) paper previ- their own interior of the colony. The head width of each ant was measured ously occupied by colony, (2) paper previously occupied a A. and controls. to the nearest 0.04 mm using a dissecting microscope equipped by neighboring trigona colony, (3) unoccupied with an ocular micrometer. To measure reactions to these three categories of paper, a wooden was in a between each test To determine whether ants responding to territorial enemies platform provided gap colony and a of A. This was con- were larger than ants attracted to food, baits were offered on 10 neighboring colony trigona. platform nected to a route a 1-2 m wooden A trees, each within a distinct colony of A. trigona. On widely sepa- major foraging by bridge. beef bait was on the to attract a of rated branches, two stimuli were offered simultaneously: (1) a food placed platform large group workers. disks were then on the bait, consisting of approximately 3 gm of tuna, and (2) a group of Paper sequentially placed plat- in random 3 cm from the bait. For each intruders, consisting of 3 to 5 workers of Azteca instabilis (F. form, order, occupied the behavior of ants Smith). When more than 30 workers had accumulated at a stimu- replicate, approaching the paper disks and the number onto the disk were recorded a 3 min lus, they were collected and measured as previously described. crossing during test period.

Glandular source of the alarm pheromone Results Preliminary observations suggested that recruitment ph?romones were released from the end of the Three posterior gaster. possible The mosaic sources of ph?romones located near the tip of the gaster - the territory Pavan's gland, the pygidial gland, and the hindgut - were dissect- ed from freshly collected workers of A. trigona and A. velox and Colonies of Azteca trigona, A. instabilis, and Cremato- crushed in 95% ethanol. The colony from which the dissected ants gaster brevispinosa defended mutually exclusive forag- 204

(a)

VW "TTd

Ar1*

20 30 40 Time(min)

50 I (c)

30 I ^ 20 J 10 Vi^1 0 10 20 0 10 20 30 Time(min) Time(min)

Fig. 2a-c Arrival rate of workers of A. trigona before and after introduction of various intruders (arrows), (a) 100 conspecifics from a different colony (b) 10 A. instabilis (c) 10 C. brevispinosa

dreds of nestmates. This reaction was shown intra- and Fig. 1 Foraging territories of Azteca ingoia (horizontal lines), A. interspecifically (Fig. 2). instabilis (solid), and Crematogaster brevispinosa (dots) in a man- Close observation revealed that three forms of com- grove forest. White areas represent unoccupied forest. Wavy lines munication coordinated group responses. First, ants indicate areas of water trees. Each Azteca open lacking polygon within 5 cm of nestmates began running in indicates a distinct Not all boundaries fighting colony. intraspecific colony detection of an alarm of C. brevispinosa were located; however, some were obvious due rapid looping motions, suggesting to gaps between trees. Small squares indicate isolated trees occu- pheromone. Alerted nestmates often adopted aggressive pied by territorial ants postures with their gasters raised and their mandibles open. Second, some ants returned to the nest in a trail- laying posture, with the tips of their abdomens pressed to the substrate. Third, a few scouts delivered a rapid ing territories (Fig. 1). Although not shown in Fig. 1, tactile display to nestmates as they returned along re- colonies of A. velox participated in the mosaic at other cruitment trails. The displaying ant stood face-to-face locations in the mangrove forest. Ants actively defended with the recipient and shook backwards and forwards both intraspecific and interspecific boundaries; posi- rapidly, bringing the antennae and mouthparts of the tions were the same both day and night. Narrow unoc- two ants into contact. cupied gaps (0.1 to 5 m) separated adjacent territories. In thirty colonies, worker behavior was quantified as Each colony of A. trigona occupied several intercon- the ants returned to their nests following contacts with nected trees. On each large tree, the ants constructed introduced opponents. On average, 20.8% ?3.0% one or more nests of carton, a fibrous material of paper- (X + SE) of returning ants deposited trails and like consistency. Azteca velox, A. instabilis, and C. bre- 5.0% ?1.4% delivered tactile displays to nestmates vispinosa nested within existing cavities in both living within 30 cm of the point of contact with their oppo- and dead trees. Ants of all four species moved from tree nents (n= 1275 ants). to tree along semi-permanent trails, using branches, fall- en wood, or the prop roots of the red mangrove, Rhi- zophora mangle. Glandular source of ph?romones

For both species, alarm responses differed significantly Recruitment behavior among gland extracts and controls (Table 1). Aggressive responses to the substrates marked with contents of the Transfers of foraging workers between colonies of pygidial glands were significantly greater than respons- Azteca stimulated vigorous defense: intruders were es to other extracts or to ethanol controls (Table 1; chased, immobilized and killed by groups of defending ? < 0.05 for both species). workers. The introduction of ten or more intruders In both species,, workers approached and oriented stimulated alarm recruitment, sufficient to attract hun- along artificial trails containing the contents of the Pa- 205

Table 1 The number of ants Glandular source for for responding to gland extracts Assay Assay trail or ethanol controls. Assay for alarm pheromone pheromone alarm ph?romones: X = the X + SE X SE number of ants responding + with aggressive postures to substrates marked with each A. trigona Pavan's 5.9 15 93.8 10 fluid. _Assay for trail ph?romo- gland ?0.8 ?15.8 nes : X = the number of wor- Pygidial gland 9.9 ?0.9 15 2.3 ?0.8 10 10 kers (in 3 min) following artifi- Hindgut 3.0 ?0.6 15 0.0 ?0.0 10 cial trails. Analysis of variance Ethanol 2.6 ?0.7 15 0.0 ?0.0 and the Kruskal-Wallis test :19.7;P<0.001 # = 27.3;P<0.001 were used to compare respon- A. velox ses ? = number of (see text), Pavan's gland 5.7 ?2.0 10 17.4 + 4.3 10 trials Pygidial gland 13.3 ?1.6 10 4.2+1.7 10 Hindgut 1.4 ?0.5 10 1.0 ?0.5 10 Ethanol 0.7 ?0.2 10 0.2 ?0.2 10 F3 36= 22.8; ? < 0.001 F3 36= 22.6; ?<0.001

25 100 ?- ? (a)

20 -

15 -

?*) 60 I 10 a

^S 40 I-1 r

15 r p (b)

io Territory Territory Recruited Recruited boundary interior to enemy to food 5 - Fig. 4 The average percentage (?SE) of majors among workers ?= of A. trigona collected at various regions within the territories of *** ten colonies. ?<0.001; Mann-Whitney U test 0.8 1.0 1.2 1.4 Head width (mm)

Fig. 3a, b Frequency histogram of head widths of workers collec- nor worker subcastes see also Wheeler ted at (a) a border defended against a neighboring colony and at (Fig. 3; 1986). (b) a foraging trail in the interior of the same colony. The dotted The division between minors and majors was at a head line indicates the division between the minor and major subcastes width of approximately 1 mm in all ten colonies (see Fig. 3); therefore, ants with head widths greater than 1.00 mm were classified as majors. Based on this criterion, van's gland (Table 1). A few workers responded to trails the proportion of major workers at territory boundaries made from the pygidial gland, but these ants moved was significantly higher than on foraging trails in the more slowly, stopping to investigate as they made their interior of the territory (Fig. 4; two-tailed Mann-Whit- = way from one end to the other. Responses to the four ney U test, ????? 96, ? < 0.001). Two border defense kinds of trails differed significantly (Table 1) with Pa- groups were composed entirely of major workers. The van's gland extracts eliciting the strongest response. proportion of major workers recruited to territorial ene- mies and to food did not differ significantly (Fig. 4; two- = tailed Mann-Whitney U test, t/10>10 61.5, NS). Caste participation When colonies were analyzed individually, workers at territory edges were significantly larger than workers The distribution of worker head widths showed a clear on central foraging trails in seven of ten colonies (two- bimodality of size corresponding to the major and mi- tailed Mann-Whitney U test, ? < 0.05). Workers recruit- 206 ed to territorial enemies were significantly larger than data). In addition to these pheromonal mechanisms, workers recruited to food in four of ten colonies. Other trail-laying scouts deliver tactile displays as they return comparisons of worker sizes showed no significant dif- from territorial battles. ferences. The ecological significance of rapid recruitment by A. trigona is revealed during battles at territory boundaries. Conflicts occur when groups of workers at- Test for a territorial pheromone tempt to expand their territories at the expense of neigh- bors. In a series of controlled field experiments, Adams During 3 min tests, no differences were detected in the (1990) showed that workers assess the relative density of numbers of workers walking onto paper previously oc- nestmates and opponents during territorial battles and cupied by their own colony (X + SE: 99.0 ?13.6), pa- that workers from the outnumbered colony are more per previously occupied by conspecific neighbors likely to withdraw. However, initial disadvantages in (97.4 + 9.3), or paper previously unoccupied by ants worker density can be overcome by rapid recruitment. (78.2?15.4; ? = 20 trials for each treatment; ANOVA, Territory battles have strong effects on territory size. ^2,56 =3.00, NS). No fecal material or other marks were Maintenance of a large territory thus depends upon visible on the paper disks. No behaviors were observed swift and intense recruitment, especially during the early in this test or in any other context that would indicate stages of a battle. chemical marking of the territory. Similar recruitment systems, with distinct long and short-range components, have been reported from other social in the context of foraging or defense (e.g., Discussion ants: H?lldobler and Wilson 1978; Traniello 1983; ter- mites: Traniello 1981 ; honeybees: Seeley 1985 and cited The ecological and behavioral patterns of competition references). This habit may be favored when rapid reac- in this mangrove ant community are remarkably simi- tions are needed within large areas extending around lar to those reported for arboreal ants in other tropical concentrated nest populations. The long-range compo- of workers from regions. Colonies of four abundant species, Azteca tri- nent attracts and directs large numbers orients re- gona, A. velox, A. instabilis, and Crematogaster bre- the nests, while the short-range component vispinosa, defend mutually exclusive territories intra- cruits to the precise location of the stimulus. of the and interspecifically. This behavior produces a mosaic Border defense is primarily the task major of territories with well-defined boundaries. Similar mo- workers, a morphologically distinct subset of the work- head width and saic patterns occur in other ant communities, especially er caste. Majors differ from minors in work- within tropical forest canopies (Strickland 1951; Way body allometry (Wheeler 1986). In most colonies, 1953; Brown 1959, 1960; Room 1971, 1975a, b; Majer ers in border defense groups were significantly larger 1972, 1976a, b; Leston 1973a, b, 1978; H?lldobler 1979; than those travelling on trails in the colony interior; of Jackson 1984). Although there have been few studies of indeed, some defense groups were composed entirely arboreal ants in Neotropical forests, Azteca spp. are majors. Among other aggressive ants with worker poly- known to defend arboreal territories in coconut planta- morphism, the major workers are often disproportion- H?lldobler tions in Guyana (Rai 1977), in citrus crops in Trinidad ately involved in defense (Wilson 1976; these this divi- (Jutsum et al. 1981), in wet forests of Costa Rica (Carroll 1981; Feener 1988). In some of species, 1979), and in secondary forest in Brazil (Leston 1978). sion of labor is accomplished by caste-specific patterns more Territory defense is organized by pheromonal and of communication, with majors responding tactile communication. Colonies of A. trigona and A. strongly to alarm recruitment than to food recruitment This does not velox employ ph?romones from two distinct glandular (Wilson 1976; Detrain and Paste?is 1992). in A. In sources, allowing responses across differing spatial and appear to be the primary mechanism trigona. recruits to territorial enemies were temporal scales. A short-range alarm pheromone, four of 10 colonies, to this stored in the pygidial gland, attracts nestmates over dis- significantly larger than recruits food; however, tances of several centimeters. This triggers immediate tendency was weak and inconsistent. Recruits may be these two contexts of trail commu- responses to intruders and pinpoints activities that shift unable to distinguish is then the of in position. The bioactive compounds in the alarm nication. If this the case, preponderance at boundaries be caused pheromone have been identified as cyclopentyl ketones major workers colony may by to withdraw from in A. chartifex (Wheeler et al. 1975). In addition, a long- an increased tendency of minors pro- encounters. range recruitment pheromone, originating in the Pa- longed agonistic found for chemical of the van's gland, is used to deposit trails, which can attract No evidence was marking hundreds of workers across distances of several meters substrate. Instead, colonies of A. trigona actively defend border-defense The after a delay of several minutes. Trail recruitment to boundaries by maintaining groups. their for territory battles can continue for hours (Fig. 2) and may ants continually probe neighbors, waiting op- of serve as the basis for semi-permanent trunk trails sup- portunities to advance into the territories adjacent other of plying border defense groups. These trunk trails may colonies (Adams 1990). By contrast, species A. mark trails or sub- persist for several months or years (Adams, unpublished ants, including foreli, occupied 207 strates with colony-specific odors (Cammaerts et al. Brown ES (1959) Immature nutfall of coconuts in the Solomon Islands. I. Distribution of nutfall in relation to that of 1977; H?lldobler and Wilson 1978; Traniello 1980; Jaffe Ambly- pelta and of certain species of ants. Bull Ent Res 50:97-133 1986), which may confer an advantage to the resident Brown ES (1960) Immature nutfall of coconuts in the Solomon territorial and Wilson colony during fights (H?lldobler Islands. II. Changes in ant populations, and their relation to 1978). vegetation. Bull Ent Res 50:523-558 The mechanisms of territory defense in A. trigona are Cammaerts MC, Morgan ED, Tyler R (1977) Territorial marking in the ant Myrmica rubra. Biol Behav 2:263-272 remarkably similar to those described for ecologically Carroll CR (1979) A comparative study of two ant faunas: The ants from Old World forests. The analogous tropical stem-nesting ant communities of Liberia, West Africa, and Co- best known of these are the weaver ants, Oecophylla sta Rica, Central America. Am Nat 113:551-561 longinoda and 0. smaragdina. Like A. trigona, weaver Cole AC Jr, Jones JW Jr (1948) A study of the weaver ant, Oeco- Am Midi Nat 39:641-651 ants are aggressive inhabitants of tree canopies, defend phylla smaragdina (Fab.). Detrain C, Pasteeis JM (1992) Caste polyethism and collective foraging space intra- and and interspecifically, possess defense in the ant, Pheidole pallidula: the outcome of quantita- multiple arboreal nests scattered throughout their terri- tive differences in recruitment. Behav Ecol Sociobiol 29:405- tories (Cole and Jones 1948; Way 1954; H?lldobler and 412 Feener DH Jr Effects of on and defense Wilson 1978; Leston 1978; H?lldobler 1979,1983). Both (1988) parasites foraging behavior of a termitophagous ant, Pheidole titanis Wheeler genera tend homopterans, prey upon living insects, and (: Formicidae). Behav Ecol Sociobiol 22:421- scavenge opportunistically (Way 1954; H?lldobler and 427 Wilson 1978). Caste structure is also similar, with a bi- H?lldobler ? (1979) Territories of the African weaver ant (Oeco- modal distribution of worker sizes and with division of phylla longinoda (Latreille)): A field study. ? Tierpsychol 51:201-213 labor between the two physical subcastes (Weber 1946, H?lldobler ? (1981) Foraging and spatiotemporal territories in 1949; Wheeler 1986). the honey ant Myrmecocystus mimicus Wheeler (Hymenopte- Furthermore, the social communication systems of ra: Formicidae). Behav Ecol Sociobiol 9:301-314 A. trigona and 0. longinoda are similar in many remark- H?lldobler ? (1983) Territorial behavior in the green tree ant 15:241-250 able details. Workers of O. longinoda employ both short- (Oecophylla smaragdina) Biotropica H?lldobler Lumsden CJ Territorial in ants. alarm and trail ?, (1980) strategies range ph?romones long-range Science 210:732-739 to territorial ph?romones organize responses H?lldobler ?, Wilson EO (1978) The multiple recruitment systems (H?lldobler and Wilson 1978). In both species, the trail of the African weaver ant Oecophylla longinoda (Latreille) (Hy- pheromone used in long-range alarm recruitment is the menoptera: Formicidae). Behav Ecol Sociobiol 3:19-60 H?lldobler ?, Wilson EO (1990) The ants. Press of Har- same as that used to recruit nestmates to large food Belknap vard University Press, Cambridge, Massachusetts items; when to territorial however, recruiting invaders, Jackson DA (1984) Ant distribution patterns in a Cameroonian workers in both species deliver a tactile display to nest- cocoa plantation: investigation of the ant mosaic hypothesis. mates to communicate alarm (H?lldobler and Wilson Oecologia 62:318-324 Jaffe ? Nestmate and territorial in 1978). (1986) recognition marking Solenopsis geminata and in some Attini. In: Lofgren CS, Van- Despite these resemblances, the two ants are not der Meer, RK (eds) Fire Ants and leaf-cutter ants : Biology and related and the territorial behaviors to closely appear management. Westview Press, Boulder, Colorado, pp 211-222 have evolved independently. Oecophylla is in the sub- Jutsum AR, Cherrett JM, Fisher M (1981) Interactions between the fauna of citrus trees in Trinidad and the family Formicinae and Azteca is in the subfamily Doli- ants Atta cephalo- tes and Azteca sp. J Appi Ecol 18:187-195 choderinae. Moreover, the glandular sources of the re- Leston D (1973a) Ecological consequences of the tropical ant mo- cruitment differ between the two O. ph?romones genera: saic. Proc 7th Internat Congress of the IUSSI, London :235- longinoda produces trail pheromone in the rectal gland 242 and alarm pheromone in the sternal gland (H?lldobler Leston D (1973b) The ant mosaic-tropical tree crops and the limiting of pests and diseases. PANS 19:311-341 and Wilson 1978). Thus, it appears that any similarities Leston D (1978) A neotropical ant mosaic. Ann Entomol Soc Am in the design of territory defense and communication 71:649-653 are due to convergent evolution. MacKay WP, Vinson SB (1989) A guide to species identification of New World ants. Sociobiology 16:3-47 Majer JD (1972) The ant mosaic in Ghana cocoa farms. Bull Ent Acknowledgements I thank Roy Snelling for identification of Res 62:151-160 ants. R.L. Caldwell provided advice and encouragement through- Majer JD (1976a) The ant mosaic in Ghana cocoa farms: Further out the project. D. Cassili and W. Tschinkel made helpful com- structural considerations. J Appi Ecol 13:145-155 ments on the manuscript. Funds were provided by pre-doctoral Majer JD (1976b) The maintenance of the ant mosaic in Ghana fellowships from the National Science Foundation and the Smith- cocoa farms. J Appi Ecol 13:123-144 sonian Tropical Research Institute. Rai BK (1977) Damage to coconut palms by Azteca sp. (Hymen- optera: Formicidae) and insecticidal control with bait, in Gu- yana. Bull Ent Res 67:175-183 Room PM (1971) The relative distribution of ant species in Gha- References na's cocoa farms. 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