Barbara L. Thome.
Termite-Termite Interactions: Workers as an Agonistic Caste.
Psyche 89:133-150, 1982.

Full text (searchable PDF, 1912K)
Durable link: http://psyche.entclub.org/89/89-133.html

The following unprocessed text is extracted from the PDF file, and is likely to be both incomplete and full of errors. Please consult the PDF file for the complete article.

TERMITE-TERMITE INTERACTIONS:
WORKERS AS AN AGONISTIC CASTE*
BY BARBARA L. THORNE
Museum of Comparative Zoology
Harvard University
Cambridge, Massachusetts 02 138
Termite soldiers are a defensive caste. Their heavily sclerotized head capsules can be equipped with hard mandibles capable of crushing, pinching, piercing, or slashing predators. Soldier castes of many phylogenetically advanced species have well-developed fron- tal glands and are capable of exuding or spraying chemical secre- tions. Such chemical armaments are toxic, irritable, or oily fluids which can impair physiological, sensory and/or mechanical facul- ties of the recipient (Prestwich, 1979). Termite soldiers are thus formidable opponents for ants and vertebrate predators. Soldiers are fed by workers and their behavior within the colony is generally limited to signaling alarm, participating in defense, and organizing foraging expeditions (Stuart, 1969; Traniello, 198 1). Despite their specialization, however, soldiers are not the only defensive caste in a termite colony: worker termites of some species (from four families) are known to be able fighters in termite-termite aggressive interactions [Kalotermitidae (Grassi and Sandias, 1896- 1897; Dropkin, 1946); Hodotermitidae (Nel, 1968); Rhinotermitidae (Pickens, 1934; Clement, 1978); Termitidae (Dudley and Beaumont, l889a,b; Andrews 19 1 I)]. This paper explores intra- and interspe- cific agonistic encounters among termites, and focuses on the roles of workers and soldiers in such conflicts. The report is presented in two sections, corresponding to two sets of experiments on this topic. Section A describes a field manipula- tion inducing intraspecific encounters among colonies of Nasuti- termes corniger in Costa Rica. Section B presents data on laboratory experiments examining intra- and interspecific interac- tions among four species of Panamanian termites. *Manuscript received hj the editor February I. 1982 133




================================================================================

134 Psyche [vo~. 89
Nasutitermes corniger (Motschulsky) is a common arboreal ter- mite ranging through much of Central and northern South America (Thorne, 1980). Large carton nests contain up to 800,000 termites (Thorne and Noirot, 1982) and, with the addition of foragers, total colony size may exceed a million individuals. Distinct foraging trails, covered by carton galleries, are visible issuing from a nest and proceeding along tree branches, trunks, and the ground surface. The termites also travel underground and in galleries located within trees or fallen logs. N. corniger foraging trails can radiate many meters from the parent colony.
Given the density of N. corniger colonies in primary forest (7.0 k 1.8 per hectare in the Hubbell Plot of Barro Colorado Island, Panama, N = 4 hectares) and in areas of young second growth (27 in one hectare in Frijoles, Panama) (Thorne, unpub. data), it is likely that, at least occasionally, foraging parties from different colonies encounter one another in the midst of exploring or exploiting a local food source. Observation of a natural inter-colony encounter would be difficult. It would require tracking single foraging trails, which would undoubtedly result in disturbance as one cleared away the forest litter to locate foragers. Even if trails could be accurately followed without disruption, it would be rare to view simultaneous interception with an active trail known to be from a second colony. Because the odds of witnessing such a natural event are low, I forced an encounter through a transplant experiment. METHODS
On the morning of 18 August, 1978 three Nasutitermes corniger nests were collected from separate areas of second growth near Sirena headquarters of Corcovado National Park, Osa Peninsula, Costa Rica. The nests measured 29.8, 52.7, and 41.9cm in height and 26.0, 29.8, and 26.0cm in diameter, respectively. Nests were sawed from their host trees and hand-carried to the experimental site. Each colony was suspended on a wire from one of two branches of a large tree (Fig. 1). The nests were hung in an equilateral triangle such that the distance from their base to the ground was 60 cm, the distance from the edge of each colony to each neighbor was 50cm, and the original compass orientation of each colony was main-



================================================================================

Thorne - Termite-Termite Interactions 135 Figure I. Field set-up for intraspecific encounter experiment involving Costa Rican Nasuiitermes corniger.
tained. A coat of tanglefoot was placed at the base of each wire strand (near the point of attachment to nest support branches) to prevent termites from crawling up the wires. A 3.5 X 3.5m2 plot beneath the nest triangle was completely cleared of leaf litter, forest debris and herbaceous plants so that movement patterns of the termite trails could be monitored. At 7:30 p.m. that evening stick "ramps" (90cm in length, 1 cm in diameter) were installed to connect the nests to the ground. The tips of the sticks were shallowly inserted into both the nest carton and ground surface for support. Bases of the ramps also ended in vertices of an equilateral triangle on the ground, 20cm from tip to tip.
RESULTS
Hanging above the ground from a single strand of wire, each nest was an island in mid-air: no escape routes were open for the ter- mites. By dusk of the day of collection, soldiers and workers from all colonies were crawling over the peripheries of their nests. This activity gained participants and momentum: at 7:30 p.m. each nest was a seething mass of termites. The stick ramps were embedded to



================================================================================

136 Psyche [vo~. 89
connect the nests to the ground. Immediately following implanta- tion termites swarmed onto the ramps, soldiers in the lead followed by a mixture of soldiers and workers. Only four white immatures were seen leaving the nests throughout the experimental period. As they reached the ground groups fanned out: termites from a single colony divided into several ribbons heading in different direc- tions. Because of the close proximity of the ramp exits, it was inevi- table that encounters occur between trails from different colonies. The meetings were not passive. Soldiers oriented towards (and apparently squirted) termites from other colonies, but this did not seem much of a deterrent to recipients. The major defense stemmed not from the soldiers, but from the Nasutitermes workers. Workers from different colonies grabbed each other with their mandibles and locked in one-on-one conflict. Pairs of workers squirmed and bent with vigor, often until the death of both. Occa- sionally a third or fourth worker would join the engagement, but usually only temporarily. Workers avidly attacked soldiers as well, grabbing at the legs and occasionally biting the abdomen. The next morning worker carcasses littered the arena over an area of approximately 1,500cm2, with some battle "patches" as far as 1.5 m from the center of the ramp triangle. The density of bodies was often quite high (25-50 dead in a 4.0cm2 area). Surviving termites did not appear to cannibalize the dead. Ants, flies, staphylinid bee- tles, and wasps began scavenging the termite carcasses. How were foraging trail routes influenced by the intersection bat- tles? Agonistic confrontations were instigated when at least one colony was in the process of establishing or changing a foraging route, i.e. in a scouting phase. Preliminary observations (Fig. 2) suggest that both colonies' foraging pathways were displaced by encounters - t,rails were repulsed from the meeting site following battles lasting 10-30 minutes. One colony may maintain a trail tangential to the "battle field", but I did not see one continuing through an area of dead termites.
It is difficult to determine the effect of agonistic encounters on final foraging path location. In isolation a colony establishes forag- ing routes by scouting in a broad network, but several hours later this highly branched fan collapses into a single actively travelled ribbon with few side trails. Thus the fact that termites have trav- ersed a given area in no way assures that route as the path of a final



================================================================================

19821 Thorne - Termite- Termite Interactions 137 Figure 2. Periodic maps of ground foraging trails departing from the tips of exit ramps attached to suspended Nu.v~/fiiertne.v corniger colonies (Section A). Central dots indicate positions of the ramps. Maps are 3.5 X 3.5 m2.



================================================================================

138 Psyche [VC=Ì 1. 89
foraging trail. Battles may be a deterrent to formation of a g% ven path, but their influence is difficult to assess independently. Foraging path trajectories from the three nests were moni t o red for two and one half days following initiation of the experiment (see Fig. 2 for the final 24 hour period). Once a scouting fan condensed into a single pathway the positions were relatively stable. M ^- nor adjustments in path locations did occur periodically, and activity on specific trails varied from day to day and even hour to hour. 0 Gca- sionally (usually in the evening) new scouting parties would emanate from the ramp tip or as a tributary of the main trail network. Construction of trail covers varied from colony to colony. Col any Ill began covering both its ramp and ground trails quickly (a t otal of 64cm of trail covered by 7 am, 20 August). In contrast, Colon %es I and I1 had only 19cm and 3.2cm of covering, respectively, at 7 a -m. on 20 August. These same relative speeds were repeated when the initial experiment was replicated from 21 to 22 August. Building behavior also showed distinct inter-colony variation, mainly in the amount of advance siding deposited before the trails were roofed. To replicate the first nights' encounters, I removed the three ramps and scraped clean the entire 3.5 X 3.5 m2 grid at noon on 2 1 August. This caused attrition of those individuals on the ground and out foraging, but the established trails had to be destroyed to i n d uce active scouting. New ramps (90cm long) were installed at 6:30 p - xn., with ends touching the ground in an equilateral triangle of side
length 25 cm.
Members of Colony I came down their ramp fairly rapidly and began three major paths from its tip, one to the southeast, one to "the
north, and one due west. At 7 p.m. termites from Colony I1 besan coming down their ramp and immediately began to fight with Col- ony 1's southeast-bound foragers. When the first workers from Col- ony 111 came down their ramp and encountered foreigners, t *ey rapidly reversed direction and returned en masse to the mouth of their nest, after which a large group of Colony 111 termites stormed down the ramp. The possibility of worker recruitment in these cir- cumstances should be investigated. The battle between Colon ics I and 111 was vehement for 20 minutes; after 30 minutes Colony" 1's southeast trail was abandoned. Colony 111 established a new t rail 180å away from the direction of original interference with Colon y I.



================================================================================

Table I: Comparative Size Measurements and Percentage of Soldiers Per Colony BODY LENGTH HEAD DRY APPROXIMATE
(INCLUDING HEAD)^ WIDTH^ WEIGHT^ PERCENTAGE (mm) (mm) (u gms) SOLDIERS
Atnitermes heaumotiii
(Termitidae, Termitinae)
Armiiermes chagresi
(Termitidae. Nasutitermitinae)
Nu.~utiiermes corniger
(Termitidae, Nasutitermitinae)
Nusui ~iermes ephratue
(Termitidae, Nasutitermitinae)
SOLDIER
WORKER
SOLDIER
WORKER
SOLDIER
WORKER
SOLDIER
WORKER
0.33
0.34
7 9%c
I .03
0.83
7 8%>c
0.34 I 8%d
0.60
(range: 8 - 27% )
0.39
1 59hd
0.65 (range: 6 -23%)
a Measurements determined from 10 specimens in each category. Morphological measurements are known to vary among colonies of A'u.vu/iterme.v (Thorne. unpub.): the figures given are from termites within a single colony. (Mean k S.D.) b Determined by drying and weighing a number of termites, then dividing their cumulative weight by the number weighed to yield this "average" per individual weight.
c From samples of termites captured while foraging. d Calculated as the average percentage (arcsin transformed) of soldiers in the neuter population (excluding immatures) of 12 colonies. chosen at random and quantitatively dissected. The range among the 12 colonies is also given.



================================================================================

140 Psyche [vo~. 89
In these and several other encounters that night, aggressive interac- tions among colonies were similar to those described earlier. To examine conflicts among colonies and species of sympatric termites I staged laboratory encounters in pairwise tests: soldiers vs soldiers, soldiers vs workers, and workers vs workers. Characteris- tics of the four species used in these experiments are summarized in Table I. Amitermes beaumonti soldiers have curved mandibles; Armitermes chagresi soldiers have long, curved mandibles and a prolonged nasus; and soldiers of Nasutiterrnes corniger and N. ephratae are nasutoid with vestigal mandibles (Fig. 3). METHODS
Experimental trials were conducted in March and April, 1981 in the Smithsonian Tropical Research Institute laboratory on Barro Colorado Island (BCI), Panama (9O 09' N, 79O 51' W). All Ami- terrnes beaurnonti and Armiterrnes chagresi were collected from nests on BCI; samples of Nasutitermes corniger and N. ephratae were from colonies in Frijoles, Panama (4 km east of BCI). Pairwise encounters were staged in petri dish arenas (4.6cm diameter) lined with moist filter paper. Equal numbers of termites, soldiers or workers, from each colony were introduced to an arena simultane- ously. Dishes were then covered and left undisturbed in darkness for 12 hours. After the interaction period survivors were counted: con- spicuously injured individuals were considered as dead. Most worker-worker trials involved 50 individuals from each colony (only large workers (Q) were used from Nasutitermes colonies; Amitermes and Armiterrnes have monomorphic worker castes). When soldiers of Amiterrnes or Armitermes were involved in a trial, and in occa- sional trials involving Amiterrnes or Arrniterrnes workers, fewer individuals were available so experiments proceeded with less than 50 termites from each colony. In Table I1 the number of individuals from each colony used in each trial is indicated in parentheses fol- lowing the survival percentages. A minimum of three trials were conducted for each intra- and interspecific interaction. Each such



================================================================================

t 98 21 Thorne - Termite-Termite Interactions 1 4 1 Figure 3. Termite-termite interactions (Section B), a. Nasuti~ermes rarnTfå£^e workers (dark heads) vs Amiierme.~ (ha~re.C soldiers (light heads). b. N. CW^Ì reefer soldiers vs Airiirermr.v,fure/i workers
c. N. corniger intraspecific worker-war- Tfccer encounter,
d. Ai?iiferti?e~,foreh soldier vs N. ephraiw worker. e. Armiiermes <å -Jza- ereit soldier vs N, cphratae worker.




================================================================================

142 Psyche [vo~. 89
trial pitted termites from different colonies. After the 12 hour encounter all dead termites from selected trials were collected and examined for injuries under a dissecting microscope. RESULTS
Survival percentages of termites involved in each trial are pre- sented in Table 11. For conspecific interactions among members of a single caste (soldier vs soldier or worker vs worker), it was not possible to differentiate colony affiliation so a single survival per- centage is indicated. These figures indicate whether or not a fight ensued, although it is impossible to determine if one colony suffered more or less mortality than the other.
Variability within and between blocks of Table I1 is high. Among some replicates mortality is low for both groups of interacting ter- mites (signified by a '-' at the base of the block). Some encounters suggest consistent "victors", represented by an arrow pointing in the direction of that party. Other groups of interactions indicate agonis- tic behavior on both sides ('+'), without clear assignment of a "winner" or "loser".
AH interspecific worker-worker encounters resulted in a fight, often with a trend suggesting a "dominant" species but with sufficient variation among trials to prevent assigning a "winner". Such varia- tion may result from relative differences in individual colony nutri- tion, age, health, and history. For example, an interaction between two strong colonies may be quite different from a similar encounter between members of a weak and a strong colony. It should be noted that soldiers are absent during worker-worker trials, which may affect the excitability and response of workers. Intraspecific worker-worker engagements demonstrated variable aggression within Nasutitermes corniger and N. ephratae, and no lethal attacks in any of the Amitermes or Armitermes trials. Fight- ing among conspecific Nasutitermes colonies is variable and appar- ently influenced by as yet uninvestigated factors. In these experi- mental trials, aggressive interactions generally occurred, although in all but one N. corniger trial well over half of the workers survived the 12 hour meeting. I have previously observed both extremes in conspecific Nasutitermes corniger encounters: 100% mortality and 100% survival, even among colonies from distant locations. Dudley & Beaumont (1 889a,b) report that mixing two N. corniger colonies



================================================================================

89821 Thorne - Termite-Termite Interactions -43 resulted in lethal fights. Variance in response may be due to ex p ri-
mental protocol, particularly isolation of a colony's soldiers a n d
workers. Under natural conditions a colony's soldiers and work ers may interactwithoneanotherinrecognitionofandresponses- to foreign termites. The soldier secretion has been demonstrated an
alarm pheromone in N. exitiosus, although workers showed 1% "ati tie reaction to fresh secretion presented on an applicator (Eisner P~T 01. 1976).
In these experiments soldiers and workers from different N. c- at-- niger or Armifermes chagresi colonies did not fight, while sold * er- worker conflict did occur in N. ephraiue and A mirermes beaum c^- ytti conspecific encounters, In the field manipulaton involving C cia- s ta Rican N. mrniger (Section A), soldier-worker battles were observ ed. Summarizing other general trends, N. ephratae workers sco *ed relatively well in worker-worker inter-specific encounters, altho u jgh they were not consistent victors over Armiiermes workers. Et 0 t h Amitermes and Armitermes soldiers faired relatively well in rr-̤ -st encounters while Nasuiitermes soldiers were less successful. In in= =a- specific A rmiiermes chagresi interactions, only soldier-soldier c <cr> n- flict was observed; among A mitermes beaumonri, only meetings bet w ^^sen soldiers and workers stirred fighting. Such patterns imply spe: <^= ies differences in communication, meaning, and recognition of a n y colony-specific odors.
Injuries suffered by the dead during the interaction experirne nts were scored for several trials, and are summarized in Table 3B. II. Presence or absence of damage to the abdomen was scored, tho u g h no analysis of extent of abdominal injury was recorded because -Ìà he exact number of wounds or punctures was difficult to assess. T h e percentage of dead with abdominal wounds is generally high. Table II (Following pages): Survival Percentages of Panamanian Termi-t<~~<s in Paired Laboratory Encounters
Pairedencounters were staged matchingequal numbers of termites (number of ind-idu- ah from tach co1ony giken in parenfhews following trial results). The total percent--e of individuals surviving ihe $2 hour meeting is given for intraspecific ddicr-soldier and worker-worker interactions- inability to identify colony aifihation prevented cornpa. å´^-s.~t ivc percentages. All other trials report the survival percentage of the termites listed to t I-*i å´= left overthat oftermites listed on lop. Arrowsal the baseofa block point in thtdirectio- of a
consistent "winner": arrows in parentheses note a less pronounced tendency, '-' indicates few deaths on either side (no fight): '+' signifies lethal interactions ong the termites but with no consistent trend toward a victor.



================================================================================

Table 11: Survival Percentages of Panamanian Termites in Paired Laboratory Encounters
Airiitertnes heaut~ionti Armitermes chagresi Nasutitermes corniger Nasuiifermes ephratae soldiers workers soldiers workers soldiers workers soldiers
workers
Ainitermes
100% survival (8) 33%/ 17% (6)
beaumonti
100% survival (8) 8O%/ 80% (5)
soldiers
93% survival (7) 80%/60% (5)
-
+
Amitermes 100% survival (50)
beauinonti 100% survival (50)
workers
100% survival (50)
Armitermes
chagresi
soldiers
Armitermes
chagresi
workers
100% survival (50)
100% survival (50)
100% survival (50)




================================================================================




================================================================================

146 Psyche [VOI. 89
Table 111:
Analysis of Injuries for 7 Paired Worker-Worker Interactions Percentage
of Mean Number
Individuals o f
with Non-Abdominal
Abdominal Wounds Per
Wounds Antenna! Legs Heads Individual
A rn7itermes chugresi ( 1 0 of 1 2)
\'S
Nusu1i1ern7e.s ephrutue ( 16)
Nusutitermes ephraiae (8)
vs
Nu.su~i/ermes corniger (4 1)
Nasutiiernie'i ephratue ( 12)
vs
Nus~~titern7e.s corniger (43)
Am'nermes beaumonti (32 of 38) 65.6%
vs
Nusu~itermes ephrutue (46) 82.6%
Nasut'nerme.~ corniger ( 19) 73.7%
vs
An7iterme.s beaumon~i (38) 50.0%
Nusutitermex corniger (37) 67.6%
\'S
Amiterme (38) 50.0%
Nusuiiiernie.~ corniger (37) 67.6%
vs
Ami/erme.'i heuutnonti (39) 35.9%
Numbers in parentheses following species names are the number of individuals exam- ined (killed). The colony with the fewest deaths is listed first for each interaction. Descrip- tions of the injury categories and criteria are described in text Section B under Results.



================================================================================

19821 Thorne - Termite-Termite Interactions 147 Damage to each antennae and leg was scored separately, and a