Forces affecting water imbibition inMacrotermes workers (Termitidae,Isoptera)

Summary Observations of putative drinking behaviour at soil surfaces by major workers ofMacrotermes subhyalinus andM. bellicosus suggested that unidirectionally arranged trichomes on the anterior hypopharynx exert capillarity on water in soil pores. To test this hypothesis thirsty major workers were placed on soil of relatively low water content. From the soil types tested we determined soil-moisture retention curves which represent graphically the water content of the soil and its corresponding capillary potential. The termites were able to obtain water from different types of clay soil against potentials in the range – 1.6 to – 1.9 bar. On sandy soil the capillary potential was found to be much higher (– 0.18 bar), i.e. closer to zero. Sandy soil has a very unfavourable water retention capacity, i.e. its water content is very low at low capillary potential, whereas clay soil retains much more water at low capillary potential. The ability of the termites to gain water from soils with relatively low water content is an important adaptive feature for survival in semi-arid areas.     

Task-specific distribution of the two worker castes in extranidal activities inMacrotermes bellicosus (Smeathman): Observation of behaviour during food acquisition

Summary Caste-specific division of labour can be observed in extranidal activities inMacrotermes bellicosus. Food is acquired through a sequence of tasks shared between the two worker castes. During the exploration phase, a network of subterranean galleries is built outwards from the nest, almost exclusively by minor workers. The frequency of excursions made by major workers during this building period is low, but increases significantly when food is needed by the colony. After a food-source has been discovered, it is hardly exploited by the minor workers and no recruitment occurs. They continue to construct galleries, while individuals which have contact with the food show local fidelity in their building activities within the gallery nearest to the food. After a single sporadic major worker accidentally comes across a food-source, the ratio of major to minor workers continually increases. New major workers aim for the food, bite off pieces and may transfer them to the minor workers. In general, only major workers are recruited after food has been discovered, and they then orientate towards the food-source more distinctly than the minor workers.     

Morphology of the gallery system around the nest and gallery development under experimental conditions in the termiteMacrotermes bellicosus (Smeathman)

Summary In the Ivory Coast (Côte d'Ivoire) we analysed the structures and the lay-out of the underground gallery system of the fungus-growing termiteMacrotermes bellicosus. We found a radial pattern of principal and lateral galleries, as well as caves, depressions and vertical passages reaching a depth of 1–2 m. According to the results of our investigations the gallery networks built byM. bellicosus are unique among all known termite species;M. bellicosus constructs the densest (3.1 m/m²) and most superficial (2–6 cm under the surface) gallery networks among all comparable termite species investigated.Under experimental conditions involving an observation arena with a glass bottom, we were able to observe the dynamics of the radial development of the exploratory passages. We also observed the manner and rapidity of the termites' exploration of new ground, as well as the role played by the discovery of food in the design of the gallery system.We were able to show that, when food was scarce, the termites gained access to the arena much more rapidly, built a much denser gallery system and came up to the surface more frequently.     

Resource availability and distribution patterns, indicators of competition between Macrotermes bellicosus and other macro-detritivores in the Comoé National Park, Côte d'Ivoire

Interspecific competition has rarely been demonstrated in field studies. For it to occur a resource must be in limited supply and potential competitors must be concurrently active in time and space. We studied the availability of plant litter during the course of the year and the activity and distribution of macro‐detritivores (termites, diplopods and earthworms) in two habitats in a Guinea savanna (Côte d'Ivoire), to test whether interspecific competition might be important. Plant litter was limited during the rainy season in the savanna, but was never limited in the gallery forest. The termite Macrotermes bellicosus, the dominant macro‐detritivore in this area, and other detritivorous termites (e.g. Microtermes spp., Ancistrotermes spp., Odontotermes spp.) were active all year round with a peak during the rainy season, when diplopods and earthworms were also active. In the savanna at the beginning of the rainy season when food became limiting, other detritivorous termite species were more active in the absence of M. bellicosus than in its presence. This complementary activity pattern of M. bellicosus and other termites indicates that interspecific competition among detritivorous termites may be occurring. However, the spatio‐temporal distribution of diplopods and earthworms suggests that interspecific competition with M. bellicosus is of minor importance.     

Colour variation and polyethism of the soldier caste in the termite Macrotermes bellicosus

Based on abdominal colour three categories of major soldiers were found in Macrotermes bellicosus (Smeathman) (Isoptera: Termitidae). The three main colour types, yellow, red and brown are due to the colour of the defence-secretion stored in the labial gland's reservoirs. The order of these categories correlates with the uric acid titres of the whole individuals. It is concluded that colour could be used as a label for the relative age of a soldier. Age dependent polyethism was observed in soldiers: the individuals of the highest age class were the only ones leaving the nest to accompany the foraging workers, whereas all age categories were found inside the nest. After a significant loss of old individuals younger individuals show flexibility by replacing the missing outgoing nestmates. Caste regulation takes place by an increased rate of soldier development.     

Hunting strategy of a generalist ant species proposed as a biological control agent against termites

We studied the hunting behaviour of Myrmicaria opaciventris (Hymenoptera: Formicidae) in order to evaluate if it can be used as a biological control agent against the termites that damage sugarcane plantations. Hunting workers foraged in groups and recruited nestmates at short-range when they encountered large termite soldiers or groups of small termite workers. Differences in prey capture concerned the: (1) means of detection (from a distance or by contact); (2) termite body part seized (small termites seized by the body; large termites by an appendage); (3) percentages of prey abandoned; and (4) use of venom. The sting of the workers is spatulated implying a topical application of the venom on the prey. Large termites were stretched by several workers whose adherence to the substrate is facilitated by well-developed arolia and claws on the legs while others spread venom on the body and carved it up. An adaptation to termite capture was noted with a distribution of tasks between the workers which subdued prey, and those which transported it. In the former case, the workers easily eliminated termite soldiers, successively attacked several termite workers and even captured new individuals while holding the first ones captured between their mandibles before retrieving them all at once. The remaining individuals were retrieved by the transporting workers. Given this particularly effective predatory strategy, we concluded that, under certain conditions, M. opaciventris can be used as a biological control agent against termites.     

Thermoregulation of termite mounds: what role does ambient temperature and metabolism of the colony play?

Summary: Termites are well known for their ability to regulate the environment of their nest such as temperature and humidity. The influence of fluctuating ambient temperature and mound characteristics on mean nest temperature and daily fluctuation of nest temperature was analysed quantitatively in the fungus-cultivating, mound-building termite Macrotermes bellicosus (Macrotermitinae) in the savanna of the Comoé National Park (Côte d'Ivoire). Additionally, the nest temperatures of inhabited and uninhabited mounds were compared to analyse the contribution of ambient temperature to nest temperature in relation to metabolic heat production of the termites and their fungi. Mound structure alone resulted in a relatively constant nest temperature. Abiotic heat production via solar radiation alone yielded nest temperatures that corresponded to mean ambient temperatures. However, only the production of metabolic heat by the termites and the fungi increased these temperatures to the actual nest temperature. Therefore, and due to the high heat capacities of the mounds, large colonies (mound height above 2.0 m) had higher nest temperatures than smaller ones. Only large colonies attain constant nest temperatures of 30 °C that are largely independent from ambient temperatures and optimal for the growth and development of the termites and their fungi.     

New observations on the tool-behavior of chimpanzees from Mt. Assirik (Senegal,West Africa)

The tool-behavior of chimpanzees were studied at the Mt. Assirik, in the Parc National du Niokolo-Koba, Senegal from December 1982 to June 1983 and from February 1985 to January 1986. Five leaf-stalks to obtain termites ofMacrotermes subhyalinus species and four sticks to obtain honey (this is the first report on the use of tools to obtain honey by wild chimpanzees in far western Africa) were found; we also report the first evidence of tools probably used as hammers to break open hard-shelled fruits ofAdansonia digitata. We conclude that Mt. Assirik chimpanzees provide evidence of a certain cultural behavior related to the use of stones.     

A novel hypothesis for the origin of the sexual division of labor in termites: which sex should be soldiers?

Sexual specialization and skewed sex ratios of the altruistic castes, especially soldiers, are common in many termite taxa. However, no theoretical or empirical studies have explained the origin of the sexual division of labor in termites. In most termite species, female alates are larger than male alates, and mature queens are much larger than kings, with females under consistent selection for high fertility. Therefore, females usually have the potential to be larger than males. Here, I present a novel preadaptation hypothesis that potential sexual differences in the suitability for the caste give rise to the sexual division of labor, and I provide the first evidence in support of this hypothesis in termites. Defense in Reticulitermes is typically performed by soldiers via mandibular and phragmotic defense in which soldiers with pluglike heads block openings, thus preventing enemies from invading the nest. Phragmotic defense requires that soldiers have heads wide enough to plug nest openings. Therefore, a size threshold for workers that develop into soldiers is a likely adaptation for effective defense. I show that sexual size dimorphism (SSD) and a size threshold for soldiers promote skewed sex ratios. A female-biased soldier sex ratio was observed in species with SSD, whereas there was no bias in soldier sex ratio in species without SSD. Thus, SSD and soldier sex ratio data from several Reticulitermes species support the preadaptation hypothesis.     

Does lack of intraspecific aggression or absence of nymphs determine acceptance of foreign reproductives in <Emphasis Type="Italic">Macrotermes</Emphasis>?

The rejection or acceptance of a foreign reproductive by an alien colony may not always be as straightforward as cue recognition between worker termites. This paper aims to determine whether adoption of foreign reproductives is caused simply by lack of intraspecific aggression or is contingent on the reproductive status of the host colony. In the fungus-culturing termites, Macrotermes gilvus (Hagen) and Macrotermes carbonarius (Hagen), major workers showed low intraspecific aggression towards non-nestmates irrespective of geographic distance between source colonies. Our results indicated that workers were hardly aggressive towards non-nestmates. In royal cell-swapping experiments, both species responded in a similar way: (1) in host colonies with nymphs present, the foreign reproductives were rejected; while (2) in host colonies without nymphs the foreign reproductives were either accepted and breeding resumed or the host colonies died eventually. Workers from the host colonies preferentially maintained offspring nymphs from which adultoid replacement reproductives develop rather than accepting foreign reproductives. There is no fitness gain for the queenless workers in accepting foreign reproductives; however, there is overall benefit to the newly born population.     

Effect of some biological factors on soil variability in the tropics

Summary Observations of a selected area in the forest zone of south western Nigeria indicate that the distribution ofMacrotermes bellicosus (Smeathman) andMacrotermes subhyalinus (Rambur) mounds are mainly affected by the drainage conditions of the soils along a toposequence. Higher number of mounds are observed on the better drained soils, ranging from 35.4 to 17.2 mounds/ha covering an area of respectively 0.84 and 0.10 per cent. The shallow and poorly drained soils show lower mound density (<1 mound/ha). The mound soil bears close resemblance to the subsoil, has higher clay content, lower pH, organic C, CEC and extractable P, but higher P retentio than the adjacent surface soil. Growth of maize (Zea mays L.) and soybean (Glycine max. (L.) Merrill) was poorer in the mound soil than in the surface soil. The problem of increased soil variability when large number of mounds are encountered in the field is discussed.     

Evaluation of predation risk in the collectively foraging termite Macrotermes bellicosus

Summary. Few studies have investigated foraging decisions in collectively foraging social insects with no studies in termites. In termites predation is assumed to be a key mortality factor. Therefore, we experimentally investigated the role of predation pressure in foraging decisions of the fungus cultivating, mound building termite Macrotermes bellicosus in two habitats of the Comoé National Park (Ivory Coast). We used the indirect approach of measuring the Giving up Density (GUD), which is the amount of food left when individuals stop foraging in a food patch, whilst experimentally varying predation pressure. Three different conditions were examined: (a) natural predation, (b) no predation, and (c) experimental predation through artificial removal of termites. In the shrub savanna, foraging termites responded to increasing predation with increasing GUDs. By contrast, in the gallery forest, there was no gradual response. Instead termites abandoned a food patch immediately after an attack by predators. Without predation GUDs were lower in the savanna than in the gallery forest indicating that food had a higher value in the former habitat. This, together with the differential behavioral responses to predation, was in accordance with high availability of food in the gallery forest and a limited supply of food in the savanna. Thus, according to our results termites traded off predation pressure differently, according to the availability of food in both habitats.     

Behavioral Interactions Between <Emphasis Type="Italic">Aphaenogaster rudis</Emphasis> (Hymenoptera: Formicidae) and <Emphasis Type="Italic">Reticulitermes flavipes</Emphasis> (Isoptera: Rhinotermitidae): The Importance of Physical Barriers

Predation pressure from ants is a major driving force in the adaptive evolution of termite defense strategies and termites have evolved elaborate chemical and physical defenses to protect themselves against ants. We examined predator–prey interactions between the woodland ant, Aphaenogaster rudis (Emery) and the eastern subterranean termite, Reticulitermes flavipes (Kollar), two sympatric species widely distributed throughout deciduous forests in eastern North America. To examine the behavioral interactions between A. rudis and R. flavipes we used a series of laboratory behavioral assays and predation experiments where A. rudis and R. flavipes could interact individually or in groups. One-on-one aggression tests revealed that R. flavipes are vulnerable to predation by A. rudis when individual termite workers or soldiers are exposed to ant attacks in open dishes and 100% of termite workers and soldiers died, even though the soldiers were significantly more aggressive towards the ants. The results of predation experiments where larger ant and termite colony fragments interacted provide experimental evidence for the importance of physical barriers for termite colony defense. In experiments where the termites nested within artificial nests (sand-filled containers), A. rudis was aggressive at invading termite nests and inflicted 100% mortality on the termites. In contrast, termite mortality was comparable to controls when termite colonies nested in natural nests comprised of wood blocks. Our results highlight the importance of physical barriers in termite colony defense and suggest that under natural field conditions termites may be less susceptible to attacks by ants when they nest in solid wood, which may offer more structural protection than sand alone.     

Experimental manipulation of termites (Isoptera,Macrotermitinae) foraging patterns in a Sahelo-Sudanese savanna: effect of litter quality

Summary The foraging pattern of four sympatric fungus-growing termite species was followed for five months of the dry season in a semi-arid savanna (Senegal). Experimental plots were established with and without termites (exclusion with insecticide) and amended with different litter quality: Acacia leaves, millet canes, ground millet (<500 µm), Combretum wood and cattle manure. Results showed different foraging patterns between the fungus-growing species. Odontotermes nilensis, for example, rapidly developed its foraging activity on the litter. In contrast, Macrotermes subhyalinus delayed its foraging activity but, extensively collected the food after its discovery. Differences in food preference were evident between the termite species: Odonto-termes nilensis foraged preferentially on millet, canes and Acacia leaves, Macrotermes subhyalinus preferred cane and ground millet. Ancistrotermes guineensis selected the millet, and Microtermes sp. was mostly recorded foraging on pieces of dead wood. Relationships between different foraging parameters were established to assess the relative intensity of this activity over the dry season. The comparison between untreated plots and plots treated with Fipronil® (Aventis) clearly demonstrated that the exclusion of termites from part of the savanna is possible and that this possibility can be used to study their role on the soil and organic matter cycle in situ.     

Origin and formation of the royal fat body of the higher termite queens

The formation of the royal fat body was studied by electron microscopy in three species of higher termites (Macrotermes bellicosus, Macrotermes subhyalinus, and Cubitermes fungifaber). The swarming alate imago has a storage fat body typical of most insects. In non-physogastric young queens, during the fasting period, the adipocytes deplete their reserves and then, along with the increased vitellogenesis, acquire protein-synthesizing structures (R.E.R.). During the development of physogastry they progressively specialize in protein synthesis and secretion and undergo many cell divisions. The cytological change is paralleled by a spatial reorganization of the fat body. Observations on the transformation of imaginal adipocytes into royal adipocytes show that the royal fat body is derived from the imaginal fat body and not from the tracheal cells as previously claimed.     

Kin recognition in a semi-natural context: Behaviour towards foreign conspecifics in the social waspRopalidia marginata (Lep.) (Hymenoptera: Vespidae)

Summary Female wasps of the tropical primitively eusocial speciesRopalidia marginata are known to discriminate unfamiliar nestmates from unfamiliar non-nestmates outside the context of their nests. Here, we show that when foreign conspecifics are introduced in the context of a nest in laboratory cages, genetic relatives among them are treated by nest inhabitants more tolerantly than non-relatives, but that no foreign conspecifics are accepted into the nests. However, some wasps may leave their nest and join the foreign relatives and non-relatives to found new colonies cooperatively. Very few of the introduced animals are severely attacked or killed; most are allowed to remain in parts of the cage away from the nest. These results suggest that factors other than genetic relatedness may be involved in regulating tolerance and acceptance of foreign conspecifics on a nest and its vicinity. Our results are different from those of similar experiments with ants, which have demonstrated that former nestmates that are removed as pupae and later introduced as adults are either accepted into the nest or attacked and killed. We attribute this difference to the fact that in a primitively eusocial species such asR. marginata, the rules governing tolerance and acceptance of foreign conspecifics must be quite different from those in highly eusocial species. We also attempt to test some predictions of the conspecific acceptance threshold models of Reeve (Am. Nat. 133:407–435, 1989). Our results uphold the predictions of his fitness consequence submodel but do not support those of his interaction frequency sub-model.     

Effects of controlled livestock grazing and annual prescribed fire on epigeal termite mounds in a savannah woodland in Burkina Faso

The diversity and abundance of epigeal termite mounds were investigated in response to controlled livestock grazing and annual prescribed fire in a Sudanian savannah-woodland in Tiogo State Forest. Sampling of termite mounds was carried out in 4×4 subplots of 0.25 ha in a split-plot experimental design during the rainy season in 2002. There were two main plots of which one was fenced to exclude livestock grazing and the second exposed to grazing. Each of the main plots included 4 subplots with annual prescribed fire since 1992 and 4 subplots without fire. Data were collected on the number and characteristics of termite mounds. A mean density of 698 mounds ha⁻¹ was recorded. Mounds built by Trinervitermes spp. were the most abundant followed by Cubitermes spp., Macrotermes subhyalinus and M. bellicosus. The large mound-builders Macrotermes spp. dominated the community interms of basal area (96% of the total) and above-ground volume (99%). The diversity of mound types was notaffected by livestock grazing and annual early prescribed fire (P>0.05). There was no statistical effect of livestock grazing on mound density, whereas a strong depressive effect of annual fire was observed for Trinervitermes spp. mound density (P=0.012). In this ecosystem, annual prescribed fire appeared to be the major determinant for termite mound abundance. Received 2 February 2007; revised 23 October 2007 and 21 January 2008; accepted 22 Feburary 2008.     

Observation of group recruitment to prey in a primitive ponerine ant,Amblyopone sp. (reclinata group) (Hymenoptera: Formicidae)

Summary Group recruitment during foraging was observed in a primitive ponerine ant,Amblyopone sp. (reclinata group) under laboratory condition. Workers searched for prey singly; however, if a item of prey was stung by a worker, other ants joined the attack. After the prey became immobile, one of the workers laid a trail directly toward the nest. This scout worker recruited additional workers (between 3 and 33). They formed a single file procession to the point of prey capture, and cooperatively transported the prey. A scout worker could stimulate nest workers to leave the nest without direct contact, and the recruited workers could trace the trail without guidance by the scout worker. This is the first report of recruitment behavior during foraging in the primitive antAmblyopone.     

X‐ray computed tomography reveals that intraspecific competition promotes soldier differentiation in a one‐piece nesting termite

Investment in soldier production in eusocial lineages involves a trade‐off between maintenance costs and defense benefits. Termites are eusocial insects that live in colonies organized into three castes: primary reproductives, soldiers, and workers or pseudergates. Neotermes chilensis (Blanchard) (Isoptera: Kalotermitidae) is a one‐piece nesting termite that nests and forages in a single piece of wood. Two scenarios may be of importance in a defense context of one‐piece nesting termites: during swarms, when colonies may be invaded by winged termites (alates) in search of a place to found a new colony, and when colonies of conspecifics are present within the same substrate. It was hypothesized that the ratio of soldiers to non‐soldiers would be higher at the onset of the swarming period and in substrates bearing more than one termite colony. A method based on X‐ray computed tomography (CT) was developed to study gallery connectivity in colonies of N. chilensis and caste composition within colonies. Computed tomography allowed the digital reconstruction of the galleries within the substrate, even when they belonged to different colonies, and was effective in distinguishing termites from substrate, and soldiers from reproductives and pseudergates. Using CT, the ratio of soldiers to non‐soldiers was shown to be highest in colonies within multicolonial scapes (i.e., neighboring colonies were present in the same substrate) during the swarming season, thus supporting our initial hypotheses. These results constitute a unique example of induced defenses arising from intraspecific interactions in termites.     

Dimorphic ergatoid males and their reproductive behavior in the ponerine antHypoponera bondroiti

Summary We studied the reproductive behavior of the ponerine antHypoponera bondroiti from Okinawa, Japan. This species has dimorphic wingless ergatoid males (major and minor), dimorphic reproductive females (alate queens and wingless reproductive intercastes), and workers. Workers have neither ovarioles nor spermatheca. Major ergatoid males are the largest colony members. Two major males fought one another in the nest until one disappeared, leaving the other to occupy the nest chambers where queens emerge and mate. Minor ergatoid males also fought one another, although they seemed to be less pugnacious, resulting in occasional cohabitation of multiple minor males in the same nest chamber. Major males never attacked minor ones, allowing them to coexist in the same nest chamber. Minor males seemed to mimic females. Both major and minor males mated with both alate queens and intercastes within the nest. After mating, some alate queens shed their wings and remained in the nest, while the others left the nest for dispersal in the laboratory. Intercastes remained in the nest.