Potential mechanisms for the communication of height and distance by a stingless bee, Melipona panamica

This study investigates the recruitment communication mechanisms of a stingless bee, Melipona panamica, whose foragers can evidently communicate the three-dimensional location of a good food source. To determine if the bees communicate location information inside or outside the nest, we conducted removal experiments by training marked foragers to one of two identical feeders and then separating these experienced foragers from potential recruits as they left the nest. The feeders were positioned to test the communication of each dimension. The results show that recruits do not simply follow experienced foragers to the food source. Height and distance are communicated within the nest, while direction is communicated outside the nest. We then examined the pulsed sounds produced by recruiting foragers. While unloading food, recruiting foragers produced several short pulses and one or more very long pulses. On average, the longest unloading pulse per performance was 31–50% longer (P ≤ 0.018) for bees foraging on the forest floor than for bees foraging at the top of the forest canopy (40 m high). While dancing, recruiting foragers produced sound pulses whose duration was positively correlated with the distance to the food source (P < 0.001). Dancing recruiters also produced several short sound pulses followed by one or more long pulses. The longest dance pulse per performance was 291 ± 194 ms for a feeder 25 m from the nest and 1858 ± 923 ms for a feeder 360 m away from the nest. The mechanism of directional communication remains a mystery. However, the direction removal experiment demonstrates that newcomers cannot use forager-deposited scent marks for long-distance orientation (>100 m from the nest). Received: 25 September 1997 / Accepted after revision: 31 May 1998     

The role of internal and external information in foraging decisions of Melipona workers (Hymenoptera: Meliponinae)

Social insect foragers have to make foraging decisions based on information that may come from two different sources: information learned and memorised through their own experience (“internal” information) and information communicated by nest mates or directly obtained from their environment (“external” information). The role of these sources of information in decision-making by foragers was studied observationally and experimentally in stingless bees of the genus Melipona. Once a Melipona forager had started its food-collecting career, its decisions to initiate, continue or stop its daily collecting activity were mainly based upon previous experience (activity on previous days, the time at which foraging was initiated the day(s) before, and, during the day, the success of the last foraging flights) and mediated through direct interaction with the food source (load size harvested and time to collect a load). External information provided by returning foragers advanced the start of foraging of experienced bees. Most inexperienced bees initiated their foraging day after successful foragers had returned to the hive. The start of foraging by other inexperienced bees was stimulated by high waste-removal activity of nest mates. By experimentally controlling the entries of foragers (hence external information input) it was shown that very low levels of external information input had large effect on the departure of experienced foragers. After the return of a single successful forager, or five foragers together, the rate of forager exits increased dramatically for 15 min. Only the first and second entry events had large effect; later entries influenced forager exit patterns only slightly. The results show that Melipona foragers make decisions based upon their own experience and that communication stimulates these foragers if it concerns the previously visited source. We discuss the organisation of individual foraging in Melipona and Apis mellifera and are led to the conclusion that these species behave very similarly and that an information-integration model (derived from Fig. 1) could be a starting point for future research on social insect foraging. Received: 16 April 1997 / Accepted after revision: 30 August 1997     

The use of waggle dance information by honey bees throughout their foraging careers

We studied the extent to which worker honey bees acquire information from waggle dances throughout their careers as foragers. Small groups of foragers were monitored from time of orientation flights to time of death and all in-hive behaviors relating to foraging were recorded. In the context of a novice forager finding her first food source, 60% of the bees relied, at least in part, on acquiring information from waggle dances (being recruited) rather than searching independently (scouting). In the context of an experienced forager whose foraging has been interrupted, 37% of the time the bees resumed foraging by following waggle dances (being reactivated) rather than examining the food source on their own (inspecting). And in the context of an experienced forager engaged in foraging, 17% of the time the bees initiated a foraging trip by following a waggle dance. Such dance following was observed much more often after an unsuccessful than after a successful foraging trip. Successful foragers often followed dances just briefly, perhaps to confirm that the kind of flowers they had been visiting were still yielding forage. Overall, waggle dance following for food discovery accounted for 12–25% of all interactions with dancers (9% by novice foragers and 3–16% by experienced foragers) whereas dance following for reactivation and confirmation accounted for the other 75–88% (26% for reactivation and 49–62% for confirmation). We conclude that foragers make extensive use of the waggle dance not only to start work at new, unfamiliar food sources but also to resume work at old, familiar food sources.     

A stingless bee (Melipona panamica) indicates food location without using a scent trail

The study of location specification in recruitment communication by bees has focused on two dimensions: direction and distance from the nest. Yet the third dimension, height above ground, may be significant in the tall and dense forest habitats of stingless bees. Foragers of the stingless bee Scaptotrigona postica recruit to a specific three-dimensional location by laying a scent trail. Stingless bees in the genus Melipona are thought to have a more sophisticated recruitment system that communicates distance through sounds inside the nest and direction through pointing zig-zag flights outside the nest. However, prior research on Melipona has not examined height communication or even established that foragers can recruit newcomers to a specific location. We used identical paired feeders to investigate recruitment to food in M panamica on Barro Colorado Island, Panama. We trained foragers from an observation hive to one feeder and monitored both feeders for the subsequent arrival of newcomers. We changed the relative positions of the feeders to test for correct direction, distance, and canopy-level communication. A 40-m canopy tower located inside the forest enabled us to examine canopy-level communication. We found that M. panamica foragers can recruit to a specific (1) direction, (2) distance, and (3) canopy level. To test the possibility that foragers accomplish this by means of a scent trail, we placed the colony on one shore of a small cove and trained bees over 116 m of open water to a feeder located on the opposite shore. We also placed a second feeder on this shore, equidistant from the colony but 20 m from the first feeder. Significantly more newcomers consistently arrived at the feeder visited by the foragers. Thus foragers evidently do not need a scent trail to communicate direction. Inside the nest, a forager produces pulsed sounds while visibly vibrating her wings after returning from a good food source. She is attended by other bees who cluster and hold their antennae around her, following her as she rapidly spins clockwise and counterclockwise. Locational information may be encoded in this behavior. However, foragers may also directly lead newcomers to the food source. Further experiments are planned to test for such piloting and other communication mechanisms.     

Social foraging by honeybees: how colonies allocate foragers among patches of flowers

Summary To understand how a colony of honeybees keeps its forager force focussed on rich sources of food, and analysis was made of how the individual foragers within a colony decide to abandon or continue working (and perhaps even recruit to) patches of flowers. A nectar forager grades her behavior toward a patch in response to both the nectar intake rate of her colony and the quality of her patch. This results in the threshold in patch quality for acceptance of a patch being higher when the colonial intake rate of nectar is high than when it is low. Thus colonies can adjust their patch selectivity so that they focus on rich sources when forage is abundant, but spread their workers among a wider range of sources when forage is scarce. Foragers assess their colony's rate of nectar intake while in the nest, unloading nectar to receiver bees. The ease of unloading varies inversely with the colonial intake rate of nectar. Foragers assess patch quality while in the field, collecting nectar. By grading their behavior steeply in relation to such patch variables as distance from the nest and nectar sweetness, foragers give their colony high sensitivity to differences in profitability among patches. When a patch's quality declines, its foragers reduce their rate of visits to the patch. This diminishes the flow of nectar from the poor patch which in turn stimulates recruitment to rich patches. Thus a colony can swiftly redistribute its forager force following changes in the spatial distribution of rich food sources. The fundamental currency of nectar patch quality is not net rate of energy intake, (Gain-Cost)/Time, but may be net energy efficiency, (Gain-Cost)/Cost.     

Modelling collective foraging by means of individual behaviour rules in honey-bees

An individual-oriented model is constructed which simulates the collective foraging behaviour of a colony of honey-bees, Apis mellifera. Each bee follows the same set of behavioural rules. Each rule consists of a set of conditions followed by the behavioural act to be performed if the conditions are fulfilled. The set of conditions comprises the state of external information available to the bee (e.g. the dancing of other bees) and internal information variables (like memorised location of a food source and homing motivation). The rules are partly observational (i.e. they capture the observable regularities between the present external information and the individual bee's behaviour), and partly involve hypothesised internal-state variables (e.g. abandoning tendency and homing motivation), because no observable (physiological) aspect has as yet been detected in the bee which correlates with changes in the internal motivation. Our aim is to obtain a set of rules that is necessary and sufficient for the generation of the collective foraging behaviour observed in real bees. We simulated an experiment performed by Seeley et al. in which a colony of honey-bees chooses between two nectar sources of different profitabilities which are switched at intervals. A good fit between observed and simulated collective forager patterns was obtained when the model included rules in which the bees (1) relied on the information acquired from previous flights to a source (e.g. profitability and time of day when the source was found), (2) used positional information obtained by attending recruitment dances and (3) did not abandon a (temporarily) deteriorated source too fast or too slowly. The significance of the following issues is discussed: the role of internal and external information, source profitability, the spatial precision of the dance communication, the ability to search for a source after the source position has been transmitted, the tendency to abandon a deteriorated source, and the concepts of scout, recruit, (un)employed forager, and foraging history. Received: 26 January 1998 / Accepted after revision: 16 May 1998     

The effect of ambient temperature on forager sound production and thoracic temperature in the stingless bee, <Emphasis Type="Italic">Melipona panamica</Emphasis>

Foragers of the stingless bees genus Melipona may produce intranidal sounds that are correlated with food location and quality. In this study, we provide the first detailed analysis of pulsed sounds produced by Melipona panamica foragers while feeding on a carbohydrate food source. We trained foragers to a 2.5-M sucrose feeder under normal, ambient temperature (23–33°C) and lower temperature (11–25°C) conditions. We recorded forager sounds under both conditions and tested the effect of temperature of the thorax, feeder plate, and air on sound temporal characteristics. Forager energetic expenditure and the number of pulses per visit were significantly higher in the cold condition than in the normal condition. Foragers spent a longer time at the feeder under the cold condition than during the normal condition. Interpulse durations were significantly shorter in the cold condition than in the normal condition and became progressively and significantly shorter at the end of each performance. Thus, pulse production increased before departure. Foragers increased their thoracic temperatures above ambient at all experimental air temperatures. Under chilled conditions, foragers had a significantly greater difference between thorax temperature and ambient air temperature than under normal conditions. Foragers must achieve a minimum flight muscle temperature before take-off, and thus forager sounds may be linked to muscle warm-up.     

Honeybee recruitment to scented food sources: correlations between in-hive social interactions and foraging decisions

Information exchange of environmental cues facilitates decision-making processes among members of insect societies. In honeybee foraging, it is unknown how the odor cues of a resource are relayed to inactive nest mates to enable resource exploitation at specific scented sources. It is presumed that bees need to follow the dance or to be involved in trophallaxis with a successful forager to obtain the discovered floral scent. With this in mind, we evaluated the influence of food scent relayed through in-hive interactions and the subsequent food choices. Results obtained from five colonies demonstrated that bees arriving at a feeding area preferred to land at a feeder carrying the odor currently exploited by the trained forager. The bees that landed at this feeder also showed more in-hive encounters with the trained forager than the individuals that landed at the alternative scented feeder. The most frequent interactions before landing at the correct feeder were body contacts with the active forager, a behavior that involves neither dance following nor trophallaxis. In addition, a reasonable proportion of successful newcomers showed no conspicuous interactions with the active forager. Results suggest that different sources of information can be integrated inside the hive to establish an odor-rewarded association useful to direct honeybees to a feeding site. For example, simple contacts with foragers or food exchanges with non-active foragers seem to be enough to choose a feeding site that carries the same scent collected by the focal forager.     

Worker allocation in insect societies: coordination of nectar foragers and nectar receivers in honey bee (Apis mellifera) colonies

Nectar collection in the honey-bee is partitioned. Foragers collect nectar and take it to the nest, where they transfer it to receiver bees who then store it in cells. Because nectar is a fluctuating and unpredictable resource, changes in worker allocation are required to balance the work capacities of foragers and receivers so that the resource is exploited efficiently. Honey bee colonies use a complex system of signals and other feedback mechanisms to coordinate the relative and total work capacities of the two groups of workers involved. We present a functional evaluation of each of the component mechanisms used by honey bees – waggle dance, tremble dance, stop signal, shaking signal and abandonment – and analyse how their interplay leads to group-level regulation. We contrast the actual regulatory system of the honey bee with theory. The tremble dance conforms to predicted best use of information, where the group in excess applies negative feedback to itself and positive feedback to the group in shortage, but this is not true of the waggle dance. Reasons for this and other discrepancies are discussed. We also suggest reasons why honey bees use a combination of recruitment plus abandonment and not switching between subtasks, which is another mechanism for balancing the work capacities of foragers and receivers. We propose that the waggle and tremble dances are the primary regulation mechanisms, and that the stop and shaking signals are secondary mechanisms, which fine-tune the system. Fine-tuning is needed because of the inherent unreliability of the cues, queueing delays, which foragers use to make recruitment decisions. Received: 15 December 1998 / Received in revised form: 6 March 1999 / Accepted: 12 March 1999     

Exploration and exploitation of food sources by social insect colonies: a revision of the scout-recruit concept

Social insect colonies need to explore and exploit multiple food sources simultaneously and efficiently. At the individual level, this colony-level behaviour has been thought to be taken care of by two types of individual: scouts that independently search for food, and recruits that are directed by nest mates to a food source. However, recent analyses show that this strict division of labour between scouts and recruits is untenable. Therefore, a modified concept is presented here that comprises the possible behavioural states of an individual forager (novice forager, scout, recruit, employed forager, unemployed experienced forager, inspector and reactivated forager) and the transitions between them. The available empirical data are reviewed in the light of both the old and the new concept, and probabilities for the different transitions are derived for the case of the honey-bee. The modified concept distinguishes three types of foragers that may be involved in the exploration behaviour of the colony: novice bees that become scouts, unemployed experienced bees that scout, and lost recruits, i.e. bees that discover a food source other than the one to which they were directed to by their nest mates. An advantage of the modified concept is that it allows for a better comparison of studies investigating the different roles performed by social insect foragers during their individual foraging histories. Received: 29 December 1999 / Revised: 25 February 2000 / Accepted: 16 October 2000     

Brood sex ratio is dependent on female mating status in polygynous great reed warblers

Females capable of adjusting the sex ratio of their offspring should be more fit than females lacking such an ability. In polygynous birds where breeding success in males is more strongly influenced by body size and/or attractiveness than in females, females might produce more sons when predicting good conditions or when mating with attractive males. Polygynous great reed warbler, Acrocephalusarundinaceus, males direct most of their feeding effort to the primary (first-hatching) nest and in these nests increase their feeding effort in relation to the brood sex ratio (proportion of sons). Therefore, with the expectation of well-nourished sons, we would predict that females which start breeding first within harems might produce more sons than those which start breeding later, and in anticipation of sons with good genes, that females mated to polygynous males might produce more sons than females mated to monogamous males. I took blood samples from hatchlings and determined the sex using DNA markers. The sex ratio of primary (monogamous and polygynous primary) broods is more male-biased (mean 0.58 males, n = 50) than that of secondary (polygynous secondary and tertiary) broods (mean 0.46, n = 25). Moreover, in the secondary broods with the largest clutch (five eggs), in which offspring are most likely to suffer food shortage, the sex ratio was distinctively female biased (mean 0.33, n = 10). In the primary broods, sex ratio was correlated to harem size. The results suggest that great reed warbler females modify the brood sex ratio to produce both well-nourished sons and sons with good genes, but the former effect is probably stronger than the latter factor. Received: 11 March 1998 / Accepted after revision: 23 May 1998     

Food-exchange by foragers in the hive – a means of communication among honey bees?

Dancing and trophallactic behaviour of forager honey bees, Apis mellifera ligustica >Spinola, that returned from an automatic feeder with a regulated flow rate of 50% weight-to-weight sucrose solution (range: 0.76–7.65 μl/min) were studied in an observation hive. Behavioural parameters of dancing, such as probability, duration and dance tempo, increased with the nectar flow rate, though with very different response curves among bees. For trophallaxis (i.e. mouth-to-mouth exchange of food), the frequency of giving-contacts and the transfer rate of the nectar increased with the nectar flow rate. After unloading, foragers often approached other nest mates and begged for food before returning to the food source. This behaviour was less frequent at higher nectar flow rates. These results show that the profitability of a food source in terms of nectar flow rate had a quantitative representation in the hive through quantitative changes in trophallactic and dancing behaviour. The role of trophallaxis as a communication channel during recruitment is discussed. Received: 14 January 1995/Accepted after revision: 14 August 1995     

On the evolutionary stability of female infanticide

Territoriality among female rodents may have evolved as an adaptation to intraspecific competition for resources or, alternatively, to defend pups against infanticide. In order to evaluate the latter, we analyse the conditions that allow an infanticidal strategy to invade a population of non-infanticidal females, and the circumstances under which infanticide may become an evolutionarily stable strategy (ESS). Our game theoretical analyses indicate that infanticide has to be associated with some direct (cannibalism) or indirect (reduced competition) resource benefits in order to invade a non-infanticidal population. We also expect that females will primarily kill litters of nearby neighbors, thereby removing the closest competitors while keeping costs at a low level. However, once established in a population, infanticide may be an ESS, even if females do not gain any resource benefits. This is theoretically possible if a female through infanticide can reduce the possibility that other, potentially infanticidal, females establish and/or stay close to her nest. While behavioral data indicate that these special circumstances sometimes occur, they may be too specific to apply generally to small rodents. Therefore, we expect that the evolutionary stability of infanticide often requires resource benefits, and that female infanticide in small rodents may, in fact, be a consequence rather than a cause of territoriality. Received: 27 June 1996 / Accepted after revision: 28 December 1996     

Honey bee waggle dance communication: signal meaning and signal noise affect dance follower behaviour

Returning honey bee foragers perform waggle dances to inform nestmate foragers about the presence, location and odour of profitable food sources and new nest sites. The aim of this study is to investigate how the characteristics of waggle dances for natural food sources and environmental factors affect dance follower behaviour. Because food source profitability tends to decrease with increasing foraging distance, we hypothesised that the attractiveness of a dance, measured as the number of dance followers and their attendance, decreases with increasing distance to the advertised food location. Additionally, we determined whether time of year and dance signal noise, quantified as the variation in waggle run direction and duration, affect dance follower behaviour. Our results suggest that bees follow fewer waggle runs as the food source distance increases, but that they invest more time in following each dance. This is because waggle run duration increases with increasing foraging distance. Followers responded to increased angular noise in dances indicating more distant food sources by following more waggle runs per dance than when angular noise was low. The number of dance followers per dancing bee was also affected by the time of year and varied among colonies. Our results provide evidence that both noise in the message, that is variation in the direction component, and the message itself, that is the distance of the advertised food location, affect dance following. These results indicate that dance followers may pay attention to the costs and benefits associated with using dance information.     

Parentage and sex allocation in the facultatively polygynous ant Myrmicatahoensis

Most social groups have the potential for reproductive conflict among group members. Within insect societies, reproduction can be divided among multiple fertile individuals, leading to potential conflicts between these individuals over the parentage of sexual offspring. Colonies of the facultatively polygynous ant Myrmicatahoensis contain from one to several mated queens. In this species, female sexuals were produced almost exclusively by one queen. The parentage of male sexuals was more complex. In accordance with predictions based on worker sex-allocation preferences, male-producing colonies tended to have low levels of genetic relatedness (i.e., high queen numbers). Correspondingly, males were often reared from the eggs of two or more queens in the nest. Further, over half of the males produced appeared to be the progeny of fertile workers, not of queens. Overall investment ratios were substantially more male biased than those predicted by genetic relatedness, suggesting hidden costs associated with the production of female sexuals. These costs are likely to include local resource competition among females, most notably when these individuals are adopted by their maternal nest. Received: 3 March 1998 / Accepted after revision: 20 June 1998     

Social foraging in stingless bees: how colonies of Melipona fasciata choose among nectar sources

In an experimental set-up, a colony of the stingless bee Melipona fasciata demonstrated its ability to choose the better of two nectar sources. This colony pattern was a result of the following individual behavioural decisions: continue foraging, abandon the feeder, restart foraging and initiate foraging. Only very rarely did individuals switch from one feeder to the other. With the first combination of a rich (2.7 M) and a poor (0.8 M) feeder M. fasciata behaved differently from Apis mellifera. Recruitment occurred to both feeders and the poor feeder was not abandoned completely. When the poor feeder was set to 0.4 M, M. fasciata abandoned the poor feeder rapidly and allocated more foragers to the rich feeder. These patterns were similar to those reported for A. mellifera with the first combination of feeders. Over a sequence of 4 days, experienced bees increasingly determined the colony patterns, and the major function of communication between workers became the reactivation of experienced foragers. The foragers modulated their behaviour not only according to the profitability of the feeder, but also according to previous experience with profitability switches. Thus, experience and communication together regulated colony foraging behaviour. These findings and the results of studies with honeybees suggest that M. fasciata and honeybees use similar decision-making mechanisms and only partly different tools. Received: 21 December 1998 / Accepted: 5 January 1999     

The role of a scent beacon in the communication of food location by the stingless bee, Melipona panamica

Melipona panamica foragers can deposit a scent beacon that influences the orientation of foragers near a food source. In misdirection experiments, newcomers (bees from the same colony as trained foragers) consistently preferred the feeder at which trained foragers had fed (training feeder) over an identical feeder at which bees had never fed (control feeder) even when the training feeder was placed at a site where experienced foragers had never foraged. Through similar misdirection experiments, the effective radius of the scent beacon was determined to be greater than 6 and less than 12 m. Foragers may deposit this beacon during a sequence of departure behaviors performed at the feeder. Prior to leaving the feeder with a load of sugar solution, bees tended to perform the following sequence of behaviors: (1) spinning, (2) grooming, (3) abdomen dragging, (4) excreting anal droplets, and (5) producing sounds, although not all behaviors were performed prior to each departure or at all sucrose concentrations (0.5–2.5 m). As sucrose concentration increased, the number of newcomers significantly increased, and the number of experienced foragers producing sounds and spinning on the feeder increased. The exact source of the scent beacon remains a mystery. However, three important sources have been excluded. When choosing between identical paired feeders, foragers were not attracted to the feeders with (1) anal droplets, (2) extracts of sucrose solution at which foragers had fed, or (3) mandibular gland extracts. They were indifferent to the first two preparations and exhibited only typical alarm behavior towards the mandibular gland (MG) extract: they oriented towards the feeder with MG extract but consistently landed on the feeder with no MG extract. Other authors have suggested that Melipona foragers deposit anal droplets to attract recruits, however the frequency of anal droplet production and the mass of anal droplets produced by M. panamica foragers are negatively correlated with sucrose concentration. Thus the scent beacon is evidently not deposited with anal droplets, infused into the feeder solution, or produced by mandibular glands. Received: 2 September 1997 / Accepted after revision: 30 January 1998     

Changes in male guppy courting distance in response to a fluctuating light environment

In the guppy (Poecilia reticulata), effective courting by a male requires visual contact with the female. Therefore, environmental light intensity may affect male display behavior, particularly initial courtship distance. We found that male guppies courted at exact and predictable distances from the female given a particular light level, both in field and laboratory studies. In lower light levels (<0.1 μmol m⁻² s⁻¹), for example at dawn, dusk, or under heavy canopy, males court females at closer and less variable distances (<3 cm). At higher light levels, which occur during most of the day and with less canopy cover, males often court from twice or three times further out. Light levels over guppy streams change over relatively short time periods and ranges, correlating with variation in courtship distances. Laboratory manipulations of irradiance confirmed that courtship distance depends on illumination. Hence, courtship distances may be set by the effect of lighting on signal efficiency, minimization of energy or time expenditures, or predation risk. Received: 16 December 1997 / Accepted after revision: 8 August 1998     

Disease resistance: a benefit of sociality in the dampwood termite Zootermopsis angusticollis (Isoptera: Termopsidae)

The benefit of sociality in relation to disease susceptibility was studied in the dampwood termite Zootermopsis angusticollis. Although contact with high concentrations of fungal conidia is lethal, the survivorship of nymphs exposed to spore suspensions ranging from 6 × 10⁶ to 2 × 10⁸ spores/ml of the fungus Metarhizium anisopliae increased with group size. The survivorship (measured as LT₅₀) of isolated individuals ranged from 3.0 to 4.8 days, but infected nymphs living in groups of 10 and 25 individuals survived significantly longer (5.6–8.3 and 5.6–9.1 days, respectively). In most cases, there were no significant differences in the survival distributions of the 10- and 25-termite groups. When nymphs were infected with concentrations of 7 × 10¹–7 × 10⁴ spores/ml and allowed to interact with healthy nestmates, fungal infections were not contracted by the unexposed termites. Moreover, infected termites benefitted from social contact with unexposed nestmates: their survival rates were significantly higher than those of infected termites living with similarly infected nestmates. Allogrooming, which increased in frequency during and after exposure to conidia, appeared to remove potentially infectious spores from the cuticle, thus increasing termite survivorship. These results suggest that allogrooming plays a crucial role in the control of disease and its death hazard in termites. The infection-reducing advantage of group living may have been significant in the evolution of social behavior in the Isoptera. Received: 18 March 1998 / Accepted after revision: 31 May 1998