Robert L. Jeanne

The organization of work in Polybia occidentalis: costs and benefits of specialization in a social wasp

SummaryNest construction, a complex social activity requiring the coordination of 3 tasks (Fig.2), was compared in large (<350 adults) and small (<50 adults) colonies of Polybia occidentalis. The 3 tasks—water foraging, pulp foraging, and building—are performed by 3 separate groups of workers (Fig.4). Of the 8 acts comprising the 3 tasks, 5 regularly involve the transfer of water or pulp from one worker to another on the nest.Small colonies required nearly twice as long (35.4 worker-min) as large colonies (20.1 workermin) to complete a unit amount of construction work. Behavioral acts involving material transfer among workers were responsible for most of the increase in small colonies. In other words, the waiting times experienced by material donors and recipients were greater in small colonies. In small colonies workers switched among the three tasks more frequently than in large colonies (Fig. 4). This was the result of more frequent switching by generalists (workers that performed 2 or 3 of the tasks), rather than by a decrease in the proportion of specialists (workers performing only 1 task type) (Fig. 3).The series-parallel system by which Polybia occidentalis organizes nest construction has a major advantage over the series operation of solitary wasps. Pulp foragers collect and carry loads that are 6.1 times as large as builders can work with at the nest, and water foragers bring in loads that appear to be limited only by crop capacity and that provide all the moisture necessary for the complete processing of 0.74 of a foraged pulp load. As a result P. occidentalis can collect and process a given amount of nest material using 2.6 times fewer foraging trips than would be required by the series system. This in turn means that P. occidentalis not only achieves an energy saving that probably more than offsets the increased costs of material handling at the nest, but it reduces the exposure of its foragers to predators in the field.

Methoprene accelerates age polyethism in workers of a social wasp (Polybia occidentalis)

Abstract. Topical applications of the Juvenile Hormone (JH) analogue methoprene to 1‐day‐old adult workers of the highly eusocial wasp Polybia occidentalis (Olivier) (Hymenoptera: Vespidae) accelerate the rate of age polyethism. Longevity of laboratory‐reared wasps is negatively correlated with dose of topically applied methoprene. Doses of 25 μg methoprene or greater are lethal. Untreated wasps show marked age polyethism in the field. Age of first performance of acts in seven behavioural categories (in‐nest, transition to outside, non‐task on nest envelope, nest maintenance, foraged material handling, defence, and foraging) is negatively correlated with methoprene dose. Topical applications of methoprene accelerate age polyethism of highly eusocial bee and wasp workers, but do not have this effect on primitively eusocial bees and wasps, suggesting that JH control of age polyethism evolved independently in advanced species of Apidae and Vespidae.

Forager specialization and the control of nest repair in Polybia occidentalis Olivier (Hymenoptera : Vespidae)

SummaryWe measured patterns of individual forager specialization and colony-wide rates of material input during periods of response to experimental nest damage and during control periods in three colonies of the tropical social wasp Polybia occidentalis.(1)Most foragers specialized on gathering a single material. While active, foragers rarely switched materials, and most switching that did occur was between functionally related materials — prey and nectar (food materials) or wood pulp and water (nest materials).(2)Individuals differed greatly in activity level, here expressed as rate of foraging. Workers that foraged at high rates specialized on a single material in almost all cases. Specialized, highly active foragers comprised a minority (about 33%) of the working foragers in each colony, yet provided most of the material input.(3)Individual wasps that responded to experimental nest damage by foraging for nest materials did not gather food on days preceding or following manipulation.(4)On the colony level, nectar and prey foraging rates were not affected by foraging effort allocated to nest repair within days, or when comparing control days with days when damage was imposed. The emergency foraging response to nest damage in P. occidentalis did not depend on effort recruited away from food foraging.

Nest construction by the paper wasp, Polistes: a test of stigmergy theory

Abstract The paper wasp, Polistes fuscatus , begins building its nest by a linear series of construction steps. Once the first cell is initiated, the building becomes more complex in that any one of several construction acts may be done at any given time. The cues controlling construction during the initial linear series of steps were investigated. The building programme of this wasp was then compared to stigmergy theory, a model of linear construction behaviour which holds that ongoing construction is regulated by previous construction. As predicted by stigmery theory, P. fuscatus uses certain features of already completed construction to provide the cues for subsequent construction. Contrary to predictions from the theory, however, this wasp uses other additional types of cues and evaluates some of the same nest features at each step of construction. Thus, this wasp is able to analyse many different aspects of its nest at one time to determine the correct building sequence and methods, a process more complex than that proposed by stigmergy theory.

Alarm recruitment, attack behavior, and the role of the alarm pheromone in Polybia occidentalis (Hymenoptera: Vespidae)

Summary1.Defensive behavior in the social wasp Polybia occidentalis involves two steps: first, in response to jarring of the nest, large numbers of adults are recruited rapidly to the outer surface of the envelope. Second, a fraction of these wasps may fly out to attack the intruder.2.Observations suggest that the first step, alarm recruitment, is released by a signal given inside the nest. Experimental introduction into the nest of the odors of various glands and body parts show that venom and venom-bearing structures (venom sac, sting apparatus) elicit alarm recruitment that is indistinguishable from that caused by jarring the nest. The wing buzzing that accompanies alarm recruitment is experimentally shown not to communicate alarm.3.Outside the nest, the odor of venom greatly reduces the threshold for release of attack behavior, but is not itself a releaser of attack. The release of attack behavior requires an appropriate visual stimulus. Dark color of models elicited more attacks than did movement.

Group size, productivity, and information flow in social wasps

Social wasp species segregate into two behavioral groups: independent founders, in which queens found new colonies independent of workers, and swarm founders, in which new colonies are founded by swarms comprising several queens accompanied by many workers. Recent work on Polybia occidentalis, a swarm founder, indicates that productivity (measured as nest size and grams of brood reared) per adult per day increases with founding swarm size. I consider four mechanisms than can account for this pattern, and adduce *evidence supporting two of them. First, large colonies appear to allocate a larger proportion of their worker population to foraging for resources. Second, foragers in large colonies transfer their materials to nest workers more efficiently than in small colonies. I suggest that differences in the stochastic properties of small versus large groups lead to shorter queuing delays and a greater ability of large colonies to keep the size of interacting worker groups in balance in the face of perturbations and changing conditions. Finally, I argue that the mode of social organization seen in the swarm founders works most efficiently for large groups, while the simpler organization of independent founders works most efficiently for very small groups.

Chemical communication during swarm emigration in the social wasp Polybia sericea (Olivier)

Abstract Communication during swarming was studied in the social wasp Polybia sericea in Brazil. After the adult population (swarm) evacuates following destruction of the nest, it forms a temporary (0.5- to 2-day) cluster on nearby vegetation and then emigrates to a new nest site. During both phases many adults drag the gaster over leaves and other substrates around the cluster and along the emigration route. The odour left on these objects is identical to that of the copious secretion of an exocrine gland opening at the base of the fifth (penultimate) sternite of the gaster. Following emigration the deposit of secretion in many individuals is depleted and shows signs of disturbance. Experimental evidence is presented to show that the swarm, if chased from its cluster site, reorients to it by means of the scent marks alone. It is further demonstrated that the swarm is guided to its new nest site by the trail of scent marks along the emigration route.

Lifelong patterns of forager behaviour in a tropical swarm-founding wasp: effects of specialization and activity level on longevity

Abstract The relationships between foraging tenure and specialization on materials, and foraging tenure and foraging activity were measured for marked, known-age workers of the social wasp Polybia occidentalis . The purpose of the study was to assess differences in cost to foragers, in terms of risk of mortality, associated with material specializations and activity level, and determine whether ontogenetic changes in forager behaviour reflect these differences in cost, such that more risky patterns of behaviour are postponed until later in adult life. Polybia occidentalis workers terminated foraging at an average of 5·9 days after their first trip, independent of their age at first foraging, suggesting that this task entailed a high risk of mortality. Lifetime foraging activity was calculated as foraging rate (mean number of trips per hour), foraging effort (mean number of time-weighted trips per hour), and as the proportion of observation days that an individual was active during her foraging tenure. Foraging tenure was not related to foraging rate or effort, but had a strong negative relationship with the proportion of observation days during which an individual foraged. By the latter measure, risk of mortality increased with foraging activity. The length of foraging tenure was negatively correlated with the proportion of foraging effort devoted to food materials (nectar and insect prey), supporting the hypothesis that gathering food was riskier than gathering nest materials (water and wood pulp). Foragers that switched between food and nest materials exhibited no tendency to specialize on nest materials first and therefore foraging for riskier materials was not always performed later in adult life. These results are discussed in terms of possible factors regulating task performances at the individual level in social insects.

A Mechanical Signal Biases Caste Development in a Social Wasp

Understanding the proximate mechanisms of caste development in eusocial taxa can reveal how social species evolved from solitary ancestors. In Polistes wasps, the current paradigm holds that differential amounts of nutrition during the larval stage cause the divergence of worker and gyne (potential queen) castes. But nutrition level alone cannot explain how the first few females to be produced in a colony develop rapidly yet have small body sizes and worker phenotypes. Here, we provide evidence that a mechanical signal biases caste toward a worker phenotype. In Polistes fuscatus, the signal takes the form of antennal drumming (AD), wherein a female trills her antennae synchronously on the rims of nest cells while feeding prey-liquid to larvae. The frequency of AD occurrence is high early in the colony cycle, when larvae destined to become workers are being reared, and low late in the cycle, when gynes are being reared. Subjecting gyne-destined brood to simulated AD-frequency vibrations caused them to emerge as adults with reduced fat stores, a worker trait. This suggests that AD influences the larval developmental trajectory by inhibiting a physiological element that is necessary to trigger diapause, a gyne trait.

Recruitment to food by the German yellowjacket, Vespula germanica

Abstract The hypothesis that Vespula germanica foragers can recruit nestmates to food resources was tested using a protocol that controlled for the biasing effects of social factors at the resource, including local enhancement and food-site marking substances. Foragers from an observation colony in the field were trained to visit a dish of scented corn syrup solution 15 m east of the nest. A second feeding station, 22 m northeast of the nest, offered incoming foragers a choice between food with the training scent and food with a control scent. Significantly more naive foragers arriving at that station chose the food with the training scent. We conclude that the German yellowjacket is able to recruit nestmates to carbohydrate food sources, and that recruits use food odor to locate the source of food being brought into the nest.