Influence of Illuminance and Forager Experience on Use of Orientation Cues in Social Wasps (Vespinae)

We tested the influence of illuminance and level of forager experience on nest orientation behavior of the social wasps Vespula vulgaris, Vespa crabro, and Dolichovespula saxonica in an artificial laboratory tunnel system. The number of wasps which oriented themselves chemically via a terrestrial trail or used visual orientation were determined at different illuminance levels for foragers which were naïve or experienced with the tunnel system. In V. vulgaris and D. saxonica, mainly the young and naïve foragers used the chemical trail for orientation in brightness. Experienced foragers used visual cues for nest orientation. In V. crabro, naïve and experienced foragers followed the chemical trail in a similar intensity. In darkness, when visual orientation was limited, the relative importance of the chemical trail increased dramatically in all species and all experience classes.     

Memory and chemical communication in the orientation of two mass-recruiting ant species

Summary The relative contribution of visual and chemical components in the orientation ofLasius niger andIridomyrmex humilis (Argentine ant) workers during mass recruitment to newly discovered food sources is analyzed over short time intervals. While both species orient in response to the trail pheromone, a large number ofL. niger foragers rapidly switch to a more individual orientation, based on their memory of environmental cues.I. humilis workers, on the other hand, predominantly use collective chemical cues. The effect of the number of reinforcements on visual learning and its interference with chemical communication show that olfactory cues always prevail in the Argentine ant. InL. niger, the proportion of ants orienting to visual cues is independent of the trail concentration. Detailed observations of the trail-laying behavior of individually marked foragers show that nearly all theI. humilis workers initially lay a trail, whereas only half theL. niger foragers do so. This proportion decreases considerably with the number of trips performed byL. niger workers, while remaining constant for the Argentine ants. These results are interpreted with respect to the species' behavioral ecology.     

Use of terrestrial chemical trails for nest orientation in an open nesting wasp, <Emphasis Type="Italic">Dolichovespula saxonica</Emphasis> F.

Summary The long-cheeked wasp Dolichovespula saxonica typically constructs exposed nests which can be reached by flying. Usually foragers do not walk on substrates in the close vicinity of the nests as cavity breeding wasps do (Steinmetz et al., 2002). Unexpectedly, when forced to walk outside the nest instead of flying in an artificial tunnel system, D. saxonica foragers lay a terrestrial trail and use it for orientation in the nest area in our experiments. 41% of the foragers followed the trail in a direction they were not accustomed to. We suggest that the foragers have employed the same orientation cues normally used for orientation in the close vicinity of the nest when approaching a free-hanging nest by flying, for example nest odour. Nest odour substances may have been transferred to the substrate as a trail as a consequence of foragers walking through the tunnels.Received 23 August 2002; revised 27 January 2003; accepted 30 April 2003.     

Chemical trail systems,orientation, and territorial interactions in the antLasius neoniger

Foraging and territoriality in the ant Lasius neonigerinvolves a series of trails which channel foragers away from adjacent colonies. Experimental studies suggest that the trails are composed of colony-specific, persistent orientation components of hindgut material that accumulate on trails during foraging. A less durable component of the hindgut trail pheromone regulates recruitment. Foraging directionality and the use of a trail could be modified by experimentally arranging confrontations with conspecifics. The orientation of foragers is mediated by visual as well as chemical cues. Components of the foraging and territorial system of L. neonigerappear to include (1) a network of subnests which change in position seasonally within each polydomous nest; (2) a series of trails emanating from each subnest that adjusts search toward resource patches and away from aggressive, neighboring conspecifics; and (3) trail communication involving an ephemeral component of the hindgut trail pheromone that regulates the organization of cooperative prey retrieval and a more persistent component that serves as an orientation guide.     

Orientation and Communication in the Neotropical Ant Odontomachus bauri Emery (Hymenoptera,Formicidae, Ponerinae)

The Neotropical species Odontomachus bauri employs canopy orientation during foraging and homing. An artificial canopy pattern above the ants is much more effective as an orientation cue than horizontal landmarks or chemical marks. However, both horizontal visual cues and chemical marks on the ground can serve in localizing the nest entrance. Successful O. bauri foragers recruit nestmates to leave the nest and search for food. However, the recruitment signals do not contain directional information. Antennation bouts and pheromones from the pygidial gland most likely serve as stimulating recruitment signals. Secretions from the mandibular and poison gland elicit alarm and attack behavior.     

Learning and time‐dependent cue choice in the desert ant,Melophorus bagoti

Foraging ants are known to use multiple sources of information to return to the nest. These cue sets are employed by independent navigational systems including path integration in the case of celestial cues and vision‐based learning in the case of terrestrial landmarks and the panorama. When cue sets are presented in conflict, the Australian desert ant species, Melophorus bagoti, will choose a compromise heading between the directions dictated by the cues or, when navigating on well‐known routes, foragers choose the direction indicated by the terrestrial cues of the panorama against the dictates of celestial cues. Here, we explore the roles of learning terrestrial cues and delays since cue exposure in these navigational decisions by testing restricted foragers with differing levels of terrestrial cue experience with the maximum (180°) cue conflict. Restricted foragers appear unable to extrapolate landmark information from the nest to a displacement site 8 m away. Given only one homeward experience, foragers can successfully orient using terrestrial cues, but this experience is not sufficient to override a conflicting vector. Terrestrial cue strength increases with multiple experiences and eventually overrides the celestial cues. This appears to be a dynamic choice as foragers discount the reliability of the terrestrial cues over time, reverting back to preferring the celestial vector when the forager has an immediate vector, but the forager's last exposure to the terrestrial cues was 24 hr in the past. Foragers may be employing navigational decision making that can be predicted by the temporal weighting rule.     

Kompass im Kopf

Ant compass – how desert ants learn to navigate Successful spatial orientation is a daily challenge for many animals. Cataglyphis desert ants are famous for their navigational performances. They return to the nest after extensive foraging trips without any problems. How do ants take their navigational systems into operation? After conducting different tasks in the dark nest for several weeks, they become foragers under bright sun light. This transition requires both a drastic switch in behavior and neuronal changes in the brain. Experienced foragers mainly rely on visual cues. They use a celestial compass and landmark panoramas. For that reason, naïve ants perform stereotype learning walks to calibrate their compass systems and acquire information about the nest's surroundings. During their learning walks, the ants frequently look back to the nest entrance to learn the homing direction. For aligning their gazes, they use the earth's magnetic field as a compass reference. This magnetic compass in Cataglyphis ants was previously unknown.     

The parasitic mite <Emphasis Type="Italic">Varroa destructor</Emphasis> affects non-associative learning in honey bee foragers, <Emphasis Type="Italic">Apis mellifera</Emphasis> L.

The parasitic mite Varroa destructor influences flight behavior, orientation and returning success of forager honeybees (Apis mellifera) infested as adults. As impaired orientation toward the nest entrance might be due to deficiency in recognition and responsiveness to stimuli in the environment, we examined effects of V. destructor on sensory responsiveness, non-associative and associative learning of honey bee foragers by using proboscis extension reaction paradigm (PER). Although infested and uninfested workers were initially equally responsive to different concentrations of sugar water, we found differences in non-associative learning. In habituation, PER to repeated sugar stimulation of the antennae occurred faster in infested foragers compared to uninfested foragers. In sensitization, infested foragers showed a lower response to an odor stimulus following sugar stimulation than non-infested foragers. Differences in non-associative paradigms were more pronounced in bees with lower responsiveness to sucrose. In conditioning learning experiments, a significant reduction in proboscis extension response was found 1 min but not 12 min after a single conditioning trial indicating that V. destructor predominantly affects the non-associative components of learning and its underlying neural and molecular processes. Jasna Kralj and Axel Brockmann have contributed equally to this study.     

The significance of visual landmarks for navigation of the giant tropical ant,Paraponera clavata (Formicidae,Ponerinae)

Summary Workers of the giant tropical ant,Paraponera clavata, use trail pheromones for orientation and recruitment of nestmates. However, chemical markings may not always be sufficient for successful navigation in complex three-dimensional terrain, and additional orientation cues may be required. Behavioral field experiments were performed to investigate the significance of visual landmarks for homing foragers. Animals which were prevented from seeing the canopy were unable to navigate back to the nest, even though trail pheromones were still present. In contrast, foragers found their way back to the nest after their trail pheromones had been abolished but their visual scenes remained unchanged. This emphasizes the important role of visual landmarks during spatial orientation in homingP. clavata foragers. Individually foraging scouts were discovered in the understory of the forest floor up to 30 m away from their nest. They were rewarded, and displaced between 0.8 m and 13.6 m. Fifteen out of 16 animals had no difficulties in finding the nest entrance despite the altered appearance of local and distant landmarks at the release site. Apparently the scouts were able to recognize the visual scenes at the release site, and used them for reference to locate the nest entrance. In contrast, ants displaced from their nest to sites around 4 m away had more difficulties to re-find the nest.     

Waste Management in the Leaf-Cutting Ant <Emphasis Type="Italic">Acromyrmex lobicornis</Emphasis>: Division of Labour,Aggressive Behaviour,and Location of External Refuse Dumps

In leaf-cutting ants, the handling of waste materials from the fungus culture increases the risk of infection. Consequently, ants should manage their waste in a way that minimizes the spread of diseases. We investigated whether in Acromyrmex lobicornis, waste-worker ants (a) also perform roles in foraging or mound maintenance, (b) are morphologically different than other ant workers, and (c) are aggressively discriminated by other worker ants from the same colony. In addition, we investigated whether the location of external waste piles minimizes the probability that wastes spread to the ant nest. In the field, we (a) marked with different colours waste-workers, foragers and mound-workers and monitored whether these ants interchanged their tasks; (b) measured head width, head length, hind femur length and total length of waste-workers; foragers and mound-workers; (c) forced field encounters between waste-workers and foragers, and (d) measured the cardinal orientation of the waste piles in relation to the colony mound. Waste-worker ants did not perform other function outside the nest; neither foragers nor mound-workers managed the waste. Moreover, waste-workers were smaller than foragers and mound-workers, and were attacked if they tried to enter their nest using foraging entrances. The location of external refuse dumps also appears to reduce contamination risks. Waste piles always were down-slope, and often followed the prevailing wind direction. The importance of behaviours such as the division of labour, aggressions against waste-workers and nest compartmentalization (i.e., the orientation of external waste piles) to minimize the spread of pathogens is discussed.     

Hierarchy of sun,beach slope,and landmarks as cues for Y-axis orientation of the supratidal amphipod Talorchestia longicornis (Say)

The semi-terrestrial amphipod Talorchestia longicornis (Say) undergoes Y-axis orientation and has a hierarchy among orientation cues. A previous study found that they used sun compass orientation and moved in the onshore direction of the home beach in both air and water. The present study determined whether this species could also use local landmarks and beach slope as orientation cues. They oriented upslope in simulated darkness in the laboratory on both dry and wet sand with threshold slopes of 2° and 4°, respectively. When tested outside in an arena in air on wet sand, they were disoriented when sun, slope, and landmarks were absent as cues. If presented with single cues, they moved upslope, toward landmarks and in the up-beach direction of the home beach during sun compass orientation. Using paired cues, sun was dominant over slope and landmarks, while slope was dominant over landmarks. In the presence of all three cues, amphipods displayed sun compass orientation in all test combinations except when slope and landmarks were paired together against the sun, which evoked a bimodal response. Thus, the hierarchy of cues for up-beach movement of T. longicornis during Y-axis orientation is the sun, then the slope, and finally the landmarks.     

<Emphasis Type="Italic">Vespula germanica</Emphasis> Foragers Do Not Scent-Mark Carbohydrate Food Sites

We tested whether foragers of Vespula germanica leave a chemical attractant at a carbohydrate food site. Foragers were allowed to make 50 or 100 visits to a feeder filled with a rich, unscented fructose solution. We then gave them a choice between this and an identical but unvisited feeder. There was no difference between the number of individuals that chose the visited feeder and those that chose the unvisited one. Instead, wasps showed a tendency to choose a feeder based on its relative position on the feeding stand. We conclude that foragers of V. germanica do not scent-mark food sites. Instead, in the absence of food odor, they rely on local visual cues to relocate carbohydrate food sources.     

Resource choice of social wasps: influence of presence, size and species of resident wasps

Summary: The role of visual cues provided by resident wasps on resource choice by yellowjacket and paper wasp foragers was investigated. Large spring queen yellowjackets and small early season yellowjacket foragers (Vespula germanica, Vespula maculifrons, and Vespula vidua) were extracted in hexane to remove odors and posed as though feeding at petri dish feeders bearing daisy-like flower models, equipped with microcapillary feeding tubes, and containing 1:3 honey:water solution. An array of five feeders was presented to foragers at a suburban and a woodland site in Saratoga Springs, New York. The visual cues provided by resident wasps influenced resource choice by approaching social wasp foragers. Vespula germanica, an introduced yellowjacket species that tends to dominate at rich resources, was the only wasp visiting the suburban feeders. Foragers of this species preferentially fed on feeders and flowers with posed wasps and fed most often next to large wasps. Polistes fuscatus foragers at the woodland site similarly preferred to feed on occupied feeders and flowers. Vespula maculifrons and V. consobrina preferentially visited unoccupied feeders. Individual V. maculifrons, V. consobrina and V. vidua foragers that landed on occupied feeders all preferentially visited unoccupied flowers on those feeders. Vespula vidua and V. flavopilosa foragers did not demonstrate a feeder preference based on the presence/absence of posed wasps. Vespula consobrina foragers that visited occupied feeders preferred those occupied by extracted V. maculifrons queens and workers; no other wasps showed species based landing preferences.     

Introduction of a scented carbohydrate resource into the nest increases departure rate in Polybia occidentalis

Social wasps do not possess a sophisticated, signal-based mechanism for recruiting foragers to food resources. Instead, in some species na?ve potential foragers use cues, specifically the scent of a resource obtained from successful foragers, to help locate the resource in the field. Prior studies have focused on the effectiveness of this mechanism on increasing the number of foragers at an artificial resource in the field; the increase is typically modest. Here, we focus on the activity at the nest in Polybia occidentalis, a tropical social wasp, and quantify the magnitude of the effect an influx of a known amount of scented carbohydrate solution added directly to the nest has on activating foragers to leave the nest in search of the resource. Under our experimental conditions, adding a scented 2.0 M sucrose solution to the nest doubled the average rate of departure. No increase occurred when the same amount of water was added as a control. This mass activation of foragers may give colonies of this species a competitive edge by enhancing their ability to rapidly exploit new resources.     

German Yellowjacket (Vespula germanica) Foragers Use Odors Inside the Nest to Find Carbohydrate Food Sources

Prior work has shown that yellowjacket waSPS remember food odors and use them as cues when foraging. There is also evidence they have mechanisms to recruit nest mates to highly rewarding food sources, as naïve individuals are more likely to go to food sources with scents similar to those visited by nest mates. We asked whether recruitment requires behavioral stimulation by returning foragers, as in honey bees, or if sampling the food source inside the nest is sufficient. We tested this by eliminating the behavior of returning foragers by inserting a scented sugar solution directly into a Vespula germanica nest. Exiting foragers were given a choice of the test scent and a control scent. WaSPS were more likely to choose the test scent. We conclude that behavioral interactions with returning foragers are not necessary to stimulate nest mates to associate an odor with a food source and search for a resource bearing that odor, and that experience with the scented reward inside the nest is sufficient to achieve this result.     

Y-axis orientation in the South American freshwater snail species Chilina patagonica (Gastropoda: Chilinidae)

Y-axis orientation, a movement perpendicular to the shore or coastline, enables aquatic animals to stay in a preferred zone in generally unstable habitats. Such behaviour is a widespread phenomenon in many freshwater and intertidal animal taxa. In the present study, an arena approach was used to test the orientation response of pulmonate freshwater snails. Using this experimental design, Y-axis orientation was shown for the first time in a freshwater snail species, the riverine Chilina patagonica. Some cues, potentially mediating Y-axis orientation, appeared to play no role in the shown orientation behaviour, such as chemical, gravity and humidity cues or a sun compass. Magnetic cues, however, could not be excluded. Since no significant differences in orientation were detected between different size classes in C. patagonica, orientation behaviour may not vary substantially throughout the snail's life history. In contrast to C. patagonica, no consistent orientation response was seen in the related lacustrine species Chilina llanquihuensis. The adaptation of C. patagonica to exhibit orientation along the Y-axis may be driven by the avoidance of high velocities in deeper water.     

Semiochemicals Influencing the Host-finding Behaviour of Varroa Destructor

Studies of Varroa destructor orientation to honey bees were undertaken to isolate discrete chemical compounds that elicit host-finding activity. Petri dish bioassays were used to study cues that evoked invasion behaviour into simulated brood cells and a Y-tube olfactometer was used to evaluate varroa orientation to olfactory volatiles. In Petri dish bioassays, mites were highly attracted to live L5 worker larvae and to live and freshly freeze-killed nurse bees. Olfactometer bioassays indicated olfactory orientation to the same type of hosts, however mites were not attracted to the odour produced by live pollen foragers. The odour of forager hexane extracts also interfered with the ability of mites to localize and infest a restrained nurse bee host. Varroa mites oriented to the odour produced by newly emerged bees (<16 h old) when choosing against a clean airstream, however in choices between the odours of newly emerged workers and nurses, mites readily oriented to nurses when newly emerged workers were <3 h old. The odour produced by newly emerged workers 18–20 h of age was equally as attractive to mites as that of nurse bees, suggesting a changing profile of volatiles is produced as newly emerged workers age. Through fractionation and isolation of active components of nurse bee-derived solvent washes, two honey bee Nasonov pheromone components, geraniol and nerolic acid, were shown to confuse mite orientation. We suggest that V. destructor may detect relative concentrations of these compounds in order to discriminate between adult bee hosts, and preferentially parasitize nurse bees over older workers in honey bee colonies. The volatile profile of newly emerged worker bees also may serve as an initial stimulus for mites to disperse before being guided by allomonal cues produced by older workers to locate nurses. Fatty acid esters, previously identified as putative kairomones for varroa, proved to be inactive in both types of bioassays.     

Experience Based Use of Landmark and Vector Based Orientation During Homing by the Ant Formica cunicularia (Hymenoptera: Formicidae)

Homing paths of Formica cunicularia foragers from an artificial food reward were analyzed on a familiar terrain and in displacement experiments on a familiar and an unfamiliar terrain. Foragers were tested either when relatively new to a foraging route (untrained group) or after a day’s experience with it (trained group). Untrained foragers followed direct homing paths to the nest site when tested in the familiar terrain but followed tortuous paths when displaced to the unfamiliar terrain. Trained foragers behaved similarly to untrained ones when tested from the food reward to the nest site in the familiar terrain but their behavior changed in displacements. Irrespective of the familiarity of the displacement site, these foragers followed paths taking them to the expected nest sites. The results showed that foragers did not rely on chemical cues for homing and revealed that untrained foragers disregarded path integration and were directed to the nest site when it is in their visual panorama. On the contrary, trained foragers may have relied on path integration on familiar and unfamiliar terrain. The results also demonstrated that experience greatly affected the preferential use of visual and vector based cues by foragers during homing.     

Context-dependent navigation in a collectively foraging species of ant, Messor cephalotes

More than 100 years of scientific research has provided evidence for sophisticated navigational mechanisms in social insects. One key role for navigation in ants is the orientation of workers between food sources and the nest. The focus of recent work has been restricted to navigation in individually foraging ant species, yet many species do not forage entirely independently, instead relying on collectively maintained information such as persistent trail networks and/or pheromones. Harvester ants use such networks, but additionally, foragers often search individually for food either side of trails. In the absence of a trail, these ‘off-trail’ foragers must navigate independently to relocate the trail and return to the nest. To investigate the strategies used by ants on and off the main trails, we conducted field experiments with a harvester ant species, Messor cephalotes, by transferring on-trail and off-trail foragers to an experimental arena. We employed custom-built software to track and analyse ant trajectories in the arena and to quantitatively compare behaviour. Our results indicate that foragers navigate using different cues depending on whether they are travelling on or off the main trails. We argue that navigation in collectively foraging ants deserves more attention due to the potential for behavioural flexibility arising from the relative complexity of journeys between food and the nest.     

Public information for solitary foragers: timber rattlesnakes use conspecific chemical cues to select ambush sites

Many animals use public information (PI) gathered from conspecificsto assess the quality of potential foraging locations. To date,research on this phenomenon has focused almost exclusively onsocial foragers that live in groups and monitor nearby individuals.PI is potentially available to solitary foragers as well, inthe form of cues (such as chemical cues) that persist in theenvironment after conspecifics are no longer present. In thisstudy, I examined the response of a solitary sit-and-wait predator,the timber rattlesnake (Crotalus horridus), to chemical cuesfrom conspecifics that had recently fed as opposed to thosethat had been deprived of food. Experiments with a T-maze indicatedthat timber rattlesnakes always follow conspecific chemicaltrails out of the maze, regardless of whether or not the individualleaving the trail had recently fed. However, an enclosure choicetest found that individuals are more likely to select ambushsites in areas with chemical cues from conspecifics that hadrecently fed. These results indicate that snakes may use conspecificchemical cues not only to find mates, shelter sites, and hibernaculabut also profitable food patches. Additionally, this study highlightsthe possibility that other solitary foragers may use PI to guidetheir foraging behavior.