The influence of past experience on wasp choice related to foraging behavior

Flexible foraging decisions made by workers of the social wasp Vespula germanica (Hymenoptera: Vespidae) in response to different resources: influence of ontogenetic shifts and colony feedback

Decisions made by foraging animals conform a complex process based on the integration of information from multiple external environmental stimuli and internal physiological signals, which in turn are modulated by individual experience and a detection threshold of each individual. For social insects in which foraging is limited to given age subcastes, individual foraging decisions may also be affected by ontogenetic shifts and colony requirements. We studied the short-term changes in foraging preferences of the generalist wasp Vespula germanica, focusing on whether the individual response to different resources could be influenced by the ontogenetic shifts and/or by social interaction with nestmates. We carried both laboratory and field experiments to confront worker wasps to a short-term resource switch between either protein or carbohydrate-based foods. We tested the response of (1) Preforager workers (no foraging experience nor interaction with other wasps), (2) Forager workers (experience in foraging and no colony feedback), and (3) Wild forager workers (foraging naturally and exposed to free interactions with nestmates). We evaluated the maxilla-labium extension response (MaLER) for laboratory assays or the landing response for field assays. We observed that for wasps deprived of colony feedback (either preforagers or foragers), the protein-rich foods acceptance threshold increased (and thus a lower level of foraging on that item was observed) if they had foraged on carbohydrates previously, whereas carbohydrates were accepted in all assays. However, wasps immersed in a natural foraging context did accept protein foods regardless of their first foraging experience and reduced the carbohydrates collected when trained on protein foods. We provide evidence that short-term changes in foraging preferences depend on the type of resource foraged and on the social interactions, but not on ontogenetic shifts.

Evidence of associative blocking during foraging in the social wasp Vespula germanica

While foraging, Vespula germanica usually return to abundant food sites. During this relocation behavior, these wasps learn to identify contextual cues associated with food position. We analyzed associative blocking in this species, that is, how an association with a conditioned stimulus (CS1) blocks subsequent learning when a novel stimulus (CS2) is added on a second foraging visit. Three groups of wasps (A, B, and C; total 74 individual wasps) were observed while collecting meat during one or two consecutive visits. In group A, an environmental cue (CS1) was paired with food placed at a specific site, and on the second visit, a second cue (CS2) was added while food remained in the same position. In a subsequent testing phase, CS1 was removed and the food source displaced nearby. We then recorded the number of hovers performed over the empty dish (previously baited). Group A wasps appeared to ignore the addition of CS2 on their second visit because they performed fewer hovers over the learned site. For group A, the duration of the decision-making process to finally fly toward the baited dish was shorter than when CS1 and CS2 were presented together on their first visit (group B). This is the first study to demonstrate the occurrence of associative blocking in vespids, confirming that a prior foraging experience influences subsequent food relocation in V. germanica. Our findings reveal that first learning episodes block further associations with novel contextual cues, contributing to understanding of complex cognitive processes involved in V. germanica´s foraging behavior.

Spatial memory in Vespula germanica wasps: A pilot study using a Y-maze assay

In the present study we analysed spatial learning in Vespula germanica wasps when dealing with a walking Y-maze. We recorded the time taken to leave the maze during two consecutive visits and which of the two short arms was chosen to exit. Two treatments were conducted to evaluate whether wasps learned to leave the Y-maze guided either by spatial or visual cues. In Treatment 1, the colour of both arms remained unchanged between two consecutive visits; and in Treatment 2, the position of the coloured arm was switched after the first trial. Our results demonstrated that the time taken to exit the maze on the second trial was less than half in both treatments and wasps left the maze from the previously chosen arm, irrespective of its colour. This is the first study to demonstrate spatial learning in V. germanica wasps by using a walking Y-maze. Free flying wasps learned to enter the Y-maze on their own volition, walk through it, collect food and find their way out more rapidly after a single foraging experience. The current experimental device is suitable for the evaluation of spatial memory processes and exploratory behaviour in this species.

How behavioral plasticity enables foraging under changing environmental conditions in the social wasp Vespula germanica (Hymenoptera: Vespidae)

The foraging strategy at abundant resources of the social wasp Vespula germanica includes scanning in the direction of the nest while memorizing resource-specific landmarks and contextual cues. In the present study, we sought to explore wasps' behavioral plasticity on foraging trips to resources whose location and composition changed after a single visit. We evaluated how contextual modifications of food displacement and replacements 60 cm apart from the original site, affect re-orientation for re-finding previously memorized food resources. The results showed that wasps detected and collected the resource faster when more changes were introduced on the following visit. If returning foragers discovered several modifications on both the location and the kind of resource, they collected food more rapidly from the displaced dish, than if only a single parameter in the environment had been changed. These findings illustrate the grade of behavioral plasticity in V. germanica while foraging on abundant resources, which may contribute to the understanding of the prodigious invasive success of this species in anthropized environments.

Feeding strategies and intraspecific competition in German yellowjacket (Vespula germanica)

The German yellowjacket (Vespula germanica) is an opportunist predator and a scavenger, whose eclectic diet also includes honey, brood, dead and live honey-bees. There is no evidence in this species of coordinated attacks against bees involving other conspecifics, although intraspecific competition has been already reported between two or more individuals during feeding. Our aim was to gain further knowledge on the feeding behavior of V. germanica in order to evaluate its role in an apiary. Sight observations of predation and necrophagy behaviors were carried out at the ground level near hives. We also investigated how intraspecific competition can influence the feeding display in this species. Our results confirm the major role of the German yellowjacket as a scavenger, because its diet is based mostly on bee carrions. Intraspecific competition during feeding was sometimes observed. When these events occurred, the interference of another wasp led to the bee escaping only in three cases. Our study also revealed that intraspecific competition events increase when the resource is fresh (predation vs necrophagy), and that the number of competing wasps was significantly higher when the food consisted of pupae and drones, compared to adult bees. When competition involved two individuals (the most frequent case), the winner was frequently the first wasp to reach the resource in both predation and necrophagy events. This suggests that the energy invested in foraging or predating activity and in defence of prey is usually rewarded.

Foraging behaviour of the exotic wasp Vespula germanica (Hymenoptera: Vespidae) on a native caterpillar defoliator

Vespula germanica is a social wasp and an opportunistic predator. While foraging, these wasps learn and integrate different kinds of cues. They have successfully invaded many parts of the world, including native Nothofagus and Lophozonia forests located in the Andean-Patagonian region, where they forage on native arthropods. Perzelia arda, a lepidopteron defoliator of Lophozonia obliqua, uses the foliage to hide in and feed on. The purpose of this work is to study whether V. germanica use olfactory cues when foraging on P. arda. To do this, we used a Y-tube olfactometer and established three treatments to compare pairs of all combinations of stimuli (larvae, leaves with larval traces, and leaves without larval traces) and controls. Data were analysed via two developed models that showed decisions made by V. germanica and allowed to establish a scale of preferences between the stimuli. The analysis demonstrates that V. germanica wasps choose P. arda as larval prey and are capable of discriminating between the offered stimuli (deviance information criterion (DIC) null model = 873.97; DIC simple model = 84.5, n = 152). According to the preference scale, V. germanica preferred leaves with traces of larvae, suggesting its ability to associate these traces with the presence of the prey. This may be because, under natural conditions, larvae are never exposed outside their shelters of leaves and therefore V. germanica uses indirect signals. The presence of V. germanica foraging on P. arda highlights the flexible foraging behaviour of this wasp which may also act as a positive biological control, reducing lepidopteran populations.

Long-term spatial memory in Vespula germanica social wasps: the influence of past experience on foraging behavior

Social insects exhibit complex learning and memory mechanisms while foraging. Vespula germanica (Fab.) (Hymenoptera: Vespidae) is an invasive social wasp that frequently forages on undepleted food sources, making several flights between the resource and the nest. Previous studies have shown that during this relocating behavior, wasps learn to associate food with a certain site, and can recall this association 1 h later. In this work, we evaluated whether this wasp species is capable of retrieving an established association after 24 h. For this purpose, we trained free flying individuals to collect proteinaceous food from an experimental plate (feeder) located in an experimental array. A total of 150 individuals were allowed 2, 4, or 8 visits. After the training phase, the array was removed and set up again 24 h later, but this time a second baited plate was placed opposite to the first. After 24 h we recorded the rate of wasps that returned to the experimental area and those which collected food from the previously learned feeding station or the nonlearned one. During the testing phase, we observed that a low rate of wasps trained with 2 collecting visits returned to the experimental area (22%), whereas the rate of returning wasps trained with 4 or 8 collecting visits was higher (51% and 41%, respectively). Moreover, wasps trained with 8 feeding visits collected food from the previously learned feeding station at a higher rate than those that did from the nonlearned one. In contrast, wasps trained 2 or 4 times chose both feeding stations at a similar rate. Thus, significantly more wasps returned to the previously learned feeding station after 8 repeated foraging flights but not after only 2 or 4 visits. This is the first report that demonstrates the existence of long-term spatial memory in V. germanica wasps.