How Long do Vespula Germanica Wasps Search for a Food Source that is no Longer Available?

Vespula germanica foragers return to a food source that has not been depleted. In this work we investigate how long wasps continue searching for a food source that is no longer available. We first trained wasps to feed on a dish surrounded by four yellow cylinders, and then, during the testing phase, we removed the food, and recorded foragers’ behavior until wasps stopped visiting the array. Two groups received different treatments: one received one feeding trial and the other three. Wasps trained with three consecutive trials searched over the original array approximately three times longer than those receiving one. Furthermore, the number of hovers and landings over the array was significantly higher for wasps trained with three trials than for wasps trained with one. Finally, initial level of response (i.e. number of hovers and landings in the first visit during the testing phase) was significantly higher in the group with three trials than in the group with one. We discuss the biological significance of memory extinction in these generalist wasps, in relation to the level of uncertainty of the resources they exploit. The plasticity to extinguish differently an association between a stimulus and a food resource could be one of the various behavioral mechanisms in V. germanica wasps that had allowed the species to get successfully established in new areas of the world.     

The importance of location and visual cues during foraging in the German wasp (Vespula germanica F.) (Hymenoptera: Vespidae)

Abstract

The way in which foraging wasps use cues for prey location and choice appears to depend on both the context and on the type of prey. Vespula germanica is an opportunistic, generalist prey forager, and individual wasp foragers often return to hunt at sites of previous hunting success. In this paper, we studied which cues are used by this wasp when relocating a food source. Particularly we analysed the response to a displaced visual cue versus a foraging location at which either honey or cat food had been previously presented. We conclude that location is used over a displaced visual cue for directing wasp hovering, although the landing response is directed differently according to bait type. When wasps are exploiting cat food, location also elicits landing, but if they are exploiting honey, a displaced visual cue elicits landing more frequently than location.     

How Context Modification can Favor the Release of Past Experience in Vespula germanica Wasps,Enabling the Detection of a Novel Food Site

Vespula germanica wasps typically make consecutive trips between an undepleted food source and their nest. Hence, relocating a rewarded location is a recurrent activity during a wasp’s lifetime. While foraging, wasps continue searching over a previously rewarded location even when food is no longer available. Moreover, when food is displaced to a location nearby, wasps still visit the previously rewarded location. We aimed to study how the modification of the local context would affect the discovery of the novel food site. By displacing food and changing the local context after wasps had learned a certain task, we evaluated whether wasps found a new food location more rapidly than if contextual conditions remained unaltered. We found that when previously associated cues were modified, wasps were more likely to ‘give up’ searching at the old location than if these cues remained unaltered. Furthermore, we observed that a higher number of rewarding trials at the initial location resulted in greater time taken to detect the new feeder location.     

Foraging niche separation of social wasps in an invaded area: Implications for their management

Foraging niche separation may be a mechanism to promote coexistence of two competing species by concentrating intraspecific competition relative to interspecific competition. The present study investigated foraging behaviour and microhabitat use of two coexisting species of invasive social wasps, Vespula germanica and Vespula vulgaris, when foraging for two different food resources. Also, we tested the attractiveness of traps baited with a synthetic lure for those two species. We found that V. germanica wasps prefer to forage at ground level regardless of the resource, while V. vulgaris prefers protein resources at the shrubland level given a choice between a protein bait at ground or at shrubland level. However, when baited with the synthetic lure, the species caught was not affected by the height at which traps were placed. That is, in a no choice scenario, the traps were sufficiently attractive to lure both species of wasps to both microhabitats (ground and shrubland levels). Thus, our results support the existence of spatial niche differentiation at least in protein foraging and suggest that the synthetic lure evaluated could be used to trap both species of Vespula wasps present in Argentina. These results could help to improve management strategies of these social wasps in an invaded area.     

Allocation of Colony‐Level Foraging Effort in Vespula germanica in Response to Food Resource Quantity,Quality, and Associated Olfactory Cues

In social insects, selection takes place primarily at the level of the colony. Therefore, unlike solitary insects, social species are expected to forage at rates that maximize colony fitness rather than individual fitness. Workers can increase the net benefit of foraging by responding to increased resource availability, by responding more strongly to higher‐quality resources, and by decreasing the uncertainty with which nestmates find resources. Unlike many ants and social bees, no social wasp is known to utilize a nest‐based recruitment signal to inform nestmates of food location. On the other hand, wasps do learn the odor of food brought to the nest and use this cue to locate the food source outside the nest. Here, we quantify the effects of three food‐associated variables on the allocation of foraging effort in the yellowjacket Vespula germanica. We used an experimental approach to assess whether resource quantity, quality, or associated olfactory information affect the probability that a forager will leave the nest on a foraging trip. We addressed these questions by inserting a known amount of sucrose solution directly into nests and recording foraging effort (departure rate) over the subsequent hour‐long observation period. No differences were found in foraging effort because of the presence/absence of olfactory cues, but there was strong evidence that foraging effort increased in response to resource influx and resource quality. Thus, while olfactory cues are learned in the nest, only resource quality and the cue of increased amount of food in the nest factor into a forager's decision of whether or not to depart on a foraging trip. However, as prior work has shown, once a wasp forager leaves the nest, it uses the learned olfactory cues to aid in finding resources.     

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.     

Foraging behavior related to habitat characteristics in the invasive wasp Vespula germanica

When foraging on carrion resources, the wasp Vespula germanica usually makes repeated visits to the feeding site until depleting the resource. In the present study we analyzed how environmental cues affect wasps' behavior when re‐locating a protein food source. We studied this behavior in two different natural habitats: closed and open habitats. As closed habitats have more references to orient wasps to the feeding site than open habitats, we hypothesized that they would return to the foraging site more frequently in closed habitats than in open ones. We tested this hypothesis by studying wasp behavior in three different natural habitat conditions: (i) closed habitats, (ii) open habitats, and (iii) open habitats artificially modified by adding five sticks with flagging. Experiments consisted of training individual wasps to feed from a certain array, and at the testing phase we removed food and displaced the array by 60 cm. Therefore, we recorded wasps’choices when returning to the training area, by counting both the wasps’first approaches and the number of visits to the original feeding site and the displaced array. Wasps' behavior while re‐locating a protein food source was different if foraging at open or closed habitats. Wasps more frequently revisited a previous feeding location when foraging in closed habitats than when foraging in open ones. Furthermore, wasps more frequently visited the displaced array than the original feeding site in all three treatments. Nevertheless, when wasps were trained in closed habitats, they returned to the original feeding site more frequently than if trained in open ones. Interestingly, when five sticks with flagging were added in open habitats, wasps responded similarly as in closed habitats without these references. The results show that foraging behavior in V. germanica seems to be different in closed and open habitats, probably associated with the existence of references that guide foragers when re‐locating undepleted resources.     

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

Memory has been little studied in social wasps. Vespula germanica （Fab.） （Hymenoptera： Vespidae） frequently revisits nondepleted food sources, making several trips between the resource and the nest. In this study, we analyzed this relocating behavior in order to evaluate whether this species is capable of remembering an established association after 1 h. To this end, we trained wasps to feed from a certain array. Then it was removed, setting it up again 1 h later, but this time 2 baited feeders were put in place, one at the original feeding site and the other opposite the first. We recorded the proportion of returning foragers, and their choice of feeder, after either 1 or 4 feeding trials. After 1 h, 78% of wasps trained with 4 feeding trials and 65% trained with 1, returned to the experimental area. Furthermore, during the testing phase, wasps trained with 4 feeding trials collected food from the previously learned feeder significantly more frequently than from the nonlearned one （P 〈 0.05）. In contrast, wasps that had been trained only once chose both feeders equally. Thus, memory retrieval could be observed 1 h after wasps had collected food on 4 consecutive occasions, but not after only 1. To our knowledge, this is the first study showing that V. germanica is capable of remembering an association 1 h after the last associative event, demonstrating that 1 h does not impair memory retention if4 feeding experiences have occurred.     

Foraging and spatial dispersion in protein-scavenging workers ofVespula germanica andV. maculifrons (Hymenoptera: Vespidae)

A series of experiments on the discovery of meat bait by scavenging workers ofV. germanica andV. maculifrons showed that workers oriented to meats by visual cues and olfactory cues. Scavening workers ofV. germanica andV. maculifrons responded positively to the sight of conspecifics at meat baits; i.e., meat with (confined) wasps received more visits than meat without wasps. This attraction to conspecific workers on meat baits provides evidence of local enhancement, in that the presence of conspecifics at meat bait directs other wasps to a particular spatial locality. Local enhancement by yellowjackets foraging for meat may contribute to the clumped distribution of worker populations noted in studies of workers captured in meat-baited traps. We hypothesize that local enhancement of foraging is a ubiquitous behavior in species of theV. vulgaris species group and may be one attribute explaining their ecological success.     

Lack of field-based recruitment to carbohydrate food in the Korean yellowjacket, <Emphasis Type="Italic">Vespula koreensis</Emphasis>

We investigated field-based recruitment via visual, chemical and acoustic cues provided by conspecific wasps on carbohydrate feeders in Vespula koreensis. A wild colony nest was excavated and artificially installed in a field site. Naïve foragers were individually marked and trained to an experimental feeder. We conducted three separate experiments in which foragers were presented with feeder dishes with different cue intensities. For the first, a different number of decoys were posed as if feeding (visual cue). In the second, dishes had been previously visited by different numbers of individuals, thus presenting different concentrations of a possible food site marking substance (chemical cue). In the third, each dish was placed in front of a covered flask with a different number of nestmates inside (acoustic cue combined with body-odor cue). We observed no social facilitation or social inhibition due to any of the experimental cues. Previous studies in Vespula species have shown a variety of foraging strategies ranging from local enhancement to local inhibition. Field-based recruitment mechanisms in yellowjackets may have evolved independently in different lineages.     

Contrasting foraging related behaviours in two sympatric wasps (Vespula maculifrons and V. germanica)

ABSTRACT.

• 1 Using pinned freshly killed wasps (yellowjackets) to simulate feeding animals, it was found that V. germanica was socially facilitated, and concentrated its foraging activity on those feeders with the most pinned wasps (twenty). V. maculifrons foragers responded inversely, preferentially foraging at feeders with few or no pinned wasps.
• 2 Using hand-painted drawing pins (thumb tacks) as wasp models, similar results were found, indicating that visual, rather than olfactory, cues were responsible for the observed distribution.
• 3 Vespula maculifrons and V. germanica exhibit aggression while foraging at honey-baited feeders. Both species attack conspecifics at frequencies lower than would be expected under random encounter.

     

Influence of visual cues on host‐searching and learning behaviour of the egg parasitoids Telenomus podisi and Trissolcus basalis

Insect parasitoids use a variety of chemical and physical cues when foraging for hosts and food. Parasitoids can learn cues that lead them to the hosts, thus contributing to better foraging. One of the cues that influence host‐searching behaviour could be colour. In this study, we investigated the ability of females of the parasitoid wasps Telenomus podisi Ashmead and Trissolcus basalis Wollaston (both Hymenoptera: Scelionidae) to respond to colours and to associate the presence of hosts – eggs of Euschistus heros (Fabricius) (Hemiptera: Pentatomidae) – with coloured substrates after training (associative learning). Two sets of experiments were conducted: in one the innate preference for substrate colours was examined, in the other associative learning of substrate colour and host presence was tested in multiple‐choice and dual‐choice experiments. In the associative learning experiments, Te. podisi and Tr. basalis were trained to respond to differently coloured substrates containing hosts in two sessions of 2 h each, with 1‐h intervals. In multiple‐choice experiments, the wasps displayed innate preference for yellow substrates over green, brown, black, or white ones. Even after being trained on substrates of different colours, both parasitoids continued to show preference for yellow substrates. The response to the colours of substrates of both parasitoids was related with the orientation to the plant foliage during the search for hosts.     

Contextual control of rats' foraging behaviour in a radial maze

This study demonstrated that with experience rats were able to discriminate the background contextual cues in order to foraging correctly in an eight-arm radial maze if the background contexts signaled to the rats which of two bait patterns was in effect in that context. Four of the eight arms were context-dependent: two arms were baited in the "night" context, while the other two were baited in the "daytime" context. The remaining four arms were context-independent: three of them were never baited, while the remaining one was baited in both contexts. The rats gradually began to avoid the arms that were uniquely baited in the other context, suggesting a contextual or conditional control of arm selection. Interestingly, these rats also showed better performance in avoiding the never-baited arms, compared with control rats. Namely, disambiguating the incentive values of the four arms by contextual cues collaterally facilitated the context-independent arm performance. Another interesting finding of the present study is that the rats did not visit the always-baited arm earlier than the arms uniquely baited in that context.     

Appetitive and aversive learning in Spodoptera littoralis larvae

Adult Lepidoptera are capable of associative learning. This helps them to forage flowers or to find suitable oviposition sites. Larval learning has never been seriously considered because they have limited foraging capabilities and usually depend on adults as concerns their food choices. We tested if Spodoptera littoralis larvae can learn to associate an odor with a tastant using a new classical conditioning paradigm. Groups of larvae were exposed to an unconditioned stimulus (US: fructose or quinine mixed with agar) paired with a conditioned stimulus (CS: hexanol, geraniol or pentyl acetate) in a petri dish. Their reaction to CS was subsequently tested in a petri dish at different time intervals after conditioning. Trained larvae showed a significant preference or avoidance to CS when paired with US depending on the reinforcer used. The training was more efficient when larvae were given a choice between an area where CS-US was paired and an area with no CS (or another odor). In these conditions, the memory formed could be recalled at least 24 h after pairing with an aversive stimulus and only 5 min after pairing with an appetitive stimulus. This learning was specific to CS because trained larvae were able to discriminate CS from another odor that was present during the training but unrewarded. These results suggest that Lepidoptera larvae exhibit more behavioral plasticity than previously appreciated.     

Temperature and forager body size affect carbohydrate collection in German yellowjackets, Vespula germanica (Hymenoptera, Vespidae)

The classic formulation of optimal foraging theory predicts that a central-place forager will gather more food if it is required to travel farther from the nest to find that food. We examined the foraging behavior of German yellowjackets (Vespula germanica) to determine whether carbohydrate foragers follow this pattern. We trained foragers to collect 2 M fructose solution at 5 or 50 m from the nest and measured the time spent feeding, load size, and the rate of delivery. We show that as a forager’s crop fills during a foraging bout, the amount of solution ingested per second decreased. However, load size did not change as wasps collected food up to 50 m from the nest. Instead, temperature and body size were better predictors of the volume of fructose a forager carried. Finally, the rate of fructose delivered to the nest was higher at warmer temperatures. Due to the fact that wasps gather more food but feed for shorter periods of time at warmer temperatures, we found an overall negative relationship between feeding time and load size. We conclude that the strong effects temperature had on the behavior of V. germanica foragers imply that feeding time may not always be an accurate predictor of the size of the load an individual carries back to the nest. Results from this study suggest that in yellowjacket colonies, foragers can collect and bring disproportionately more food back to the nest during the warmest days of the summer, a time of year when this pest species reaches peak population size during its annual colony cycle.     

Essential oils as vespid wasp repellents: Implications for their use as a management strategy

Recently, plant‐based repellents have been proposed as a potential alternative to classic pesticides against pest wasps, in certain scenarios. Here, the repellent effect of Dysphania multifida essential oil and one of its main terpenoid components, α‐terpinene, were tested under field conditions with natural populations of wasps in Patagonia Argentina. D. multifida essential oil (paico), as well as α‐terpinene, repelled V. germanica wasps in the field. A strong avoidance of food baits treated with the essential oil or α‐terpinene was observed in choice and no‐choice tests. In no‐choice tests, the time it took wasps to arrive at the bait was significantly greater in treated baits than in control baits. Also, the total number of arriving wasps in 30 min was significantly greater in untreated baits in comparison with treated baits, under similar environmental conditions and wasp density. As the wasps’ flight season progressed, wasp density and motivation for proteinaceous food sources increased. This was evidenced by a greater total number of wasps in untreated baits with time. On the contrary, the number of wasps in treated baits remained low throughout the peak season. Both the paico essential oil and the α‐terpinene act as powerful repellents for V. germanica wasps, generating an avoidance response to treated food sources. Thus, these compounds have potential to be used as repellents to prevent wasps’ approaches and foraging, when applied in close proximity to a food source.     

Past Experience: a Help or a Hindrance to <Emphasis Type="Italic">Vespula germanica</Emphasis> Foragers?

In this study we investigate associative learning related to food location in Vespula germanica social wasps. Wasps were trained to associate a certain location with food, and their behaviour after food displacement was recorded. The effect of a different number of previous feeding experiences on the detection of the novel food source was evaluated. When these wasps associated a certain location with food, they returned to the original site despite the fact that food was no longer available. This occurred even when a new food source was placed very close to the learned location. The results demonstrate that this learning seems to temporarily impair the detection of new food sources. We discuss how previous experience seems to condition perception, delaying the detection of more rewarding contexts.     

<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.     

Effects of Rewarding and Unrewarding Experiences on the Response to Host-induced Plant Odors of the Generalist Parasitoid <Emphasis Type="BoldItalic">Cotesia marginiventris</Emphasis> (Hymenoptera: Braconidae)

Associative learning is known to modify foraging behavior in numerous parasitic wasps. This is in agreement with optimal foraging theory, which predicts that the wasps will adapt their responses to specific cues in accordance with the rewards they receive while perceiving these cues. Indeed, the generalist parasitoid Cotesia marginiventris shows increased attraction to a specific plant odor after perceiving this odor during contact with hosts. This positive associative learning is common among many parasitoids, but little is known about the effects of unrewarding host searching events on the attractiveness of odors. To study this, preferences of female C. marginiventris for herbivore-induced odors of three plant species were tested in a six-arm olfactometer after the wasps perceived one of these odors either i) without contacting any caterpillars, ii) while contacting the host caterpillar Spodoptera littoralis, or iii) while contacting the non-host caterpillar Pieris rapae. The results confirm the effects of positive associative learning, but showed no changes in innate responses to the host-induced odors after “negative” experiences. Hence, a positive association is made during an encounter with hosts, but unsuccessful host-foraging experiences do not necessarily lead to avoidance learning in this generalist parasitoid.     

Odour-mediated foraging by yellowjacket wasps (Hymenoptera: Vespidae): predation on leks of pheromone-calling Mediterranean fruit fly males (Diptera: Tephritidae)

Predation is probably the most important male mortality factor in insect species with courtship displays that render males performing them conspicuous targets of predators. Sexually active Mediterranean fruit fly males, Ceratitis capitata (Wied.), aggregate in leks, where they participate in agonistic encounters and engage in visual, acoustic and pheromone-calling displays to attract receptive females. The objective of this study was to assess: a) whether sexually displaying C. capitata males in leks inside host and non-host foliage are subject to predation by the most prominent predators yellow-jacket wasps, Vespula germanica (F.), and if so, b) whether olfactory, visual or auditive stimuli are used by foraging wasps in locating male C. capitata prey. Studies were carried out in a citrus orchard and surroundings on the island of Chios, Greece. Observations were conducted using perforated containers hung within mulberry, fig or citrus foliage. Living C. capitata flies of different sex and either mature or immature were placed inside. Our results show that the yellowjacket wasps have learned to associate the presence of sexually active medfly males aggregated in leks with their prey's pheromone (kairomone). Foraging wasps, flying through the crowns of host trees, responded to the odour source of C. capitata male pheromone by approaching from downwind. Even inside dense citrus tree foliage, wasps keyed in on aggregations of pheromone-calling males using olfactory stimuli. Stimuli of visual and acoustic male signalling were only used at close range, after having followed the pheromone plume close to its source. Visual cues played a greater role in directing wasp foraging under more open and exposed host foliage conditions. Odour-based foraging of wasps inside host foliage in the mid-morning hours, when medfly male lekking activities peak, shifted gradually to a more visual-based host fruit patrolling in the afternoons to capture ovipositing and feeding medfly females. On ripe fruit, particularly fig, V. germanica visual prey hunting also included the capture of feeding medfly males, other feeding Diptera, as well as medfly larvae extracted from wasp-made perforations in the fruit.