The importance of worker behaviour in the colony organization of the social wasps,Vespula Vulgaris (L.) andV. Germinaca (F.) (Vespidae; Hymenoptera)

Summary With two combs and one or a small number of workers it was found that the comb itself without brood was less attractive than a comb with cocoon caps or larvae, but single workers were equally attracted to combs with a large or small number of larvae, or queen or non-queen larvae. A worker walked at random when off a comb and tended, when on a comb, to stay with the first group of larvae that it found.Observations in the field showed that adults formed a group at night at the bottom of the nest.Records from six observation nests of whole or almost whole colonies have been collected over a period of three years. In all cases a dominant comb, which carried a larger percentage of the workers than any other comb and usually the queen if present, was soon established. The dominant comb always contained brood, was nearest or one of the combs nearest the entrance, received most foragers, and workers grouped on it more frequently than other combs.The grouping behaviour of workers on a comb can be related to background temperature and caused comb temperature to increase to 29° C–32.5° C.The worker attention a larva received increased as the number of workers on its comb increased.Reasons for and the consequences of grouping behaviour, the appearance of a dominant comb and the position of the latter in the nest, are discussed.

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Résumé Au cas où il y a deux rayons et soit un seul, soit un petit nombre d'ouvrières, on constate que le rayon sans couvain attire moins les ouvrières que celui operculé (cocons ou larves). Pour ce qui est d'un petit nombre ou d'un grand nombre de larves, ou encore des larves de reines ou de non-reines, l'attraction est égale pour chaque ouvrière. L'ouvrière ne se trouvant pas sur le rayon se déplace au hasard. De plus, quand elle est sur un rayon elle a tendance à rester avec le premier groupe de larves qu'elle trouve.L'examen des observations effectuées sur le terrain montre que les adultes se groupent la nuit, au fond du nid.Six nids, contenant des colonies entières ou presque entières, ont fait l'objet de plusieurs observations pendant une période de trois ans. Durant la même période, les résultats ont été enregistrés. Dans tous les cas, un rayon dominant s'est établi dans un bref délai. Ce rayon avait un plus grand pourcentage d'ouvrières que tout autre, et comportait généralement la reine. Le rayon dominant contenait toujours du couvain; il se trouvait le plus près de l'entrée du nid (ou bien était parmi les plus près); il recevait le plus grand nombre de butineuses, et des ouvrières s'y groupaient plus fréquemment que sur d'autres rayons.Il est possible d'établir un rapport entre le comportement des ouvrières lorsqu'elles se groupent sur un rayon, et la température ambiante. En effet, ce comportement a entrainé une hausse allant jusqu'à 29° C–32,5° C sur le rayon.L'attention que prêtait une ouvrière à la larve augmentait à mesure que le nombre d'ouvrières sur son rayon augmentait.On traite dans cet article du comportement observé lors d'un groupement, les raisons et les conséquences; ainsi que de l'apparition d'un, rayon dominant et de la position de celui-ci dans le nid.

     

The significance of worker size in the seasonal development of the wasps Vespula vulgaris (L.) and Vespula germanica (F.)

An account is given of the variation of worker size in Vespula vulgaris and V.germanica during the vespine season and of pupal size, as indicative of larval feeding conditions, on the same comb and on different combs in the same nest.     

Variation in colour markings of German wasps Vespula germanica (F.) and common wasps Vespula vulgaris (L.) (Hymenoptera: Vespidae) in New Zealand

Abstract

German wasps (Vespula germanica F.) and common wasps (V. vulgaris L.) both show variations in colour markings in New Zealand. Overlap in the ranges of markings of the head and thorax is limited enough for ready distinction of queens and workers of the two species. Abdominal markings overlap considerably between the species. Colour markings of males were too similar to identify the species, which were completely separated by the shape of their genitalia. The frequency of occurrence of “intermediate” markings in V. germanica populations did not increase in areas where the two species overlap. This suggests there is little or no genetic exchange between the two species.     

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.

     

The potential distribution of German wasps (Vespula germanica) in Argentina

Abstract

In the early 1980s, the German wasp (Vespula germanica) arrived in Argentina and became established in northern Patagonia. We use an ecoclimatic computer‐based program (CLIMEX) to predict the potential spread of wasps to other areas of the country. The model suggests that much of Argentina does not appear to be very suitable for the species’ establishment. However, more suitable areas than those currently colonised by the wasp occur in the centre of the country. Based on CLIMEX results, we suggest that, if the wasps ever break through the barrier of unfavourable habitat that surrounds their current distribution, they will continue dispersing to those areas. Notwithstanding this, factors other than climate may explain why German wasps are firmly established in areas otherwise considered to be inhospitable for the species.     

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.     

Comparative characteristics of nests of Vespula germanica (F.) and Vespula vulgaris (L.) (Hymenoptera: Vespinae) from Christchurch City,New Zealand

Abstract

From July 1987 to June 1989, 141 nests and 365 nests, respectively, of the adventive social vespines the German wasp, Vespula germanica (F.), and the common wasp V. vulgaris (L.), from the City of Christchurch, New Zealand, were evaluated for seven major characteristics.

There were few, if any, differences in nest sites, and from spring to early summer in nest traffic, nest size, and numbers of combs. However, Getman wasps showed no preference for direction of nest entrances, while common wasp nests were more numerous in areas most exposed to the morning sun. Some Getman wasp nests survived the winter and began producing new worker cells by late June, but all common wasp nests died by June. Because common wasp nests have been reported surviving the winter in beech forest, which produces honey dew, and honey dew is not available in Christchurch City, common wasp nest survival over winter may be more dependent upon carbohydrates and/or prey dependent upon carbohydrates than the survival of German wasp nests. The presence of large, expanding wasp nests from early spring must impose localised predation pressures virtually unknown in the Northern Hemisphere where overwintering nests are rare. Wasp population dynamics, and impacts of wasps on fauna, are likely to vary between different geographical areas of New Zealand, but as targets for biological control, the two wasp species can generally be considered to be quite similar.     

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.     

Overwintering colonies of German (Vespula germanica) and common wasps (Vespula vulgaris) (Hymenoptera: Vespidae) in New Zealand

Abstract

Nests of both common (Vespula vulgaris) and German wasps (V. germanica) sometimes overwinter in New Zealand. Three overwintering common wasp colonies were found in low-altitude honeydew beech forest; about 2% of the colonies initiated there in 1988 survived the winter. Wasp traffic rates from nests in Nelson city and a nation wide survey of wasp abundance, showed that more German wasp than common wasp workers were on the wing in winter and spring. German wasp colonies in Nelson city were more likely to overwinter than were common wasp colonies. Of the active German wasp colonies recorded in Nelson in January and February 1989, only two (4%) had previously overwintered, but these two nests accounted for 38% of all German wasp workers estimated to leave nests in the area. Had other overwintering colonies not been poisoned, overwintering colonies might have accounted for up to 11 % of nests and produced up to 64% of German wasp workers on the wing in January and February 1989.

Overwintering common wasp colonies did not produce queens or drones in their first year or second spring, but all 10 overwintering German wasp colonies examined produced sexuals at both times. German wasp queens produced in winter and spring may influence the number of colonies successfully initiated and affect the population dynamics of German wasps in New Zealand.     

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.     

Colony structure and nest characteristics of European wasps, Vespula germanica (F.) (Hymenoptera: Vespidae), in Victoria, Australia

Abstract European wasps, Vespula germanica , are common across southern and south-eastern Australia and have a negative impact upon urban areas, primary industries, and natural ecosystems. Aspects of colony structure and nest characteristics are examined for nests located in the ground and collected from urban and rural sites in Victoria during two summer−autumn field seasons (1996 and 2001). On average, nests were located 28 cm beneath the surface (range 5−58 cm). The average number of combs in the nest and the total area of the nests increased from early February to late May. In addition, the proportion of cells used to produce workers and different life stages (larvae, pupae) also varied throughout the season; being consistent with studies from New Zealand. No differences in colony structure or nest character­istics were detected between urban and rural nests.     

Carbohydrate bait preferences of wasps (Vespula vulgaris and V. germanica) (Hymenoptera: Vespidae) in New Zealand

Abstract

Carbohydrates are both a source of food and a potential bait for control of common and German wasps. Carbohydrate preferences of wasps were determined in a series of paired trials by counting the number of wasps caught in traps baited with carbohydrate‐based baits versus a standard protein‐based bait. Factors influencing wasp attraction to carbohydrate‐based baits included bait type, season, weather, and location. A 30% sucrose solution was more attractive than honey, jams, gels, or dry (solid) sugars. The sucrose solution was more attractive in spring and autumn than in summer, probably because rainfall washed away natural carbohydrate supplies. There was a significant relationship between rainfall in the previous week and the proportion of wasps caught in traps baited with sucrose solution versus sardine cat‐food. A higher proportion of German wasps than common wasps was caught in sucrose‐baited traps. This may have been related to seasonal differences in abundance and/or behavioural differences between the two species. In some locations, more wasps were caught in traps baited with sucrose solution than in those baited with sardine cat‐food. The proportion of wasps caught in sucrose‐baited traps was higher in locations without beech scale honeydew than with beech scale honey‐dew. Proportionally more non‐target species (mainly honey bees) and fewer wasps were caught in traps baited with sucrose solution than in those baited with sardine cat‐food. All five bee repellents tested also repelled wasps. These results indicate the importance of determining the bait preferences of wasps (carbohydrate or protein) and the presence of non‐target species before attempting a poison‐baiting operation. They also emphasise the need for a wasp‐specific carbohydrate‐based bait.     

Resting metabolism and critical thermal maxima of vespine wasps (Vespula sp.)

Vespine wasps are known for their high endothermic capacity. Endothermic activity is directly linked to respiration. However, knowledge on wasp respiration is sparse and almost nothing is known about their resting metabolism. We investigated the yellowjackets' CO(2) production in a flow-through respirometer chamber overnight. Endothermic and behavioral activity was observed by real-time infrared thermography. Most resting wasps were ectothermic or only slightly endothermic (thoracic temperature excess against abdomen <0.6°C). In the investigated temperature range (T(a)=2.9-42.4°C) mean CO(2) production rate of resting wasps increased steeply according to an exponential function, from 5.658 μl g(-1) min(-1) at 8.3°C to 8.504 μl g(-1) min(-1) at 20.2°C, 58.686 μl g(-1) min(-1) at 35.3°C and 102.84 μl g(-1) min(-1) at 40°C. The wasps' respiratory critical thermal maximum (CT(max)), marking the upper edge of their viable temperature range, was 45.3°C. The respiratory CT(max) did not differ significantly from the activity CT(max) of 44.9°C. CT(max) values were considerably below that of honeybees (48.9 and 49.0°C for respiration and activity, respectively). This allows honeybees to kill wasps by heat-balling. Comparison with other arthropods showed that vespine wasps are among the insects with the highest mass-specific resting metabolic rate and the steepest increase of metabolism with ambient temperature.     

Local dynamics of worker activity of the invasive Vespula germanica and V. vulgaris (Hymenoptera: Vespidae) wasps in Argentina

1. The abundance of insects depends essentially on the reproductive success of individuals. In social insects, however, the abundance of sterile workers outside a nest depends on colony size but is also determined by ontogeny, nest demands, and local environmental factors. For invasive social wasps, the drivers of worker abundance are important because they determine the impact that these species have on the native systems, people, and their goods. 2. The aim of the present study was to understand the relative importance of endogenous and exogenous factors on the abundance of workers of populations of Vespula spp., by analysing 12 years of trap captures in NW Patagonia. This is the first attempt to model the activity levels of invasive Vespula spp. wasps over time in Argentina. 3. It was shown that between years, the worker activity of both vespids presents fluctuations, and that of V. germanica is determined by the spring mean temperatures. Within the flight season, V. germanica worker activity is affected by the relative abundance of workers in that year, whereas for V. vulgaris, activity it is affected by the relative abundance of both species that year. We found no relationship between individual weather variables and activity within a flight season for both wasps. 4. The patterns observed for Argentina are similar to those observed in all invaded temperate areas where Vespula spp. are established. This study provides useful information to understand the driving factors that affect Vespula spp. worker activity in Argentina. This could be a necessary step to develop plans to manage these invasive social insects.     

Dispersal behavior of yellowjacket (Vespula germanica) queens

Understanding the factors that affect animal dispersal behavior is important from both fundamental and applied perspectives. Dispersal can have clear evolutionary and ecological consequences, but for nonnative insect pests, dispersal capacity can also help to explain invasion success. Vespula germanica is a social wasp that, in the last century, has successfully invaded several regions of the world, showing one of the highest spread rates reported for a nonnative insect. In contrast with nonsocial wasps, in social species, queens are responsible for population redistribution and spread, as workers are sterile. For V. germanica, it has been observed that queen flight is limited to 2 distinct periods: early autumn, when new queens leave the nest to mate and find sheltered places in which to hibernate, and spring when new colonies are founded. Our aim was to study the flight behavior of V. germanica queens by focusing on the different periods in which dispersal occurs, characterizing as well the potential contribution of queen flight (i.e., distance) to the observed geographical spread. Our results suggest that the distances flown by nonoverwintered queens is greater than that flown by overwintered individuals, suggesting that the main queen dispersal events would occur before queens enter hibernation. This could relate to a behavioral trait of the queens to avoid the inbreeding with related drones. Additionally, given the short distances flown and remarkable geographical spread observed, we provide evidence showing that queen dispersal by flight is likely to contribute proportionately less to population spread than human‐aided factors.     

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.     

Diversity,abundance and foraging behaviour of insect pollinators in Radish (Raphanus raphanistrum subsp. sativus L.)

Insect pollinators and flowering plants have co-evolved together for millions of years, developing a wide array of mutualistic interactions. Several cultivated plant species depend exclusively on insect-mediated pollination services for their subsistence, reproduction and survival. Radish, Raphanus raphanistrum subsp. sativus, a popular edible root vegetable (Family: Brassicaceae) completely depends on pollinators as self-pollination is totally absent due to sporophytic self-incompatibility. The present study was conducted at the experimental fields of the ICAR-Indian Institute of Horticultural Research, Bengaluru, to understand the diversity and foraging behaviour of insect pollinators in R. sativus. Continuous survey during the flowering period revealed that a total of fifteen insect species that belong to three insect orders (Hymenoptera, Diptera and Lepidoptera) were found to visit R. sativus flowers. The most abundant species was Apis florea L., followed by Apis dorsata F., Tetragonula iridipennis (Smith), Apis cerana F., Lassioglossum sp. and Ischiodon scutellaris F. Floral visitors differed significantly in terms of their visitation frequency, with A. florea (0.76 ± 0.22 visits/flower/ min) being the most frequent visitor followed by A. dorsata (0.66 ± 0.21 visits/flower/ min) and T. iridipennis (0.59 ± 0.14 visits/flower/30 min). The maximum visitation rate was recorded for A. dorsata (7.8 ± 1.40 flowers visited/min) followed by A. cerana (6 ± 1.15). The maximum stay time on individual flower was recorded for Lassioglossum sp. (48.2 ± 3.67 sec) followed by T. iridipennis (44.2 ± 4.24 sec). The maximum numbers of pollen grains were deposited by A. dorsata (206.70 ± 56.45) followed by A. cerana (151.20 ± 31.84). All the floral visitors except A. florea made contact with stigma on every single visit (100 %). While, only 53 per cent of total visitation by the Apis florea led to stigma contact. Further, nectar robbing behaviour was majorly exhibited by A. florea and Delta conoideum compared to all other insect pollinators observed. Based on the overall pollinator effectiveness per day A. dorsata was found to be the most effective single pollinator species.     

Changes in abundance of Vespula germanica and V. vulgaris in England

1. Thirteen time series, varying from 17 to 27 years, of the abundance of Vespula germanica and V. vulgaris from lowland England are examined. The time series depend on either spring queens and workers taken in Malaise or suction traps, or collected colonies. 2. During the late 1970s and early 1980s, the abundance of V. germanica declined abruptly but that of V. vulgaris did not. 3. During the early 1980s, the 2‐year cycle of annual abundance of V. vulgaris changed to a nearly perfectly damped pattern of annual abundances. 4. The most likely factor causing these population changes was the increased use of pesticides acting directly by killing the wasps and indirectly by reducing their food resources. 5. The difference in response of the two species to increased pesticide use may be related to a difference in foraging ability.