Unmated queens in the primitively eusocial waspRopalidia marginata (Lep.) (Hymenoptera: Vespidae)

Summary In the primitively eusocial tropical waspRopalidia marginata, five out of eleven colonies studied had an unmated female as their queen. In two colonies this was the case despite the presence of another mated individual in the colony. We found no detectable differences between colonies with unmated queens and those with mated queens. We argue that in species such asR. marginata, where intracolony relatedness is expected to be low and where sociality is likely to be maintained because several individuals have opportunities for direct reproduction in the future, individual selection is likely to override the good of the colony and lead to such phenomena as that of unmated queens.     

Factors affecting the acceptance of alien conspecifics on nests of the primitively eusocial wasp,Ropalidia marginata (Hymenoptera: Vespidae)

In the primitively eusocial wasp, Ropalidia marginata,individual females are known to drift from one newly founded nest to another. In the laboratory, young (<6- to 8-day-old) alien wasps are accepted onto unrelated colonies, while older (>6- to 8-day-old) wasps are not. Here we have investigated the factors that could influence the acceptance of foreign conspecifics onto unrelated nests. Individually marked wasps of different ages, isolated immediately after eclosion from the natal nest and from each other, were introduced onto unrelated recipient nests. Considered separately, both age and ovarian condition seemed to influence the probability of acceptance as well as the levels of aggression and tolerance received by the introduced wasps. However, partial correlation analysis and multiple regression analysis indicated that only age had a direct influence and that the ovarian condition acts only through age, a variable with which it is highly correlated. The observed acceptance of young aliens and rejection of old aliens are less likely to be due to the perception of older wasps as a reproductive threat rather than some age-related factor, other than ovarian condition, for example, the relative ease with which younger wasps can be molded into desired roles.     

The role of larval nutrition in pre-imaginal biasing of caste in the primitively eusocial wasp Ropalidia marginata (Hymenoptera: Vespidae)

Abstract.

• 1 When freshly eclosed females of the primitively eusocial wasp Ropalidia marginata (Lep.) are isolated, only about 50% of them build nests and lay eggs thereby suggesting a pre-imaginal biasing of caste.
• 2 Wasps that lay eggs take a very variable amount of time after eclosion to start doing so.
• 3 Females eclosing from nests where larvae are fed at a relatively higher rate are more likely to become egg-layers and are likely to take less time after eclosion to begin to lay eggs.
• 4 Thus, both forms of pre-imaginal biasing of caste, namely, differences in egg laying capacity and differences in the time taken to attain reproductive maturity, appear to be influenced by larval nutrition.

     

Evidence for multiple mating in the primitively eusocial waspRopalidia marginata (Lep.) (Hymenoptera: Vespidae)

Asymmetries in genetic relatedness created by haplodiploidy have been considered to be crucially important for the evolution of worker behaviour in Hymenoptera. Multiple mating by the queens destroys this asymmetry and should make kin selection less powerful. The number of males that social insect queens mate with is thus of considerable theoretical interest especially in primitively eusocial species. The results presented here provide evidence for multiple mating by foundresses of the primitively eusocial waspRopalidia marginata (Lep.)     

Kin recognition in a semi-natural context: Behaviour towards foreign conspecifics in the social waspRopalidia marginata (Lep.) (Hymenoptera: Vespidae)

Summary Female wasps of the tropical primitively eusocial speciesRopalidia marginata are known to discriminate unfamiliar nestmates from unfamiliar non-nestmates outside the context of their nests. Here, we show that when foreign conspecifics are introduced in the context of a nest in laboratory cages, genetic relatives among them are treated by nest inhabitants more tolerantly than non-relatives, but that no foreign conspecifics are accepted into the nests. However, some wasps may leave their nest and join the foreign relatives and non-relatives to found new colonies cooperatively. Very few of the introduced animals are severely attacked or killed; most are allowed to remain in parts of the cage away from the nest. These results suggest that factors other than genetic relatedness may be involved in regulating tolerance and acceptance of foreign conspecifics on a nest and its vicinity. Our results are different from those of similar experiments with ants, which have demonstrated that former nestmates that are removed as pupae and later introduced as adults are either accepted into the nest or attacked and killed. We attribute this difference to the fact that in a primitively eusocial species such asR. marginata, the rules governing tolerance and acceptance of foreign conspecifics must be quite different from those in highly eusocial species. We also attempt to test some predictions of the conspecific acceptance threshold models of Reeve (Am. Nat. 133:407–435, 1989). Our results uphold the predictions of his fitness consequence submodel but do not support those of his interaction frequency sub-model.     

We know that the wasps 'know': cryptic successors to the queen in Ropalidia marginata

Unlike other primitively eusocial wasps, Ropalidia marginata colonies are usually headed by remarkably docile and behaviourally non-dominant queens who are nevertheless completely successful in maintaining reproductive monopoly. As in other species, loss of the queen results in one of the workers taking over as the next queen. But unlike in other species, here, the queen's successor cannot be predicted on the basis of dominance rank, other behaviours, age, body size or even ovarian development, in the presence of the former queen. But the swiftness with which one and only one individual becomes evident as the potential queen led us to suspect that there might be a designated successor to the queen known to the wasps, even though we cannot identify her in the queen's presence. Here, we present the results of experiments that support such a 'cryptic successor' hypothesis, and thereby lend credence to the idea that queen (and potential queen) pheromones act as honest signals of their fertility, in R. marginata.     

Behavioral role differentiation in the primitively eusocial waspBelonogaster juncea juncea (Hymenoptera: Vespidae)

With a view toward describing behavioral variability among individuals of the primitively eusocial speciesBelonogaster juncea juncea, we recorded the time-activity budget spent on five behavioral categories (foraging, building, feeding, inactivity, and reproduction) by 52 individuals belonging to four postemergence colonies. A principal-components analysis coupled with a hierarchical cluster analysis enabled us to discern four behavioral roles. The reproductive role is reserved to one individual (functional monogyny) and the workers’ role is differentiated into foragers, builders, and guards. The foragers are females that spend the most time (82.6% of their time) foraging, supplying the nest with prey load and liquid matter. The builders are individuals (with 41.5% of their time off the nest) that tend to bring pulp into the nest and then undertake building activities. The guards are those females that spend the most time (79.7% of their time) being inactive on the nest.     

Colony founding in the primitively eusocial wasp, Ropalidia marginata (Hymenoptera: Vespidae)

Abstract.

• 1 In a 16-month study in Bangalore, India, about 35% of the newly founded colonies of Ropalidia marginata were single foundress colonies and the remainder were multiple foundress colonies with two to twenty-two individuals.
• 2 Larger colonies did not have a significantly higher per capita productivity, did not produce significantly heavier progeny and did not produce them significantly faster than smaller colonies did.
• 3 Predation by the hornet Vespa tropica appeared to be independent of group size.
• 4 Single foundress colonies failed more often but not often enough to make them have a lower average per capita productivity, compared to multiple foundress colonies.
• 5 Some of the advantages of multiple foundress associations came from the greater predictability of their attaining the mean per capita productivity, the relatively lower rates of usurpation experienced by them compared to single foundress colonies, and the opportunities provided by queen turnovers for workers to become replacement queens and gain direct individual fitness.

     

Regulation of worker activity in a primitively eusocial wasp, Ropalidia marginata

Ropalidia marginala, a tropical, primitively eusocial, polistinewasp, is unusual in that the queen (the sole egg-layer) is neitherthe most behaviorally dominant nor the most active individualin the colony. The queen by herself rarely ever initiates interactionstoward her nest mates or unloads returning foragers. There arealways a few workers in the colony who are more dominant andactive than the queen. Absence of the queen from her colonydoes not affect colony maintenance activities such as foragingor brood care, but it always results in one individual becomingvery aggressive and dominant. The dominant worker becomes thenext queen if the original queen does not return. The queendoes not appear to play any significant role in colony activityregulation. Instead, colony activities appear to be regulatedby several mechanisms including dominance behavior toward foragers,feeding of larvae, and the unloading of returning foragers,all mediated by workers themselves. Regulation of colony maintenanceappears to be based on direct evaluation of the needs of thecolony by the workers themselves. The queen however has perfectreproductive control over all workers; workers never lay eggsin the presence of the queen. It appears therefore that themechanisms involved in regulation of worker activity and workerreproduction are separate in R marginata. These findings contrastwith other primitively eusocial species where the queen actsas a "central pacemaker" and controls both worker activity andworker reproduction.     

A possible novel function of dominance behaviour in queen-less colonies of the primitively eusocial wasp Ropalidia marginata

Unlike the queens of other primitively eusocial species, Ropalidia marginata queens are strikingly docile and non-aggressive individuals, never at the top of the behavioural dominance hierarchy of their colonies. Nevertheless, these queens are completely successful at suppressing worker reproduction, suggesting that they do not use aggression but employ some other mechanism (e.g. pheromones) to do so. Upon removal of the queen from a colony, a single worker, the 'potential queen', immediately begins to display highly elevated levels of aggression towards her nest mates. This individual becomes the next docile queen if the original queen is not returned. We attempt to understand the function of the temporary and amplified dominance behaviour displayed by the potential queen. We find that the dominance behaviour shown by the potential queen is unrelated to the number of her nest mates, their dominance ranks or ovarian condition. This suggests that aggression may not be used to actively suppress other workers and counter threat. Instead we find evidence that dominance behaviour is required for the potential queen's rapid ovarian development, facilitating her speedy establishment as the sole reproductive individual in the colony.     

Dominance behaviour and regulation of foraging in the primitively eusocial wasp Ropalidia marginata (Lep.) (Hymenoptera: Vespidae)

Ropalidia marginata is a primitively eusocial, polistine wasp widely distributed in peninsular India. In spite of its primitively eusocial status, queens of R. marginata are surprisingly docile and behaviourally non-dominant (except during the first week or so of their careers as queens). Yet they successfully maintain reproductive monopoly throughout their careers, probably through the use of pheromones. Workers exhibit dominance-subordinate interactions but these behaviours are not involved in regulating reproductive competition among the workers because workers with high dominance ranks are not necessarily the ones who replace lost queens. We have speculated and provided correlational evidence before that dominance-subordinate interactions among the workers have been co-opted in this species for the workers to regulate each other's foraging. Here, we provide experimental evidence in support of the speculation, by reducing demand for food and showing that this results in a significant decrease in the frequency of dominance-subordinate interactions among the workers.     

Workers of the primitively eusocial wasp <Emphasis Type="Italic">Ropalidia marginata</Emphasis> do not perceive their queen across a wire mesh partition

Queens of primitively eusocial wasps generally have active and behaviourally dominant queens who use physical aggression to suppress worker reproduction. Although a Ropalidia marginata queen is strikingly docile and behaviourally non-dominant, she is completely successful in maintaining reproductive monopoly. R. marginata queens must achieve such reproductive monopoly by some means other than overt physical aggression. Upon loss or removal of the queen, one of the workers (referred to as the potential queen) becomes extremely aggressive and will eventually go on to become the next queen of the colony, if the original queen is not returned. The fact that potential queens are not discernible in the presence of the queen but become obvious within minutes after removal of the queen raises the question of how workers in general and the potential queens in particular, perceive the presence or absence of their queens. Here, we have conducted experiments in which we separate half of the workers from their queen by a wire mesh screen and study their behavioural response to such separation. We demonstrate that the presence of the queen is not perceived across the wire mesh screen, which suggests that if the queen uses a pheromone to signal her presence, then that pheromone is not very volatile.     

Queen brood reared in worker cells by the social wasp,Vespula germanica (F.) (Hymenoptera: Vespidae)

Summary The rearing of queen brood from worker cells in the nests ofVespula germanica (F.) in Australia was found at all stages of the colony cycle from early summer to autumn. Worker cells used to rear queens were 17% wider at their open ends than cells used for worker production, and in all other respects their dimensions were greater. The volume of a worker cell used for queen nearing was 21% larger than cells used for rearing workers but half the volume of a normal queen cell. Queen pupae reared in worker cells were significantly smaller than those reared in queen cells of the same nest. The spatial distribution of queen pupae in worker comb tended to be random although some evidence of nonrandom clustering was noted.The significance of this phenomenon is discussed in relation to caste differentiation and queen-control of gyne initiation and production. It is concluded that the phenomenon is neither seasonal nor due to some intrinsic component of the colony's annual cycle, and that it is unlikely to be an emergency queen-rearing response. Development of queens in worker cells may have occurred during favourable feeding regimes, perhaps determined by the benign Australian environment.     

Absence of chemical alarm in a primitively eusocial wasp (Belonogaster petiolata,Hymenoptera: Vespidae)

Summary The hypothesis thatBelonogaster petiolata (fam. Vespidae) is able to communicate alarm chemically, using odours released with the venom, was tested in bioassays involving presentation of artificial targets to a wasp colony, simultaneously with crushed venom apparatuses. The odour of venom did not lower the threshold of attack and visual stimuli alone (particularly a black, moving object) were sufficient to release attack. Venom odour on a previously stung target probably does not play a role in focusing further attacks on such a target. The results therefore support the null hypothesis that a venom-based alarm pheromone is absent in this species.     

Mating structure and genetic relatedness among gynes in the primitively eusocial wasp Polistes snelleni (Hymenoptera: Vespidae)

Mating structure and genetic relatedness among gynes (potential reproductive females) of the paper wasp Polistes snelleni were investigated using DNA microsatellite markers. All colonies had one foundress inseminated by a single male, and no sign of inbreeding was detected. The mean genetic relatedness among gynes was 0.734 ± 0.028 (SE), which is not significantly different from the expected value of 0.75 for full sisters.     

Colony dynamics in a primitively eusocial halictine beeLasioglossum (Dialictus) zephyrum (Hymenoptera: Halictidae)

Summary Proximate control of colony dynamics was studied in the primitively eusocial halictine beeLasioglossum (Dialictus) zephyrum using allozyme markers. The results indicate that workers produce on average 15% of the male brood (range=0–50%) in small laboratory colonies made up of unrelated, single-generation, uninseminated females. This proportion is not influenced by colony size, but is influenced by the relative size of the queen. Large queens are more successful in dominating their workers than are small queens, the queen being defined as the female that is the mother of most of the brood produced in the colony. Older and larger females tend to become queens. Thus, while small differences in age (up to 4 days) influence which female becomes a queen, her ability to control her workers is primarily influenced by her relative size. The proportion of reproduction that is co-opted by the queen is negatively correlated with colony reproductivity (the number of males/day/female). Colony reproductivity is also negatively correlated with the standard deviation in size among females.     

Reproductive and worker castes in the primitively eusocial wasp Belonogaster petiolata (DeGeer) (Hymenoptera: Vespidae): evidence for pre-imaginal differentiation

Until recently, morphological differences between castes in independent-founding polistine wasps were considered absent. This paper investigates the extent of morphological and physiological differences between reproductive (foundress and gyne) and worker castes of Belonogaster petiolata, and tests the hypothesis that caste differentiation in this species occurs pre-imaginally.Foundresses were significantly larger than workers, to the extent that foundress/worker ratios were comparable with those between queens and workers in some swarm-founding Polistinae. Early emerging workers were small, but body size increased over the colony cycle such that late-season workers were similar in size to gynes. In proportion to body size, workers possessed broader heads while foundresses and gynes had broader thoraces and gasters. All queens, 98% of subordinate foundresses, and 95% of over-wintering gynes were inseminated. Workers were never inseminated and lacked mature ovaries in colonies with active queens. However, in the absence of the queen (and other foundresses), 11% of workers developed mature ovaries. Ovarian size and fat content of foundresses and gynes was significantly greater than that of workers. The differences in external morphology and reproductive physiology between castes support the hypothesis that differentiation occurs pre-imaginally. However, imaginal factors, in particular social dominance of the queen, maintain the reproductive subordinance of workers.     

Trophallaxis in a primitively social sphecid wasp

Summary In a total of six hours of observation of severalMicrostigmus nigrophthalmus nests with two or more adult wasps, nine buccal contacts, six between females and three between females and males were observed. Except for two cases, these occurred soon after one of the females involved (the apparent donor) had returned to the nest and involved transfer from older to younger individuals. Experimental feeding of colored solution confirmed the occurrence of trophallaxis. InM. nigrophthalmus, trophallaxis seems to have arisen as a prolongation of maternal care since food is transferred from an older to a younger individual.     

Variation in the quality of Vespula vulgaris (L.) queens (Hymenoptera: Vespidae) and its significance in wasp population dynamics

Abstract

Density‐related variation in queen quality has been proposed as a possible mechanism regulating population fluctuations in Vespula species. We investigated annual variation in the quality (size, weight, and fat content) of adult V. vulgaris queens representing four stages of their life cycle (spring, founding, developing, and emerged) taken from six sites in beech forest, South Island, New Zealand. For each queen the dry weight, head width, and thorax length was measured. For a subsample of queens, the fat content was determined by ether extraction. The size of queen cells was measured from a subsample of nests. Size, weight, and fat content of queens varied between wasp colonies and sites. The smallest juvenile queens were under‐represented in the reproductive population. There was no direct link between body size and food supply. Size and weight of developing queens increased as the number of cells in the nest increased. The size of the queen cells varied significantly among layers in a nest and among nests. The under‐representation of small queens in the reproductive population suggests that queen quality may affect survival and/or competitive ability by increasing winter fat storage, nest building activity, and/or success in usurpation disputes.     

Juvenile hormone accelerates ovarian development and does not affect age polyethism in the primitively eusocial wasp,Ropalidia marginata

Juvenile hormone modulates post-imaginal reproductive division of labor in primitively eusocial species and promotes the production of queens (e.g., Polistes) while it modulates age polyethism and promotes the production of foragers in highly eusocial species (e.g., the honey bee). Ropalidia marginata is a primitively eusocial wasp that shows both post-imaginal regulation of reproductive division of labor as well as age polyethism. Hence, R.marginata is a particularly interesting model system to study the effect of juvenile hormone. We demonstrate here that a single, topical application of 100 micro g of juvenile hormone-III per female wasp accelerates ovarian development of wasps held in isolation. Similar application to wasps released back on to their natal nests has no effect on their rate of behavioral development as witnessed from the age of first performance of feed larva, build, bring pulp and bring food. We conclude therefore that in R.marginata, juvenile hormone has retained its function of modulating reproductive division of labor and has not acquired the function of modulating age polyethism.