Demography of the Okinawan eusocial wasp Ropalidia fasciata (Hymenoptera: Vespidae) II. Effects of foundress group size on survival rates of colonies and foundresses, and production of progeny

Using demography data for the primitively eusocial wasp Ropalidia fasciata collected at 10 survey stations over 5 years, the effects of foundress group size (FGS) on colony survival rate and production of progeny were examined. The distribution pattern for the frequency of nests established by different numbers of foundresses fit a 0‐truncated negative binomial distribution. The rate of nest failure up to the beginning of June decreased with FGS, and colony survival rate up to June and September increased with FGS. Although there were large variations among stations and years, the survival rate of colonies established by a single foundress (haplometrotic colonies) was significantly lower than that of colonies established by two or more foundresses (pleometrotic colonies). The number of new adults that emerged per colony up to the end of July increased with FGS, but there was no significant correlation between number of new adults per foundress and FGS. The number of potential foundresses produced per colony tended to increase with FGS, but there was no significant difference among the values produced per foundress for the three FGS categories. The percentage parasitism by an ichneumon parasitoid, Arthula formosana, tended to be higher in colonies established by a small number of foundresses. The relation between FGS and the productivity of the new foundresses was not statistically significant, suggesting that independent founding may be a better strategy for future subordinate foundresses. However, the long colony life span (mean 100 days, maximum 240 days) as compared with the shorter life span of foundresses (40 or 50 days) may be a good condition for the coexistence of many egg‐layers in a colony.     

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.

     

Size-dependent reproductive dominance in foundresses of Ropalidia plebeiana, an Australian paper wasp forming nest aggregations (Hymenoptera: Vespidae)

The relationship between reproductive status and body size in foundresses of Ropalidia plebeiana, an Australian endemic paper wasp forming huge aggregations of nests, was examined. Foundresses with developed ovaries (laying foundresses) in multifoundress colonies tended to be larger than foundresses in single‐foundress colonies and foundresses with undeveloped ovaries (non‐laying foundresses). However, the laying foundress was not always the largest of the foundresses in a colony. Body shape in foundresses varied according to simple allometric growth, while foundresses and first brood females diverged in their growth parameters in the preimaginal stage.     

Effects of human presence on two social wasp species

Abstract.  1. The effects of human presence on the behavioural response and productivity of a native wasp species of North America ( Polistes fuscatus ) and an invasive wasp species ( Polistes dominulus ) were examined in a field experiment. Over a 3-month period, colonies of each species were exposed to human presence at either low (biweekly) or high (daily) levels. At 2-week intervals, wasp response to human presence was recorded for all colonies via an index, ranging from no response (0) to an attack (4).
2. The levels of human presence had no effect on wasp response or colony productivity but foundresses of both species increased their response level the closer a human was to the nest. In addition, foundresses of P. fuscatus became more aggressive over time, corresponding to after adult offspring emerged, whereas foundresses of P. dominulus did not change their response level after the emergence of offspring.
3. The adult offspring of P. dominulus responded to human presence at a level similar to that of the foundress, whereas adult offspring of P. fuscatus exhibited a lower response to human presence than that of the foundress. The more distinctive aposematic coloration of P. dominulus may play a role in the behavioural differences between species; it may be more effective in deterring predators, and with the result that leaving the nest to defend it is less often necessary. Accordingly, the less aggressive response to human presence by P. dominulus may contribute to its success as an introduced species in North America.     

Reconstruction of fig wasp mating structure: how many mothers share a fig?

Abstract.  1. Fig wasps (Hymenoptera: Agaonidae) represent an important model system for studies of sex ratio evolution, mainly because they may adjust their sex ratios in response to the numbers of ovipositing females (foundresses) that enter a fig and their clutch size.
2. Until recently, it was assumed that all foundresses fail to re-emerge from the figs that they have entered to oviposit, but there is increasing evidence that such re-emergence may be routine. The common practice of counting the number of dead foundresses present in a fig in order to deduce the number of foundresses is therefore questionable in species where failure to re-emerge has not been confirmed.
3. In this study, the alternative approach of microsatellite markers was used to reconstruct the within-fig breeding structure of a pollinating fig wasp by genetic analysis of the offspring. Broods of Liporrhopalum tentacularis , a species where foundresses regularly re-emerge from figs, were collected from figs of Ficus montana in their natural habitat in Indonesia as well as from an experimental glasshouse population in Leeds (U.K.).
4. The estimated foundress densities in the glasshouse population were similar to those in the field and ranged from one to six foundresses per brood.
5. Nearly 40% of all broods were produced by a single foundress, indicating that mating in these broods occurs exclusively between full siblings. High levels of inbreeding are therefore common in this species.     

Behavioral Profiles Related to Dominance Hierarchy in Associated Foundresses of Belonogaster juncea juncea (F.) (Hymenoptera: Vespidae)

This study was conducted to examine the phenomenon of task partitioning among associations of foundresses of the primitively eusocial wasp Belonogaster juncea juncea (F.). The time–activity budget for five main behavioral categories (foraging, building, feeding, inactivity, and reproduction) for each foundress belonging to trigynic associations was recorded using the instantaneous scanning technique. After ranking the individuals on the basis of agonistic encounters, data were submitted to a canonical discriminant analysis. The results show behavioral differences between individuals of each rank. The proportion of time allocated to foraging behavior is a good rank index. The females of the first rank spent less time on foraging behavior and significantly more time (13.6% of their time) on reproductive behavior than females of other ranks. The females of the second rank also spent less time on foraging behavior and showed a tendency toward building behavior. The females of the third rank spent significantly more time (77.28% of their time) on foraging behavior. The behavioral profile of each foundress was therefore determined by its rank on the dominance scale.     

Colony development and social structure in a subtropical paper wasp,Ropalidia fasciata (F.) (Hymenoptera: Vespidae)

More than 50% of nests of Ropalidia fasciata were founded by association of foundresses (multifemale nests). The multifemale nests were generally initiated earlier and grew faster than the single-female nests. The survival rate of the multifemale nests was significantly higher than that of single-female nests, and the productivity as measured by the number of cells produced per foundress had a peak at a foundress-group size from 6 to 10. The number of marked foundresses which were seen on their original nest decreased as the colony cycle proceeded, but some of them continued to coexist on the original nests after emergency of many female progeny. Except in the case where a large number of foundresses attended a young nest so that some foundresses could not sit on the nest, the dominance interactions among cofoundresses were mild. More than twothirds (71.4%) of nests (including those at the post-emergence stage) had multiple egg-layers. The foundress association in this species is considered to be beneficial for every foundress because it raises ability to avoid predation or to reconstruct their nests when the nests are destroyed by typhoons.     

The consequences of clustering by Aphis fabae foundresses on spring migrant production

Aphis fabae (Homoptera: Aphididae) foundresses were shown to have a clustered distribution on leaves of their primary host, Euonymus europaeus. Two field experiments were carried out to determine the costs or benefits of this clustering behaviour to aphid clones. The first experiment, in spring 1996, excluded predators from colonies formed by single fundatrices or clusters of three. No density-dependent effects on colony growth were observed early in the season, but the total production of migrants per foundress was significantly lower for clustered foundresses. This demonstrated that there was no synergistic effect of group feeding on clonal performance. All colonies were initiated on randomly selected leaves and all grew successfully, therefore clustering was not due to a shortage of feeding sites. The second experiment, in spring 1997, tested whether natural enemies cause selection for selfish herding by the foundress generation. Colonies were initiated by one or three foundresses, but half were left unbagged. If natural enemy attack is a selective force inducing clustering behaviour in foundresses, the costs of clustering should have been reduced or negated in unbagged colonies. Colonies grown from clusters produced significantly fewer migrants per foundress, irrespective of bagging treatment. Other potential factors causing clustering behaviour are discussed. Received: 19 August 1998 / Accepted: 16 November 1998     

Colony productivity and foundress behaviour of a native wasp versus an invasive social wasp

Abstract.  1. Colony productivity, prey utilisation, and foundress behaviour of a North American native wasp ( Polistes fuscatus ) versus an European invasive wasp ( Polistes dominulus ) were investigated in a controlled field experiment with optimal versus natural foraging conditions. Colonies with the optimal prey foraging conditions were provided with prey ad libitum within an enclosed area. The other colonies foraged in the adjacent field–woodland but had the same nest conditions as the other treatment.
2. When given prey ad libitum , both wasp species captured similar amounts of prey and the conversion to total offspring biomass was similar. But P. dominulus colonies produced 2.5 times the number of workers as P. fuscatus colonies, reflecting the smaller size of P. dominulus wasps.
3. Foundresses of P. dominulus were observed more often building or repairing the nest, thereby contributing to the production of colonies with twice as many cells as colonies of P. fuscatus . Foundresses of P. dominulus showed more acts of aggression toward workers than did P. fuscatus foundresses, which was not a function of adult density on the nest.
4. At the end of the experiment, P. dominulus colonies with optimal prey foraging conditions still had a high level of egg-laying and peaked in the number of pupae then, whereas egg-laying and the number of pupae per colony of the other treatments began to decline 2–3 weeks earlier. These results indicate that P. dominulus is more opportunistic than P. fuscatus , which may account in part for P. dominulus 's success as an introduced species in North America.     

Costs and benefits of joint colony founding in Australian Acacia thrips

Facultative joint colony founding by social insects (pleometrosis) provides an outstanding opportunity to analyze the costs and benefits of sociality. Pleometrosis has been documented for a range of social insects, but most studies on the adaptive benefits of this behavior are restricted to the Hymenoptera. In this study, we provide the first analysis of costs and benefits associated with pleometrosis for Australian Dunatothrips, which form domiciles by glueing together phyllodes (leaves) of their Acacia host plant. In Dunatothrips aneurae, the distribution of foundress numbers per nest indicated that females formed associations non-randomly. Furthermore, average group size was independent of both the number of foundresses on the host plant and the number of mature colonies, suggesting that this behavior was not simply a response to limited availability of nesting sites. Although per capita reproduction declined with increasing group size, we also identified two benefits of pleometrosis: (1) individual foundresses in groups had higher survival than solitary foundresses during the brood development period, and (2) larger colony sizes resulting from pleometrosis provided a benefit later in colony development, because a higher proportion of D. aneurae adults survived invasions by the kleptoparasite Xaniothrips mulga when colony size was larger. These results demonstrate that the reproductive costs of pleometrosis are at least partially counterbalanced by survival benefits. Received 4 April 2006; revised 9 September 2006; accepted 20 September 2006.     

Co‐foundress confinement elicits kinship effects in a naturally sub‐social parasitoid

Kinship among interacting individuals is often associated with sociality and also with sex ratio effects. Parasitoids in the bethylid genus Goniozus are sub‐social, with single foundress females exhibiting post‐ovipositional maternal care via short‐term aggressive host and brood defence against conspecific females. Due to local mate competition (LMC) and broods normally being produced by a single foundress, sex ratios are female‐biased. Contests between adult females are, however, not normally fatal, and aggression is reduced when competing females are kin, raising the possibility of multi‐foundress reproduction on some hosts. Here, we screen for further life‐history effects of kinship by varying the numbers and relatedness of foundresses confined together with a host resource and also by varying the size of host. We confined groups of 1–8 Goniozus nephantidis females together with a host for 5+ days. Multi‐foundress groups were either all siblings or all nonsiblings. Our chief expectations included that competition for resources would be more intense among larger foundress groups but diminished by both larger host size and closer foundress relatedness, affecting both foundress mortality and reproductive output. From classical LMC theory, we expected that offspring group sex ratios would be less female‐biased when there were more foundresses, and from extended LMC theory, we expected that sex ratios would be more female‐biased when foundresses were close kin. We found that confinement led to the death of some females (11% overall) but only when host resources were most limiting. Mortality of foundresses was less common when foundresses were siblings. Developmental mortality among offspring was considerably higher in multi‐foundress clutches but was unaffected by foundress relatedness. Groups of sibling foundresses collectively produced similar numbers of offspring to nonsibling groups. There was little advantage for individual females to reproduce in multi‐foundress groups: single foundresses suppressed even the largest hosts presented and had the highest per capita production of adult offspring. Despite single foundress reproduction being the norm, G. nephantidis females in multi‐foundress groups appear to attune sex allocation according to both foundress number and foundress relatedness: broods produced by sibling foundresses had sex ratios similar to broods produced by single foundresses (ca. 11% males), whereas the sex ratios of broods produced by nonsibling females were approximately 20% higher and broadly increased with foundress number. We conclude that relatedness and host size may combine to reduce selection against communal reproduction on hosts and that, unlike other studied parasitoids, G. nephantidis sex ratios conform to predictions of both classical and extended LMC theories.     

An experimental analysis of pleometrotic advantage in the desert seed-harvester antMessor pergandei (Hymenoptera; Formicidae)

Summary Starting colonies of the desert seed-harvester antMessor pergandei are clumped in the field and face severe intraspecific competition through brood raiding. Single foundress laboratory colonies ofM. pergandei are more likely to succeed at brood raiding with conspecific colonies if they are given additional workers and mature pupae several days prior to brood raiding. Per foundress fecundity remains constant across laboratory starting colonies established with 1, 3 and 5 foundresses. These results suggest that the selective advantage of cooperative colony foundation (pleometrosis) in this and similar species may derive directly from the ability of multiple foundresses to produce a larger brood raiding force.     

Demography of the Okinawan eusocial wasp Ropalidia fasciata (Hymenoptera: Vespidae) I. Survival rate of individuals and colonies, and yearly fluctuations in colony density

We conducted a series of demographic studies of the primitively eusocial wasp Ropalidia fasciata in Okinawa, a subtropical part of Japan, and found the following. The colony cycle of this wasp is annual, spanning from April to November or even December; this is longer than the colony cycles of other temperate polistine wasps so far reported. The survival rate of the marked foundresses was 40% to June, dropping to 1.4% by September. These survival rates are similar to other subtropical and tropical species. Most females that emerged in November were probably second generation adults (progeny of the original foundresses), which would participate in founding nests in the following spring. These facts indicate that R. fasciata in Okinawa is at least partially bivoltine. Survival of a nest to September was 10–20%; however, because a failed nest is often rebuilt, survival of the colony to September was as high as 50%. The mean number of new foundresses produced per foundress was 7.5, and their overwintering survival was 16%. Hence, a single foundress produced, on average, 1.2 progeny foundresses to the following year. Density dependence was shown in the rate at which the progeny foundresses were produced. These results explain the remarkable stability of nest densities from year to year in the area. The above results reveal that R. fasciata in Okinawa shares many demographic characteristics with other primitively eusocial wasps, particularly year‐to‐year stability of nest density and a long colony cycle.     

Consequences of foundress aggregation in the brown citrus aphid Toxoptera citricida

1. A field study was conducted in which colonies of Toxoptera citricida (Kirkaldy) were initiated with different numbers of foundresses on ungrafted citrus trees var. ‘Carrizo’ within an existing citrus grove in central Florida. 2. The growth rate, longevity, and final size of T. citricida colonies were all positively correlated with number of foundresses. 3. Colonies initiated by many foundresses produced alatae earlier than those initiated by fewer foundresses. 4. Nymphal developmental time was reduced in colonies initiated by more foundresses but the mean number of grand‐progeny per foundress was lower when only surviving colonies were compared. 5. The longevity of foundresses was unaffected by their number but foundress fecundity and nymphal survival decreased as foundress number increased. 6. The most abundant natural enemies were Diptera: Syrphidae, primarily Pseudodorus clavatus (F.), and Chamaemiidae (Leucopis sp.), followed by Coleoptera: Coccinellidae, primarily Cycloneda sanguinea (L). 7. Colonies initiated with more foundresses attracted more oviposition by dipteran predators than did colonies initiated with fewer foundresses.     

Pleometrosis in phyllode-glueing thrips (Thysanoptera: Phlaeothripidae) on Australian Acacia

Pleometrosis, or colony founding by more than one female, is common in various social insects and it engenders opportunities for social cooperation as well as cheating. The life cycles of four species of thrips on Australian Acacia trees were examined to elucidate the extent and nature of colony founding by multiple individuals. Data from colonies of three species of thrips from the genus Dunatothrips Moulton and one species of Lichanothrips Mound were used to infer the prevalence of pleometrosis in each species. The results indicate that Dunatothrips species show high levels of cofounding, with up to 50% of colonies having more than one foundress. By contrast, colonies of Lichanothrips are predominantly established by a female and a male. As in some communal insects, pleometrosis is facultative in Dunatothrips , foundresses show more or less constant per capita reproduction with foundress number, and the selective pressures for pleometrosis may involve predation pressure during founding or survivorship insurance for the brood. In Lichanothrips , male founders are probably engaging in mate guarding, which also occurs in some species of gall-inducing thrips on Acacia . The differences in founding patterns between Dunatothrips and Lichanothrips may be due in part the nature of their domiciles: Dunatothrips engage in extensive construction of a domicile using anal secretions, whereas many Lichanothrips primarily improve a pre-existing partial enclosure. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 467–474.     

Benefits of foundress associations in the paper wasp Polistes dominulus: increased productivity and survival, but no assurance of fitness returns

Successful Polistes dominulus nests can be started by one ormore nest founding queens (foundresses). Consequently, thereis much interest in the specific benefits that induce cooperationamong foundresses. Here, we experimentally demonstrate one majorbenefit of cooperation, namely that multiple foundresses increasecolony productivity. This increase is close to the value predictedby subtracting the productivity of undisturbed single-foundresscolonies from the productivity of undisturbed multiple-foundresscolonies. However, we found no evidence that an associatingfoundress' contribution to colony growth is preserved if shedisappears (assured fitness returns). Our correlational datasuggest that cooperation provides survival benefits, multiple-foundresscolonies are more likely to survive to produce offspring thanare single-foundress colonies, and individual foundresses inmultiple-foundress groups are less likely to disappear beforeworker emergence than foundresses nesting alone. Therefore,association provides substantial productivity and survival benefitsfor cooperating foundresses.     

Foundress behaviors and interactions in polygynous colonies of the haplometrotic Japanese paper wasp Polistes snelleni (Hymenoptera: Vespidae)

Only two out of 959 pre‐emergence colonies of the paper wasp Polistes snelleni de Saussure surveyed between 1989 and 1996 in Sapporo, northern Japan, were found to be two‐foundress colonies, and the others were single‐foundress colonies. The two foundresses in one of the two colonies showed neither aggressive dominance behavior nor clear division of labor between them during a total of approximately 30 h in the first half of the pre‐emergence stage. Although both of the foundresses foraged for pulp and laid eggs, only one foundress foraged for prey and delivered it to the other.     

Geographic Variation in Air Temperature Leads to Intraspecific Variability in the Behavior and Productivity of a Eusocial Insect

In primitively eusocial insects, air temperature is the environmental factor that primarily affects colony cycle. Several studies demonstrated interspecific differences in the adaptation of eusocial insects to local air temperature. Nevertheless, studies on intraspecific adaptations are rare. In this study, we investigate the influence of air temperature on local adaptations in behavior and colony productivity of Polistes biglumis foundresses living in warm and cold temperate zones. We hypothesized that foundresses from warm temperate zones would show a higher activity level compared to those from cold temperate zones before brood emergence, based on differences in air temperature between the two zones. After brood emergence, we expected a reduced foundress activity level in the warm climate zone, due to workers’ help. In contrast, foundresses living in the cold-climate zone, which do not produce workers, were expected to remain active throughout the nesting season. We also hypothesized that colony productivity was higher in warm-climate colonies. As expected, warm-climate foundresses reduced their activity level after brood emergence and, with their relatively large number of workers, continued egg production throughout the nesting season. Further studies are necessary to assess if these intraspecific differences are attributable to phenotypic plasticity or genetic divergence.     

Honey supplementation and its developmental consequences: evidence for food limitation in a paper wasp, Polistes metricus

ABSTRACT.

• 1 Polistes metricus Say (Hymenoptera: Vespidae, Polistinae) field colonies were supplemented with dilute honey during the pre-emergence and early post-emergence phases of colony development.
• 2 Supplementation did not increase number of nest cells constructed or rates of loss to predation or foundress disappearance compared with controls.
• 3 Colonies receiving honey supplementation produced first offspring earlier in the season than control colonies. The difference is due to a shorter time span between founding and first emergence.
• 4 Foundresses of supplemented and control colonies did not differ in wing length or per cent body fat.
• 5 Offspring of both supplemented and control colonies had shorter wing lengths than did foundresses of supplemented colonies. Offspring of control colonies had shorter wing lengths than did foundresses of control colonies but not foundresses of supplemented colonies.
• 6 The per cent body fat of offspring from control colonies was lower than that of all foundresses and of offspring from supplemented colonies.
• 7 The per cent body fat of offspring from supplemented colonies was higher than that of all foundresses.

     

Microsatellite-based parentage analysis reveals non-ideal free distribution in a parasitoid population

Habitat selection by dispersers is the focus of much theoretical models, most of which are based on the assumption of negative density dependence. The archetype of these models is the ideal free distribution, characterized by an evolutionary stable state where more competitors aggregate in better habitats, so that the fitness benefit of resource abundance is equally offset by the cost of competition in all habitats. In this study, we used parentage analysis on microsatellite genotypes to test the ideal free distribution in a natural population of aphid parasitoids. Parentage analysis was conducted on parasitoids emerging from aphid colonies. We inferred the number of foundress females which had reproduced in each colony, as well as the number of offspring for each foundress. As predicted by the ideal free distribution, the number of offspring per foundress per colony did not depend on the number of hosts per colony. However, contrary to ideal free distribution predictions, it was affected by the number of foundresses per colony. In surprising contrast with the basic assumption of negative density dependence, individual fitness increased with the number of foundresses. Moreover, parentage analysis revealed a very low number of offspring per foundress per colony (mean = 1.8). This observed distribution questions the validity of classical models of habitat choice based on competition. Indeed, our results provide a new illustration reinforcing a growing body of theory and data on positive density dependence. Our results also suggest that the avoidance of hyperparasitism and predation, although generally neglected, may shape the distribution of parasitoids in the field.