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.     

Distribution of foundress group size in Ropalidia fasciata and R. plebeiana (Hymenoptera: Vespidae): an analysis using zero-truncated distribution models

Distribution patterns of the number of foundresses per newly established nest (foundress group size, FGS) of two primitively eusocial, independent-founding wasps, Ropalidia fasciata and R. plebeiana, were studied using zero-truncated distribution models. The distribution pattern of the FGS of R. fasciata is significantly different from a zero-truncated Poisson distribution but fits the zero-truncated negative binomial distribution well, indicating a strongly contagious distribution. R. plebeiana sometimes establishes new colonies by reusing old nests. In this case, distributions are strongly contagious. Competition among foundresses may be one reason for the contagious distribution of FGS in R. fasciata and in cases of old-nest reuse by R. plebeiana, but further studies, especially on the behaviour of foundresses in relation to FGS, are necessary. Electronic Publication     

Population consequences of huge nesting aggregations ofRopalidia plebeiana (Hymenoptera: Vespidae)

Nest survival rates and reproductive rates of females of the Australian paper wasp, Ropalidia plebeiana, in nest aggregations under a concrete bridge were studied. The annual colony cycle commenced in August with the reutilization of old nests and by the founding of new nests, mainly by associations of foundresses. Distribution patterns of the number of foundresses per nest was nearly random on new nests while contagious on old nests. About one-third of the increase in number of nest was achieved by dividing large, old nests and two-thirds by founding new nests. Nest survival rates for old nests (August to April) and new nests (November to April) were 89.6% and 88.8% respectively, far higher rates than those of other polistine wasps so far reported. The numbers of nests and reproductive females increased during a colony cycle by 2.30 and 10.98 times, respectively. Thus, huge aggregations of nests are probably beneficial for this species by enabling the realization of high reproductive rates. We could find no density-dependent effect in nest growth rate or production of female reproductives. Ratio of cells parasitized by ichneumonid wasps was low. Nests in the central part of an aggregation were prasitized at significantly lower rates than nests on the periphery or scattered nests outside a dense aggregation, suggesting a selfish herd effect.     

Comb cutting inRopalidia plebeiana: a new process of colony fission in social wasps (Hymenoptera: Vespidae)

Summary Females of an Australian polistine wasp,Ropalidia plebeiana, often use their mandibles to cut their nest-comb in spring, dividing it into two or more completely independent nests. Prior to the division, each of the major egg layers, often with some subordinates, tended to occupy a different part of a single comb. These females gnawed cells in the intermediate zone between such territories, and ultimately divided the comb. Many other females also built new nests near the nest aggregations, but addition of new nests by comb cutting represented 34.8 % of the increase in nest number. This method of colony fission is so far unknown in any eusocial Hymenoptera.     

Early-season colony development of the paper wasp Ropalidia plebeiana (Hymenoptera: Vespidae) in Canberra, Australia

This study presents the first observations of early-season colony development of Ropalidia plebeiana in Canberra, Australia. The growth pattern of three R. plebeiana nests was measured during weekly observations from October 2006 to January 2007 and showed that nests steadily increase in size over the early summer to approximately 50 cells when the nest is newly established and to approximately 170 cells when nests from the previous season are re-used. A first generation of adult females is produced by December, and the bimodality of the curves of egg, larval and pupal numbers indicates that these three developmental stages last approximately 2–3 weeks each. The nesting cycle of R. plebeiana in Canberra commences approximately 2 weeks later than in coastal Australia, the shorter summers in this inland region restricting the length of the active season. R. plebeiana did not form dense nesting aggregations in Canberra as described elsewhere, with only small colonies consisting of a single or just a few nests. Characteristic comb-cutting behavior of the species was observed but this did not result in complete nest division as recorded from coastal populations.     

Nest site competition between cavity nesting passerines and golden paper wasps Polistes fuscatus

Nest boxes provide sheltered nesting sites for both passerines and paper wasps. Although neither wasps nor birds appear to evict the other once one is fully established, it is unclear which is the dominant competitor at the onset of the breeding season. Using wire mesh, we excluded birds but not golden paper wasps Polistesfuscatus from alternating boxes along a transect through edge habitat in North Carolina from 2006 – 2008. If wasps dominate Carolina chickadees Poecile carolinensis and eastern bluebirds Sialia sialis during the early spring (all have similar nest initiation dates), we would expect wasps to settle in both box types at equal frequencies. However, if birds dominate wasps, we would expect wasp nests to be concentrated in “bird‐proof” boxes. We found wasps in bird‐proof boxes significantly more often than in bird‐accessible boxes, indicating that secondary‐cavity nesting birds are able to exclude wasps from available nest sites. Additionally, we found that during the period of nest initiation, birds usurp wasps more often than vice versa.     

Social behaviour of an Australian paper wasp,Ropalidia plebeiana,with special reference to the process of acceptance of an alien female

Social interactions amongRopalidia plebeiana females on a nest were observed in Brisbane, Australia. Although a single female (queen-like female) tended to remain on the nest most of the time, and received food most frequently from females which returned from foraging trips, no dominance/aggressive acts were directed by her to regular nestmates. When a possibly alien female tried to join the female group, however, the queen-like female attacked this female strongly. The frequency of these attacks gradually decreased and the newcomer was accepted as a regular member by the eighth day. The attacked female showed a special, possibly ritualized, posture and this seemed to have reduced the frequency of attacks.     

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.     

Spatial Nest‐Settlement Decisions in Digger Wasps: Conspecifics Matter more than Heterospecifics and Previous Experience

Research into the driving forces behind spatial arrangement of wasp nests has considered abiotic environmental factors, but seldom investigated attraction or repulsion towards conspecifics or heterospecifics. Solitary female digger wasps (Hymenoptera) often nest in dense aggregations, making these insects good models to study this topic. Here, we analysed the nesting patterns in an area shared by three species of the genus Bembix, in a novel study to discover whether female wasps are attracted to or repulsed by conspecific nests, heterospecific nests or their own previously established nests when choosing nest‐digging locations. Early in the season, each species showed a clumping pattern of nests, but later in the season, a random distribution of nests was more common, suggesting an early conspecific attraction. Such behaviour was confirmed by the fact that females started building their nests more frequently where other females of their species were simultaneously digging. The distances between subsequent nests dug by individual females were shorter than those obtained by random simulations. However, this pattern seemed to depend on the tendency to dig close to conspecifics rather than remain in the vicinity of previous nests, suggesting that females' experience matters to future decisions only on a large scale. Nesting patches within nest aggregations largely overlapped between species, but the nests of each species were generally not closer to heterospecific nests than expected by chance, suggesting that females are neither repulsed by, nor attracted to, congenerics within nest aggregations. A role of the spatial distribution of natural enemies on the observed nesting patterns seemed unlikely. Bembix digger wasp nest aggregations seem thus to be primarily the result of female–female attraction during nest‐settlement decisions, in accordance with the ‘copying’ mechanisms suggested for nesting vertebrates.     

Little effect of seasonal constraints on population genetic structure in eusocial paper wasps

Climate has long been suggested to affect population genetic structures of eusocial insect societies. For instance, Hamilton [Journal of Theoretical Biology 7 (1964) 17] discusses whether temperate and tropical eusocial insects may show differences in population‐level genetic structure and viscosity, and how this might relate to differences in the degree of synchrony in their life cycles or modes of nest founding. Despite the importance of Hamilton's 1964 papers, this specific idea has not been tested in actual populations of wasps, probably due to the paucity of studies on tropical species. Here, we compare colony and population genetic structures in two species of primitively eusocial paper wasps with contrasting ecologies: the tropical species Polistes canadensis and the temperate species P. dominulus. Our results provide important clarifications of Hamilton's discussion. Specifically, we show that the genetic structures of the temperate and tropical species were very similar, indicating that seasonality does not greatly affect population viscosity or inbreeding. For both species, the high genetic differentiation between nests suggests strong selection at the nest level to live with relatives, whereas low population viscosity and low genetic differentiation between nest aggregations might reflect balancing selection to disperse, avoiding competition with relatives. Overall, our study suggests no prevalence of seasonal constraints of the life cycle in affecting the population genetic structure of eusocial paper wasps. These conclusions are likely to apply also to other primitively eusocial insects, such as halictine bees. They also highlight how selection for a kin structure that promotes altruism can override potential effects of ecology in eusocial insects.     

Polymorphic microsatellite loci for primitively eusocial wasp Ropalidia marginata

We report here development and characterization of 48 novel microsatellite markers for Ropalidia marginata, a tropical, primitively eusocial polistine wasp from peninsular India. Thirty‐two microsatellites showed polymorphism in a wild population of R. marginata (N = 38) collected from Bangalore, India. These markers will facilitate answering some interesting questions in ecology and evolutionary biology of this wasp, such as population structure, serial polygyny, intra‐colony genetic relatedness and the pattern of queen succession.     

Cooperative nest building and brood care by nestmates and non nestmates in Ropalidia marginata : implications for the evolution of eusociality

In the primitively eusocial wasp, Ropalidia marginata, low levels of intra-colony genetic relatedness, lack of intra-colony kin discrimination and acceptance of young wasps into alien colonies, prompted us to investigate whether or not there exists a cost of such high genetic variability. Freshly eclosed wasps were paired either with their nestmates or with their non nestmates and their performance in nest building and brood care were compared. There was no demonstrable difference between nestmate and non nestmate pairs in terms of success in raising adult offspring, time required for nest initiation, brood developmental period and productivity. There was also no difference in the efficiency of cooperation and division of labour between the nestmate pairs and non nestmate pairs. These results reinforce the idea that the haplodiploidy hypothesis is insufficient to explain the prevalence of worker behaviour in R. marginata and emphasize the importance of factors other than genetic relatedness in the evolution of eusociality. Received: 27 April 1998 / Accepted: 10 July 1998     

Behavior during artifically induced swarm emigration in an old world polistine wasp,Ropalidia romandi (Hymenoptera: Vespidae)

Absconding swarms of the Australian swarm-founding wasp,Ropalidia romandi, were artificially induced. Workers may initially search for new nesting sites and once a new nest site is decided, they recruit their nest mates including multiple queens there. During the swarm emigration, workers often land on prominent objects, such as tree leaves, and drag the metasoma; those that do not drag usually antennate the object surfaces. These findings suggest thatR. romandi workers use a scent trail during swarm emigration. Artificial transfer of colonies resulted in clustering of wasps from different colonies, indicating thatR. romandi may not act exclusively against non-nestmates. In the formation of tentative aggregation of wasps prior to commencing emigration, and also in recognizing a new nesting site by following swarm members that have been guided by a scent trail, a visual cue (aerial swarm formed around an aggregation of wasps) seems to play an important role.     

Observations onApoica pallens,a nocturnal neotropical social wasp (Hymenoptera: Vespidae,Polistinae, Epiponini)

Summary Colonies and nests ofApoica pallens in the llanos region of Venezuela range from small foundress nests to large mature colonies. Nests are sited on small diameter, near-horizontal branches in a variety of shrub and tree species. During the day, adult wasps cluster on the face of the nest in an array that seems to be determined by orientation to gravity; defense of the colony against parasitoids and ants by the resting wasps may be more a passive than an active behavior. Wasps fan their wings to cool the colony during the day, but no foraging for water accompanies the fanning behavior. Nightly foraging activity begins with the explosive departure from the nest of hundreds of wasps, most of which rapidly return. Moderate foraging levels early at night give way to very low foraging levels in pre-dawn hours. The period of moderate foraging may be extended for longer hours during increased moonlight. Foraging wasps collect arthropod provisions for larvae. Larvae produce a trophallactic saliva; adults engage in inter-adult trophallaxis; brood are cannibalized. During cluster formation prior to swarm emigration, adult wasps do not appear to scent-mark substrates such as leaves. Instead,A. pallens exhibits a calling behavior, unique among polistine wasps studied to date, in which the gaster is held rigidly away from the thorax and metasomal sternal glands are exposed. Swarms can emigrate during the day.A. pallens may incorporate absconding and colony relocation as features of its colony cycle in the highly seasonal llanos.     

Pulp partitioning and worker specialization in polistine wasps (Hymenoptera,Vespidae, Polistinae)

The character of pulp partitioning was studied in three Palaearctic polistine wasps (Polistes dominula and P. gallicus in the Black Sea Biosphere Reserve, and Polistes nimpha in the Lugansk Nature Reserve, Ukraine) and in five Neotropical species (P. lanio, P. versicolor, Mischocyttarus injucundus, M. alfkeni, Metapolybia cingulata, and Protopolybia exigua in Trinidad). In independent-founding Polistes and Mischocyttarus species, all cases of pulp partitioning were connected with aggression on the part of the foundresses. An experimental increase of nesting density of P. dominula led to changes in the relative abundance of workers in the polyethic task groups. Some workers practically stopped hunting and switched over to pulp delivery; some of these workers possessed well-developed ovaries and were able to lay eggs. The experimentally removed part of the nest envelope in the swarm-founding wasp Metapolybia cingulata was restored only in colonies that included young workers. The specific features of nest building activity in independent-founding and swarm-founding polistine wasps are discussed.     

Population dynamics of the cattle tick Rhipicephalus (Boophilus) microplus in a subtropical subhumid region of Argentina for use in the design of control strategies

The population dynamics of Rhipicephalus microplus (Ixodida: Ixodidae) in northwest Argentina was analysed to support the design of strategic methods for its control. Both parasitic and non‐parasitic phases were studied. The seasonal activity of R. microplus in its parasitic phase was characterized by three peaks in abundance: the first in mid–late spring; the second in summer, and the third in autumn. The non‐parasitic phase of R. microplus was characterized by a long total non‐parasitic period observed after exposures of females from mid‐summer to early autumn, a short total non‐parasitic period observed after exposures of females from late winter to late spring, a short period of larval longevity in early and mid‐summer, and no hatch of the eggs produced by females exposed in mid‐ and late autumn and winter. Treatments of cattle administered during the period from late winter to late spring will act on small cohorts of R. microplus, preventing the emergence of larger generations in summer and autumn. A 17‐week spelling period starting in late spring and early summer will be necessary to achieve optimal control of R. microplus free‐living larvae. If spelling begins in mid‐ or late summer or in autumn, the required period will be 26–27 weeks.     

Social behaviour and social structure of Neotropical paper waspsMischocyttarus angulatus Richards andM. basimacula (Cameron)

Social behaviour and social structure of 2 Neotropical polistine wasps,Mischocyttrus angulatus andM. basimacula, were investigated in the Canal Area, Republic of Panama. About 80% ofM. angulatus colonies and a half ofM. basimacula colonies were founted by multiple females having mature eggs in their ovaries. All of single-female colonies examined failed before the emergence of the first progeny. During the pre-emergence period, neither biting nor chasing was observed among females coexisting on the multifemale nests of both species. Although one of the females tended to stay on her nest for most of the time (‘queen-like female’), she was often replaced by a different individual on differrent days. In the post-emergence period, however, frequent aggression among females (including the foundresses and the first brood adults) was observed. The roles of pleometrosis and dominance behaviour in social lives of the 2 species in the wet tropics are discussed.     

Some aspects of interrelations between ants (Hymenoptera,Formicidae) and polistine wasps (Hymenoptera,Vespidae)

Embodied, situated and enactive aspects of relationships of polistine wasps with ants are considered within the framework of the theory of autopoiesis. The idea of the embodied interaction implies specific nestbuilding and protective behavior in polistine wasps. The paper examines the adaptive role of applying ant repellent on the petiole and nest and the latitude gradient of such behavior in re-social wasp species. The situated interaction is considered in the environmental context: the mortality of Polistes gallicus (L.) colonies as a result of predatory attacks of ants Myrmica bergi Ruzsky is analyzed in the Lower Dnieper basin (Ukraine). The enactive interaction includes both spontaneous autonomous activity of its participants as a result of self-organization and specific features of the spatial structure of the prey’s population forming under the impact of the predator. The applicability of some “predator-prey” models is discussed.     

Population ecology of the velvet gecko,Oedura lesueurii in south eastern Australia: Implications for the persistence of an endangered snake

Abstract Ecological specialization, such as major dependence upon a single‐prey species, can render a predator taxon vulnerable to extinction. In such cases, understanding the population dynamics of that prey type is important for conserving the predator that relies upon it. In eastern Australia, the endangered broad‐headed snake Hoplocephalus bungaroides feeds largely on velvet geckos (Oedura lesueurii). We studied growth, longevity and reproduction in a population of velvet geckos in Morton National Park in south‐eastern Australia. We marked 458 individual geckos over a 3‐year period (1992–1995) and made yearly visits to field sites from 1995–2006 to recapture marked individuals. Female geckos grew larger than males, and produced their first clutch at age 4 years. Males can mature at 2 years, but male–male combat for females probably forces males to delay reproduction until age 3 years. Females lay a single clutch of two eggs in communal nests in November, and up to 22 females deposited eggs in a single nest. Egg hatching success was high (100%), and juveniles had high survival (76%) during their first 6 months of life. Velvet geckos are long‐lived, and the mean age of marked animals recaptured after 1995 was 6.1 years (males) and 8.4 years (females). Older females (7.5–9.5 years) were all gravid when last recaptured. Like other temperate‐climate gekkonids, O. lesueurii has a ‘slow’ life history, and population viability could be threatened by any factors that increase egg or adult mortality. Two such factors – the removal of ‘bush rocks’ for urban gardens, and the overgrowth of rock outcrops by vegetation – could render small gecko populations vulnerable to extinction. In turn, the reliance of predatory broad‐headed snakes on this slow‐growing lizard species may increase its vulnerability to extinction.     

Effects of intense wildfires on the nesting ecology of oviparous montane lizards

In midsummer 2002–2003, intense wildfires raged through the Brindabella Range of south‐eastern Australia, including sites where we have studied the ecology of scincid lizards (especially Bassiana duperreyi) for decades. Data‐loggers measured the thermal regimes experienced by eggs during these fires (revealing lethally high temperatures in nests under logs in the forest but minimal effect in nests under rocks in clearings). Eggs from forest‐clearing nests hatched successfully. Reproductive output of lizards in one area was reduced in the years post‐fire (perhaps because of inadequate food [insect] abundance to fuel female reproduction) but soon recovered. The fires reduced vegetation density and thus increased the availability of sun‐exposed rocks that serve as potential nest sites. However, the magnitude and duration of these effects differed among sites. Five years after these intense fires, canopy openness (and thus, sunlight penetration to create thermally suitable nest sites) was indistinguishable from pre‐fire conditions. Our data reveal strong spatial heterogeneity both in the immediate effects of fire on lizard reproduction and in longer‐term post‐fire changes in habitat quality. Surprisingly, these intense wildfires had only transitory and local effects on nest‐site availability for the heliothermic lizards that we study, but impacts likely were more severe on sympatric taxa that depend upon moist cool microhabitats.