Lasioglossum (Dialictus) tenax (Sandhouse) (Hymenoptera: Halictidae) as a solitary sweat bee

Summary Nine nests ofLasioglossum (Dialictus) tenax were excavated near Calgary, Alberta, Canada over a time period encompassing the entire brood production period in 1988. Each nest contained a maximum of one active adult female, nest productivity peaked in mid July, protandry was noted and no significant size difference between foundresses and the earlier emerging females was detected. These data suggest that this species is solitary. These results are compared with data for the sympatrically nesting eusocial speciesL. (D.) laevissimum.     

Nesting biology of tropical solitary and social sweat bees,Lasioglossum (Dialictus) figueresi Wcislo andL. (D.) aeneiventre (Friese) (Hymenoptera: Halictidae)

Summary The nesting biology of a mainly solitary bee,Lasioglossum (Dialictus) figueresi, is compared with that of a possible relative and mainly eusocial bee,L. (D.) aeneiventre. These bees nest in the ground in highly disturbed areas in the Meseta Central of Costa Rica. Information is provided on social organization, male production, diel and seasonal activity patterns, pollen utilization, natural enemies and nest architecture. L. (D.) figueresi nests within aggregations in vertical earthen banks, and 80–90 % of females are solitary during the nest-provisioning phase. Social nests contain two (or rarely three) females which may be either equal or unequal in reproductive status (i.e. mated with developed ovaries or not). Solitary nests and two-female nests do not experience different rates of parasitism. Mid-way through the dry season, females cease provisioning at a time when otherL. (Dialictus) remain active. Females typically remain within their nests, although they occasionally forage for nectar. This behavior is similar of that of spring gynes of temperate eusocial species. The egg-to-adult developmental rate ofL. (D.) figueresi is unusually slow for halictine bees, however, so that all the adult females die before their brood eclose in April and May, precluding overlap of generations. The eclosed offspring remain in open cells within their natal nests until mid-June, when both males and females emerge to mate. These newly mated females either establish new nests or re-use old ones. L. (D.) aeneiventre nests within aggregations in horizontal ground or in vertical banks. A foundress female digs a nest at the beginning of the dry season, although some re-activate old nests. Foundress nests develop into colonies with various kinds of social organization. In contrast toL. (D.) figueresi, L. (D.) aeneiventre is active nearly all year round, except during periods of heavy rain, and produces up to three broods per year.Sweat bees (Hymenoptera: Halictinae) are a socially heterogeneous group of mainly ground-nesting bees which are abundant world-wide. Intra-specific variation in social behavior is prevalent both within and among populations, presumably indicating social and environmental control of behavioral modifications (see e.g. Sakagami and Munakata, 1972; Eickwort, 1986; Packer, 1990; Yanega, 1988; reviewed in Michener, 1990). The initial stages of hymenopteran social evolution are represented by solitary individuals and those in undifferentiated societies, yet their biology is not well known, as is true for the numerous tropical halictine species or populations (see Michener, 1990).The subgenusDialictus ofLasioglossum is a primarily New World group of several hundred species (Moure and Kurd, 1987). These bees are monotonously similar in structure and appearance, yet diverse in social behavior. FemaleLasioglossum (Dialictus) figueresi are usually solitary, and structurally are very similar to their social relativeL. (D.) aeneiventre (Wcislo, 1990 a). The systematic placement of these species with respect to otherL. (Dialictus) is uncertain, but they have no obvious affinities to other recognized species groups (G. C. Eickwort, pers. comm.). Unusual morphological features, such as large size, yellowish wings and pubescence, and features of the genital organs, may indicate thatL. (D.) figueresi is the more derived of the pair, and may therefore be secondarily solitary, as is known for other sweat bees (Packer, 1991).     

Social polymorphism in the sweat bee <Emphasis Type="Italic">Lasioglossum (Evylaeus) baleicum</Emphasis> (Cockerell) (Hymenoptera,Halictidae) in Hokkaido,northern Japan

Summary The life cycle and social behaviour of the sweat bee Lasioglossum (Evylaeus) baleicum (Cockerell) was investigated in two geographically separate populations in Hokkaido, northern Japan. Colonies were excavated throughout the brood rearing season from an aggregation in Nishioka forest park, Sapporo, and near Kawakita in eastern Hokkaido during 2000 and 2001. The Nishioka population produced two discrete broods during the year and was weakly eusocial; 57% of workers were mated and 28% exhibited some ovarian development, 12–16% of the first brood was male, and workers were on average 4.5% smaller than their respective queen. In contrast, the population at Kawakita was solitary, and produced a single brood per year with an unbiased sex ratio. In addition however, there were some solitary colonies in the Nishioka population and evidence of a partial second brood in some colonies at Kawakita, suggesting differences between the populations are not fixed and that this species is truly socially polymorphic. L. (E.) baleicum is a member of the fulvicorne species group, which includes other examples of social polymorphic species as well as solitary and eusocial species, though this is the only species of this group so far known to exhibit a solitary/non-delayed eusocial polymorphism. Recent studies suggest that social polymorphism has both genetic and environmental influences, raising questions as to the relative import of each.     

Ontogenetic patterns of volatiles identified in Dufour's gland extracts from queens and workers of the primitively eusocial halictine bee,Lasioglossum malachmum (Hymenoptera: Halictidae)

Summary Ontogenetic patterns of volatile compounds identified in Dufour's gland extracts from queens and workers of the primitively eusocial sweat beeLasioglossum malachurum (K.) were compared. Only young unmated queens showed high proportions of isopentenyl esters, while macrocyclic lactones were dominant in old breeding queens, spring queens, and workers. In young queens the relative and absolute amounts of volatiles changed one day after mating. A discriminant analysis revealed significant differences in odor patterns of unmated and mated young queens. The fat body was the largest in young females, while eggs could be recorded only in breeding queens. Possible functions of different odor components in the investigated female groups are discussed.     

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.

     

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.     

Patterns of provisioning and iteroparity in a solitary halictine bee,Lasioglossum (Evylaeus) fratellum (Perez), with notes onL. (E.) calceatum (Scop.) andL. (E.) villosulum (K.)

Summary On Dartmoor, UK the temperate halictine beeLasioglossum (Evylaeus) fratellum is solitary and univoltine. A significant proportion of individually marked foundresses reproduce during two different seasons (iteroparity). This could represent a form of risk-spreading in environments where conditions are harsh and unpredictable. Perhaps associated with iteroparity, foundresses put in relatively low reproductive effort, often failing to provision their nests on suitable days, despite the small number of days available on Dartmoor. Foundresses stopped provisioning asynchronously, then remained in their nests until well after offspring emergence. There was a small proportion of digynous nests, in which nest-sharing appeared to be temporary.L. (E.) calceatum had a similar life-cycle on Dartmoor.L. villosulum was also solitary, and was able to provision its nests under less favourable weather conditions than the other two species. Information is also provided on nest productivity andSphecodes parasites.     

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.     

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.     

Colony social organization of <Emphasis Type="Italic">Lasioglossum malachurum</Emphasis> Kirby (Hymenoptera,Halictidae) in southern Greece

Summary We studied the nesting and social biology of two aggregations of the obligately eusocial halictine bee Lasioglossum malachurum at Agios Nikolaos Monemvasias (ANM) in southern Greece. Observations and nest excavations carried out from May to June 2000, revealed social and demographic variation between aggregations and years at ANM, as well as notable differences between these and other European populations. In southern Greece, the colony cycle includes multiple broods: the first two broods comprise only workers, whereas the third brood comprises workers, males, and gynes. Although pleometrosis is unknown in other populations, in the ANM region, as many as 10% of nests have more than one foundress. Newly emerged workers and gynes exhibit non-overlapping size distributions, but a few queens are worker-sized, indicating that workers occasionally overwinter and become foundresses. Although the vast majority of workers are unmated and most exhibit no ovarian development, an increase in worker ovarian development at the time of male production suggests that many males may develop from worker-laid eggs. Worker reproduction seems to be inhibited by the presence of queens, and annual variation in queen mortality may underlie annual variation in worker ovarian development. Across Europe, the major demographic and social differences among L. malachurum populations are in the number of worker broods and the extent of worker ovarian development. This contrasts with the results of a principal components analysis of social traits among 15 social L. (Evylaeus) populations, which shows that interspecific social variation is defined by the proportion of males in the early brood, the proportion of workers mated, queen-worker size dimorphism, gyne overwintering locale, and the proportion of workers with developed ovaries.Received 17 June 2002; revised 16 January 2002; accepted 27 January 2003.     

Queen succession in the primitively eusocial tropical waspRopalidia marginata (Lep.) (Hymenoptera: Vespidae)

Females of the primitively eusocial wasp Ropalidia marginata can be classified into three behavioral groups: Sitters, Fighters, and Foragers. It has been speculated that both Sitters and Fighters may be hopeful queens and that the Foragers may have little or no opportunities for direct reproduction. Here we show that in 9 of 12 queen-removal experiments where such a behavioral differentiation could be discerned, the individual that became a queen (the potential queen) was a Sitter in 6 cases, a Fighter in 2 cases, and a Forager in only 1 case. Although potential queens spent significantly more time absent from the nest and showed significantly higher rates of dominance behavior compared to the mean values for nonqueens in their colonies, they were intermediate with respect to all behaviors and age when compared to the range of values for nonqueens in their colonies. Potential queens were not necessarily the highest-ranking individuals among the nonqueens. The pattern of queen succession in this species appears to be quite different from the temperate pattern, where an old and active forager of high dominance rank is the potential queen. Although somewhat similar to the tropical pattern of a relatively younger female that has performed relatively little foraging being the potential queen, it is perhaps more accurate to describe the potential queens of R. marginata as unspecialized intermediates.     

Phylogeny of eusocial Lasioglossum reveals multiple losses of eusociality within a primitively eusocial clade of bees (Hymenoptera: Halictidae)

We performed a phylogenetic analysis of the species, species groups, and subgenera within the predominantly eusocial lineage of Lasioglossum (the Hemihalictus series) based on three protein coding genes: mitochondrial cytochrome oxidase I, nuclear elongation factor 1alpha and long-wavelength rhodopsin. The entire data set consisted of 3421 aligned nucleotide sites, 854 of which were parsimony informative. Analyses by equal weights parsimony, maximum likelihood, and Bayesian methods yielded good resolution among the 53 taxa/populations, with strong bootstrap support and high posterior probabilities for most nodes. There was no significant incongruence among genes, and parsimony, maximum likelihood, and Bayesian methods yielded congruent results. We mapped social behavior onto the resulting tree for 42 of the taxa/populations to infer the likely history of social evolution within Lasioglossum. Our results indicate that eusociality had a single origin within Lasioglossum. Within the predominantly eusocial clade, however, there have been multiple (six) reversals from eusociality to solitary nesting, social polymorphism, or social parasitism, suggesting that these reversals may be more common in primitively eusocial Hymenoptera than previously anticipated. Our results support the view that eusociality is hard to evolve but easily lost. This conclusion is potentially important for understanding the early evolution of the advanced eusocial insects, such as ants, termites, and corbiculate bees.     

Spatio-temporal variation of colony structure and eusociality level of the Japanese sweat bee<Emphasis Type="Italic"> Lasioglossum</Emphasis> (<Emphasis Type="Italic">Evylaeus</Emphasis>)<Emphasis Type="Italic"> duplex</Emphasis> (Hymenoptera: Halictidae)

Colony structure and eusociality level of the sweat bee Lasioglossum (Evylaeus) duplex were studied in 2001 in Sapporo and Assabu, Hokkaido, northern Japan. Sakagami and his colleagues had also studied this species in Sapporo in 1957–1968. Brood size, sex ratio and queen–worker size dimorphism were geographically and temporally variable, indicating spatio-temporal variation at the eusociality level. Inseminated workers constituted only 7.9% of the populations in 1957–1968 Sapporo but about 60% in 2001 in Sapporo and Assabu. A few of the inseminated workers were believed to leave natal nests for independent colony founding. Thus, partial bivoltinism is likely in this sweat bee species. The presence of workers with developed ovaries and/or corpora lutea suggests the occurrence of worker oviposition.     

Alternative Reproductive Strategies of a Gregarious Ground-Nesting Bee, Dieunomia triangulifera (Hymenoptera: Halictidae)

I studied reproductive behavior of females of the gregarious ground-nesting bee Dieunomia triangulifera (Halictidae). During peak bloom of the host plant, Helianthus annuus, some females consistently brought pollen to one nest (provisioning bees), whereas others visited many nests without taking pollen to any (searching bees). Searching bees were more likely to have two or more developed oocytes and crops full of pollen. The ingested pollen probably provided protein for egg production. The differing behavior of provisioning and searching bees combined with contrasting internal morphology, indicated that these two sets of behaviors were alternative reproductive strategies. Three possible explanations for the searching bees' behavior included: usurpation, floating, or intraspecific cleptoparasitism. Each of these is evaluated as a possible function of searching behavior. Given the evidence I conclude that intraspecific cleptoparasitism is the most likely explanation.     

Colony structure of a bamboo-dwellingTetraponera sp. (Hymenoptera: Formicidae: Pseudomyrmecinae) from Malaysia

Summary The colony structure of the bamboo-inhabiting SE-Asian pseudomyrmecine antTetraponera sp. PSW-80 nearattenuata F. Smith was investigated at the Ulu Gombak Field Studies Centre, Selangor, West-Malaysia. Based on the dissection of 54 stem internodes from 12 different culms of the large bambooGigantochloa scortechinii Gamble and on the mapping of three colonies, the following demographic characteristics emerge. The colonies are monogynous but highly polydomous (at least up to 36 internodes and up to 9 stems occupied) and very populous for a pseudomyrmecine not involved in an ant-plant mutualism. One completely censused colony had 6953 adult workers and 2079 alates (adults plus pupae). The single queen suppresses gyne development in her own nest and, to a lesser extent, in other nests within the same stem. The overall numerical sex ratio was 0.961 (females:males), the investment sex ratio, 2.931, i.e., almost exactly the 31 ratio expected for a monogynous outbred hymenopteran in which the colony queen also produces all the male offspring. Brood is distributed to all other nest chambers from the queenright chamber. The symbiotic pseudococcids (Kermicus wroughtoni Newstead) are present in all inhabited internodes, with small early instar individuals prevailing numerically by far over the larger stages. The rieht well secluded honeydew supply within the internode and the efficient architectural protection provided by the internode wall (access usually only through a 2 × 3 mm-hole) allowT. sp. PSW-80 to reach an unusually large colony size without being an aggressive and protective plant mutualist like other members of its subfamily with similar demographic features.     

Social and ecological contexts of trophallaxis in facultatively social sweat bees, Megalopta genalis and M. ecuadoria (Hymenoptera, Halictidae)

Exchange of liquid food among adults (trophallaxis) is documented for the first time in New World sweat bees (Halictinae). Megalopta genalis and M. ecuadoria are facultatively social, and in social groups foragers regularly give food to the oldest resident female bee, which dominates social interactions. In turn, the oldest resident sometimes re-distributes this food, and shares it with younger foragers. Food is sometimes offered freely, but often the dominant bee exhibits escalating aggressive behavior until she is fed, whereupon she immediately ceases to be aggressive. The occurrence of trophallaxis in a species with mass-provisioned larvae provides an opportunity to examine the ritualization of social behavior. Trophallaxis also increases survivorship of males and females by almost 50% under experimental conditions, suggesting the behavior is also important in ecological contexts. Received 25 July 2005; revised 22 November 2005; accepted 23 December 2005.     

The biology of the primitively eusocial Augochloropsis iris (Schrottky, 1902) (Hymenoptera, Halictidae)

Summary: This work investigated Augochloropsis iris, its annual colony cycle, brood size and survival rate, caste differentiation, and sex ratio, and is the first detailed account of a clearly eusocial species of this genus. The population studied is located in the Campos do Jordão State Park, São Paulo, Brazil. The annual colony cycle extends from August to March and consists of three phases of cell provisioning separated by two phases of inactivity, and followed by an emergence of future queens and males. Provisioning during the first phase is carried primarily out by solitary females. The daughters, after emerging from the cells, remain in the natal nests, carrying out foraging activities, while the mother engages in reproduction. New nests are initiated during each of the provisioning phases by solitary females, principally by females from the second-phase brood which, soon after emerging from the cells, leave their natal nests to found their own nests, which they provision during the third phase. The females resulting from the third-phase brood in general mate and excavate their own nests, in which they diapause, with provisioning delayed until the following August. On average, the queens are significantly larger (5%) than the workers. In general, the workers do not have developed ovaries, but all are mated. Kin selection can be accepted as the selective force responsible for worker behavior of A. iris in eusocial colonies when the queen has mated once and semisocial colonies if the queen mated only once. The percentage of males produced in the first, second and third broods and in the brood of new nests founded by solitary females active in the second and third phases was: 20.7%, 22.2%, 13.3% and 0.0% respectively. The resultant sex ratio of the third brood suggests that the third-phase workers of eusocial nests are at least in partial control of their colony's sex ratios, in cases where the queens mated only once.     

Colony migration in the tropical honey beeApis dorsata F. (Hymenoptera: Apidae)

Summary To obtain insights into the organization and adaptive significance of seasonal migration by colonies of the giant honey bee,Apis dorsata, we monitored the arrivals and departures of colonies in a rain forest habitat in northeastern Thailand, compared patterns of honey bee abundance with other measures of habitat variability, and observed the role of dance communication in organizing the migratory departure of a colony. Colonies arrived in the area during the end of the dry season, reproduced, and then departed early in the rainy season. During the immigration phase, early-arriving colonies stayed only temporarily, as if assessing habitat quality. Colonies departing after a long stay always left barren combs behind, suggesting that they had left in response to deteriorating resource quality. These observations support the idea that migration allows colonies to track seasonally varying resources in different regions. Our observations of a colony preparing for migration revealed that the dance language is involved in organizing the colony's departure, but that dancers signal only the direction to be taken, rather than, as in dances to feeding sites, both the direction and distance of a particular location.